FRACTIONAL DISTILLATION OF ESTERS IN VACUO 41 



produced by a Geryck vacuum pump, as described by Fischer and 

 Harries [1902]. In order to preserve the high vacuum in this process 

 liquid air is used for condensing the alcohol vapour arising from 

 the decomposition of the esters ; carbonic acid has been used by 

 other investigators, and Levene and Van Slyke [1908, i] employed 

 sulphuric acid, contained in cotton wool and cooled by a freezing 

 mixture, as an absorbent for this purpose. A small quantity of 

 ester also passes over with the alcohol ; this cannot be recovered if 

 Levene and Van Slyke's modification be used. The accompanying 

 figure shows the arrangement for the distillation at low pressure. 

 At 10-12 mm. pressure the receiver should be cooled in a freezing 

 mixture. 



FIG. i. 



From Berichte der Deutschen Chemischen C^esellschaft, 35, 2160. 



The temperatures at which the various fractions are collected are 

 those of the vapours of the esters at 10 mm. pressure, and those of 

 the water-bath at 100 and of an oil-bath, which replaces the water- 

 bath for the higher temperatures up to 1 60, at 0-5 mm. pressure. 



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. 



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

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

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



