CHEMICAL COMPOSITION OF PROTEIN MOLECULE 23 



Formerly the lower boiling fractions were again distilled in vacuo 

 so as to obtain a further fractionation, but each fraction, even then, 

 did not generally contain a single ester of an amino acid. A second 

 fractionation is therefore no longer carried out. 



FIG. i. 



Reproduced by kind permission from the Berichte der Deutschen Chemischen 



Gesallschaft. 



In the case of the higher boiling fractions a second fractionation is 

 not necessary, since the esters contained in them can be separated by 

 their varying solubility in water, ether and petroleum ether. Accord- 

 ing to Osborne and Jones the distillation of the esters boiling above 

 noC. can be dispensed with. An equally good separation of this 

 residual mixture can be effected if it be carried out in the same way 

 as is described for the esters after they have been distilled. 



The following table shows the fractions which are collected, and 

 the amino acid esters which they may contain : 



