ON ARTIFICIAL REFRIGERATION. 



913 



(5.) WTien by the soparatiou of ice tlie 

 proportion of the cryoliydrato is reached 

 (nearly independent of pressure) ice and 

 the salt separate simultaneously. 



(G.) The two bodies (ice and salt) being 

 crystallizable solids, unite to form a crys- 

 tallizable cryohj'drate which exhibits a 

 constant gravimetric composition. 



(7.) A cryohy(h-ate in the act of solidi- 

 lication shows ideutitj'^ of composition be- 

 tween the solid and liquid portions. The 

 temperature of soliditication is constant. 



(5.) "Wlien by the seiiaration of v^ipor 

 the proportion of saturation is reached, 

 (very dependent on prcssui-c), vai)or and 

 the salt separate simultaneously. 



(G. ) One being a solid and the other a 

 vapor, they do not unite, but in their sep- 

 aration i^reservc a constant gravimetric 

 ratio under like conditions of pressure. 



(7.) A satm-ated solution, when boiling, 

 shows the same ratio between the vajjor 

 formed and the salt precipitated as exists 

 between the liquid water present and the 

 salt it holds in solution. The temperature 

 of boiling is (under like pressure) constant. 



J.— OEGANIC CEYSTALLOIDS IN WATEE. 



iu discussing the "behavior of a few organic crystalloids in aqueous solu- 

 tions on being cooled and being heated, Professor Guthrie says: "With 

 regard to gl,ycerine, a very remarkable circumstance may be noticed. That 

 it is crystalloid, we have had until lately (1) the indirect evidence depend- 

 ing upon its being an alcohol, and upon several alcohols being known in 

 the solid and crystalline state, wliile others wliich are not so known get 

 united with crj'stallijie salts; (2) the direct evidence obtained from its 

 diffusion through colloid septa. Lately, it has been observed to assume 

 the form of a crystalline solid. Again, it has lately been employed in 

 aqueous solution in Pictet's ice-machine as a non-freezable liquid, to 

 yield heat to vaporizing sulphurous acid, and take it from water for the 

 purpose of freezing the latter. The latter faculty of its solution to resist 

 sohditication below 0^ C. proves, first, that it will form a cryogen, and, 

 secondly, that it will form a cryohydratej the latter fact again i)roving, 

 as we shall see, that it is a crystalloid. Pure glycerine dried by being 

 kept for a week over oil of vitriol in vacuo, when mixed with finely-crushed 

 ice forms a cryogen whose temi)erature is — 19^ C." Professor Guthrie 

 was not aware, when writing the above, that I originated the idea of using 

 the aqueous solution of glycerine in ice-machines, and Mr. Pictet only 

 emi)loyed it at the exhibition of scientific apparatus in South Kensington 

 with my permission. The iiractical advantages have been demonstrated 

 by the total cessation of accidents from ice forming in the relrigerator- 

 tubes and bursting them, and from the absence of all galvanic or corrod- 

 ing action on the metals. 



58 F 



