NUTRITION — OSBORNE. 



227 



The greatest loss is caused by decomposition of the esters during distilla- 

 tion, whereby products of unknown nature are obtained in the higher-boiling 

 fractions of the esters and a relatively large amount of undistillable residue 

 is formed. These losses can be reduced to a considerable extent by distilling 

 as rapidly as possible to a temperature sufficiently high to carry over all of 

 the leucine ester and then treating the undistilled esters according to the 

 method usually applied to the higher-boiling fractions. This procedure sim- 

 plifies the process and materially decreases the labor involved. 



The losses caused by incomplete separation of the amino-acids can be re-- 

 duced to a comparatively small amount by careful work and by using the 

 method of Levene and Van Slyke for separating leucine and a method de- 

 vised for separating the dibasic glutaminic and aspartic acids from the mono- 

 basic amino-acids by aid of their acid sodium salts. 



Much larger losses than have heretofore been assumed have been found 

 to take place when alcohol or ether are distilled from the free esters and the 

 yield, especially of alanine, can be greatly increased by taking the necessary 

 precautions to recover it from the distillate. 



The extent of these losses has been learned by making several analyses of 

 zein and by analyzing known quantities of the amino-acids which this pro- 

 tein contains mixed together in the same proportion as these were obtained 

 from this protein. By assuming the losses in the analysis of zein to be equal 

 to those that occurred in the analysis of this mixture, it has been found that 

 over 92 per cent of this protein almost certainly consists of those amino-acids 

 which were previously known as its decomposition products. In making this 

 estimate, account was taken of the water which is eliminated when the amino- 

 acids are combined in polypeptide union. 



By taking advantage of the knowledge gained in this study the total quan- 

 tity of decomposition products actually isolated from zein in a pure form 

 has been very materially increased above that earlier obtained by working 

 under the formerly employed conditions. This is shown by a comparison of 

 the following figures : 



Analysis of Zein. 



As zein constitutes 5 per cent of the corn crop, its enormous commercial 

 value justifies the expenditure of much time and money in learning every- 

 thing possible about its constitution. The increased knowledge of its decom- 



