ox ARTIFICIAL REFRIGERATION. 911 



crystals of four sides, wliicli are streaked parallel to tlie sides. By and 

 by these crystals become perfectly white and opaque, and a third axis of 

 crystallization is developed, which was at iii'st suppressed. The crys- 

 tals are perfectly beautiful, resemblmg, where opaque, frosted silver. 

 On allowing a thick cup to freeze, and breaking it, an exquisite pearly 

 appearance is presented. The structure appears then quite fibrous, the 

 fibres running perpendicular to the axis of the cup ; and tlie appearance, 

 as far as structure is concerned, is similar to that of sublimed chloride 

 of ammonium. The temperature remains constant at —15^ C, even to 

 perfect drjmess." 



Shortly after my return to England from Texas, in 18G9, where I felt 

 the want of a harmless antisex)tic, I was the cause of the manufacture, 

 commercially, of the chloride of aluminium. The strong solution obtained 

 by the double decomposition of chloride of calcium and sul^jhate of alumina 

 absorbs water from the air with great avidity. On immersin g fish in a dilute 

 solution of this chloride, a very remarkable phenomenon was observed. 

 Aluinina was deposited on the surface, and hy drochloric acid penetrated 

 the tissues, preserving them under proper management with very slight 

 adventitious flavor. I found that strong solutions would resist congela- 

 tion to below — 10<3 Fahr. Professor Guthrie found that when thrown 

 upon several times its own weight of ice, the two would liquefy, and the 

 temperature stand above 0<^ C. "The strongest commercial solution of 

 chloride of aluminium, however, when at the temj)erature of the air, or 

 at 0'^, or at 100c> C, will reduce the temperature to — 13° C. when poured 

 upon three or four times its own weight of ice." "I suppose," con- 

 tinues Mr. Guthrie, "the anhydrous chloride may be viewed as separat- 

 ing the atoms of the water-molecule, as is supi)osed to be the case with 

 the chlorides of i)hosx)horus." 



In using hydrochloric acid as a cryogen with ice. Professor Guthrie 

 obtained a normal acid, and poured it, in various proportions, upon ice 

 at 0^. Fifty grammes of ice were used in each experiment. The table 

 shows within what small limits of ratio the minimum temi)erature is 

 reached. The weight of ice is taken as unity. 



" We are, therefore," says Mr. Guthrie, "when dealing ^\ith a cryogen, 

 one of whose constituents is a liquid, much more limited in the range of 

 ratio which we may employ, to procure the maximum cold, than is the 

 case when both are solid." 



