AGRICULTURAL CHEMISTRY — AGROTECHNY. 605 



tion of the black deposit which tends to accumulate in the condensers and 

 adapters of the distillation racl^ is suggested. 



A colorimetric method for the estimation of amino-acid a-nitrogen, V. J. 

 Harding and R. M. MacLean (Jour. Biol. Chcm., 20 {1915), No. 3, pp. 217-230, 

 figs. S). — ^A method for the estimation of amino-acid a-nitrogen has been de- 

 vised, as follows: 



"One cc. of the solution to be estimated, containing- not more than 0.05 mg, 

 of amino-acid a-nitrogen and neutral to phenolphthalein, is mixed with 1 cc. of a 

 10 per cent aqueous solution of pure pyridin and 1 cc. of a freshly prepared 

 2 per cent solution of trilietohydrindene hydrate and heated in a rapidly boiling 

 constant-level water bath for 20 minutes. At the end of that time the test- 

 tube is removed, cooled, and diluted to a suitable volume, usually 100 cc. ; but 

 if the amino-acid a-nitrogen is very small in amount a correspondingly smaller 

 dilution can be used. The solution of coloring matter thus obtained is com- 

 pared with the standard color in the usual way in a Duboscq colorimeter." 



The method has been found to be as accurate as the Van Slyke method 

 (E. S. R., 25, p. 710). It is inaccurate, however, for cystin. From 0.005 mg. 

 to 0.05 mg. of amino-acid a-nitrogen per cubic centimeter can be estimated 

 with the method. It has been found to be applicable to the determination of 

 amino-acid a-nitrogen liberated in protein hydrolysis. 



Improvements in the m^ethod for analysis of proteins by determination of 

 the chemical groups characteristic of the different amino acids, D. D. Van 

 Slyke {Jour. Biol. Client., 22 {1915), No. 2, pp. 281-285). — Improvements in the 

 original method, as previously noted (E. S. R., 26, p. 22), include the use of a 

 2-in. BUchner funnel with a fiat circle of hardened filter paper for filtering 

 the phosphotungstic acid precipitate ; the use of the washing solution at 0° C. ; 

 the decomposition of the basic phosphotungstates (removal of the phosphotung- 

 stic acid) by extraction with an ether-amyl alcohol (1:1) mixture in an acid 

 solution ; the determination of the amino nitrogen in the bases with the micro- 

 amino apparatus ; and the determination of the total nitrogen of the bases in 

 duplicate by diluting the residue from the arginin determination to from 100 

 to 200 cc. and dividing into halves. 



A method for the estimation of the tryptophan content of proteins, 

 involving the use of baryta as a hydrolyzing agent, Annie Homee {Jour. 

 Biol. Chcm., 22 {1915), No. 2, pp. 369-389).— The hydrolysis of the protein by 

 barium hydroxid, removal of the hydroxid with sulphuric acid, precipitation of 

 the tryptophan with mercuric sulphate, decomposition of the precipitate, and 

 the subsequent bromination of the tryptophan solution is recommended as a 

 procedure for the determination of tryptophan. 



The estimation of fat, H. Rosenthal and P. F, Tkowbkidge {Jour. Biol. 

 Chem., 20 {1915), No. Jf, pp. 111-717).— The estimation of fat by the use of 

 solvent alone gives all substances soluble in the extraction medium used, but 

 by simple extraction only approximately true results for fat are obtained, 

 especially when other soluble substances are present. The authors have, there- 

 fore, proposed the following method : 



" The sample is heated for two hours with 30 cc. of a 20 per cent sodium 

 hydroxid solution. Place the beaker in the water bath and cover with a 

 funnel having the stem cut off. During this saponification the mixture is 

 stirred a few times, 



" The solution while still warm is transferred to a glass-stoppered separatory 



funnel of about 300 cc. capacity. The beaker is washed out two or three times 



with warm water. The solution is then acidified with 35 cc. of a 20 per cent 



hydrochloric-acid solution (specific gravity 1.1). After thorough cooling the 



31501°— No. 6—16 2 



