G. Williams 199 



Fraction 2. 



The acids of this fraction left after extraction of prohne were recrystal- 

 lised from water in the same manner as those of Fraction 1. 



Crop 1 is probably a mixture of vahne and leucine. Crops 2, 3 and 

 4 seem to contain more and more alanine mixed with the leucine and 

 vaHne. Crop 5 and the residue seem to be predominantly made up 

 of alanine mixed with valine and perhaps a httle leucine. 



Separation of leucine and valine. 



This was carried out by Levene and Van Slyke's lead method^. 

 This method was first of all apphed to the first crop obtained from 

 Fraction 2. 



0-1502 grm. of the mixture on combustion gave 0*2967 grm. COg 

 and 0-1292 grm. HgO = 53-87 % carbon and 9-55 % hydrogen. 



On the assumption that only vahne and leucine are present, this 

 indicated the presence of about 70 per cent, of leucine in the mixture. 



Percentage of C in mixture — Percentage of C in valine 

 Difference between percentage of C in leucine and valine 



53-87 -51-28 2-59 ,„^ ^yn 4 o/ i • 

 = 54-96 -51-28 = 3:68 ^ ^^^ = ^^'^ % ^^^^^*"" 



A similar calculation based on the nitrogen content of the mixture, 

 however, indicated the presence of about 60 % of leucine in the mixture. 



11-22 — 10-69 



— — X 100 = 41-4 per cent, valine or 58-6 per cent, leucine. 



It was decided to treat the mixture on a basis of 60 % of leucine 

 first of all. 



Owing to losses for analysis the acids weighed 23-22 grms. now. They 

 were reduced to a fine powder in a mortar, and seven parts of water 



1 Journ. of Biol. Che.m. vi, p. 391, 1909. 



