I'JiiOJ AGllICULTURAL CHEMISTRY AGROTECIINY, 505 



ilillerence between these two titrations represents tlie free amino acid acidity. 

 The total amino acid acidity is determined by a similar procedure with an 

 aliquot of the sample after saponification with dilute IICl. From these two 

 results the unesterilied amino acid is calculated by difference. 



In the case of hiy;lily colored mixtures, decolorization should lirst be effected 

 by the addition of aluminum sulphate to the hydrolyzate made alkaline with 

 barium hydroxid and subsequently filtered. 



The results are given of the application of this method to mixtures of amino 

 acids from casein, vignin, gelatin, and vegetable albumin, to mixtures rich iu 

 duuuiuo acids, and to individual amino acids. In a single esterification alanin 

 was esterified 96, lysin 82, and glutamic acid 85 per cent. In the case of 

 mixtures of amino acids a single esterification yielded as high as 90 per cent 

 of the amino acid acidity. 



A method for the determination of cystin, Y. Okuda {Jour. Col. Ayr., Imp. 

 Univ. Tuhiio, 7 (liUO), Ao. 1, pp. 60-76).— In the method described, 10 cc. of a 

 20 per cent NaOH solution is added to 10 cc. of a 5 to 10 per cent IICl solution 

 of cystin. The solution is then titrated with a solution of potassium bromate 

 containing 8.35 gm. KBrOa in one liter of water until the faint yellow color 

 produced remains for one minute. 



The presence of histidin, which also absorbs bromin, is said not to interfere 

 with the reaction, as the velocity of the reaction of cystin for bromin is uuich 

 higher than that of histidin. In the presence of tyrosin the bromate titration 

 corresponds to the sum of tyrosin and cystin. This necessitates either a 

 separate determination of the tyrosin or of the cystin by one of the customary 

 methods. 



Some observations on the color changes of the diphcnylamin reaction, 

 E. M. Harvey {Jour. Amer. Chem. Sac, Jf2 {1920), No. 6, pp. 12^5-12Ji7, fig. 1).— 

 The author reports a study at the Oregon Experiment Station of factors 

 influencing the production and intensity of the coloration of the diphenylamin 

 reaction as a inichrochemical test for nitrates in plant tissues. 



The concentration of the sulphuric acid was found to be the most important 

 factor, three distinct color changes resulting from a gradual increase in con- 

 centration. The amounts of diphenylamin and of nitrate which could be used 

 without altering the reaction varied within rather wide limits. Variable 

 temperatures between 20° and 50° appeared to have vei*y Ittle effect except 

 on the time required for the development of maximum coloration. A considera- 

 tion of these and other less important factors has led to the suggestion of slight 

 modifications in the usual formulas, as follows : 



The modified I'eagent is made up of 0.05 gm. of diphenylamin, 7.5 cc. of 95 

 to 96 per cent PLSOj, and 2.5 cc. of a 10 per cent aqueous solution of potassium 

 chlorid. This salt is substituted for hydrochloric acid on account of its form- 

 ing less free HCl during the mixing. This reagent is applied directly to a thin 

 section of the tissue on a glass plate or microscope slide. 



Determination of lactose in altered milk, E. Hildt {Ann. Falsif., IS 

 {1920), No. 135-136, pp. 2i-25).— Previously noted from another source (E. S. 

 R., 43, p. 14). 



Butyl alcohol as a medium for the determination of saponification num< 

 bers, A. M. Pakdee, II. L. Hasciie, and E. E. Reid {Jour. Indus, and Engin. 

 Chem., 12 {1920), No. 5, pp. ^81, 7/82).— The results are reported of duplicate de- 

 terminations of the saponification numbers of various fats, oils, and waxes with 

 ethyl and butyl alcohols as fat solvents. The data corroborate the conclusions 

 of Pardee and Reid previously noted (E. S. R., 42, p. 502) that butyl alcohol 

 Is superior to ethyl alcohol as a medium for quantitative saponification. 



