ON ARTIFICIAL REFRIGERATION. 



913 



(5.) Wlion l)y the sop.iratiou of ico tlio 

 proportion of the cryohydrate ia reached 

 (nearly iudopoiulcnt of pressure) ico and 

 the salt separate siinultaueously. 



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

 crystallizable solids, unite to form a crys- 

 tallizable cryohydrato which exhibits a 

 constant grav^iinetric composition. 



(7.) A cryoliydrate in the act of solidi- 

 fication shows identity of composition be- 

 tween the solid and li(piid portions. The 

 temperature of solidihcatiou is constant. 



(5.) When by the separation of vapor 

 the proportion of saturation is n.-ached, 

 (very dejicndent on pniasure), vapor and 

 the salt separate simultaneously. 



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

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

 aration i)reservo a constant gravimetric 

 ratio under like conditions of pressure. 



(7.) A saturated solution, when Ijoiling, 

 shows the same ratio between the vapor 

 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.— OEGAKIC CEYSTALLOIDS IN WATEE. 



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

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

 regard to glycerine, 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, while others which are not so known get 

 united with crystalline salts j (2) the direct evidence obtained fromlt« 

 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 hquid, 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 

 sohcUiication below 0° C. proves, first, that it will form a cryogen, and, 

 secondly, that it will form a cryoliydrate; the latter fact again proving,, 

 as we shall see, that it is a crystalloid. Pure glj^cerine dried by being, 

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

 ice forms a cryogen whose temperature 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 

 employed it at the exhibition of scientific apparatus in South Kensington 

 with my permission. The practical advantages have been demonstrated 

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

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

 ing action on the metals. 



i 



58 F 



