CHEMICAL COMPOSITION OF PROTEIN MOLECULE 15 



acid for three to five hours. The hot solution is then neutralised to 

 congo red by adding sodium acetate in the form of crystals. Almost 

 the whole of the cystine separates out on standing. After several 

 hours the precipitate is dissolved in 3-5 per cent, hydrochloric acid, 

 the solution is boiled with charcoal, and the hot colourless solution is 

 neutralised as before by adding a hot concentrated solution of sodium 

 acetate. Cj*stine separates out in the characteristic hexagonal plates 

 as the solution cools. No data of the yield are given. 



The mother liquor on dilution and on standing deposits tyrosine. 

 This is most readily purified by dissolving in hydrochloric acid, de- 

 colorising the solution with charcoal, and then neutralising exactly 

 with ammonia, when almost pure tyrosine separates out. 



Some experiments which have been carried out in my laboratory 

 with hair and other keratins by this process have sometimes given a 

 mixture of cystine and tyrosine on neutralising with sodium acetate ; 

 sometimes tyrosine has separated out first. This agrees with Morner's 

 results in which the first product to separate out was the one present 

 in greatest amount. The separation was effected by phosphotungstic 

 acid. 



