26 Frederick Guthrie on Salt- Solutions 



§ 236. Diethylamine. — Let us now replace another equivalent 

 of hydrogen by the same organic radical, and examine the 

 relation towards water of diethylamine, NH(C 2 H 5 ) 2 . This 

 liquid boils at 54° (57°, Hofmann) at 31*02 B. The solutions 

 were prepared precisely as in the preceding case. 



The four weakest solutions, which contained 5, 10, 15, and 

 20 per cent, of base respectively, gave no trouble. But from 

 this point the curve (fig. 1) descends very sharply towards the 

 cryohydrate, and rises again with equal steepness. A 22-per- 

 cent, solution yields ice on incipient solidification at 9 0, 9; while 

 a solution containing only 1 per cent, more, a 23-per-cent. 

 solution, yields subcryohydrate at the same temperature of 

 9°*9. To this difficulty has to be added the circumstance that 

 I have not met with a substance which shows so extraordinary 

 an aptitude for supersaturation. The solutions of the sub- 

 cryohydrate in the anhydrous base (all those to the right of 

 the cryohydrate in fig. 1) and the cryohydrate itself may be 

 cooled to — 20°, and diligently stirred without showing signs 

 of solidification. The solidification may then be started by a 

 cryogen of solid carbonic acid and ether. Moreover, the solu- 

 tions near the saturated conditions are as viscid as glycerine ; 

 so that the appeal from one part of the liquid to another in the 

 matter of crystallization, and consequent change of composition 

 of the residual liquid, is tardy. These circumstances made it 

 impossible to obtain the cryohydrate pure for analysis in the 

 ordinary way by automatic purification. But they also made 

 it unnecessary ; for since a 22 per cent, gives up ice and a 

 23 per cent, gives up subcryohydrate at the same temperature 

 (9°'9), it follows that a 22'5-per-cent solution must, within a 

 probable error of about 0*2 per cent., have the composition of 

 the cryohydrate. Having made such a solution, and cooled 

 it to —10° in a salt-ice cryogen, the bottom of the tube con- 

 taining it was dipped in a little carbonic-acid cryogen until a 

 little white opaque regulus of crystals was formed. The whole 

 being then restored to the ice -salt cryogen and stirred, opaque 

 solidification began, the rounded tufts of crystals much re- 

 sembling oatmeal in suspension. From first to last the tem- 

 perature now remained constant at ll o, C. Of course there 

 was no need to analyse a body thus synthesized. 



