RECENT WORK IN AGRICULTURAL SCIENCE. 



AGRICTJLTTJRAL CHEMISTHY— AGROTECHNY. 



The hexone bases of casein, D. D. Van Slyke (Jour. Biol. Chem., 16 (19U). 

 No. 4, pp. 531-538).— In a preliminary description (B. S. R., 25, p. 710) of tlie 

 method for the analysis of proteins by the determination of the chemical groups 

 characteristic of the different amino acids, an analysis of casein was reported. 

 The results agreed well with the analysis reported by other investigators in 

 work with the Kossel method. " The discrepancy, noted in the preceding article, 

 between the free amino nitrogen of casein, and the lysin content previously 

 determined, rendered a repetition of the nitrogen distribution in this protein 

 desirable." The bases were determined by the method of Kossel and Patten as 

 modified by Osborne, Leavenworth, and Brautlecht (E. S. R., 20, p. 1102), and 

 the bases and nitrogen distribution were redetermined by the modified Van 

 Slyke method. 



The most significant difference between the present results and the previous 

 ones occurred in the lysins. By exercising particular care in the Kossel method, 

 9.36 per cent of the casein nitrogen was obtained as the analytically pure 

 picrate. The group determination gave 10.3 per cent which is believed to be 

 more nearly correct, as the amount of lysin picrate which one can crystallize 

 represents necessarily the minimum amount present. 



" For ai'ginin the results are practically the same, 7.4 to 7.8 per cent of the 

 total nitrogen, as those previously obtained by both methods. The histidin 

 results are a little higher than previously, but not to a marked extent. 



" The source of error in the author's former results for lysin lay in the cystin 

 determination. The lysin is estimated from the total amino nitrogen of the 

 bases precipitated by phosphotungstic acid, after the cystin nitrogen has been 

 subtracted. The cystin was estimated from the amount of organic sulphur 

 precipitated with the bases. The original form of the method, however, made 

 the cystin figures liable to error from the fact that sulphates could be dissolved 

 from a glass flask used in one stage of the operation." 



In the form in which the method was modified (E. S. R., 26, p. 22), the 

 sources of error in the cystin and lysin determinations have been eliminated. 

 " In the determination by the picrate method, as usually performed, it appears 

 that the most probable source of loss lies in the decomposition of lysin phos- 

 photungstate with barium hydrate. In this operation one insoluble precipitate 

 (lysin phosphotungstate) is transformed into another (barium phosphotung- 

 state) a process the completeness of which is necessarily difficult to judge. 

 Moreover, the bulky barium phosphotungstate has marked adsorptive proper- 

 ties, so that even skill and experience might not insure against loss from this 

 source. In working out the details of the group determination method, it was 

 noticed that several per cent of the total nitrogen of the protein could be lost 

 from the base fraction through adsorption or occlusion by the barium precipi- 

 tate." A practice is made of reducing this loss to a minimum by completely 

 dissolving the bases precipitated by phosphotungstate acid with alkali and pre- 

 cipitating the barium phosphotungstate in a dilute solution. The best results 

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