Introduction to Ferrous Metallurgy

7/28/2019 Introduction to Ferrous Metallurgy

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TIGHT BINDING BOOK


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( 6 o of its volume at 0F.(460R.) for each 1F. change in temperature. The formulagiven under Charles's law applies equally well when the tempera-tures are in Fahrenheit; the only precaution to observe is that theabsolute temperature must be obtained by adding 460 to obtainthe Rankine scale rather than 273 as in the case of changing thecentigrade to the Kelvin scale.

Pressure. In the metric system the pressure exerted by theatmosphere at sea level is capable of supporting a column ofmercury 760 mm. high. If the height of this same column ismeasured in inches, it will be found to be 29.92 in. high. Inindustrial installations pressures are often given in inches ofmercury and the volume of a gas bears the same relation to inchesof mercury as it does to millimeters. The only difference is thedifference in the size of the units used in measuring the column.The relation between inches and millimeters is 1 inch = 25.4millimeters. In the English system pressures are also frequentlyexpressed in pounds per square inch and also in inches of water.The pressure of the atmosphere will support a column ofwater nearly 34 ft. high. The exact height of the column ofwater may be calculated by multiplying 29.92 hi. of mercuryby 13.6 (mercury is 13.6 times as heavy as water).

29.92 X 13.6 = 406.9 in. of wateror approximately 33 ft., 11 in. Since the column of watersupported by a given pressure is much greater than the columnof mercury that would be supported by the same pressure, wateris often used for measuring small pressures, for the longer columncan be measured more accurately.A column of mercury 1 in. high exerts a pressure of 0.491 p.s.L29.92 in. of mercury exerts a pressure of 14.69 p.s.L Thus thepressure exerted by 1 atm. is approximately 14.7 p.sd. Thevolume of any gas is inversely proportional to the pressure inany of the units described. The following factors may be usedto convert values expressed in one set of units to another:


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20 INTRODUCTION TO FERROUS METALLURGY1 atm. = 760 mm. of mercury1 atm. = 29.92 in. of mercury1 atm. = 33.9 ft. of water1 atm. = 14.7 p.s.i.

1 in. of mercury = 25.4 mm. of mercury1 in. of mercury = 1.13 ft. of water1 in. of mercury = 13,6 in of water1 in. of mercury = 0.491 p.s.i

Volume. The volumes' of gases are usually expressed in cubicfeet in the English system. One cubic foot equals 28.3 liters or28,300 cc. Standard conditions in the English system are32F. and 1 atm. pressure.Example: If a certain gas occupies 89.7 cu. ft. at 29.1 in. of

mercury and at 68F., find its volume at standard conditions(32F. and 29.92 in. of mercury).

Original conditions:Vi = 89.7 7\ = 528R. (460 + 68) PI = 29.1

Final conditions:V2 = ? T2 = 492R. (460 + 32) P2 = 29.92

4Q2 2Q 1F2 = 89.7 X X ^ = 81.29 cu. ft.528 29.92THE KINETIC-MOLECULAR HYPOTHESIS

We know that when a gas is compressed, i.e., its volumedecreased, it is under a higher pressure than before compression.Also, we know from experience that when a fixed volume of gasis heated, its pressure also increases. If the pressure is keptconstant and the gas is heated, an increase in volume takes place.These facts require explanation and can be explained most com-pletely by the conception of the internal structure of matterknown as the 'kinetic-molecular //,,'' -".

This hypothesis first assumes that all matter is composed ofexceedingly minute particles called molecules, the molecules ofany particular substaflce being all alike in. nature and weight,I solids and liquids these molecules are packed closely together


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GENERAL INORGANIC CHEMISTRY 21more so in solids than in liquids. In gases, however, the mole-cules are widely scattered with much vacant space between them.In the second place, the hypothesis assumes that the molecules ofall substances under ordinary conditions are in rapid motionand consequently possess kinetic energy. Whereas in liquidsand solids this motion occurs within a definite and limitedvolume, the molecules of a gas are free to distribute themselvesthroughout all of the containing vessel. The bombardment ofthe molecules of a gas on the walls of the containing vessel producethe effect commonly known as pressure. The hypothesis gets itsname from these two assumptions and has been found to be truein all respects.

According to the foregoing ideas of the internal structure of agas, compression of the gas involves only compression of theempty space between the molecules. Since the molecules are inrapid motion in straight lines except when they come in contactwith other molecules or with the walls of the vessel, compressionof the gas increases the frequency (number of times per second)with which the molecules strike the walls of the Vessel. This isbecause the compression has reduced the space through whichthe molecules must travel before striking the walls of the vessel.There is no tendency for a gas to settle in its containing space

because the pressure of a gas on the top and bottom of its con-tainer can be found to be exactly equal. Because of this fact, wemust assume that the molecules of the gas are in constant motionwithout loss in energy because if they slowed down some settlingwould take place. We must further assume that each moleculeof any one gas is exactly like every other molecule of that gas,because if any difference in energy or weight were present, settlingwould again occur. We therefore reason that the moleculesare perfectly elastic, i.e., they bounce back from contacts withother molecules and from the walls of the container without lossof energy. This property of molecules is unlike any aggregatesubstance, because a rubber ball, for example, when dropped onthe floor will lose energy at each bounce until it comes to rest.It is therefore not perfectly elastic. The speed of motion ofmolecules of a gas is very high; in fact the velocity of a hydrogenmolecule at room temperature is about 1,840 m. per sec.The fact that the pressure of a gas at constant volume increaseswith increase in temperature can be explained by assuming that


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22 INTRODUCTION TO FERROUS METALLURGYthe velocity of each molecule is increased as the temperature israised, an assumption that can be proved. This increase invelocity increases the kinetic energy of the molecules and, there-fore, the pressure, since the frequency of bombardment of theconstant number of molecules against the walls of the containerincreases with an increase in their velocity.At ordinary pressures, the njolecules of a gas show almost nodesire to stick together (to cohere). At very high pressures,however, the empty space between them reaches such a lowvalue that the molecules are close enough together to show somecohesion. We find experimentally that all gases can be liquefied(changed to the liquid state) if the temperature is sufficientlylow and the pressure great enough. When the kinetic energy(energy of motion) of the molecules is reduced low enough bycooling and the molecules are brought close enough together bycompression, the gas will condense to a liquid state. It is furtherfound that the kinetic energy must be reduced to a certain lowvalue for each gas in order that liquefactionmay occur at any pres-sure, however great. This means that the gas must be cooled toa certain temperature, called the critical temperature for thatgas, and the farther below this temperature the gas is cooled,the smaller the amount of pressure necessary to liquefy it. Thecritical temperature of hydrogen is -234C. (-389F.), ofoxygen -118C. (-180F.), of carbon dioxide 31.35C. (88F.),and of water 374C. (705F.). By changing the pressure andfurther cooling the liquefied gas, the liquid can be frozen to thesolid state. For example, the melting point of solid hydrogen is-260C. (-436F.).

In the liquid state, the molecules are packed so closely togetherthat compression takes place only by using enormous pressures.The molecules are so close together that cohesion is quite pro-nounced and the liquid hangs together in drops and, when presentin a container of larger size than its volume, does not completelyfill the container but possesses a surface at its upper boundary.The liquid does possess, however, the general properties of a gasto a modified degree and, as the temperature of the liquid israised, the differences between the liquid and the gas become lessand less until, at the critical temperature, they become identical.The temperatures at which the solid changes to the liquid stateand the liquid changes to the gaseous or vapor state are known


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GENERAL INORGANIC CHEMISTRY 23as transition points and each occurs at a definite temperature foreach substance at a fixed pressure. The temperature at whichthe solid-to-liquid change occurs is known as the melting orfreezing point and the temperature of the change from liquid togas the boiling point.For the purpose of studying the relations between the liquidand the vapor state in greater detail, let us assume that a quan-

tity of liquid water is introduced into a previously evacuated con-tainer of greater volume and in such a way that a vacant spaceexists above the liquid. Let us further assume that the temper-ature remains constant. In spite of the great cohesive forcesexisting between the molecules in the liquid state, the motionof the molecules causes some of them to break through thesurface layer of the liquid and enter the previously empty spaceabove where they move around as molecules of a gas. As soonas a few of them are present in the vapor space, they begin toexert a pressure upon the liquid below by their bombardment ofits surface. In so doing, some of them reenter the liquid buttheir places are immediately taken by other molecules shootingforth from the liquid. At first, emission of molecules from thewater takes place while there are no molecules in the vapor stateto reenter the liquid. The pressure of the vapor increases,however, as the concentration of molecules in the vapor spacebecomes greater. Also, the number of vapor molecules plungingback into the liquid increases in proportion to the degree to whichthey are crowded together in the vapor space. The rate at whichmolecules return to the water begins at zero and increasessteadily, while the rate at which molecules leave the water main-tains a constant value. Hence the rate (number per unit time)at which vapor molecules enter the water must finally equal therate at which water moleculea leave the liquid. A greater numberof molecules cannot leave the liquid than return to it because thepressure in the vapor space is too high for additional moleculesto overcome. Likewise, if more molecules enter the liquid in agiven time than leave it, the pressure of the vapor space decreasessufficiently to allow the escape of more molecules from the liquid.A balanced state, therefore, sets in, in which the number ofmolecules leaving the vapor space is exactly balanced by thenumber entering it, and the pressure in the vapor space remainsat a fixed value. This pressure can be measured and is known


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24 INTRODUCTION TO FERROUS METALLURGYas the vapor tension of the liquid and, in the case of water, isknown as the aqueous tension.Such a balanced state as that just described is known as a

state of equilibrium. It is emphasized that this condition is nota static state (at rest) but a dynamic one (in motion). There arethree important characteristics of a state of equilibrium:

1. There are always two opposing tendencies which, whenequilibrium is established, exactly balance each other. In theprevious case, one tendency is the hail of molecules leaving theliquid, a constant value that represents the vapor tension of theliquid. The other tendency is the hail of returning moleculeswhich increases from zero to its final value. This is known as thevapor pressure of the vapor. These have the effect of opposingpressures and, when they become equal, equilibrium is reached.We can symbolize the two opposing tendencies by arrows, thus,

Water (liquid)


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GENERAL INORGANIC CHEMISTRY 25esis. Thus, we can say that a liter of hydrogen contains just asmany molecules as a liter of oxygen, a liter of chlorine, or a liter ofany gas measured under the same conditions of temperature andpressure.

LAWS OF CHEMICAL COMBINATIONIn the previous section we studied two of the laws governing

chemical action:1. The law of conservation of mass, which states that within

the limits of experimental accuracy no change in the total massof matter can be detected as a result of any transformation thatmatter may undergo; and

2. The law of definite composition, which states that the com-position of a pure compound is always precisely the same.

In this section we extend these laws.Combining Weights. In the law of definite composition we

found that the elements making up a compound did so in a.definite weight ratio. These combining weight ratios are easily

TABLE 4-1. A FEW COMBINING WEIGHTS


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26 INTRODUCTION TO FERROUS METALLURGYcalculated from the analysis of pure compounds. Since most ofthe elements combine directly with oxygen, it is possible to learnfrom experiment what weight of each will combine with a fixedweight of oxygen. These weight numbers may then be compared.

Table 4-1 shows a list of relative weights in which some of theelements combine with 8 g. of oxygen. We immediately wonderwhy the chemist has chosen oxygen and exactly 8 g. of oxygen.Since the combining weight of each element is a true constant ofnature, it was essential to select one element as a standardand determine what weight of every other element will combinewith some fixed weight of this standard. Convenience has beenthe chief guide in selecting oxygen as the standard. Convenienceagain has been the factor in assigning the value of eight to oxygen.Any number might have been chosen since the combining num-bers are merely relative to the arbitrary value assigned to thestandard. This integer of eight is the smallest convenient onesince it is found that 8 g. of oxygen unite directly with 1.008 g.of hydrogen to form water. Any smaller value would make thecombining weight of hydrogen, the lightest known substance, lessthan unity-and it is well to have all values at least as great asunity.From this table we may derive a partial list of combining orequivalent weights:

Oxygen. 8.0 Hydrogen 1 .008Magnesium 12. 16 Aluminum 9.0Copper 31.8 Carbon 3.0Calcium 20.03

From this table we might postulate that, since 1.008 g. ofhydrogen are equivalent to 8 g. of oxygen, the weight of anyelement uniting with 1.008 g. of hydrogen would probably unite(if at all) with exactly 8 g. of oxygen. Thus, it is found that35.46 g. of chlorine will unite exactly with 1.008 g. of hydrogen,and, according to our above postulation, this amount of chlorineshould combine with 8 g. of oxygen, which it does do.

Fluorine will not combine with oxygen, but it will combinewith silver to form silver fluoride. It is possible to find the com-bining weight of fluorine by using equivalent weights. Thus wecan say

Oxygen Hydrogen Chlorine Silver Fluorine8g. l.OOSg. 35.46g. 107. 88 g. 19 g.


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GENERAL INORGANIC CHEMISTRY 27This table states that 19 g. of fluorine are equivalent to 8 g. ofoxygen since 19 g. of fluorine combine with 107.88 g. of silver,which combine with 35.46 g. of chlorine, which combine with1.008 g. of hydrogen, which combine with 8 g. of oxygen.There are many instances where two elements combine indifferent proportions to form a series of compounds. It wouldseem possible then for some of the elements to have at least twocombining weights. Let us take the two* oxides of hydrogen,for example.

Similarly, we may consider the two oxides of carbon.

Considering the combinations of nitrogen and oxygen, we findthat five oxides are formed with radically different properties.

From these illustrations we can see that the elements combinein the ratio of their combining weights or simple whole multiplesof these. Thus the law of multiple proportions may be stated inthe following way: In a series of compounds that are made up ofthe same elements, a simple ratio exists between the weights ofany one element that combine with a fixed weight of another


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28 INTRODUCTION TO FERROUS METALLURGYIt should be emphasized again at this point that the law of

multiple proportions applies equally when the units of weight arein the English system, expressed as ounces, pounds, or tons. Theprincipal thing to remember is that a simple ratio exists betweenthe weights regardless of what the units are, provided all weightsare expressed in the same units.

ATOMIC HYPOTHESISWe have found in the previous study that the combining

weights are different for different elements. There is apparentlysomething significant in the fact that, in the compounds of oxy-gen with hydrogen, the amount of oxygen combined with a givenweight of hydrogen is eight, or twice eight, times the weight ofthe hydrogen.

Since water is composed of 8 parts by weight of oxygen and 1part of hydrogen, the smallest masses of water must have thiscomposition. For the same reason, the smallest masses ofhydrogen peroxide must contain 16 parts by weight of oxygen to1 of hydrogen. Why is eight the characteristic of oxygen, andwhy is there no compound of these elements in which the ratiois 10 : 1 or 20 : 1 ? These facts may be explained by the atomichypothesis.

It was John Dalton, an English scientist, who made certainassumptions in looking for an explanation for the facts to describethe laws of definite composition and of multiple proportion, fromwhich the atomic theory has been developed. His theory is asfollows:

1. The ultimate particles of a pure substance, simple or com-pound, are alike in size and weight.

2. The " simple atoms'* of an elementary substance areindivisible, and can neither be created nor destroyed.

3. The " compound atoms M of a chemical compound areformed by the union of two or more elementary atoms.

4. Combination between atoms takes place in the simplestpossible ratios, e.g., one atom of A with one, two, or three atomsof B.

If we now think of the universe as being composed of atoms,we immediately ask the question whether there is an infinitenumber of different kinds of atoms, corresponding to the almostendless variety of material things or whether all material things


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GENERAL INORGANIC CHEMISTRY 29are composed of relatively few different kinds of atoms. Inanswer, we believe now that there are only 92 kinds of atoms,as many as there are elements. From these elements or atomsthe thousands of complex materials are formed by bringing theminto special groupings or arrangements, each having the char-acteristics of a given material.Such combinations, formed by atoms entering into chemicalunion with one another, are now called molecules. A moleculeis, therefore, the smallest particle of any. pure substance. If wewere to take a molecule of sugar apart, we should have particlesthat no longer taste like sugar. They would merely be atoms ofcarbon, hydrogen, and oxygen. The smallest particles of ele-ments taking part in chemical reactions are thus called atoms. Achemical reaction, then, is merely a regrouping of the atoms innew combinations. Two or more atoms of the same kind mayunite to form molecules of an elementary substance.

This theory explains the law of conservation of mass since areaction taking place between substances in a closed vessel isfound neither to gain nor to lose weight. In other words, all theatoms in the reacting substance are accounted for in the newsubstance.

It explains the law of definite composition for, when one ele-ment unites with another, the combination always takes placebetween a definite number of each kind of atom. In the for-mation of water it is found that the percentage of oxygen andhydrogen by weight is always the same.

It also explains the law of multiple proportion in that, whentwo atoms of hydrogen unite with two atoms of oxygen, insteadof one as in water, a new compound is formed which is quitedifferent from water. This compound is called hydrogenperoxide.Modern Atomic Theory. Dalton's atomic theory did notexplain why some elements react with each other and others donot, what forces hold atoms together in molecules, and how theconstituent atoms are arranged. It has been only in recent yearsthat scientists have been able to obtain information on the struc-ture of the atom and this has been done principally through theuse of the X-ray beam and the study of radioactive elements.Although the ideas of scientists vary somewhat as to the details,the following concept is fairly well established at the present time.


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30 INTRODUCTION TO FERROUS METALLURGYAccording to the modern concept an atom consists of a posi-

tively charged nucleus which is very small compared to the sizeof the atom. In this nucleus is located nearly all of the mass ofthe atom. Around this nucleus there is a distribution of plane-tary particles called electrons in orbital motion. The atom,therefore, consists of small particles each of which has an elec-trical charge. The positively charged particles are calledprotons and the negatively charged particles electrons. All theprotons in the atom are identical and each possesses one unit ofpositive electricity. Likewise all electrons are identical and eachpossesses one unit of negative electricity. The nucleus is foundto be made up of both protons and electrons, closely associated ina group. The nucleus contains all the protons and, since thereare always a greater number of protons than electrons in thenucleus, it has a net positive charge. The total charge on theplanetary electrons is just equal to the net positive charge onthe nucleus. This atom is like a planetary system with thenucleus replacing the sun and the electrons replacing the planets.The size of these central suns differs from atom to atom and thenumber of planetary electrons also differs from atom to atom.

It has been found that the positive charge of the nucleus isdifferent for each element and that this nuclear charge is equalto the sequence number of the element in the periodic system.If we examine the periodic table shown on page 46, we shallnote that the figures appearing above the abbreviations of theelements start with hydrogen as unity and that successivevalues differ from each other by unity. The elements, thus, arearranged in a general order from 1 to 92. This arrangement andinterpretation were made possible through the studies byMoseley. He was able to show that this regularity was due toregular changes of the charge on the nucleus. The charge on thenucleus of the hydrogen atom is found to be 1, of the heliumnucleus 2, etc. This number is known as the atomic number andrepresents the number of positive charges on the nucleus of anatom of the element and denotes its position in the series ofelements. To illustrate: The number of hydrogen is taken as 1,which means that the hydrogen atom is made up of one protonas a nucleus and one electron in orbital motion about thisnucleus (Fig. 2-1). In this case the positive charge on theproton is just equal to the negative charge on the electron so


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GENERAL INORGANIC CHEMISTRY 31that the atom in the normal condition is neutral. When we passfrom hydrogen, which has an atomic weight, atomic number, andatomic charge of unity, we next come to helium with an atomicweight of 4 and an atomic number or nuclear charge of 2. Thehelium nucleus, with which is associated most of the massof the helium atom, consists of four hydrogen nuclei or protons.These four protons would give a nuclear charge of four' units,but the nuclear charge is 2 so that there must also be two elec-trons in the nucleus. The effective nuclear charge is thustwo units of positive electricity (Fig. 2-1). The atoms oflarger atomic weight are thus formed by adding additionalunits to the core of the atom and additional electrons to theregion outside the core.

^' -x /Electron-( "\\ / A '^__^ ^Nucleus'' ^----'H HeFIG. 2-1. Hydrogen and helium atoms.

The entire chemical beha.vior and most of the physical proper-ties of the atoms are determined by the planetary electrons.Even though there is an electrical attraction between the elec-trons (negative) and the protons (positive), some of the outerplanetary electrons are known to escape to other atoms. Forexample, some of the most active atoms like those of the metalssodium and potassium have a very great tendency to give awaytheir outer electrons, while some of the most active nonmetallicatoms like those of fluorine and chlorine have a reluctance togive away electrons but have a strong tendency to take onelectrons. Thus we can see why two such active metallic atomswill not react with each other each of these two types is tryingto do the same thing, throw off an electron. To illustrate thistendency, let us consider a typical chemical reaction. We findthat sodium reacts with chlorine, because of the fact that thechlorine atom takes the electron that the sodium atom is willing togive away and we have a chemical reaction to form a molecule ofsodium chloride (salt). This electron transfer is shown in Fig.3-1. Here we see that the electrically neutral sodium atom loses


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32 INTRODUCTION TC FERROUS METALLURGYan electron and leaves an excess of one proton, or positive charge,on the atom, while the neutral chlorine atom gains an electronand makes that atom negatively charged. Thus we have twooppositely charged atoms held together in the molecule of saltby electric attraction.

In some types of reaction outer planetary electrons are sharedby the atoms in pairs. In the simplest case two atoms share asingle pair of electrons. For example, two fluorine atoms com-bine to form a fluorine molecule. Before combining, each fluorineatom has the desire to take on one electron, so rather than onerob the other they compromise by sharing electrons. Thissharing of electrons is also true of a few other elements, such as

t (@! T

Na * Cl * Ma* CiFIG. 3-1. Electron transfer and chemical reaction.

oxygen, hydrogen, nitrogen, and chlorine. Hence the moleculeof these elements is composed of two atoms.The atoms of inert gases like helium, neon, and argon areso stable that they neither gain nor lose planetary electrons;consequently they never react with anything and thus form nocompounds. With these gases, therefore, one atom constitutesa molecule.Atomic Weights and Molecular Weights. We have seenhow the combining weights of the elements can be determined

with accuracy and how the atomic theory interprets thesecombining weights to be the relative weights of the atoms.The difficulty is, however, that nearly all elements combinein more than one ratio and, therefore, have more than onecombining weight. For example, hydrogen and oxygen unite inthe ratio of 1 :7.94 to form water and in the ratio of 1 : 15.88 toform hydrogen peroxide. To determine whether 7.94 or 16* 8 isthe relative^ atomic weight of oxygen, we must first know therelative weight of the water molecule and how many atoms ofeach element it contains.


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GENERAL INORGANIC CHEMISTRY 33According to Avogadro's hypothesis, we found that equalvolumes of gases under identical physical conditions contain thesame number of molecules. From this we can deduce that the

weights of equal volumes of two gases are in the same ratio asthe weights of their molecules. Thus, if we find that a liter ofcarbon dioxidp gas is about one-third heavier than the samevolume of oxygen gas under the same conditions of temperatureand pressure, we know that the molecule of carbon dioxideis about one-third heavier than a molecule of oxygen. It must benoted that this method applies only to gases and vapors and notto liquids or solids. Other methods which will not be describedhave been found for obtaining the relative weights of the mole-cules of substances that are not readily gasifiable.Oxygen has been chosen as the standard of comparison in

finding the relative weights of atoms and molecules, since it canbe made to combine with nearly all the elements. A moleculeof oxygen is arbitrarily taken as 32 units of weight so that thelightest known substance (one atom of hydrogen) comes out witha weiglit very close to 1.The average weight of the molecule of a given substance, incomparison with a molecule of oxygen, taken as 32 units, iscalled the molecular weight of the substance. Thus, when wesay that a gas has a molecular weight of 64, we imply that oneof its molecules is twice as heavy as a molecule of oxygen.Having determined the relative weights of molecules, we cannow find the relative weights of the atoms of which they are

composed. Such relative weights of atoms in comparisonwith a molecule of oxygen, taken as 32 are called atomicweights.The approximate atomic weights of an element may be deter-*mined by noting the least weight of each element found in amolecular weight of any of its compounds. The least weight ofan element in a molecular weight apparently then corresponds tothe least possible number of atoms in a molecule, or one atom.For example, in the analysis of carbon compounds the leastweight of carbon ever found in any of them is 12. Therefore,this is the relative weight of one atom of carbon on the scalethat makes a molecule of oxygen weigh 32. Atomic weightshave thus been determined for all the elements except the inertgases, which have beea determined by other means. The approx-


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34 INTRODUCTION TO FERROUS METALLURGYimate atomic weights are found to range from 1, which is theatomic weight of hydrogen, to 238, which is that of uranium.The atomic weight of oxygen, hydrogen, and nitrogen is justone-half of the molecular weight and accordingly there must betwo atoms in a molecule of each of these elements.The atomic weights have been referred to as approximate ones.

This is due to the fact that the molecular weights from whichthey were determined were also slightly in error. However, whena very pure compound is very carefully analyzed, the chemisthas been able to correct the atomic weights of the elements itcontains. The accurate atomic weights may be found by refer-ring to the periodic table on page 46.Molar Volume. Having adopted the arbitrary value of 32as the molecular weight of oxygen, we should like to know whatvolume 32 g. of oxygen gas would occupy. One liter of oxygenweighs L429 g., so 32/1.429 = 22.4, the number of liters occupiedby 32 g. of oxygen. For convenience, let us imagine a cubictank that will hold exactly 22.4 liters. If this tank were filledwith oxygen or any other gas under standard conditions, theweight of the contents in grams must be the formula weight ofthat gas, since we see that it is true for oxygen. Thus, accordingto Avogadro's hypothesis, since this tank must hold the samenumber of molecules of any gas, the weights vary as the weightsof the single molecules. If, therefore, the tank were filled withhydrogen, it would weigh 2.016 g. and the molecular weightwould be and is 2.016. The gram-molecular volume of ammoniaweighs 17 g. Thus, the molecular weight of ammonia is 17.

In practice it would be very awkward to weigh exactly 22.4liters, so we simply weigh any convenient volume, say 100 cc.and calculate the weight of 22.4 liters.By the English system the molar volume may be calculated as

follows: One cubic foot of oxygen weighs 0.089 lb., so32 =3590.089

the number of cubic feet occupied by 32 lb. of oxygen. Thisnumber, 359 cu. ft., is generally called the pound-molar volumeto distinguish it from the molar volume found by using gramsand liters (22.4) which is called the gram-molecular volume.


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GENERAL INORGANIC CHEMISTRY 35Both these figures hold for any gas regardless of its composition,providing its molecular weight is known.

SYMBOLS, FORMULAS, AND EQUATIONSChemical Symbols. We have seen that each element is

represented by its symbol. Not only does each symbol standfor a certain element, but it also represents a definite weight ofthe element, namely, a weight proportional to its atomic weight.If we employ the gram as our standard of weight, then thesymbol indicates 16 g. of oxygen; H indicates 1.008 g. ofhydrogen. Such a weight is called the symbol weight or gram-atomic weight of an element.

If we employ the pound as our standard of weight, then thenumber representing its atomic weight also indicates the numberof pounds for which the symbol stands. Thus O stands for16 Ib. of oxygen and H equals 1.008 Ib. of hydrogen. Whenthe pound is used as the unit of weight, the atomic weightis known as the pound-atomic weight.Chemical Formulas. A chemical formula is a group of symbolsshowing what kinds of atoms and how many of each are present inany given molecule. Symbols refer to atoms. Formulas referto molecules. To represent the formula of a compound, wesimply join the symbols of the constituent elements and attachsmall subfigures to represent the actual number of atoms in themolecule. In expressing the composition of the compound, wemight use the symbols merely to indicate the elements present inthe compound and also give the percentage of each, thus: H,11.19 per cent; 0, 88.81 per cent. It is much more convenientand concise to make use of the atomic weights of the elementsconstituting the compound. The united symbols H2O representthe formula for water and tell us that two atoms of hydrogenand one atom of oxygen make up a single molecule of water.The weight of the molecule, 18.016, is the sum of the weights ofall the atoms in it; thus (2 X 1.008) + (1 X 16) = 18.016.Since this weight represents the sum of the atomic weights ofthe elements in the formula, it is called the formula weight ormolecular weight of the compound that the formula represents.

In the case of the formulas for the elements, we have alreadyfound in the study of the atom that the molecule of such elementsas oxygen and hydrogen is composed of two atoms; hence the


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36 INTRODUCTION TO FERROUS METALLURGYmolecular weights of these elements are twice their atomicweigttts. The formulas for these elements, when existing asgas or vapor and when uncombined with other elements, arealways represented as O 2 , H 2 , N 2 , C12 , etc. In the case of theinert gases, where one atom constitutes a molecule, the atomicweight is identical with the molecular weight.When we deal with a solid element, such as carbon, sulfur,phosphorus, or solid metals, in the crystalline state, there is nodefinite number of atoms in the molecule and no definite molec-ular weight. We therefore usually represent solid elements bythe symbols of their individual atoms and do not try to indicatetheir true, or molecular, formulas.The formula for a substance may be found in several differentways, depending upon what is known. For example, if we areunable to determine the molecular weight of a compound byexperiment, we can still deduce its simplest formula from itspercentage composition alone, though we cannot be sure thatsome multiple of this simple form is not the real formula. Weknow by experiment that water is composed of 88.81 per centof oxygen and 11.19 per cent of hydrogen. If we divide the per-centage of oxygen by its atomic weight (16), the quotient (5.55)will be the relative number of oxygen atoms in 100 parts of water.Similarly, if we divide the percentage of hydrogen by its atomicweight (1.008), the quotient (11.10) will be the relative number ofhydrogen atoms in 100 parts of water. The two numbers 5.55and 11.10 represent the ratio between the number of oxygenand hydrogen atoms in 100 parts of water. This ratio reduced toits simplest form is *

11.10 -f- 5.55 = 2 5.55 + 5.55 = 1The ratio of hydrogen atoms to oxygen atoms in a molecule ofwater is therefore 2:1, and the simplest formula of water, aswell as the real formula in this case, is H 2O.

If we are able to determine the percentage composition of acompound and its molecular weight, we can therefore deduce theformula of the compound as follows: Suppose we know that themolecular weight of water vapor is approximately 18. Thisrepresents the sum of all the atomic weights in the molecule.Multiplying 18 by the percentage of hydrogen (11.19) gives 2.016as the sum of the weight of hydrogen atoms present, or 2 atoms.


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GENERAL INORGANIC CHEMISTRY 37Multiplying 18 by 88.81 per cent gives the sum of the weight ofoxygen atoms 15.99 or almost exactly 16, or 1 atom. Thus, theformula is H 2O.

Equations. With the use of symbols and formulas we can nowrepresent chemical changes (reactions) very simply and clearly.Fos example, the equation

2H + O -> H 2which is sometimes written with an equals sign instead of anarrow :

2H + = H2This equation reads qualitatively that the union of hydrogenand oxygen forms water, and quantitatively that 2 gram-atomicweights of hydrogen (2.016 g. or Ib.) combine with 1 gram-atomic weight of oxygen (16 g. or Ib.) to form 1 gram-molecularweight of water (18.016 g. or Ib.).We know, however, that the molecules of oxygen and hydrogencontain two atoms each so that the formulas for these gases are

written O 2 and H 2 rather than 20 or 2H which would representtwo atoms uncombined. To state these facts our equation willhave to read 2H 2 + 2 = 2H 2This type of equation, known as the molecular equation, willordinarily be used in future studies.The equality sign, more definitely than the arrow, indicatesthat the sum of the weights of the reactants is always equal tothe sum of the weight of the resultants (law of conservation ofweight). It also states that the total number of atoms of eachkind in the left-hand part of the equation (left of the arrow orequality sign) must equal the total number in the right-handportion. When this condition is true, the equation is said to bebalanced.A great amount of practice is necessary before equations canbe balanced easily. For example, in the reasoning necessary, letus suppose that by laboratory observation we know that hydrogenreacts with hot iron oxide to form iron and steam. This equationthen can be tentatively written as follows:

H2 + Fe3O4 -> Fe + H2O (trial)


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38 INTRODUCTION TO FERROUS METALLURGYbut on observation we see that all the atoms in the reactingsubstances are not found in the products. We know that in theformation of any new combinations of elements all the atomsmust be accounted for, hence there must be an equal number ofH atoms, of O atoms, and of Fe atoms on both sides of the equa-tion. First of all let us try one molecule of Fe3 4 . In equationswe do not prefix " 1 " to molecules; it is understood if no numberis given. As a result of the decision to use one molecule of Fe 3O4,we must account for 3 atoms of Fe on the right side of the equa-tion. With this change the equation will read

H2 + Fe3 4 - 3Fe + H 2 (trial)We see immediately that the 4 oxygen atoms in Fe3 4 are notfound in a single molecule of H 2O. It is, therefore, necessaryto have 4 molecules of H 2O to dispose of the 4 oxygen atomsbecause each molecule of H 2O uses only one atom of oxygen.This change will bring a further improvement.

H 2 + Fe3 4 - 3Fe + 4H 2 (trial)With 4 molecules of H 2O on the right side there are required 8atoms of hydrogen, found in 4 molecules of H2 , on the left sidefor proper balance :

4H 2 + Fe 3O 4 -> 3Fe + 4H 2 (balanced)Every atom is now accounted for on both sides of the equationwhich is, therefore, properly balanced.A chemical equation, then, must represent the reacting sub-stances, the products formed, and the relative weights involved.It does not, however, name the conditions temperature, etc.,necessary to cause the reactions to take place nor does it tellhow rapidly or to what extent the reaction occurs.From our previous observations we can set up a system for

making an equation. This is as follows:1. Write on the left of the arrow ( ) the formulas (or sym-

bols) of the substances entering into the reaction, and on theright the formulas (or symbols) of the substances formed.

2. Balance the equation or modify it, if necessary, so thatthere will be just as many atoms of each element on one side ofthe equation as on the other.


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GENERAL INORGANIC CHEMISTRY 39Type of Reactions. After a study of many reactions, the

chemist has found that equations may represent processes ofdecomposition, direct combination, simple replacement, anddouble replacement. We shall find almost all the reactions thatwe have met and shall meet can be assigned to one of theseprocesses. Many of the equations used to illustrate theseprocesses will not be familiar; however, they are used here toaid the student in formulating completed equations.

Decomposition is the separation of one compound into othercompounds or elements. The equations that describe thepreparation of oxygen by applying heat to certain substanceswill serve to illustrate this process. They areFrom mercuric oxide:

2HgO -> 2Hg + 2 (1)From potassium chlorate > potassium chloride + oxygen:

2KC1O 3 -> 2KC1 + 3O 2 (2)Direct combination is the formation of one compound fromtwo or more elements. This is illustrated by the combustionof elements in oxygen and by the action of hydrogen on differentelements.Combustion of phosphorus > phosphorus pentoxide:

4P + 5O 2 -> 2P2O 5 (3)Combustion of iron magnetic iron oxide :3Fe + 2O 2 -> Fe3O 4 (4)

Hydrogen + chlorine > hydrochloric acid:H 2 + C12 -> 2HC1 (5)

Hydrogen + nitrogen > ammonia:3H 2 + N2 - 2NH8 (6)Hydrogen + oxygen > water:

2H 2 + O 2 - 2H2 (7)Simple replacement, or simple displacement, means that one

element may take the place of another in a compound, the


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4b INTRODUCTION TO FERROUS METALLURGYsubstituted element being set, free. This is illustrated by thefollowing reactions:

Preparation of hydrogen from acids by the action of metals:Iron + hydrochloric acid > ferrous chloride + hydrogen:

Fe + 2HC1 -> FeCl 2 + H2 (8)Iron + sulfuric a,cid > ferrous sulfate + hydrogen :

Fe + H2SO 4 - FeSO 4 + H2 (9)Preparation of hydrogen from water by the reaction as follows:Water + sodium > sodium hydroxide -f hydrogen :

2H 2O + 2Na - 2NaOH + H2 (10)Water + iron magnetic iron oxide + hydrogen :

4H 2O + 3Fe -> Fe3O 4 + 4H 2 (11)Doubk replacement, or double decomposition, probably themost common type of reaction, consists in the interchange of

tw,o elements present in two different compounds, thus resultingin the formation of two new compounds. This may be illustratedby another equation showing the formation of hydrochloric acid.This involvesSodium chloride (salt) + sulfuric acid sodium sulfate +hydrochloric acid:

2NaCl + H 2SO 4 -> Na2SO 4 + 2HC1 (12)In this case the sodium of the sodium chloride and the hydro-

gen of the acid change places to form two new compounds.Application of Equations. The balanced equation of a reaction,

in which molecular formulas are used, tells us a great deal regard-ing the reaction besides the mere statement of the substancesentering into and resulting from it. For example, from theequation below, the succeeding quantitative data can be deduced:

2H 2 + O 2 - 2H 2OWeights: 2 X 2.016 g. 32 g. 2 X 18.016 (= 36.032 g.)Molecules: 2 1 2Given the formula for a chemical compound, we can easily

calculate the percentages of the constituents in it. A sample


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GENERAL INORGANIC CHEMISTRY 41calculation to discover the percentage composition of potassiumchlorate (KClOs) follows. The first step is to look up the atomicweights of the elements involved and calculate the formulaweight, the weight of substance represented by the molecularformula. The atomic weight of potassium is 39. 1, that of chlorine35.46, and that of oxygen 16. The formula weight of the sub-stance is therefore

39.1 + 35.46 + 3 X 16 = 122.5639 1The percentage of potassium is TSo1^ X 100 = 31.9-f per cent

. f U1 . . 35.46 X 100 00 A ,The percentage of chlorine is THS"^ == 28.9+ per centJLJJ.oDThe percentage of oxygen is 10^-r-A X 100 = 39.1+ per cent

Another way of stating the above is as follows: If 39.1 parts ofpotassium are contained in 122.56 parts of KC1O 3 , X parts willbe contained in 100 parts of KC1O 3 . The proportion is

39. 1: 122.56 ::X: 100X =

and the result is the same as the first statement.It is often necessary or desirable to know the amount of a

product that can be obtained from a chemical reaction when theweight of the original material is known. For example, let usdetermine the weight of ferrous sulfide that can be producedfrom 100 g. of iron, assuming that the necessary sulfur is athand. The necessary steps in the solution are as follows:

1. Write the balanced equation:

Fe + S - FeS2. Place under each formula the weight it represents.

Fe + S - FeS55.84 32.06 87.90

3. Read the expanded equation. In this case: 55.84 partsof iron combine with 32.06 parts of sulfur to give 87.90 parts offerrous sulfide.


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42 INTRODUCTION TO FERROUS METALLURGY4. Reread the original problem: "What weight of ferrous

sulfide can be made from 100 g. of iron?" Then place theamount given in the problem (100 g. of iron) under the formulaof the substance in question arid an X under the formula of thesubstance, the amount of which is desired in the answer (FeS).

Fe +. S -* FeS55.84 32.06 87.90100 g. X

5. Read the problem as now written: 55.84 g. of iron give87.90 g. of ferrous sulfide. Therefore, 100 g. of iron will produceX g. of FeS.

6. State the proportion and solve:55.84 : 87.90:: 100 :Xx _ 87.90X - 5T.84 X 10X = 157.4 g. of FeS

In such a simple problem, some parts of this procedure seemunnecessary. In more intricate problems, however, such a pro-cedure is necessary in order to arrive at the correct result withouterror and the student is advised to get into the habit of using theabove method in detail in order to avoid trouble in more complexcases.Another type of problem is one involving both weights andvolumes. For example, to find the weight of lime and the volume

of carbon dioxide gas resulting from the burning of 1 ton of purelimestone.

1. The equation:CaCO 3 -> CaO + CO 2100.0 56.0 44.0

2. The weight of lime produced:CaCO 3 - CaO + CO2100.0 56.0

2,000 Ib. X100:56: :2,000:X

v _ 56 X 2,000X ~ 100X = 1,120 Ib. of lime


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GENERAL INORGANIC CHEMISTRY 433. The volume of CO 2 produced: The pound-molecular volume

of any gas equals 359 cu. ft.CaCO 3 -OaO + CO 2100.0 44.0

2,000 Ib. X100 : 44:: 2,000 :XY _ 2,000 X 44A _ _____X = 880 Ib. of CO2

OOA880 Ib. C0 2 - Tr = 20 Ib. molecules4420 Ib. molecules X 359 = 7,180 cu. ft.Volume of CO2 = 7,180 cu. ft. at standard conditions

Problems Involving Calculations of Gas Volume. It is oftennecessary to calculate the volume of a gas that can be obtainedin a given reaction when measured under ordinary laboratoryconditions or the weight of materials that are required to producea given volume. Equations, as we know, deal with weights, soit is necessary to determine first the weight of the gas and fromthis calculate the volume. Since it is always necessary toreduce a measured volume of gas to standard conditions beforeits weight can be calculated, for convenience the weights andvolumes of a few of the more common gases are as follows :TABLE 5-1. VOLUMES AND WEIGHTS OF COMMON GASES AT 32F. (0C.)AND 1 ATM. PRESSURE


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44 INTRODUCTION TO FERROUS METALLURGYProblem: What volume of oxygen, measured under ordinary laboratory

conditions (say, 760 mm. and 20C.), may be obtained by heating 100 g. ofmercuric oxide?

2HgO -> 2Hg + Ot433.22 (2 X mol. wt. HgO):32 (mol. wt. of 2) - 100:XX ==7.38 g. of oxygen1 liter of oxygen (standard) weighs 1.429 g.

7.38 4- 1.429 - 5. 16 liters (standard)41The determination of the volume that this will occupy under laboratory

conditions necessitates the use of the gas laws. Therefore,

V (standard) -^X-lL>< **?v ^standard; ~ 760 x rSubstituting,*ift 750 X Vi X 273" 760 X 283V (laboratory) = 5.63 liters

If we were asked to determine the number of grams of mercuric oxide toyield 10 liters of oxygen measured at 750 mm. pressure and 20C., we wouldproceed as follows:

T7 PXFX273 750X10X273 10 ...V. - -" -~"~ " 9 ' 19 htera9.19 X 1.429 = 13.13 g. oxygen2HgO -> 2Hg + 2

32:433.22 13.13 X xx = 177.75 g. mercuric oxide

Problem: What volume (in cubic feet) of carbon dioxide is produced bythe burning of 1,300 Ib. of. pure carbon with oxygen under standardconditions? C + 2 -> C0 2

12 32 441,300 X12:44: :1,300:Xv 1,300 X 44x . 12X - 4,766 X 8.15 38,843 cu. ft.

PERIODIC TABLEIn the previous studies it was found that each element has

certain peculiar properties that distinguish it from all otherelements. However, if all the elements are considered together,it is found that there are certain groups that have very similarchemical properties. Mendelyeev, a Russian chemist, was thefirst to discover this relationship between the elements and in


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GENERAL INORGANIC CHEMISTRY 451869 he proposed a system of classification in which the elementsare arranged according to their properties. This system isknown as the periodic system and is shown in Table 6-1.

In this chart the symbols of the elements are*given with theatomic weight of each directly below it. A study of the chartreveals that the elements are arranged in horizontal rows of ninein the order of increasing atomic weight. There are nine regulargroups marked Groups to VIII, and the elements contained ineach of these groups have similar chemical properties. Theformulas R20, RO, etc., placed above each group represent thegeneral type of combination of elements in that group which willcombine with oxygen. Similarly H4R, H 3R, H 2R, etc., representthe general type of combination of elements in that group whichwill combine with hydrogen. The groups are further dividedinto (a) and (b) columns. The elements in column (a) havesome properties in common that differentiate them from theelements in column (b). However, all the elements in thevertical group have one important chemical property in common.This chemical property is known as valence.

Valence. Valence may be defined as that property of anatom which enables it to combine with a certain number of atomsof another element, the number of other atoms being the valeflpeof the atom in question. The elements in group do not have thepower of combining with other elements, hence their valence fiszero. The elements of group I have a valence of one, the ele-ments of group II a valence of two, etc. Elements may havepositive valence (+) or negative valence ( ). The .elementsenclosed in the heavy-lined area are known as the nonmetals andusually have negative valence; those elements outside the heavyline are the metals with the exception of hydrogen and the ele-ments of group and usually have positive valence. Althoughhydrogen does not have metallic properties, its chemical proper-ties are similar to those of the metals and it has a valence of +1-As a general rule, elements having a positive valence combinewith those having a negative valence. Thus the metals usuallycombine with thje nonmetals to form compounds. The elementsin group VII have a valenoe of 1, those in group VI a valence of

2. Thus, we see that positive valence increases as we^go fromleft to right in the periodic table while negative valenoe increasesas we go from right to left.


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46 INTRODUCTION TO FERROUS METALLURGY

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GENERAL INORGANIC CHEMISTRY 47A few examples will help to clarify the concept of valence.The chemical formula of common salt, sodium chloride, is writtenNaCl. Sodium falls in group I and is a metal; therefore, it has

a valence of + 1. Thus one atom of a metal with a valence of + 1can combine with only one atom of a nonmetal having a valenceof 1. The one atom of chlorine fulfills this requirement.

In writing the formula for aluminum chloride, we find thataluminum has a valence of +3 and that of chlorine is 1. Themolecule of aluminum chloride must have such a combination ofatoms that the sum of all the valences of the aluminum atomsequals the sum of all the valences of the chlorine atoms. There-fore, the aluminum atom with a valence of +3 requires threeatoms of chlorine with a valence of 1, to make the combination.The formula of this compound is A1C1 3 . As another example,suppose we wish to write the formula for aluminum oxide.According to the table, aluminum has a valence of +3 and oxygen

2. Again we must make the combination of atoms of alumi-num oxide so that the sum of all the valences of the aluminumatoms equals the sum of all the valences of the oxygen atoms.The number 6 is divisible by both 3 and 2. Therefore it takes twoaluminum atoms and three oxygen atoms to make the combina-tion. The formula of aluminum oxide is A1 2O3. The formulas ofchemical compounds must obey the rule of valence which statesthat in every formula the algebraic sum of all the units ofvalence, both positive and negative, is equal to zero. Theunits of valence are obtained by multiplying the valence of anelement by the number of atoms of that element present in thecompound. Applying the rule to A1 2O3 we get:

(+3 X 2) + (-2 X 3) = 6 - 6 = 0.Thus, Al 2Os is the correct formula for aluminum oxide.Some of the elements have more than one valence. Sulfuris a very common element exhibiting this property. In hydrogensulfide, H 2S, it has a valence of 2, in sulfurous acid, H2SO 3,it has a valence of +4, and in sulfuric acid, H 2S(>4, it shows avalence of +6. The ending -ous is always used in compoundsin which the element has the lower positive valence and -ic whenit has the higher positive valence. Table 7-1 shows the valencesexhibited by the common elements and radicals. When tryingto determine the valence of an element in a compound, we


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48 INTRODUCTION TO FERROUS METALLURGYshould remember that hydrogen always has a valence of +1 andoxygen always has a valence of 2.The two acids, H 2SOs and H 2SO 4, each contain what is knownin chemistry as a radical. A radical is a group of atoms, usuallytwo or three, which are combined chemically so that they actthe same as the atom of a single Element and the radical has avalence of its own which is different from the valence of anyof its constituent atoms. In H 2SO 3 the radical is SOa, knownas the sulfite radical. It has a valence of 2 because it com-bines with two atoms of hydrogen. The valence of a radicalmay be obtained from the algebraic sum of the valences of itsconstituent elements, if their valences are known. We knowthat in H 2SOs sulfur has a valence of *+4 and the valence ofoxygen is always 2. Applying the rule of valence we get+4 + 3(- 2) = +4 - 6 = -2 as the valence of the sulfiteradical. In H 2SO 4 the radical SO 4 has a valence of 2 since theSC>4 radical combines with two atoms of hydrogen. The valenceof sulfur in the SO 4 radical may be found as follows:

S + O4 = ~2 or S + 4(-2) = -2S+ (-8) = -2 S - +6The valence of sulfur in H 2SO 4 is, therefore, +6. SO 4 is knownas the sulfate radical. The ending -tfe on the name of a radicalindicates the lower valence of the element from which theradical takes its name and -ate the higher valence state of theelement. Radicals may have either positive or negative valences.The radicals having positive valence have chemical propertiessimilar to metals and those having negative valence act like non-metals. The ammonium radical NH4 has a valence of +1, theformula for ammonium sulfate being written (NH4) 2SO4 . Whenmore than one molecule of a radical combines in a compound itis written inside the' parentheses with the subscript outside; thesubscript is used as if the radical were one element.

In compounds having only two elements present, the ending-ide is generally used on the name of the negative element. Inthis class are the oxides (ferrous oxide, FeO; ferric oxide, Fe 2OsJzinc oxide, ZnO, etc.), the chlorides such as sodium chloride,NaCl, and stannous (tin) chloride, SnCl2, also the sulfides,carbides, nitrides, bromides, iodides, etc.


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GENERAL INORGANIC CHEMISTRY 49Before we leave the discussion of the periodic table there aretwo exceptions to the general classification that have not as yetbeen mentioned. The first is group VIII of the table containing

nine metallic elements. This group is known as the transitiongroup and its elements, as the transition elements. Their proper-ties do not conform to the regular periods of the table and so they

TABLE 7-1. VALENCES OF COMMON ELEMENTS AND RADICALS

are placed in a separate group. There are three horizontal rowsin this vertical group and the elements of each horizontal rowhave similar chemical properties. For example, in the top row,iron, cobalt, and nickel all have properties very nearly alike andshow the same valences in compounds.The second exception to the general rule of the table is agroup of 15 elements known as the rare-earth elements. Theyhave a valence of +3 and their properties are almost identical.They are placed together in one position in group III-A. Their


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50 INTRODUCTION TO FERROUS METALLURGYatomic weights run from J39 to 174. These elements are not asyet of great practical importance and will not be consideredfurther.

WATER AND ITS CONSTITUENT ELEMENTSThe methods of obtaining chemical elements and their com-

pounds, as well as the means used in determining their properties,can best be illustrated by a brief study of the most importantcompound substance known to man the compound called water.Water is the most plentiful of all compound substances becauseit covers about three-fourths of the surface of the earth. It isalways present in the atmosphere and is necessary for the con-tinuance of all kinds of life. It is composed, as we have seen,of the elements oxygen and hydrogen, both gases at ordinarytemperatures and pressures. These two elements will be studiedfirst.Oxygen. Oxygen is an element of utmost importance to us as

all living things would die without it. Nearly 50 per cent of thematter composing the earth and its atmosphere is oxygen.Water contains about 89 per cent oxygen and about one-fifthby volume of the air is free oxygen. Air is a mixture of oxygenand nitrogen with less than 1 per cent total of several rare andinert gases.Commercial oxygen is prepared from liquefied air, which

consists essentially of a mixture of liquid oxygen and liquidnitrogen. Since oxygen boils (changes from the liquid to thegaseous state) at a higher temperature ( 182.5C., 297F.,under 1 atm. of pressure) than nitrogen ( 194C., 317F.)about 96 per cent oxygen can be obtained by allowing liquid air toevaporate slowly under controlled conditions. Oxygen can beliberated from natural substances only with difficulty. Saltpeter(potassium nitrate) can be made to give up some of its oxygen byheating it. In the laboratory, oxygen can best be prepared byheating potassium chlorate, a white crystalline substance usedin the manufacture of fireworks. This reaction may be expressedin the following way:

2KC1O 8 -> 2KC1 + 3O2Potassium chlorate Potassium chloride OxygenIf manganese dioxide is mixed with the potassium chlorate,evolution of the oxygen occurs at a much lower temperature


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GENERAL INORGANIC CHEMISTRY 51(below 200C.). The manganese dioxide is said to catalyze thereaction as it does not enter into the reaction at all but remainsunchanged throughout the experiment. Substances that hastena chemical action without themselves undergoing any permanentchange are called catalytic agents or catalysts and the processis called catalyst**. Still another method of preparing oxygen isby the reaction of sodium peroxide and water. The peroxidereacts with the water to form sodium hydroxide and oxygen asfollows:

2Na2O 2 + 2H?O - 4NaOH + O 2Sodium peroxide Water Sodium hydroxide OxygenOxygen has neither color, taste, nor odor. It is slightly

heavier than air and much heavier than hydrogen. It can beliquefied by pressure if cooled below 1 18C., 180F. Qxygenis only slightly soluble in water (3.1 volumes of the gas in 100 vol-umes of water at 20C.) but this is a very important~property asfish obtain oxygen from that dissolved in water. These are allspecific physical properties of oxygen.

Oxidation. By means of certain experiments it is possible toshow that the action of oxygen upon another element consists inthe union of the two elements to form a compound. Thus, whensulfur burns in oxygen, a new gaseous compound is formed, knownas sulfur dioxide. Likewise, when phosphorus, iron, carbon, andhydrogen burn in oxygen, there are formed compounds of theseelements with oxygen. In general, oxygen combines with mostof the metallic elements (metals), particularly when heated. Theaction of oxygen upon compounds is similar to its action uponelements and usually consists in the union of oxygen with oneor more of the elements present in the compound. Thus, whenhydrocarbons (compounds of carbon and hydrogen) burn in thepresence of oxygen, both the carbon and the hydrogen combinewith the oxygen to form carbon dioxide, CO 2 , and water vapor,H2O. In some cases the compound as a whole unites with theoxygen.

Thus, when any substance or any of its constituent partscombines with oxygen, the substance is said to be oxidized, andthe process or change that takes place is called oxidation. Itshould be noted that this term oxidation is not confined to suchchanges as just mentioned but has a much broader application


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52 INTRODUCTION TO FERROUS METALLURGYin a large group of reactions, in many of which oxygen takesno part.

Oxides. When an element combines with oxygen, the result-ing compound is known as an oxide of that element. Some ofthe oxides are gases, others are liquids, and others are solids atordinary temperatures.The following are a few worth remembering:

Colorless GasesCarbon monoxide COCarbon dioxide CO2Sulfur dioxide SO2White SolidsSodium peroxide Na2OaMagnesium oxide MgOZinc oxide ZnOPfy>8phorus pentoxide PzO*Sulfur trioxide SO 8Silicon dioxide SiOa

Colorless LiquidsHydrogen oxide (water) H^OHydrogen peroxide H 2Oa

Colored SolidsMercuric oxide (red) HgOSilver oxide (brown) Ag 2OMagnetic iron oxide (black) Fe 8O4Ferric oxide (steel gray, reddish brown, or black) Fe 2OsCopper oxide (black) CuOLead monoxide litharge (yellow) PbOManganese dioxide (black) MnO 2The prefixes, mono-, di-, per-, refer to the relative amounts of oxygencombined with the other elements.

Conditions Affecting the Rate of Oxidation. The rate atwhich oxidation takes place is dependent upon several factors :

1. The nature of the substance. Other things being equal,iron will oxidize more readily than mercury or silver.

2. The temperature. Temperature is probably the mostobvious influence affecting the speed of oxidation. At hightemperature oxidation takes place rapidly; at lower tempera-tures the speed decreases until at ordinary temperatures itmay be impossible to detect any action. For example, thehigher the temperature of a piece of charcoal the faster it willburn. Iron rusts more rapidly in hot water than in cold, pro-vided the water is equally aerated in the two cases.


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GENERAL INORGANIC CHEMISTRY 533. The concentration of oxygen per unit volume and the

surface exposed. Anything that tends to increase the quantityof oxygen in contact with the surface of the burning substancewill also tend to hasten the reaction. The rapidity of the burningis also governed by the surface exposed. One reason why sub-stances burn more rapidly in oxygen than they do in air is thatthe concentration of oxygen in pure oxygen is about five timesits concentration in air. Thus, union with oxygen goes on aboutfive times as rapidly in pure oxygen as in air, other things beingequal. Instead of increasing the concentration of oxygen, wemay often hasten the oxidation by increasing the surface of thesolid substance. A log of wood burns much more slowly than ifit had been whittled into shavings. A lump of coal burnsrather slowly, but when it is finely powdered and suspended inthe air as dust and ignited by a spark, it will burn instantaneouslywith explosive violence.

4. A catalyst. The speed of oxidation may sometimes beincreased by the action of some suitable catalytic agent. Thusthe reaction

2SO2 + O 2 -> 2S0 3has a very slow rate, but in the presence of finely divided platinumthe speed is greatly increased. The sulfur trioxide formed thenreacts with water to form sulfuric acid, H 2SO 4 .Importance of Oxygen. A considerable amount of the decom-

position of rocks (weathering) is due to natural oxidation. Theprocess is extremely slow in dry climates, but in moist humidareas oxidation takes place at a relatively rapid rate. Theoxidation of rock is aided by the presence of water.

Pyrite (iron pyrites or fool's gold) is a common constituentfound in the coal measures and in sedimentary rocks. Theoxidation of pyrite (iron sulfide, FeS 2) leads to the formationof sulfuric acid which in turn is an active agent in rock weather-ing. Ugly stains and pits on building stones are generallyaccounted for by the oxidation of pyrite. The reaction is asfollows:

2FeS2 + 2H 2O + 7O 2 = 2FeS0 4 +Water Oxygen lion sulphate Sulfurio acidIt can be shown how oxides react with oxides in nature to

form oxidation products. If water is added in the reaction, the


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54 INTRODUCTION TO FERROUS METALLURGYprocess is called hydration. If carbon dioxide, CO 2, is added,the process is known as carbonation. Both reactions are commonin nature and may take place in the same reaction.

Igneous rocks (granite, lava flows, etc.) are composed ofminerals that combine with oxygen under proper conditions.One of the minerals is potash feldspar (orthoclase K Al Si s O 8 orK2OAl2O 8-6SiO2 ).

Clays, sand, rocks or stone, abrasives, refractories, mortar,cement, fluxes, and metallic ores represent only a small num-ber of the compounds in the great list of oxides of commercialimportance.Hydrogen. Free hydrogen is found in the gases issuing fromsome volcanoes and in pockets in certain rock salt deposits while

only a trace of it is present in the air. In its combined forms, itmakes up about 11 per cent by weight of water, is an essentialconstituent of all acids, and is a part of natural gas, petroleum,and all animal and vegetable bodies.Hydrogen can be liberated from cold water by the action ofmetals that combine with oxygen more readily than does hydro-

gen. These metals are calcium, sodium, and potassium, and theaction involves the formation of compounds known as hydroxidesof these metals. For example, the reaction that takes placewhen water is decomposed by sodium is as follows :

2Na + 2H 2O -> 2NaOH + H 2Sodium Water Sodium hydroxide HydrogenHydrogen is also evolved when steam reacts with metals at

high temperatures, producing an oxide of the metal and hydrogen.The reaction is as follows:3Fe + 4H 2O - Fe3 4 +Iron Water Iron oxide Hydrogen

Hydrogen can be prepared by the action of dilute acids (of whichhydrogen is a necessary constituent) on most of the commonmetals. The metals are arranged in the accompanying list inthe order of their activity as referred to hydrogen. This list isalso referred to as the electromotive series. Metals abovehydrogen in this list will displace hydrogen from dilute acidsand from water, although much more slowly. Those belowhydrogen in this series will not react to evolve hydrogen. Potas-sium is the most active metal and gold the least active.


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GENERAL INORGANIC CHEMISTRY 55The reaction using zinc, for example, may be stated as fol-

lows:Zinc (65.37) + hydrochloric acid > hydrogen (2.016) + zinc chloride(72.936) (136.29)

Hydrogen 2.016 Zinc 65.37Chloride 70.92 Chlorine 70.92

Zn + 2HC1 -* 2H + ZnCl 2It can be seen that 65.37 parts by weight of zinc liberate 2.016parts by weight of hydrogen. This is true regardless of whetherhydrochloric or some other acid is used. 65.37 parts of zincand 2.016 parts of hydrogen are an example of chemically equiva-lent quantities. Chemically equivalent quantities or equivalentsof two substances are exact quantities that enter into or resultfrom a chemical reaction.

i

ORDER OF ACTIVITY OF THE METALSPotassiumSodiumBariumCalciumMagnesiumAluminumManganeseZincChromiumIronCadmiumCobaltNickelTinLeadHydrogenAntimonyBismuthArsenicCopperMercurySilverPlatinumGold

Finally, hydrogen may be prepared by a process known aselectrolysis, which means the decomposition of a compound bythe use of electric energy. If the dilute solution of an acid


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56 INTRODUCTION TO FERROUS METALLURGYis subjected to the passage of direct current, bubbles of hydrogenappear on the negative pole (the cathode). All the other con-stituents are attracted to the positive pole (the anode), the exactconstituents depending upon what acid is used. Electrolysis ofhydrochloric acid produces chlorine gas and of sulfuric acidproduces oxygen at the anode.Hydrogen is a colorless, tasteless, odorless gas. Since it is

over fourteen times lighter than air, it is used to inflate bal-loons. It can be liquefied by pressure if cooled below 234C.(-389F.). It is only slightly soluble in water. At 20C.(68F.) the solubility is 1.8 volumes of gas in 100 volumes ofwater. The gas burns in air or pure oxygen with an almostinvisible blue flame which is so hot that a temperature of 2500C.(4532F.) can be produced in a closed space. Hydrogen andoxygen combine so slowly at ordinary temperatures that nochange is noticed even after several years. At higher tem-peratures, however, the reaction proceeds faster until at 700C.(1292F.) the reaction is almost instantaneous. Finely dividedplatinum will catalyze the reaction at room temperature.Hydrogen acts upon the oxides and chlorides of iron and the

metals below iron in the order of activity of the metals. Forexample,

Fe 3 4 + 4H 2 - 4H 2O + 3FeMagnetic oxide of iron (231.52) + hydrogen (8.064) iron

(167.52) + water (72.064)This reaction is an example of a process known as reduc-

tion and is the exact opposite of oxidation. The removal ofoxygen from a compound by its union with some other substance(in this case, hydrogen) is called reduction and the substanceis called a reducing agent. In iron metallurgy, carbon is moreoften used as a reducing agent than hydrogen.Water. Water is formed by the union of hydrogen and oxygenin the ratio of 1.008 parts by weight of hydrogen and 8 parts byweight of oxygen. On a volumetric basis, it is found that onevolume of oxygen reacts with two volumes of hydrogen to pro-duce 2 volumes of steam a shrinkage of one volume. In otherwords,

1 volume oxygen + 2 volumes hydrogen 2 volumes steam


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GENERAL INORGANIC CHEMISTRY 57One volume may represent a liter, quart, cubic centimeter, orany unit or fraction of a unit as long as the experimenter isconsistent. This fact leads to the law of coin-bit, in


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58 INTRODUCTION TO FERROUS METALLURGYThe product of a reaction of this type is known as hydroxide ora base and, as bases have certain typical properties, will beconsidered more fully later. The oxides that produce baseson reaction with water are called basic oxides. Other oxides unitewith water to form acids, which differ from bases in many impor-tant respects and will also be discussed later. This class isrepresented by such oxides as sulfur dioxide and phosphoruspentoxide. - Oxides that have these properties are known asacidic anhydrides or acidic oxides. We may classify the chemicalelements on this basis. The elements, like iron, nickel, andsodium, whose oxides react with water to form bases, are knownas metallic elements whilfe those, like phosphorus and sulfur,whose oxides react with water to form acids are called non-metallic elements.Many substances unite with water when placed in contact

with it, the resulting substances being known as hydrates. Thewater picked up by the substances is rather loosely held incombination in most cases and can be driven off in the form ofvapor by the application of heat. Hydrates are true compoundsbecause they contain definite proportions by weight of water andthe anhydrous (water-free) substance. They differ from bothwater and the anhydrous substance in physical properties. Somesubstances are called deliquescent because they are able topick up water vapor from the atmosphere. For example, anhy-drous calcium chloride picks up enough water vapor to dissolveitself and is sprinkled on roads to lay the dust. Some hydratesare so unstable that the water passes off in vapor form at roomtemperature when the hydrate is left in an open vessel and aresaid to effloresce. For example, common washing soda (ahydrate of sodium carbonate, Na2C03'10H 2O) is efflorescent,decomposing into monohydrated sodium carbonate, Na2C03'H 2O,and water at room temperature.

SOLUTIONSIn a previous section a distinction was made between a

mixture and a compound. In mixtures we found that the par-ticles of different properties could be readily distinguished so itwas not perfectly uniform. In a compound we found that everyportion was identical in composition to every other portion.


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GENERAL INORGANIC CHEMISTRY 59Between these there is a large class of substances called

solutions, the most familiar of which are the solutions of solidsin liquids. Solutions differ most noticeably from mixtures in thatthey are perfectly uniform in character, or are homogeneous.Mixtures are termed heterogeneous in character. They differfrom definite chemical compounds in that their composition canbe varied within wide limits. A solution, therefore, may bedefined as "a substance of homogeneous character whose com-position may be varied continuously between certain limits."As a further limitation, solutions are nonsettling. Thus, anintimate mixture of salt and water may be termed a true solution.If a given mixture is less intimate so that the particles of thesolid can be seen under a microscope, we may call it a suspension.If two liquids are mixed, they may combine to form a true solutionbut, if they are less thoroughly mixed, minute droplets of oneliquid may be Nfound to be suspended in the other. Such amixture is called an emulsion. Milk is an example. Suspensionsand emulsions are found to settle, sooner or later, and are nothomogeneous under severe tests. A true solution is one, then,in which the particles of the dissolved substance are singlemolecules or, at the most, groups of a few molecules.Types of Solutions. The most familiar type of solution is

the solid in liquid. We also have solutions of gases in liquids.For example, we find that a beaker of tap water when warmedwill give off bubbles of dissolved air. Furthermore, solids dis-solve in solids and liquids dissolve in liquids. For an example ofthe former, some alloys are mixtures of metals which are sointimate that they deserve the name solution. An example of thelatter is alcohol dissolved in water. We also have the case ofgases dissolved in solids. Thus we find that iron has a definitesolubility for oxygen and nitrogen.Most of the substances will dissolve quite simply. However,in some cases the substance may first form a soluble compound,which then dissolves. Iron does not really dissolve in nitric acidbut is converted to iron nitrate, which dissolves.Water is probably the most universal solvent, but alcohol,ether, benzene, carbon disulfide, and thousands of other liquidsare solvents for various substances. .The liquid in which a solid or gas has been dispersed to form

a solution is called the solvent, while the substance that is being


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60 INTRODUCTION TO FERROUS METALLURGYdissolved is called the solute. If we are dealing with two liquidsor two solids, we can say that each one is dissolved in the other;however, the one that is present in the larger quantity is usuallytermed the solvent.The concentration of a solution is a frequent term. By thiswe mean the amount of solute dissolved by a definite quantity

of the solvent, often referred to as so many grams per 100 cc.of solvent or per 100 cc. of solution. If this solution containsrelatively a small quantity of the solute, it is termed a dilutesolution. Solutions may be made more concentrated, up to acertain point, by adding more solute and shaking and stirring forsome time or by evaporating a dilute solution to remove part ofthe vplatile solvent. If we evaporate to the extreme or to drynessin the case of solids in liquids, we recover the solute as a drysolid.

If we were to place a lump of sugar in a beaker and cover itwith water, the lump of sugar would gnu hi: illy diminish in sizeand pass into solution and diffuse through the solvent water.If we add sufficient sugar and allow sufficient time for solution,the concentration of the sugar will reach a definite limiting valuewhere the sugar ceases to dissolve and the solution is said to besaturated. At this point, it appears that an equilibrium hasbeen reached. In other words, the rate at which the sugar mole-cules in solution deposit on the lumps of solid sugar just equalsthe rate at which the solid throws molecules into the solution.A saturated solution is defined as one that is in equilibrium withthe undissolved solute.Temperature Effect. The solubility of a substance in a given

solvent is dependent upon the temperature. In most cases thesolubility increases with a rise in temperature, but the reverse istrue in some others. For example, 100 g. of water will dissolve13 g. of KNO 3 at 0C. (32F.) and 150 g. at 73C. (163F.). Onthe other hand, the solubility of Na2SO 4 decreases from 55 g.at 32C. (90F.) to 42 g. (per 100 g. of water) at 100C. (212F.).The solubilities of other substances vary continuously withtemperature, most of them between these extremes. Theconcentration of a saturated solution of a gas has been found to beproportional to the pressure at which the gas is supplied.

If the saturated solution of a substance whose solubilitydecrease? with decrease in temperature is slowly cooled, excess


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GENERAL INORGANIC CHEMISTRY 61solute will be rejected from the solution in the form of solidcrystals. With further decrease in temperature these crystalsgrow in size, corresponding to the amount of solute materialthrown out of the solution. In this process, there is commonlysome delay in the appearance of the crystals if no undissolvedsolid is present, i.e., the solution may be slowly cooled severaldegrees below its saturation value without the appearance ofthe crystals, a condition known as supersaturation. If thesupersaturated solution is stirred, shaken, or inoculated by theintroduction of a solid crystal of the solute substance, crystal-lization of the excess solid takes place rapidly. Such a conditionalso occurs when pure substances and metallic alloys are cooledthrough their freezing points. For example, pure water can becooled carefully several degrees below 0C. before the formationof ice begins to occur. The freezing point of a substance, then,is the temperature at which the solid and liquid forms can existin equilibrium and not necessarily the temperature at which theliquid freezes on cooling. Only under carefully controlled condi-tions are these temperatures identical.Molar and Normal Solutions. A molar solution contains a

molecular weight in grams (one mol) of solute in a liter of solution.For example, the molecular weight of sulfuric acid, HUSO^ is98 and a molar solution of this acid, therefore, contains 98 g.per liter. The student should note particularly that we did notrefer to 1,000 cc. of solvent, but to 1,000 cc. of solution.A normal solution of an acid, base, or salt contains 1 gram-equivalent weight of the solute in 1 liter of solution. In anearlier discussion we learned that the equivalent weight ofhydrogen is 1.008, of oxygen 8, of sodium 23, but these are allelements. Now in the following equation we see that 36.468 g.of hydrogen chloride (in water solution) are equivalent to 23 g.of sodium.

Na + HC1 -> H + NaCl23 g. 36.468 g. 1.008 g. 58.46 g.

We have already noted that 23 is the equivalent weight of sodiumso we can now say that 36.468 is the equivalent weight of HC1.In fact, the equivalent weight of a compound is that weightwhich reacts exactly with one equivalent weight of any elemenk


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62 INTRODUCTION TO FERROUS METALLURGYA normal solution of an acid contains 1.008 g. of replaceable

hydrogen in 1 liter of solution. A normal solution of a base must,consequently, contain 17.008 g. of hydroxyl ( OH groups)per liter of solution. The following equation demonstrates thisstatement:

NaOH + HC1 - H 2 + NaCl40.008 g. 36.468 g. 18.016 g. 58.46 g.

The symbol for a normal solution is N. A twice normalsolution would then be 2N and a tenth normal, 0.1N, or JV/10.When it is desirable to convert molar and normal solutions toEnglish units, use may be made of the following factors.

1 g. solute in 1,000 cc. of solution = 0.132 oz. solute in 1 gal.solution.

1 g. solute in 1,000 cc. of solution = 0.00029 Ib. solute in 1 gal.solution.

Problem: How many pounds of Na 2SiO 3 are there in 5 gal. of a 1(W solu-tion of sodiumsilicate?Molecular weight of Na 2SiO 3 =122Equivalent weight of Na 2SiO 8 = 611OAT solution contains 61 X 10 = 610 g. Na 2SiO 8 per liter1 g. per liter = 0.00029 Ih. per gal.610 X 0.00029 X 5 = 0.885 Ib. Na 2SiO 3 in 5 gal. 1QN solutiont

ACIDS, BASES, AND SALTSIn general, solutions of compound substances iA water may

be classified as acids, bases, or salts. For this reason, it is neces-sary to study in some detail the properties of these three classes ofcompounds in solution. It should be remembered that the prop-erties discussed in this section refer to the substances dissolvedin water only. For example, hydrogen chloride gas has entirelydifferent properties from the same compound dissolved in water.The substances known as acids have the following propertiesin common:

1. The solutions are sour in taste.2. They change the color of litmus, a vegetable coloring

matter, from blue to red.3. The solutions are conductors of electricity and are decom-

posed by the current, hydrogen being liberated at the negative


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GENERAL INORGANIC CHEMISTRY 634. When the metals preceding hydrogen in the "order of

activity" are introduced into acids, hydrogen is displaced andliberated.We have mentioned some acids previously but the common onesare listed below :Hydrochloric acid .......... HC1 Nitric acid .............. HNOtSulfuric acid .............. H 2SO4 Hypochlorous acid ....... HOC1Phosphoric acid ............ HsPO* Acetic acid ..............The substances known as bases have the following properties

in common:1. Their solutions have an acrid or bitter taste.2. They change the color of litmus from red to blue.3. Their solutions are conductors of electricity and are decom-

posed by the current, oxygen being liberated at the positivepole of the circuit^The common bases are listed below:Sodium hydroxide ........ NaOH Calcium hydroxide ....... Ca(OH)2Potassium hydroxide ...... KOH Cupric hydroxide ........ Cu(OH)iAmmonium hydroxide..... NH 4OH Zinc hydroxide .......... Zn(OH) 2Sodium and potassium hydroxides possess the foregoing proper-ties to a very high degree and are specifically known as causticalkalies. The other bases exhibit the properties given abovebut not to such a high degree.When hydrochloric acid and sodium hydroxide react, sodiumchloride (common table salt) is one product.

HC1 + NaOH ^ NaCl + H 2OIn general, when an acid reacts with a base, one of the productsis a substance having properties much like sodium chloride, thisproduct, therefore, being known as a salt. The other productof the reaction is water. This process is known as neutralization.Some typical salts are given in the following list :

Sodium chloride ........... NaCl Potassium chlorate ........ KClOsSodium sulfate ............ Na 2SO4 Zinc sulfide ............... ZnSPotassium nitrate ......... KNO8 Potassium iodide .......... KIAmmonium chloride ....... NH 4C1 Sodium carbonate ......... Na2COsCupric sulfate ............. CuSO4 Lead sulfide .............. PbSIt will be instructive for the student to write the reactionsinvolved in producing these salts.


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64 INTRODUCTION TO FERROUS METALLURGYBy comparing the formula of the acids, bases, and salts listed

above, several important facts can be discovered. The importantones are as follows:

1. Every acid contains hydrogen combined with one or moreother atoms. The H atom is the necessary constituent of allacids.

2. The same atoms or radicals that are combined with hydro-gen as acids also appear in salts, such as the radicals SO 4 andN0 8.

3. Every base contains the hydroxyl (OH) radical and usuallyone other atom but sometimes more than one, for example, (NH 4).

4. The atoms or radicals that are combined with OH in basesare present in salts.When an aqueous (water) solution of hydrochloric acid issubjected to the passage of an electric current, the acid is decom-posed and hydrogen is liberated at the negative pole. Sincethis pole or electrode attracts only positively charged particles,hydrogen is called a positive atom. This is true because, inelectricity, unlike charges attract each other while like chargesrepel each other. Similarly, the rest of the acid molecule, Cl,is attracted to the positive electrode and is known as a negativeatom. When a current

Introduction to Ferrous Metallurgy

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