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 Gesellschaft, 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 1 00 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 fractionation is 

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

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



