THE PTOMAINS OF THE URINE. 317 



A small portion of the diamins remains in the first filtrate. To 

 isolate these, the liquid is acidified with sulphuric acid and ex- 

 tracted with ether. The ethereal extract is evaporated, and the 

 final solution, before congealing, placed in as much of a 12 per 

 cent, solution of sodium hydrate as is required for its neutralization. 

 From three to four times as much of the alkali solution is then 

 added. On standing in the cold, sodium benzoyl-cystin separates 

 out, together with the benzoylated diamins. The crystals are fil- 

 tered off' and placed in cold water. This dissolves the cystin com- 

 pound, while the diamins remain undissolved. They are soluble in 

 warm alcohol, and can then be separated from each other, as has 

 been described. 



More recently, Lowy and Neuberg have advised another 

 method which is based upon the isolation of diamins as phenyl 

 cyanates, and which has the advantage that phenyl isocyanate in 

 aqueous solution does not unite with carbohydrates, and that the 

 cystin derivative does not separate out if the reaction is kept 

 alkaline. For a detailed account the reader is referred to Lowy and 

 Neuberg's paper (Zeitschr. f. physiol. Chem., 1904, vol. 43, p. 338). 



