1 6 THE CHEMICAL CONSTITUTION OF THE PROTEINS 



di-amino acids are then precipitated with phosphotungstic acid (pp. 60, 

 98) ; from this precipitate they are obtained by decomposition with 

 baryta and separated by means of their silver compounds as described 

 in section B (p. 55). The filtrate is freed from phosphotungstic acid 

 and sulphuric acid with baryta, excess of which is removed with carbon 

 dioxide and sulphuric acid, and then treated for the other mono-amino 

 acids as described in section A (p. 33). 



On the whole it is not advisable to combine the two processes, 

 since the phosphotungstic acid precipitation does not effect a perfect 

 separation of the two groups and considerable loss occurs. 



