a. Williams 201 



pure lead acetate and evaporation of the filtrate. (Any excess of lead 

 acetate was removed by hydrogen sulphide.) A slight residue was 

 invariably left. The phosphotungstic acid was purified by Winter- 

 stein's method as recommended by Levene and Van Slyke. The acid 

 was dissolved in water, from which it was shaken out ^^'ith ether, with 

 which it formed an oily layer much hea\aer than water. The ether 

 solution was washed several times with water and the ether driven off 

 with constant stirring on the water bath. The dry residue was then 

 groimd up. The product obtained was white, non-hygroscopic, and 

 dissolved readily in water forming a colourless solution. 



Preparation of alanine and valine mixture. 



Crops 2, 3 and 4 of Fraction 2 (see page 199), and Crop 1 of Fraction 

 1 (see page 197), all of which contain between 12 and 13 per cent, of 

 nitrogen, were combined together and recrystalhsed. Two crops of 

 9-48 and 5-32 grms. respectively were removed, and a mother hquor 

 residue of 6-3 grms. obtained. This residue should contain any alanine 

 which may have been present in the mixture. To this were added all 

 those crystal fractions which contained between 14 and 16 per cent, 

 of nitrogen, namely Crops 2 and 3 and mother hquor residue of Fraction 1 

 (see page 197) and Crop 5 and mother hquor residue of Fraction 2 (see 

 page 199). The gram of acids recovered from the distillates was also 

 added. This mixture which weighed 25-23 grms. and contained 14-20 

 per cent, of nitrogen was considered to be a mixture of alanine and 

 vahne only. 



Upon combustion 0-1460 grm. of the mixture gave 0-2395 grm. CO2 



= 44-73 per cent, of carbon. 



Vahne contains 51-28 per cent, of carbon and alanine contains 

 40-45 per cent. This indicated the presence of about 40 per cent, 

 of valine and 60 per cent, of alanine in the mixture. 



44-73-40-45 ,^^ 4-28 ^.^ _. _, ^ t r i 



i^r~;^ TTTTv X 100 = TTTWi. y- 100 = 39-51 per cent. 01 vahne and 



51-28—40-45 10-83 



60-49 per cent, of alanine. 



A similar calculation based on the nitrogen content of the mixture 

 also indicated the presence of about 40 per cent, of valine. 



14-20-11-97 ,„ 2-23 ,^^ ^n oi ^ * 1 - a 



— -^— — X 100 = ^-=^ X 100 = 59-31 per cent, of alamne and 



40-69 per cent, of vahne. 



