712 EXPERIMENT STATION RECORD. [Vol.40 



a less even deposit of platinum. Allyl alcohol causes no reduction. The method 

 as described is said to be rapid and complete. 



The gravimetric and volumetric determination of mercury precipitated as 

 mercury thiocyanate, G. S. Jamieson (Jour. Indus, and Engin. Chem., 11 

 (1919), No. 4, pp. 296, 297). 



Colorimetric determination of organic substances, H. Heidenhain (Jour. 

 Indus, and Engin. Chem., 11 (1919), No. 4, pp. 297-299, fig. 1).—A method is de- 

 scribed for the colorimetric determination of organic substances which is an ap- 

 plication of the author's method for the volumetric determination of organic 

 substances. 1 This is based on the fact that organic compounds can be oxidized 

 by a mixture of a dilute solution of potassium bichromate and sulphuric acid 

 with the production of different shades of color from pure green to orange, de- 

 pending upon the amount of the organic substance present. 



The standards are prepared by boiling for five minutes with a reflux con- 

 denser a mixture of 25 cc. of N/5 bichromate solution, 30 cc. of concentrated 

 sulphuric acid, and varying amounts (from 2.5 to 25 cc.) of the pure compound 

 which is to be determined in the substance tested. The solutions after cool- 

 ing are transferred to cylindrical bottles and made up to 80 cc. 



For the determination of the substance 25 cc. of a solution of the substance 

 to be tested, the concentration of which must not exceed that of the N/5 solu- 

 tion, is treated as above with 25 cc. of the N/5 bichromate solution and 30 cc. of 

 sulphuric acid, made up to a volume of 80 cc, and compared with the standards. 

 It is said that substances to be tested may be dissolved in alkalis, ammonia, 

 and sulphuric and acetic acids, but that hydrochloric and nitric acids interfere 

 with the test. 



Suggested uses of the method are the determination of carbohydrates in 

 waste liquors of glucose plants, of glycerol in soap lyes, of tartrates in baking 

 powders, and of alcohol in vinegars. 



The determination of zinc and copper in gelatin, G. S. Jamteson (,/oi/r. 

 Indus, and Engin. Chem.. 11 (1919), No. 4, pp. 828-325).— The author, at the 

 Bureau of Chemistry of the U. S. Department of Agriculture, describee a method 

 for determining zinc and copper in gelatin. This depends upon the hydrolysis 

 of the gelatin with hydrochloric acid, precipitation of the zinc and copper with 

 ammonium sulphid, and subsequent separation of the two metals by solution 

 of the sulphids in nitric acid and reprecipitation of copper with hydrogen 

 sulphid and of zinc from the filtrate with ammonium sulphid. Both are con- 

 verted into oxids and determined gravimetric ally. 



The technique is described in full and it is stated that in order to obtain 

 satisfactory results the directions must be followed in every detail. 



The chemical investigation of spoiled meat, K. G. Fat.k, E. J. Bat-mann, 

 and G. McGuire [Jour. Biol. Chem., 87 (1919), No. 4, pp. 525-546, figs. 9).— The 

 experiments reported here were conducted for the most part on samples of 

 meat or meat broth inoculated with organisms isolated from meat thought to 

 be responsible for actual cases of poisoning. The general method employed 

 was to study the chemical changes produced by the organism in the following 

 components: Total nitrogen, nonprotein nitrogen, ammonia nitrogen, total 

 creatinin nitrogen (creatin plus creatinin), and purin nitrogen. Bfost of the 

 organisms were of the colon-typhoid group, but for comparison Streptococcus 

 brcris and the spore-forming Bacillus suit His were used. The methods em- 

 ployed for each determination are described in detail and the results obtained 

 reported in tabular form. 



»Jour. Auier. Chem. Soc. 15 (1893), No. 2. pp. 71-77. 



