1919] AGRICULTURAL CHEMISTRY — AGROTECHNY. Gil 



phate, sodium oxalate, or hydrogen peroxld, and titration of the excess of 

 reducing agent with permanganate. It is said that the titration is not inter- 

 fered with by moderate amounts of chlorld or small amounts of broinid. 



Silver uitrlte is not considered a satisfactory material for use as a standard 

 in nitrite determinations. The authors recommend a sodium nitrite solution 

 standardized with potassium permanganate according to the method described 

 above, or gravimetrically by the reduction of silver bromate to silver bromid 

 according to the method of Busvold (E. S. R., 33, p. 204). 



On amino acids, II. D. Dakin (Biochem. Jour., 12 (1918), No. 4, PP- 290- 

 317). — The author discusses a new method of extraction of amino acids by 

 partially mlscible solvents, and describes the isolation by means of this method 

 of a new amino acid and a new peptld. 



The method consists essentially of the separation, by the use of butyl alcohol 

 as a solvent, of the hydrolysis products of a protein into the following groups: 

 (1) Monamino acids, both aliphatic and aromatic, insoluble in alcohol but ex- 

 tracted by butyl alcohol; (2) prolin, soluble in alcohol and extracted by butyl 

 alcohol; (3) peptid anhydrids (diketopiperazins) extracted by butyl alcohol, 

 but separated from (2) by sparing solubility in alcohol or water; (4) dicar- 

 boxylic acids, not extracted by butyl alcohol ; and (5) diamino acids, not ex- 

 tracted by butyl alcohol, but separable from (4) by phosphotungstic acid and 

 other means. 



The method is considered to be of particular value in that the groups are 

 composed of chemically similar individuals; each group can readily be obtained 

 in solid form, aliquot parts of which may be used in the search for individual 

 acids; no indications of any racemization have been observed; and materially 

 higher yields of many amino acids may be obtained from proteins than by 

 existing methods, thus permitting a more nearly quantitative analysis of the 

 proteins themselves. The possibilities are pointed out of other purposes to 

 which this method of extraction by partially mlscible solvents may be applied, 

 such as the selective extraction of sensitive substances from tissue extracts, 

 the quantitative extraction of tryptophan from the products of tryptic digestion 

 of caseinogen, and the study of the products of the hydrolysis of proteins by 

 enzyms. 



The technique of the method as applied to the separation of the hydrolysis 

 products of caseinogen is described in detail, and experimental proof is given 

 of the structure of the new compounds obtained, /3-hydroxyglutamic acid, 

 COOH.CH (NH,).CH(OH).CH2.COOH and a new peptld, isoleucylvalin an- 

 hydrid. 



The quantitative determination of hippuric acid, E. Fit.ippi (Arch. Far- 

 macol. Spcr. e Sci. Aff., 26 (191S), No. S, pp. 243-256).— Various methods of de- 

 termining hippuric acid in urine are reviewed and a new method is described. 

 This consists essentially of a preliminary separation of benzoic acid and other 

 impurities from the concentrated urine by warming at from GO to Go* C for 

 two hours with a mixture of two parts of benzene and one part of alcohol-free 

 ether, oxidation of the purified urine with manganese dioxid and sulphuric 

 acid, distillation of the benzoic acid formed from the hippuric acid, and extrac- 

 tion with successive small portions of ether. 



The method is said to be rapid and complete. 



Estimation of acidity in barley by titration in stages, A. Reichard (Ztschr. 

 Gesam. Brauw., 41 (1918), Nos. 8, pp. 57-60, fig. 1; 9, pp. 65-68; 10, pp. 75-77; 

 11, pp. 83, 84; 12, pp. 89, 90; abs. in Jour. Inst. Bracing, 24 (1918), No. 5, pp. 

 219-221). — A study is reported of the acidity in barleys as determined by titra- 

 tion of an alcoholic extract of the ground barley with alkali, first with litmus 



