[VOL. LXXII, No. 1868

duced by A. A. Noyes). It was the purpose of theexperiments here reported to attempt a separation of thesymmetric and antisymmetric types of iodine moleculeby means of a photochemical reaction in which one ofthese molecular types is selectively activated. The selec-tive activation was effected by irradiation with the greenmercury line, 5461 A, which is absorbed by only one ofthe molecular types, and the acceptor chosen for theactivated molecules was gaseous hexene. If the photo-chemical reaction were of the simplest kind, namely theaddition of the activated iodine molecules onto the hexenedouble bond, the reaction would proceed until half theiodine is used up, the molecules remaining being of thetype which does not absorb the green mercury line. Ex-periments on mixtures with a partial pressure of iodineof about 0.17 mm and of hexene of about 6. mm showthat the mechanism of the reaction is actually more com-

plicated, and may possibly involve energy transfers be-tween the two types of iodine, or the production of iodineatoms at some stage of the process. However, fluores-cence experiments on mixtures in which half the iodinehad reacted indicated a small but definite excess of themolecular type which does not absorb the 5461 A line,over that found in the equilibrium iodine mixture. Thisexcess does not disappear in several days when the gas

mixture is kept in the dark.

The ring structure of mannose: HORACE S. ISBELL (in-troduced by George K. Burgess). The ring structure ofthe various forms of glucose and mannose has been thesubject of considerable controversy. It has been claimed(Hudson, Jour. Amer. Chem. Soc., 52: 1682, 1930) that a

decision between the rival classifications of rings mightbe obtained from a comparison of the optical rotationsof a pair of sugars which can exist only in one ringform. Two pairs of substances which fulfil these re-

quirements, cellobiose and 4-glucosido-mannose, and lac-tose and 4-galactosido-mannose, were pointed out by C.S. Hudson. A comparison of the approximate rotationsof these sugars as given in the literature shows that thedifference between the molecular rotations of the firstpair differs widely from the value obtained for the seconidpair. Thus it was necessary to obtain more accuratedata upon the rotations of these substances. The prepa-

ration of 4-glucosido-a-mannose monohydrate has beeijrepeated and the initial rotation as extrapolated to zero

time was found to be [a] = 14.6. A comparison of theD

molecular rotations of cellobiose and 4-glucosido-a-man-nose gives an "'epimeric" difference of 16,900. Thisis of the same order of magnitude as the values ob-tained from a-mannose and at-methyl mannoside, 14,900and 15,300, respectively, but it differs markedly fromthe value 6,700 obtained from f-mannose. On the otherhand, a comparison of the approximate rotations of4-glucosido-fI-mannose and 4-galactosido-fI-mannose indi-cates that they agree with the value derived from,B-mannose. These results are interpreted as indicatingthat 4-glucosido-a-mannose has a structure similar toa-mannose, while 4-glucosido-j3-mannose and 4-galacto-sido-f3-mannose have structures similar to f-mannose.

Since the disaccharides just mentioned can not form a1, 4 ring, probably neither a- or f-mannose has a 1, 4ring structure.

Crystalline alpha and beta methyl-d-gulosides: HORACES. ISBELL (introduced by George K. Burgess). The reac-tion between reducing sugars and methyl alcohol in thepresence of hydrogen chloride gives a mixture of isoinericmethyl glycosides. Frequenitly amorphous products are

obtained which can not be brought to crystallization bythe usual methods. The separation of two isomericmethyl gulosides from such a mixture was accomplishedby means of crystalline coordination compounds withcalcium chloride. So far as known these compounds arethe first compounds of this type to be prepared from themethyl glycosides. The calcium chloride was removed byimeans of silver oxalate, and crystalline a-methyl-d-gulo-side (monohydrate) and f3-methyl-d-guloside were ob-tained for the first time. The following new compoundsare reported:

a-Methyl-d-guloside CaCl2 2H2O,

(a-Methyl-d-guloside)2 CaCl2 * 3H20,

a-Methyl-d-guloside- H,O,

f-Methyl-d-guloside CaCl2. 2H2O,

(approximately).(fI-Methyl-d-guloside), CaCl2,

f3-Methyl-d-guloside,

La20-t G7

D

20[u] = + 83.

D

+109.D

[ L20 46

D

20[a]

D65.

20_[La 83.D

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