(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).
most interest to chemists are such as inventors, famous scientists, interesting experiments, optical illusions, scientific inventions and discoveries, etc. A set may
contain anywhere from ten to one thousand cards. With customary Teutonic thoroughness, Germany produces most of the higher numbered sets. For those who are interested in this subject an inquiry of the hobby editor of any newspaper or hobby magazine will supply the required information as to how to build up a collection. EUGENE W. BLANK
ments and their bearing upon our undergraduate instruction. A number have expressed their desire to cooperate on the preparation of a set of semi-micro procedures in organic chemistry. Feeling that there are doubtless many others who have a similar interest along these lines, the writer takes this opportunity to invite their cooperation. During the coming summer, the writer plans to puhlish in planograph form the exercises as they have been developed in the organic laboratories a t Purdue University. Those who desire to cooperate on the project are invited to use these manuals during the coming year, and make their contributions toward their revision. In the revised form, the manual will be puhlished as a cooperative project. Those who are interested should communicate at an early date with the writer.
AUTOMATIC FILTERING SET-UP DONALD H. WEST L. L. Wright High Schaol, Imnwwd, Michigan
It IS often necessary to prepare a quantity of a filtered solution such as limewater for the use of the chemistry class. When suction is not feasible or available the tedious task of keeping funnels full may be avoided by using the simple filtering arrangement shown in the accompanying diagram. A two-liter flask is fitted with a two-holed stopper and two glass SEMI-MICRO ORGANIC TECHNIC tubes. One of the tubes extends T o the Editor nearly to the bottom of the flask and is about a centimeter in inner diameter. For this a glass tube The developments of the past few years have stimufrom a broken condenser may be lated an interest in micro- and semi-micro procedures used. The other tube is about four that is being felt in our educational institutions. A millimeters in inner diameter and demand is being created for a new technic that must extends into the flask only the length he given some consideration ultimately, at least, in of the neck. Both tubes extend our regular undergraduate courses. outward an inch or two from the About seven years ago a t Purdue University, the orstopper. It is convenient to have a ganic division undertook the revision of the undershort section of rubber tubing and graduate course so as to meet, in some measure, this a pinch clamp on the outer end of apparent need. Year by year the course has been rethe smaller tuhe. vised, the amounts of chemicals decreased, the proceThe flask is filled with the liquid dures improved, and the technic simplified until we to be filtered and, with the smaller are offering what approximates a semi-micro course in tuhe closed, it is inverted over the undergraduate organic chemistry. We have made a funnel and suspended on a ring stand. The height is beginning, but there still remains much to be done. adjusted so that the tubes extend into the funnel below The ~ & ~ o n relative se to papers presented a t recent the upper edge of the filter paper. The small outlet chemical meetings is ample evidence that a number of tube is opened, and the funnel is then kept full autoinstructors are keenly interested in these newer develop- matidy-.
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