THE PROTEOSES 



183 



5. Among the important reactions of proteins is Rose's or Piotrowski's 

 reaction that is, the coloration produced by copper sulphate and a caustic 

 alkali ; the term ' biuret reaction ' is applied to the rose-red colour which 

 proteoses and peptones give with these reagents, because biuret (a derivative 

 of urea) gives a similar colour (see p. 39). Gnezda found that if a dilute 

 solution of nickel sulphate is used instead of copper sulphate, the native pro- 

 teins give different colours from the peptones and proteoses, and Pickering 

 has found the same with cobalt. Their results may be given in the following 

 table : 



Proteiu 



| Albumins and\ 

 globulins / 



Proteoses and \ 

 peptones / 



6. Another delicate test introduced by McWilliam may here be mentioned. 

 Salicyl-sulphonic acid precipitates albumins and globulins : on heating, the 

 precipitate is coagulated. The same reagent precipitates proteoses. On 

 heating, the precipitate dissolves and reappears on cooling. It does not 

 precipitate peptones. 



7. The use of trichloracetic acid for the separation of various proteins 

 may be illustrated by the following experiment. Take some blood and add 

 to it some solution of Witte's peptone (i.e. proteoses and peptone). Add to 

 this mixture an equal volume of a 10-per-cent. solution of trichloracetic acid. 

 There is an abundant precipitate. Boil rapidly and filter hot. The filtrate 

 contains the proteoses and peptone, all the other proteins being contained in 

 the precipitate. On cooling, the filtrate deposits some of the proteose. The 

 proteose and peptone may be detected in the usual way. 



