about the regulation and control of the chemical proc- man (j),the "Internatioual Critical Tables" (6),and esses of the human body. We control states of Mulliken (7) state that the molecular weight of racemic equilibrium in the laboratory but not in our physical acid with one molecule of water is 168.07. That this has proved very confusing not only to the bodies. The second ideal which needs to be strongly recommended to the ideal chemist is to have an ideal writer but to numerous other workers can be definitely of some sort which is as large or larger than the one shown. outlined under I,p. 202, JOURNAL OF CHEMICAL EDUCA- In 1933, Dr. A. K. Anderson, under whom the writer once had the pleasure of studying physiological chemisTION,13, May, 1936. W. MUHLEMAN try, published in collaboration with A. H. Rouse and GEORGE T. V. Letonoff a paper [Ind. Eng. Ckm., Anal. Ed., 5, HAMLINE UNIVERSITY SAINT PAUL. MINNESOTA 19 (1933)l entitled, "A Colorimetric Method for the Determination of Tartaric Acid." The method is of distinct value in the analysis of tartrate baking powders and can be used in the presence of aluminum. The following paragraphs from this paper are of interest.
THE MOLECULAR WEIGHT OF RACEMIC ACID To the Editor DEARSIR: During the course of some theoretical work on the optical isomerism of tartaric acid the writer found that racemic acid was yielding results only half of that expected and given by the ( d ) and (1) forms of the acid. Compounds possessing two asymmetric but structurally similar carbon atoms, of the general formula Cabc-Csbc exist in three different configurations. Two of these spatial arrangements are optically active and opposite in sign (antipodes). The third is represented by an internally compensated structure and cannot be resolved into-active components (meso form). A fourth compound, the racemic form, is produced by the union of the two active enantiomorphs and can be resolved or separated into its optically active components by special methods. A paradigm may help in elucidation. Let each of the two asymmetric carbon atoms be represented by A and their different spatial configurations by the signs and - . The following arrangements are possible.
+
(1)
(2)
(3)
(4)
+A
-A -A
+A -A
-A +A
+A
(5)
[(E) ( 3 1
As a matter of interest the application of the colorimetric method to the determination of other forms of tartaric acid was studied. Using &tartaric acid as a standard, it was found that l-tartaric acid, l-ammonium tartrate, and meso-tartaric acid produce a color equivalent to that of the standard. With racunic acid the color intensity was approximately one-half that of the standard. This reaction of racemic acid was surprising. I t was thought that possibly there might be some union of the d- and l- forms in racemic acid which was causing an interference in the reaction, but molecular weight determinations by the freeziug-point method indicate no such union. With regard to the purity of the racemic acid used (obtained from the Eastman Kadak Company) i t may be said that it was optically inactive and that it required the theoretical amount of sodium hydroxide for neutralization. The melting point wss 202%. whereas the accepted value is 205-206'C. A mechanical mixture of equal parts of dand l-tartaric acids did not react like racemic acid hut gave the proper color intensity. Two different samples of racemic acid were analyzed with identical results. No satisfactory explanation can be made for this hehavior of racemic acid.
In view of the foregoing statement that racemic acid should be represented by the formula 2CnHsOs 2H20 and not C&HsOs H20as given in all the standard sources of information, little need be added in explanation of the apparent discrepancy in the colorimetric analysis of racemic acid except to point out that this communication helps to substantiate the essential accuracy of the work reported by Dr. Anderson and his collaborators. EUGENE W. BLANK
+
+
+
Figures (1) and (2) represent respectively the (d) and (1) forms of tartaric acid. Figures (3) and (4) are identical and represent the (i) or meso form of tartaric acid. These three compounds have each a molecular weight of 150.05. Figure (5) represents dl-tartaric acid or racemic acid. With a little thought it will be realized that its molecular weight must be twice that of the other forms of tartaric acid, not including the water of crystallization usually associated with it. Schmidt and Rule (1)in reference to racemic acid say, "The crystalline acid has the composition 2C4H606 2Hz0." Bernthsen and Sudborough (2)likewise plainly state this fact. However, Richter (,?), Olsen ( 4 ) , Hodg-
LITERATURE CITED
(1) SCHMIDT AND RULE, "A texthwk of organic chemistry," 2nd ed., D. Van Nostrand Co., Inc., New York City, 1932, p. 281. (2) B E R N ~ S E N AND SUDBOROUGR, "A textbook of organic chemistry," new edition, D. Van Nostrand Co., Inc., New York City, 1922. (3) RICHTERAND SPIELMANN, "Organic chemistry," Vol. 1, 2nd ed.. P. Blakiston's Son & Co.. Philadel~hia. . . Penn-
' Sixth Issue,
+
ed., 1934, p. 686.
(6) "International critical tables," Voi. I, McGraw-Hill Book Co., lnc., New York City. 1926, p. 136. (i) S. P. ML'LLIKEN, "IdenliGcation of pure organic compounds," \'ol 1, John Wilcy P; Sons, Inc..Nrs \'ark Ciry, 1905, p. 50.
PREPARATION OF HYDROBROMIC ACID SOLUTION OF CONSTANT BOILING POINT
Thus in the pages of 'THISJOURNAL several articles have recently appeared showing the relation of chemistry to everyday life and The writer has long been interested in chemistry as reflected by philately, numismatics and press clippings, hut in these studies no reference to chemistry and cigarette cards has ever been found. Perhaps the fact that cards are no longer packed with domestic dgarettes has caused them to be overlooked and neglected as
To the Editor I was interested in the paper by G. B. Heisig and E. Amdur in your issue for April, 1937, pp. 187-8, on the preparation of hydrobromic acid in solution, from potassium bromide and sulfuric acid. The authors were good enough to mention the modification I introduced into Pickles' method, using stannous chloride to reduce any free bromine liberated in the reaction. I have made enquiries among British chemistry teachers and find the method is widely used in this country. As given in the original paper the method has the disadvantage that it introduces some hydrochloric acid into the distillate, but I have not observed any sulfuric acid in the hydrobromic acid so prepared, nor, for that matter, stannous or stannic sulfides. Sulfur has been known to appear in the condenser, and should any reach the receiver it could be removed by filtration. As little as 0.01 g. stannous chloride is adequate for addition to 30 g. of pure potassium hromide in 50 cc. of distilled water for treatment with 20 cc. of pure sulfuric acid. I am informed that metallic tin itself can be used (to avoid any HCl in the HBr) but I imagine this could introduce sulfur or hydrogen sulfide into the distillate and I prefer the addition of a trace (not more than 0.04 per cent.) of sodium sulfite to the bromide. The hydrobromic acid obtained boils constantly between 124°C. and 126% according to the Dressure. and although the liquid distilled may hecome orange yellow in color, no free bromine passes into the receiver and the distillate remains quite colorless. Although I still incline to the use of a trace of some reducing agent in this reaction, I should like to congratulate the authors upon having found what seems to be the most convenient method of making hydrobromic acid solution of constant b. p.
GERALD DRUCE 56, BISHOPSPARKRD. N O R B ~ S.W. ~ Y , 16. ENGLAND
CIGARETTE CARDS AND CHEMISTRY To the Editor DEARSIR: Collateral material dealing with the various branches of chemistry is to be found everywhere for the seeking.
a source of chemical information. Cigarette cards are very apt to be dismissed with an indulgent smile as fit playthings for juveniles, but card collecting is indulged in by many serious adult collectors and is enjoying great popularity on the continent of Europe with the natural consequence that many of the older sets are now selling a t a premium. Originally cards were simply plain pieces of cardboard put in to stiffen a paper packet of cigarettes and bore neither print nor picture. In the trade cigarette cards are still known as "Stiffeners." In 1887 the first advertisement appeared, being printed in red and black. Following this came pictured advertisements, hut it was not until 1895 that the first true pictures arrived in the form of a set of ships. However, in this set there was no printed information on the reverse side of the card, and i t was not until a year later, in 1896, that a set was issued having both a pictorial front and informative back. Figures 1 and 2 show reproductions of several hiological and chemical cards from the writer's collection. Sets are available on almost every conceivable subject. A recent catalog listed well over one thousand different sets. Biological subjects are especially prolific in both number and variety. Among the cards of H. F. SCnARFPER, "Philately server chemistry," J. CKEM. (1934). E ~ u c . 11,259 , J. CUSKMAN,"Sources of pictures," ibid., 13, 328 (1936).
