JOURNAL OF RESEARCH of the National Bureau of Standards-A. Physics and Chemistry Vol. 66A, No.5, September- October 1962

I Monolayers of Adipate Polyesters at Air-Liquid Interfaces 1

Wendell M. Lee, Robert R. Stromberg, and J. Leon Shereshefsky Z

(June 13, 1962)

The surface pressure-area isotherms at 24.5 °C a re r eported for poJy (et hylene adipate) , poly(trimethylene adipate) , and poly(propylene adipate), spread as monolaye rs at a ir­aqueous interfaces. The monolayers were spread on dist ill ed water a nd 0.01 N I-I Gl, using benzene, chlorofor m, and acetone as spreading solvents. Poly(propylene adiptate) was the least compressible of t he t hree, and poly(ethylene adipate) t he most. Poly (propylene adipate) did not collapse at the hi ghest p ressures studied . The spreading characterist ics of both poly(ethylene adipate) a nd poly (propyJene adipate) were independent of t he amount of material used. The spreading of poly(trirnethylene adipate) appeared to depend upon the spreading solvent. The effect of st ru cture on the surface p ressure- area isotherms and the specific a reas for each poly mer a re discussed.

1. Introduction

The monolayer properties of a series of lin ear succinfLte polyC'sters, with fL number-averfLge molecu-lar weight (l\IJn) of the order of 4,500, at air-aqu eous interfaces were recently reported [1 ]. It was shown that th e monolaye r of poly(ethylene succinate) was highly expanded but that it collapsed fLt very low surface pressures. Poly(pentametllylene suc­cinate) monolayers were also expanded. They did not collapse ~rjth increasing pressure, but the surface compressibility went through a maximum and co n­tinued to decrease as the pressure increased. An iso mer of this polymer , poly(neopentyl succinate) , produced a much less expanded film which collapsed at a surface pressure higher than that observed for collapse or pressure deer'ease for the other two polymers. It also gave th e smallest extrapolated sp ecific ar ea per repeating uni t . Other work has been reported on polyesters by Harkins, Carmen, and Ries [2] and Moss [3].

The work reported in this paper is concerned with a surface film balance study of three linefLr saturated polyesters of ad ipic acid at the liquid-air interface.

2 . Experimental Procedure

The polyesters used in this investigation were: poly(ethylene adipate) [-0 (CH Z)20 CO(CH2)4CO-]n, poly( trimethylene adipa te) [-O( CH 2)30CO( CH2)4 CO-] 'o and poly(propylene adipate) [-OCH (CH 3)CH20CO (CH2)4CO-]n' These poly mers were prepared by Dr. James Farr, Jr. , of the Thiokol Ch 8mical Company and were synth esized from the melt withou t catalyst. They were purified by reprecipitation [rom chloroform solution with ethyl eth er and dri ed in vacuum . Some of the b ulk properti es of" t hese polymers fi r e given in table 1.

The fUlll baJan ee usrd to s tudy the monobyers of the spread ftlIns h as b een described previously [1]. The water used as a subpha se was red istilled from an all-quartz sys tem. The spreadi ll g solven ts were twice distilled fLnd tested for active impuri ties by

1 'l'his work was supported uncl eI' a project sponsored b y tho Bureau of Naval vVcapons, Department of the ]\Ta vy .

2 Howard U niversity, \ Vashington , D.C.

measurements of the surface pressure of the solvent alone. The polymer solut ions were spread from micropipets and 10 min usually allowed for solvent evaporation . The average tim e o[ an experim ent was 1 hr. All measurements were made at 24.5 ± 0.5 °C.

TA 13 LE 1 . Bulk p"opeTties

Soft r n- M olccu- Bul k Polymer ing la r dc ns it~r P hysical s ta te

pOint weight aL.,27 ° 0 a( 23 cC. b fil n a

------cC ulcm'

l'oly (r t h ylc nc adipa lc) ________ 51 3800 1. 3 Crystall i ne Pol y (trilllclh yle nr ad ipa lc) ____ 40 4000 1.3 Cr~7s la lline l'oly (prop ylene adipa te) __ _____ -- - - --- - -- 5400 1. 2 Viscous liquid

tl '\ ( 11) number average molecula r woight determ ined from; slIPplicd end grOllP anal ysis.

b C rys ta llini ty dctccted b y X ·ra y diO·raction .

3. Results

The monolayer properties of poly(ethylene adipate) spread from b enzene and chloroform on the two substrates ar e given in figures 1 a nd 2. The sur face pressure in dynes per cen t im eter is shown as a func­t ion of the speeific ar ea of th e polymer (area per unit weight) . All o[ the rLlns shown in figure 1 were obtained using b enzene as th e spreading solvent. Extrapolation of th e l inear portion of the curve drawn gives a limiting specifie area of 2.6 m2/mg . In order to obtain the entire isotherm 30.36 X ] 0- 3

mg of polymer ,vas used for the region of high surface pressure and 5.50 X 10- 3 mg for th e region of low surface pressure and large ar ea . Both regions were reprod ucible as shown b~T duplicated experim ents. The two regions overlapped and a smooth continuous isotherm was obtained .

The available area of th e balance for ini tial spreading of t he film was of the order of 800 cm2 •

Using the specific surface ar ea, the larger quantity of polymer corresponds to an area of approximately 790 em2 and the smaller to a n area of approxim ately 145 cm 2 • The iso th erm was, th erefore, independent of the quantity of material used over this relatively

439

12

10

E u ",;;8 '" c >-

-0

W cr: iii 6 (f)

W cr: a.. w u <{

~4 OJ (f)

4 6

AREA, m2/mg 8 10

FIGURE 1. SUlface pl'eSS1tre-area i sotherm of poly(ethylene adipate) spreadfl'om benzene at 24 ± O.5 cc.

Distilled wa ter subphase 0 , • 30.36X IO-3 mg. D, . 5.50 X lO-3 mg.

0.01 NHel subpbase I:> 30.36X lO-3 m g.

wide range, which included a quantity near the maximum capacity of the balance. The absence of any change in the isotherm with quantity of mate­rial spread suggests that the films were completely spread and existed as monolayers. The use of 0.01 N HCl with a pH of 2 resulted in the same isotherm as the use of distilled 'water with a pH of 6.5. The collapse pressure of the fiL1JS spread from benzene was 11.1 dynes per cm, as shown by figure 1. A quantity of polymer intermediate between the two amounts described above also resulted in the same isotherm as those spread from benzene, as shown in figure 2. Fihns spread from chloroform on distilled water also yielded the identical isotherm, but the collapse pressure was slightly higher, 12 dynes per cm.

The isotherm of poly(propylene adipate) spread from chloroform on distilled water is shown in figure 3. The properties for very dilute surface concentration were not studied for this film. The extrapolated specific area at zero surface pressure was 2.2 m2jmg. Films of this polymer did not collapse. Two quantities were again used to obtain different portions of the isotherm. These two sec­tions overlapped and a smooth isotherm resulted. The spreading characteristics were, therefore, not dependent on the quantity of material deposited, within this range. The larger quantity, 29 .94 X 10- 3

mg, corresponded to an area of approximately 660 cm2 at zero surface pressure, while the smaller quantity corresponded to one-half this amount.

12.0

10.0

E U "-~ 8.0 c >-

"0

W cr: OJ (f) (f)

~ 6.0 a..

4.0

2.0

O ~ ______ ~ ______ -L ______ ~ ______ ~

o 2 4 6 8 AREA, m 2/mg

FICURE 2 . SUlface pressure-area isotherm of poly(ethylene adipate) on disti lled water at 24 ± O.5 cc.

Spread from benzene D 17.51 X IO-3 mg. Spread from chloroform 0 , • 12.12X IO-3 mg.

This independence on the amount of polymer suggests that the films were monolayers.

Poly(trimethylene adipate) was sensitive to the spreading solvent.. Films spread from benzene on 0.01 N HCl subphase exhibited the surface charac­teristics shown by curve A in figure 4. A limiting area of 3 .1 m 2jmg was obtained from this isotherm. The quantity of polymer spread, 5.47 X 10- 3 mg, corresponds to an area of approximately 170 cm2,

and because of the small quantity should represent a completely spread film .

The effect. of the spreading solvent on the charac­teristics of the film is shown by isotherm B in figure 4. Polymer was spread from acetone solution in two different quantities onto a distilled water subphase. In one case 50" C"= 10- 3 cma) and in the other, 100" were spread, using the same concentration of solu­tion. Within the experimental errol', both quantities resulted in the same isotherm, with a smaller specific area. The isotherm showed no signs of expansion to higher specific areas for the smaller quantity of solution spread. Repeat runs for both quantities resul ted in the reproducible isotherm shown in figure 4. The fact that the maA"imum spreading area for the isotherm with the smaller amount of polymer was twice as large as that for the larger amount of polymer appears to indicate the spreading of the polymer with this solvent was complete.

440

18

16

14

E I 2 u '-'" '" c >-

"0 -10

w a: :::> If) If)

w a:: 8 <L

W u <I "-a: :::>

6 If)

4

2

0

0 2 4 6 8 10 AREA, m2/mg

FIG U RE 3. S U1jace pTessure-area isotherm of p oly(propylene adipate) on disti Lled water spread from chloTofoTin at 24.5 ± O.S DC.

0 , 29.94 X IO-3 mg. 0 , 14 .95X lO-3 mg.

4. Discussion

4 .1. Physical Properties

In table 2 are given values for the thickness of the monolayers , the energies of compressing the film s to collapse or the point of inflection, and compressi­bilities. The approximate thicknesses of the films were calculated from the bulk density and the limiting specific area of the completely spread film . As seen in table 2 they are within the range of 3 to 4 A and are of a reasonable thickness for monolayers. They fall in approximately the same range as did the succinate polyesters [1], and indicate that these polyes ters lie relatively flat on the surface. In tegra-

12

10

E u '-'" '" c 8 >-

"0

W a: :::> If)

~6 B a:

<L

w u <I "-g:; 4 If)

6 8 10 12 ARE A , m2 / mg

FIC lIHE 4. S wface pl'eSSUre-aTea isotherm ene adi1Jate) at 24.±O.SoC.

of poly (tTimethyl-

Our ve A Spread from benzene on 0.01 NIlCl su b phase 0 , • 5.47XlO-3 mg.

C urve B Spread from ace tone sol ution on to distilled water subphase 0 , • 23.39X 10-3 m g. . , !::,. 11.70 X 10-3 m g.

tion Or the ar ea under the isot herm s from very large segm en t areas to tb e poin t of collapse for poly­(ethylene adipate) and to the poin t or inflection fo r poly (propylene adipate) gives t he energy to compress the film to a position or unstab ility. '1'JlO energies shown in table 2 ar c rather hig h, one being or the order of 700 ctnd t he other 800 eal/mole/segment. F or the succinate pol.lrestel's s tudied previously [I J, only poly(neopen Lyl succinate) gave an energy ftbove 700 , as shown in table 2. Poly(etbylene succin ftte) gave an energy oJ 349, and poly (pentameLh ylene succinate) an energy of 568 eal/mole/segment. The compressibili ties given in La ble 2 were calculated from the eq uation :

where K is the co mpressibility, A o the extr apolated specific area at zero surface pressure, and Al th e specific area at surface pressure 71" 1.

TABLE 2

Polymer

Poly(et hylene adi pale) ________ __ ____ .__ Pol y(pl'opylcne adipaLe) ______________ _ Poly(tl'imcthylene ad ipote) ___________ _ PolY(CLhylenc sue'inate)& __________ __ Poly(pcntamcth ylcne sll ceinatc)a _____ _ Poly(nco pcntyl suecin::tte) ~ ___ ________ _

& R eference [1] .

Extrap­olated speci fi c

area

m2/ m(J 2.6 2.2 3. 1 2. :l 2.9 2. 0

Area per segment Energy to compress

film to Compl'es- Thickness coll a pse, sibility at ". = 0

Calculated Observed cal molo-I

A' 67 67 74 55 74 60

441

A' 75 68 98

60 to 70 90 63

segmcnt- 1

il6 807

349 568 734

em/dy ne 0.067

. 048

. 058

. 11 .056 . 028

A 3. 0 3. 8 2. 7 3. 1 2.9 3.9

4.2. Compressibility

The compressibility values for all the polyesters studied , except for poly (ethylen e succinate) [1], are in t he range observed for linear polyesters, such as the self ester of the hydroxydecanoic acid studied by H arkins, Carmen , and Ries [2], and poly (vinyl acetate) films studied by Ries, Ahlbeck, and Gabor [4]. The latter polymer contains the ester groups as "ide chains.

The compressibili ty data 1'01' the adipate mono­layers and the succinate monolayers, as reported previously , point to the general observation that the compressibili ty of the monolayer decreases with t he number of carbon atoms in the glycol and acid glOiIp" and also with the arrangement of' these groups.

Second, it is to be observed that the polyesters with the lower numbel' of carbon atoms between the carboxylic groups have greater compressibilities than t hose with large numbers, as evidenced by comparison of the compressibilities of poly (ethylene succinate) with poly(ethylene adipate) . Sirnilarly the compress­ibilities of' polyesters containing th e ethylene gly col grouping have greater compressibili ties than t hose having segmen ts of longer glycols. This is evidenced by a comparison of poly(ethylene adipate) with poly(trimethylene adipate) as well as a comparison of poly (ethylene s Llccina te) with poly(pentamethyl­en e succin ate) .

Third, it appears that differen ces in the arrang'e­ment of the carbon aLmns in t he glycol chain also affects the compressibility. Thus, poly (propylene adipate) and poly (trimethylene adipate) diffcr in their compressibilities in that the branched three carbon gro up has a lower compressibili ty than t he straight chain al'l'angement. Similal' b ehavior is observed in a comparison of poly(n eopentyl suc­cinate) with poly( pentamethylene succinate) .

The spreading of polym.er films has b cen shown by others [2 , 5] to be independent of molecular weigh t,. Crisp [5J has shown that polymel' films arc completely spread when the specifi c ar cas are reproducible and independent of the solvent or solu tion concentration over a moderate concentration range. The spreadin g of both poly (e t hylen e adipate} and poly(propylenc adipate) were independent of the quantity of m a­terial spread, over th e con cen tration range studied, as shown in figures 1 to 3. As completely spread fil ms a re assum ed to be independent, of molecular weight, the smface pressure was plotted as a func tion of the area of the ['Cpeating stl'Uctmal unit. Such isotherms for the three polyesters aro given in figure 5. Experimen tal points from different runs are given on each curve, except those of poly (trimethylene ad ipate) spread from acetone.

There is a large difference in the isotherm of poly (ethylene adipate) , as shown in curve C, figure 5, and that of poly (e thy lene succinate) (fig. 5, ref. 1) . The increase in the length of the repeating uni t by the addition of two met1lylene groups in th e acid changed the collapse pressure from approximately 4 cl ynes/cm for the succinate to approximately 12 dynes/cm for the adipate polymer. This is very likely du e to th e greater freedom of orientation of

16 r

1 14 1

E 11 -::; ! IO I ~ 8

~

i 6

o~~~~~~~~~~~==~ o 10 40 60 80 100 110 140 160 180 100 220

ARE A PER SEGMENT. A1

F I GU RE 5. S U1jace p1'eSSU1'e-a1'ea i sotherms of linear satumted polyestel's on aqlwous s'Ubphases at 21,.5 ± 0.5 °C.

Curve A P oly(trime tbylene adipate) Curve B Pol y(propylene adipa te) Curve C Pol y(ethy lene adipate)

the carbonyls in th e in terface, r esul ting in a high er vertical component of the dipole. The extrapolated segment area for th e adipate polymer is 75 .112 and 60 to 70 A2 for the succinate polym er. These values arc somewhat larger than the minimum calculated from molecular models.

The monolayer properties of poly (trimethylene adipate) spread from benzene, curve A, are similar to . those of poly(ethylene adipate), curve C, at moderate surface pressures. At all surface pressures studied th e segm ent areas ar e larger for th e poly­(trimetll ylene adipate) than for th e poly(ethylene adipate ) . The extrapolated segment area of 98 A2 is 23 A2 larger than th e value obtained for the pol~' (ethylene adipate) which is ill good a.greement with th e cross-sectional area of a long cham h ydro­carbon, as established by monolayer measurements.

5 . Summary Differen ces in th e surface pressure- area isoth erms

of the t hree adipate polyesters studied wcre found to b e related to differ en ces in tIl e ch emical structure. Large differen ces were also observed bet,,:een thes.e polyesters and succinate poly esters studIed prevl­ously. A large difference was observed between the o bserved and the calculated specific area for the repeating uni t of pol~T ( triJlleth~'len e adipate) . As in th e case of the succinate polyesters, one of the adipate polyesters studied did not collapse at high pressur es.

6. References [1] W. M. Lee, J. L. Shereshefsky, and R. R. Stromberg, J .

Research NBS 65A (Ph ys. and Chem.) No. 1, 51 (1961). [21 W. D . H ar kins, E. F. Carmen, and H. E . Ries, Jr. , J .

Chem. Ph ys. 3, 692 (1935). [3] S. A. Moss, Jr. , J. Am. Chem. Soc. 56, 41 (1934) . . [41 H . E. Ries, Jr. , R. A. Ahlbeck, and J. Gabor, J . CollOid

Sci . H, 354 (1959) . [51 D. J . Cri sp, J . Colloid Sci. 1, 49 (1946).

(Paper 66A5- 178)

442

JO URNAL OF RESEARCH of the National Burea u of Standards-A. Physics a nd Chemistry

Vol. 66A, No.5, September-October 1962

Publications of the National Bureau of Standards*

Correction

In the July-August 1962 issue of th is Section, t he abstract fo r the paper JA W Temperature Thermometry, R. P . H ud son, ,B oole, Experimental Cryopl!ysics, P11. 2l4-253 (B utterworth & Co., Lon don, England, 1961), was presented IOcor­rectly. T he following abstract refers to this paper :

The principa l methods for t hermometry in t he r a nge 10 K t o 900 K a re crit ica lly reviewed, the discussion coverin g the physical pr inciples involved , ty pes of apparatus, and factors determining t he attaina ble precision and accura cy. Supple­mentary data are provided in t ables, some wi t hin t he body of t he article and others in append ices t o t he volu me of w hi ch t he a r t icle constitu tcs a chapter .

Selected Abstracts Spark-gap flashove r meas ureme nts for steeply ris in g voltage impulses, J. H . P a rk and H. N. Co nes, N BS J. R esem'ch 66C (Eng. & I nstr.) No . 3, 197 (July- S ept. 1962). Dividers made up of special t hin ribbon rcsistors wit h very low t ime co nstants were used for meas urin g lincarly rising chopped impulscs wi t h pcak voltagcs up to 300 k v a nd t imcs to spa rkovcr fr om 0.03 to 50 microseconds. T otal errors werc dedu ced by a co mb ination of co mpu tat ion a nd experimenta­t ion to be p robably not gren,ter t ha n 1. 5 percent for t imes to spa rkover greater t ha n 0.1 m icrosecond.

From a la rge number o f oscillograph recO!'ds data werc der ived giving a relation between ra te of ri se (or rise t ime) a nd Aash­over vol tage for (1) 12.5 cm diameter spheres sp aced 6 cm apa rt, (2) 25 cm d ia meter spheres spaced 6 cm, a nd (3) u lli for m. field electrodes spaced 5 cm . It is recomnlCnd cd t hat t he volt-t ime cur ve showing t hese relations for t he 25 cm di a meter spheres be used as a reference standa rd fo r inte rla borato ry compariso n of meas urement met hods.

A furnac e for thermocouple calibrations to 2 ,200 ° C, D. B. Thomas, N BS J. HeseaTch 66C (Eng. & Instr.) N o. 3, 255 (J u ly- Se pt. 1962).

A t a ntalum t ube furnace has been constru cted to cali brate a nd investigate t he t herm oelectri c behav ior of hi gh tcmpera t ure t hermoco uples. The furn ace a nd its associated equ ipm cnt were designed wit h emphasis 0 11 features t hat would ass ure a h igh degree of acc uracy in meas urements t hat a re made at hiO'h te mperatures a nd also wi t h emph asis on t rouble-free pe~·formance. D ata t hat were obtained during furn ace operation showed t hat t herm oco up le dep t h of im mersion into a properly des igned blackbody is of considera ble importance if a good agreemen t is t o be realized between a calibrated opt ical py rometer a nd a cali bra ted t hermocouple t hat has bee n placed in t he hot zone of t he furnace. H igh puri ty helium gas can be used in the furnace t o keep t hermocouple conta mination t o a minimum.

Method of meas uring emissivities of metal s in the infrared, A. G . M aki a nd E. K. Plyler, N BS J. Research 66C (En g. & I nstT.) No.3, 283 (J u ly-Sept. 1962) .

A meth od of meas uring nor mal sp ect ral emissivit ies in t he infrar ed region from 1 t o 13 J1. is descr ibed . It consists of compa ring t hc r ate of emi ssion of r adia nt energy fr om a blac kbody wit h t hat from t h e specimen. TllC t wo observed ra d ia nccs a rc made equ al by adjusting t hc tc mperatures. An eq uat ion is derivcd for li se in calculating t he emissivi ty for t he observed te mpcratur cs . The ma in sources of elTor ar ise in t he meas urement of Lhe te mperature of t he specimen a nd t he temperature of t he blackbody. As a n exa mplc of t he method t he norm al spectra l cmissiv ity of gold h as bcen measur~d in t he spectral range from 4 to 13 J.L wit h tempera­t ures from 550 t o 1,000 OK . The emi ssivi ty was found t o ra nge from 0.014 at 4 J1. a nd 550 OK t o 0 .0256 at 9 J1. a nd 1000 OK. A table is in cluded wh ich lists t he values of cmis­sivitv fr om '1 to 13 J1. a nd fr om 550 t o 1,000 OK at inte r vals of 50 o'K.

Tables of s pectra-lin e intens iti es. Part I. Arranged by ele ments, \~T . F . Megge rs, C. H. Corliss, a nd B . F . Scribner, N BS Mono. 32, Pt. I (Dec. 29, 1961) $4.00. The relat ive in tensit ies, o r radi a n t powers, o f 39,000 spectral lines wi t h wavelengt hs betwce n 2000 a nd 9000 Angst roms have been detcrmined on a unifor m ene rgy scale for seve nty chemical elemcnts . Thi s was done by mixing 0.1 ato mi c percent of eac h cle ment in po wd ercd copper, p ressing t he powder-mi xtur e to form solid electrodcs w hich wcrc burned in a 10 a mpere 220 v ol t dircct-curre nt a rc, a nd photogra phi ng t he spectra wi t h a st igmatic co ncave grati ng w hi le a ste p sector was rotating in fron t of t hc s li t. T he sectored spectro­gra ms fac ili tated t he estimation of in tcns it ies of n,ll clc ment lines relative to copper lines which \\'ere t hen calibrated on an energy scale p rov ided by standa rdized la mps a nd all es ti­mated line intensities \yer e fina lly adjusted to fi t t his ca,libra­t ion . Compariso ns wit h other intc nsity meas urements in ind ivid ual spectra in di cate t hat the Nationa l Bureau of Stand a rds spect ral-l ine inte nsi t ies may havE' average errors of 20 percent, bu t first of a ll t llf'Y p rov ide uni fo rm quantitative valu es for t he seve nty chcmi cal clements co mmonly det er­mi ned by spectroc hemists. These data a rc p rese n tcd ~Y clemen t in p ar t I and all 39,000 obscrvcd lincs a re given III order of wavelcngth in pa r t II.

Analysis of coaxial two-terminal conical capacitor, M . C. Selby, N BS M ono. 1,6 (ApI'. 6, 1962) 20 cenls . . Ad justable capacito rs havi ng e lectrodes in t hc form of coaXial co nes 0 1' fru st ums have bee n used on rare occas ions in t he pas t ; but t heir pote n tia l superio ri ty to other types of capaci­to rs for so me i mportant a pplications have bee n overloo ked. The ad vantagc of t his geo metry ovcr cylindrical or disk forms is t hat t he prac tical capac itance ra ngc is sevcml limes la rgcr. An example citcs t he capaci tance ranges of a disk, cy lindrical, a nd conical type to be 10, 40, a nd 16 to ~n c, respcctivel.): . An approximate equation was de rived for t hLs cOl1lcal capacI­tor a nd close agree ment is s hown betwee n compu ted a nd meas ured values of capacit<tncc , 'NS US electrode displace mcnt. Mul t iple cone and differen t sluLpe cleetrodes a re suggested to obtain la rge values of capacitancc wi t h an <tpp reciab]e sav ing of space a nd fur t her in creascd rangc of .capacitance. The electric fi eld is p lotted a nd i ts constructIOn step .; for aX ial sy m meLI'y a rc g iven.

Dissociation co nstant of 2-ammo nium-2-methyl-l , 3-pro­pa nediol in water from 0 to 50 ° and related t hermod ynamic quantities, H . B. H etzer and n . G. Bates, J . Phys. Chem. 66, 308-311 (1962) .

The base 2-a mino-2-methyl- l ,3-p ropa nediol, like t he clo:,ely rela ted compound t ris- (hydroxy methyl)-aminomet ha ne, IS a solid substa nce of conside ra blc usc as a biological buffer ma­terial. The acidi c d isRocil,tion constan t, K bh, of t he substi­tuted a mmoniu m ion conj ugat.e to t he free base now has been determin ed at 11 termperatures from 0 to 50 ° by measurement of t he electrom otive force of hydroge n-sil ver chl oride cells wit hout liqu id junction . The resul ts a re given as a fun ction of t he temperature ('I') in oK. by t he equation - log K bh = 2952. 00/ '1' - 2.2652 + 0.00390921'. The standa rd cha nges of free energy, cnt ha lpy, ent ro py a nd heat capacity for t he dis­sociation p roccss have bee n calculated from t be te mperature coe ffi cient of t h e dissocia t ion constan t. For t he aC Ldl c d iS­sociation of 2-ammonium-2-metbyl-l ,3-propanedi ol at 25°, t hc followin g r esul ts were ob tained: L Go= 50,238 j . mole- I, L I10= 49,860 j. mole- I, L 80 = - 1.3 j. deg.- ' mole- I, a nd LCpo= - 45 j . deg.- I mole- I For the basic dissori at ion of 2-amin o-2-methyl-l ,3-propanediol at 25 °, t he co rrespond Ing qua ntit ies a re L Go= 29,656 j . mole- I, L I1°= 6720 J .. Inole- I, L80 = - 76.9 j . deg.- 1 mole- I, and LCpo = - 150 J. deg.- l

mole- I.

Study of electro nically excited hydroxyl radicals in the H + 0 3

atomic flame , H. P . Broida, J . Chem. Phys. 36, No.2, 444-448 (J an. 1962) .

443

Ultraviolet emlSSlOn of t he A2~+-> X2II i transition of OH h as been observed in low-pressure fl ames of hydrogen atoms and ozone. In t hese flames, at pressures near 1 mm Hg, the in tensity of this uv emission was found to be directly propor­tional to the square of t he intensity of t he rotation-vibration bands in the electronic ground state, 2II i . Under similar conditions, r eactions of hydrogen atoms with oxygen atoms or with hydroxyl radicals were fo und to give too li ttle emis­sion to account for the observed radiation. It is concluded that colli sions of two vibrationally excited OH radicals, 2II i ,

lead to t he electronically excited radicals, 2~+ . Approxi­mately 500 photons are emitted by all the vibrationally excited radicals (,,= 1 t o 9,211;) for each photon emitted in the electronic t r ansition A 2~+-> X 2II i . Steady state partial pressures of vibrationally exci ted OH, 2IJ i, are estimated to be 10- 7 mm Hg for a total flame pressure of 1 mm.

Theory of thermal diffu sion in dilute alloys, R. E. Howard and J . R. Manning, J . Chem. Phys . 36, No.4 , 910- 916 (Feb. 1962). A kinetic a nalvsis is made of the t hermal diffusion of a dilute impurity in an f.c.c. metal. Expressions a re derived for the impurity current, t he steady-state Soret gradient, and t he mean atom displacement. It is shown how t he "heats of tran .'>port" appearing in these expressions can be studied ex­perimentally. An extension of the analysis to cases of non­thermal type gradients, in particula r, a chemical concentra­t ion gradient, is briefly considered.

Hydrogen formation in the gamma-radiolysis of ethyle ne, P . Ausloos and R. Gorden, Jr ., J . Chem. Phys . 36, No. 1, 5- 9 (J an. 1962). The radiolysis of ethylene-d, a nd C,H 4-C,D4 mixtures has been investigated in t he gas, liquid, and solid phases. The data indicate t hat hydrogen may be formed by two distinc t molecula r-elimination processes: CH,CH,-> CH,C + H , and CH 2CH 2->CH = CH + H ,. The effect of xenon and pressure on t he yields of H" HD, and D , in t he gas-phase radiolysis of CH ,CD , h as b8en investigated. The results for the (2PJ)Hg­sensitized and t he 1237 A-photochemical decomposition h ave been compared with those for radiolysis.

Impurity e ffects in high purity metal, L. L. Wym an and G. A. Moore, (Symp. Major Effects of Minor Constituents on the Properties of Materials. Sixty-fourth Annual Meeting ASTM, Atlantic City, N.J . June 26, 1962) , ASTM Spec. T ech. P ub!. No. 304- ASTM Materials Sci. Series 2, 3- 16 (J une 26, 1961). Obtaining metals of the highest possible degree of purity is a problem of ma jor concern in both science and engineerin g. The determination of impuriti es, t heir effects, and control, demand extreme effor ts in process ing a nd analysis. Impuri­t ies in metals a re characteri zed b y the na ture of t heir occur­r ence and t heir effects on host metals. Specific examples illustrate impurity effects in a number of currently important appli cations.

Vibration-rotation inte raction s in cyanamide; the question of planarity of amides, D . R. Lide, Jr., J . Mol. Sp ectroscopy 8, No.2, 142-152 (Feb. 196'B). The cyanamid e molecule is approximat.ed by a simple model which allows for a large-a mplitude out-of-plane vibration of t he N H , group. The kinetic energy of t his model is derived, and t he quantum-mechanical problem is formu lated. P er­turbation expressions suita ble fo r t he case where there is a potential hump in t he planar confi guratio n are given. Some of the consequences of t he vibration-rotation inte ractions a re discussed.

Vacuum ultraviolet photochemi s try. III. Primary processes in the vacuum ultraviolet photolysis of water and ammonia, J . R. McNesby, I. Tanaka, and H. Okabe, J . Chem. Phys . 36, No . 3, 605- 607 (Feb. 1962). Water and ammonia have each been photolyzed in t he ab­sence and presence of C2D, which served to scavenge H atoms. W avelengths used were : for a mmonia, 1849 and 1236 A ; for water, 1236 A. Under conditions where H atoms are effici ently scavenged by C2D" the production of H z signifies a primary photochemical process giving molecular

H z directly. It is found that at 1849 A, ammonia decomposes a lmost entirely to H + NH 2• At 1236 A, two primary proc­esses are observed .

NH 3->H z+ NH, NH3->H + NH 2•

(a) (b)

Process (a) is about t as probable as process (b). At 1236 A, the photolysis of water proceeds via t wo primary processes.

H 20 ->H + OH, H ,O->H ,+ O.

(C) (d)

The probability of process ,c) being t hree times t hat of process (d) . It is suggested t hat primary process (d) constitutes a reasonable photochemical mechanism for hydrogen formation in the earth's upper atmosphere.

Accuracy of analytical procedures, W. J. Youden , J. A ssoc. O,fficial Agricultural Chemists -15, No.1, 160- 173 (Feb. 1962). Most analytical chemistry procedures are expected to give correctly, excep t for random analytical errors, the amount p resent. This means that if the amounts found are plotted against the amounts present, t he poin ts should lie closely along the line y=x where y is t he amount found for a mate­rial containing amount x. Some procedures may recover only a constant percentage of t he amount present and t he best fi tting line would be of t he form y = bx. Other proce­dures may be subject to a constant error and t he appropriate line would correspond to t he equation y = a+ x . A si mple statistical technique is described that may be used to ascer­tain whether the data constitute evidence that the t heoretical line, y= X, does not adequately r epresen t t he rela tionship between t he a mount taken and t he amount found. Some remarks on round robins are included.

Other NBS Publications

Journal of Research 66B (Math. & Math. Phys.) No.2 (Apr.­June 1962) 75 cents. Hindsight techn ique in machine translation of natural lan­

guages. I. Rhodes and F. L . Alt. An extension of J ensen's theorem for t he derivative of a

polynomial and for infrapolynomials. O. Shisha. Two matrix eigenvalue inequalities. S. H aber. Graphs for determining the power of Student's t-test. M.

C. Croar kin.

Journal of Research 6B (Math. & Math. Phys.) No.3 (July­Sept. 1962) 75 cents. The first run preceded by a quota. A. J . Goldman and

B. K. Bender. Two theorems on matrices. Morris Newman. Mill 's ratio for mul tivariate normal distributions. 1. R.

Savage. Angle as a fourth fundamental quantity. J. E . Romain. I nval idi ty of Meixner's t heorem in irreversibile thermo­

dynamics. R E. Nettleton. Selected bibliogrftphy of statistical literature, 1930 to 1957: I

VI. Theory of estimation and testing of hypotheses, sam­pling distribu tions, and t heory of sample SllJ'veys. L. S. D eming.

Journal of Research 66C (Eng. & Instr.) No.3 (July- Sept. 1962) 75 cents. Measurement of longitudinal spheri cal aberration in t he

extra-axial r egion of lenses. F . E. Washer and VV. R . Darling.

Spark-gap flashover meas urements for steeply rising voltage impulses. J . H. Park and H. N. Cones . (See a bove I

abstracts.) Evaporated-film electric hygrometer elements. F. E. Jones. Methods of measuring t he resistivities of anisotropic con­

ducting media in s it u . S. Rush . Corrosion of steel p ilings in soils. M . Romanoff. Corrosion rates of ferrous alloys (F e-Cr a nd Fe-Cr-Si)

measured by polarizatioe technique. W. J. Schwerdt feger. A furn ace for t hermocouple calibrations to 2,200 DC. D . B.

Thomas. (See above a bstracts.)

444

Total hemispherical emittance of coated a l1d un coated Inconcl a nd types 321 and 430 stainless steel. J . C. Richmond and \V. N . H a rri son.

" Mail Separator " control comp uter p relimina ry logical design. S. Henig and E. C. Palasky .

Method of meas uring emissiv ities of metals in the in f rared. A. G. Maki and E. K P lyler. (Sec a bove abstr acts. )

Journal of Research 66D (Radio Prop.) No . 5 (Sept.- Oct. 1962) 70 cents . Theory of magneto-telluric fields. J. R. vVait. Propagation chaTacteristics of magneto-ionic plas ma col umns.

D. Formato and A. Gi la rdini . Dielectric loadin g of electric dipole anten nas. J . Galeis . Possible infiuence of t he ionosphere on t h e impedance of a

ground-based antenna. J . R. Wait . Some statistical theor y for the analysis of radio propagation

data. M. M. Siddiqui . Auroral sporadic-E ionization. R. D. Hunsucker and L.

Owre n. Comparat ive study of the co rrelation of seasonal and d iurnal

cycles of trallsbori zO Il radio t r a nsmission loss a nd s urface refract ivity. B. R. Bean.

Enhance ment of the lunar t ide in the noon cri t ical frequency of the F'2 laye l' ovcr t he magnetic eq uator. R. G. Rastogi.

Scattering from a conducti ng sp l1Cre embedded in a semi­infinite diss ipaLi ve medium. J. Galejs.

Higl1-freq uency scatte ri ng from a coated sp here. V. H . Wcsto n and R. H e menger.

P ropagation of sphe rical waves through an ionosphere containing anisot ro pic irrogula rit ies. K . C. Yeh.

Radiation patterns in the lower ionos phere and Fresncl zo nes for elevated an tenn as over a sp he rical earth, R. G. M errill and W. V. Mansfield, NBS Mono. 38 (April 2, 1962) 70 cents.

Effect of exposurc site on weather resistance of porcela in enamels exposed for t hree years, D. G. Moorc and A. Potter, NBS Mono. 44 (Ap ril 10, 1962) 15 ec n ts.

F i re tests of p recast cellular concrete floors and roofs, J . V. Ryan and E. \V. Bender, NBS Mono . '15 (April 12, 1962) 15 cents.

An ultraviolet multiplet table, C. E. Moore, NBS Circular 488, Sections 3, 4, a nd 5 (April 6, 1962) Section :3 , 60 cen ts; Section 4, 45 cents ; Section 5, 30 cents.

Mean electron density var iations of the quiet ionosphere­September 1959, J . W . Wright, L. R. Wescott, and D. J . Brown, NBS Tech. Note 40- 7 (PBI51399- 7) (1962) $ l.50.

Mean electron density variat ions of the qu iet ionosphe re No . 13; Summary of one yea r of data, May 1959- April 1960, J. W. Wright, NBS T ech . Note 40- 13 (PBI51399- J3) (1962) $1. 50.

Bibliography on auroral rad io wave propagation , 'vV. N upen, NBS Tech. Note 128 (PB161629) (1962) $2.75.

Airborne television coverage in t he presence of co-c hannel in­terfer ence, M. T . D ecker , NBS T ech . Note 134 (PBI61635) (1962) $2.00.

ronosonde observations of a rtificially produced electron clouds: Firefly 1960, J . W. Wright, N BS Tech. Note 135 (PBI61636) (1962) $2.50.

Some problems of fatigue of bolts and bol ted joints in air­craft applications, L. Mordfin, NBS T ech. Note 136 (PB161637) (1962) $1.25.

A bibliography of t he t hermophysical properties of oxygen at low te mpe ratures, J . C . Hust, L . D. Wallace, J . A. Crim, L . A. H all , and R. B. Stewart, NBS Tech. Note 137 (PBI61 638) (1962) $2.25.

Ver t ical cross sections of t he ionosphere across t he geomag­netic equator, J . W. Wright, NBS Tech. Note 138 (PBI61639) (1962) $1.00.

Siting cri teria for HF commu nication centers, vV. F. Utlaut, NBS T ech . Note 139 (PBI61640) (1962) $1.25.

Atlas of Fourier coeffic ients of diurnal variat ion of foF2, 'tV. B. J ones, NBS T ech. Note 142 (PBI61643) (1962) $2.50.

N umerical rcs ul ts for t he surface im pedance of a stratified conductor, C. M. J ackson, J . R. Wait, and L . C. Walter, N BS Tech. Note 143 (PBI61644) (1962) $1.25.

Cryoge ni c temperature measurement wi t h platinum resist­ance t her mometers- Is fi xed-point cali bratio n adeq uate? R. J. COlT ucc ini , NBS Tech. Note 147 (PB161648) (1962) 50 cents.

An introduction to flame photometry a nd a review of recent studies, M. Margoshes, Phys. Tech. B io logical Research t, 215- 260 (1962).

Congruences for the pa rt it ion fu nction to compos ite modul i, M. Newman, Ill inoi s J. Math. G, No. 1,59- 63 (Mar. 1962).

Research a nd t he savi ng of teeth, 0. C . Pafre nba rger, J . Prostetic Dentistry 12, No.2 , 369- 383 (l\1ar.-Ap r. 1962).

Displaceme nt a nd st ra in-energy d istribu t ion in a longitudi­nally vibrating cy lindrical rod with a viscoe last ic coating, P. H e rtclendy, J . App!. Mec h. Tra ns. ASMJ:i; 29, Se ries E, No.1, 47- 52 (Mar. 1962) .

Properties of s ili co-phospl1ate ccments, J . N. Anderso n and G. C. Paffe nbarger, D ental Progress 2, No.2, 72- 75 (Jan . 1962) .

Comme nts on paper by W. D . Westfall , " P red iction of VLF d iu rnal phase ch a nges and so lar fla re effect," J. R . -Wa it, J . Geophys. Research Gi, No.2, 916- 917 (Feb. 1962).

The shape of t he geomagnetic fi eld boundary under un iform extern al press ure, R . J . Slutz, J . Geop hys. Research G7, No.2, 505- 513 (Feb. 1926).

Plat ing standards and spec ificat ions, F . Ogburn, E lectro­plating Eng. JIa ndb . 2d . ed ., Ed. E:. Graham , ch. 7, p. 257-262 (Reinhold Pub!. Co. , New York, N. Y., 1962).

Surface effect on bo nd stre ngth of steel beams embedded in concrete, J. O. Bryson and 11. G. Mathey, J . Am. Concrete Inst. 59, No.3, 397- 406 (Mar. 1962) .

Inequ ali ties for the pe rmane nt fun ction, M. Marcus and M. Newm a n, Ann. M ath. 75, No . 1, 47- 62 (Jan. 1962).

E ffcct of monome ri c reage nts on the m elting (contraction) and rec rystalli zation of fibrou s prote ins, L . Mandelker n, W. T . Meyer, and A. F. D io rio, J . Phys. Chem. GG, 375- 376 (1962) .

A co rrection to the exosphe ri c elcctron density est imate using the nose w hist le rs of March 19, 1959, J. U . Pope, J. Geophys. R escarcl1 G7, No. 1, 412 (J'tn. J962).

Investigat ion o f t he sp ectrophotomet ri c method of m eas uring the fe rr ic io n y ield in t he fcrrou s s ulfa te dos imeter, K. Scharf and R . M. Lee, Radiat ion Hesearch IG, No.2, 115- 12'[ (Fe b. 1962) .

M icrowave spectrum and nonplanari ty of cyanamide, D. J . M ille n, G . Topping, and D. R. Lide, Jr., J . Mol. Spectros­copy 8, No.2, 153- 163 (Feb. 1962).

Long-d istance one-hop _ FI propagat io n through the a uroral zone, L. II. Tveten, J . Geop hys. Researeh GG, No.6, 1683-168-10 (June 1961).

Preparation of a nd electroplating of uranium, D. E. Couc h, r lat ing 49, No.4, 363- 367 (Apr. 1962).

T e ns ile st rength and modulus o f elast icity of tooth st ructure and several resto rative materia ls, R. L . Bowen and M. S. Rodriguez, J . Am. Dental Assoc. G4, No.3, 378- 387 (Mar. 1962).

Vacuum microbala nce techniques, R. F. ViTalker, Ed ito r, Vo lume 2, 179 pages, Proc. Con E. at the National Bureau of Standa rds, Apr. 20- 21, 1961 (Plenum Press, New Yo rk, N. Y., 1962).

First pulsed radio soundings of t he tops ide of t he ionospherc, R . W. Knecht and T. E. Van Zandt, J . Geophys. Research 6G, No. 9, 3078- 3081 (Sept . 1961).

Cryoge nics and nuclear physics, n. P. Hudson, Science 134, 1733- 1736 (D ec. 1961).

Vacuum ultraviolet photochemistry. II. Phol-olysis of ethy l­ene, H . Oka be and J . R McNesby, J . Chem. P hys. 36, No.3, 601- 60-1 (Feb. 1962).

Experim ental stUdy of t he stark broadelli ll g of t he balmer lines H'Y, W. L. Wiese. D . R. Paquette, a nd J . E. Sola rski , P roc. Fifth In tern. Con f. Ionization Phenomena in Gases, Mu nich, pp. 907- 912 (North Holland Pub!. Co., Amster­dam, The N etheriands, 1961).

Internal magnet ic fi elds in nickel-r ich nickel-cobalt alloys, L. H . Bennett a nd R. L . Streever, Jr., J . App!. Phys. Supp!. 33, No.3, 1039- 1094 (Mar. 1962).

Strong blast waves in spherical, cylindrical and plane s hocks, D. L. Jones, Phys. of Fluids 4, No.9 (Sept. 1961) .

Approximations to t he moments of t he sample median, M. M. Siddiqui, Ann. Math. Stat. 33, No.1, 157- 168 (Mar. 1962).

· 445

Kin etic equation for plasmas with collective and colli"ional correlations, C. M . Tchen, Proc. Fifth Conf. on I onization Phenomena in Gases, Munich , pp. 825- 841 (Nor th Holla nd Pub!. Co., Amsterdam, The Netherlands, 1961).

Plasma with net charge, J. L. J ackson, D. B. Levi ne, and R. A. Piccirelli, Phys. of Fluids 5, No. 2, 250- 251 (Feb. 1962).

Solubility product phenomena in hydroxypatite-water sys­tems, H . M . Rootare, V. R. D eitz, and F . G. Carpenter, J. Colloid. Sci. 17, No.3, 179- 206 (Mar. 1962).

Worldwide patterns of ionospheric blackout occurrence, V. Agy and K. D avies, J. Atmospheric and T errest.. Phys. 23,202- 205 (Dec. 1961).

Fluorescence and rotational relaxation of OH radicals in flames, T . Carrington, Eighth Symp. (Intern.) on Com­bustion, pp. 257- 262 (The Willia ms & vVilkins Co., Balti­more, Md., 1960).

R efraction effects of large-scale ionospheric irregularities ob­served at Boulder, Colorado, R . S. Lawrence and .T. L . J espersen (Proc. 2d Intern . Space Science Symp., Florence, Italy, Apr. 10- 14, 1961), Space R esearch II. 258- 276 (North Holland Pub!. Co., Amsterdam, The Netherlands, Apr. 1961).

P hysical properties of 113 domestic marbles, A. H ockman, Architectural Record, pp. 192- 193 (Apr. 1962).

On the nature of equatorial slan t sporadic E, R. Cohen, K . L . Bowles and 'V. Calvert, J. Geop hys. Research 67 , No.3, 965- 972 (Mar. 1962).

A survey of carbon-carbon bond lengths, D . R. Lide, Jr. , Tetrahedron 17,125- 134 (1962).

I . Strange sounds in the atmosphere, R. K. Cook, Sound-Its Uses and Control 1, N o. 2, 12- 16 (Mar- Apr. 1962).

An uluminum magnet cooled wi t h liquid hydrogen, J. R. Purcell, Proc. Intern. Conf. on High Magnetic Fields, Mass. Inst. T ech ., Cambridge, Mass., Nov. 1- 4, 1961, pp. 166- 169 (Mass. Inst. T ech. Press, Cambridge, Mass., and John Wil ey & Sons, Inc., New York, N.Y., 1962).

Possible solar fl are effects in the P region of t he ionosphere, R. W . I{necht and K. Davies, Nature 192, No. 4800, 347-348 (Oct . 1961).

Microwave struc t ure determin ations on tertiary butyl acety­lene and tertiary butyl cyanide, L. J . Nugent, D. E . Man n, and D. R. Lide, Jr., J. Chern. Phys. 36, No.4, 965- 971

,- (Feb. 1962) . Static dielectric constant of rutile (Ti02), 1.6- 1060 OK, R. A.

P arker, Phys. Rev. 12<1, No.6, 1719-1722 (D ec. 1961). Translational en ergy acco mmodation in the nickel-chlmine

surface reaction, J . D . McKinley, J. Phys. Chern. 66, 554-555 (Mar. 1962).

Auroral-zone geomagnetic micropulsations with periods of 5 to 30 seconds, W. H. Campbell and S. Matshu shita, J. Geoph ys . R esearch 67, No.2 , 555- 573 (Feb. 1962) .

Some problems of color ident ificatio n, K . L. K elly, J . Am. L Inst. Architects 37, No.3, 80-82 (Mar. 1962) .

Lorentz corrections in rutile , R . A. Parker, Phys. R ev. 12<1, No.6, 1713- 1719 (Dec. 1961 ).

Some observations of 2.89 Mc/s equivalent antenna t empera­t ures at t he auroral zone, C. G. Litt le, G. M . Lerfa ld , a nd R . Parthasarathy, J . Atmospheric and Terrest . Phys. 23, 275- 286 (Dec. 1961) .

The structure of regions of coronal-line emission, J . T. J efferies, C. W. Pecker , and R. N. Thomas, Astrophys. J . 135, 653- 655 (Mar. 1962).

A digital ray-tracing program for ionosphere research , R . S. Lawrence and D . J . Posakony, (Proc. 2d In tern. Space Science Symp., Florence, Italy, Apr . 10- 14, 1961), Space Research II, 258- 276 (No rth Holland Pubt Co., Amster­dam, The Netherla nds, Apr . 1961).

E lectrical properti es of non stoichiometric semiconductors, J. H . Becker and H. P. R. Frederikse, J . App!. Phys. Supp!. 33, No.1 , 447- 453 (Jan. 1962) .

Pulsed radio soundings of the topside of t he ionosphere in t h e presence of spread F, R . W. Knecht and S. Ru ssell , J . Geophys. Research 67, No.3, 1178- 1182 (Mar. 1962).

R ecent studies on rutile (TiO z), H. P. R. Frederikse, J . Appl. Phys . Suppl. 32, No. 10, 2211- 22 15 (Oct. ]961).

The resistive t ransition in Mb3Sn, D. Cline, R. I-I. Kropschot, V. Arp, and J . H . Wilson, Proc. Intern. Co nf. on High Magnetic Fields, Mass . Inst . Tech ., Cambridge, Mass., Nov. 1- 4, 1961 , pp . 580- 583 (Mass. Inst. Tech. , Press Cambridge, Mass., and John \Vi ley & Sons, In c., New YOf'k , N. Y. , 1962 ).

E lectronic co nduct.ion in rutile (,fiOz) , IT . P . R . Frederikse, W. R. Hosler and J . S. Beck er, Proc. Intern. Co nE. Semi­conductor Phys., Prague, Czechoslova kia , pp. 868- 871 (1960).

Structure and photodetachrncnt spectrum of the atomic carbon negative ion, M . L. Seman a nd L. M. Branscomb, Ph ys. Re v. l25, No.5, 1602- 1608 ( '\1ar. 1962).

Modulated photoelectric measurement of vibrat ion, V. A. Schmidt, S. Edelman , E. R. Smi t h and E . T. Pierce, J . ACOllst, Soc. Am. 3<1, No.4, 455- 458 (Apr. 1962) .

A lligh mod e tunab le cav ity for micro\\'ave-gas inter'1ctions, A. J . Estin , Rev. Sci. Instr. 33, 369- 371 (Mar. 1962).

Propagat ion of the low frequency radio signal, J . R . Johler, Proc. IRE 50, 404- 427 (Apr . 1962) .

*P ublications for which (I price is indicated (except for T echnical Notes) are available only from the Superintendent of Documents, U.S. Government P rinting O.ffice, ·Washington 25, D .C. (joTeign postage, one~fourth additional ). T echnical Notes are available only from the Office of T echnical S ervices, U .S. DepaTtment of Commerce, Washington 25, D.C. (ordeT by PB number) . R eprints fTom outside journals and the NBS J ournal of R esearch may often be obtained directl y f l'om the auth01's.

446 U, S . GOVERN MENT PRINTIN G OFFICE, l 962