240 CHEMISTRY OF THE PROTEIDS CHAP. 



with the lead sulphide test. The percentage composition of sulphur 

 is not altered by oxidation. 



By oxidising oxyprot-sulphonic acid with KMn0 4 at room-temper- 

 ature, neutralising the resulting fluid with acetic acid and then pre- 

 cipitating firstly with lead acetate and subsequently with mercuric 

 acetate, Bernert obtained two fractions, which he called peroxyproteic 

 acids A and B. The compound B gives with phosphomolybdic and 

 phosphotungstic acids dense precipitates soluble in an excess of HC1 ; 

 mercury-potassium iodide, picric acid, and tannin do not cause a 

 precipitate; with silver nitrate a precipitate is obtained which is 

 soluble in both ammonia and in nitric acid. Boiling with baryta 

 water yields with the B-fraction leucin, acetic and butyric acids, and 

 probably pyridin, while the A-fraction gives in addition glutaminic 

 and benzoic acids and benzaldehyde. 



Ehrmann, using the same method as Bernert, obtained from serum 

 albumin and casein also two peroxyproteic acids, neither of which could 

 be precipitated by such alkaloidal reagents as phosphotungstic acid, 

 or by means of mercuric acetate or nitrate. 



The ratio of C : H : N : was the same in Ehrmann's acid as in 

 Maly's acid. 



C H N 



Peroxyproteic acid of Maly .. 4*4 7*3 1 2*4 

 Ehrmann's silver salt . . 4'2 7'0 1 2 '3 



0. v. Fiirth has made the most thorough examination of Maly's 

 compounds. Peroxyproteic acids were prepared from defatted casein, 

 which in the course of some weeks was gradually oxidised by KMn0 4 

 in an alkaline solution. When oxidation was complete, the clear 

 yellow filtrate was treated with glacial acetic acid till it was just- 

 alkaline, and was then precipitated with an excess of lead acetate. 

 The heavy precipitate, consisting for the greater part of lead oxalate, 

 was suspended in water and decomposed while warm with H 2 S. As 

 the peroxyproteic acid adheres firmly to the lead sulphide, the latter 

 had to be extracted with hot water 6 to 13 times, the sulphide after 

 each extraction being suspended in water, and again saturated with H 2 S. 

 The combined filtrates were freed from H 2 S by passing air through 

 the solution ; the oxalic acid was removed by means of barium 

 hydrate, and the excess of barium with C0 2 . Then the solution was 

 precipitated with silver nitrate ; the silver precipitate suspended in 

 water and decomposed with H 2 S ; the filtrate inspissated at 50, and 

 then dried in vacuo over H 2 S0 4 . The resulting mass, looking like 

 varnish, was called 'Peroxyproteic acid A.' The filtrate from the 



