and Attached Water. 209 



merce, fumes strongly in the moist air, so great is its avidity for 

 water. Thrown upon several times its own weight of ice, the two 

 liquefy and the temperature stands above 0°. The strongest 

 commercial solution of chloride of aluminium, however, when at 

 the temperature of the air or at 0° or at 100° C, will reduce the 

 temperature to — 13° when poured upon three or four times its 

 own weight of ice. I suppose the anhydrous chloride may be 

 viewed as separating the atoms of the water-molecule, as is 

 supposed to be the case with the chlorides of phosphorus, 



§ 52. Hydrochloric Acid as a Cryogen with Ice. — Ordinary 

 commercial hydrochloric acid when poured upon ice may produce 

 as much as 22° of cold. The amount of HC1 in the hydrochloric 

 acid, however, is here to be as much considered as it would have 

 to be if we dealt with ice and a solution of NaCl. In the expe- 

 riments which are given in the succeeding paragraphs as far as 

 §54, the hydrochloric acid employed was formed by saturating 

 water with the gas, while the liquid was kept after absorption 

 had ceased for half an hour at 0° while the acid passed through. 

 The barometric pressure was 770 millims. This may be consi- 

 dered a normal acid. 



§ 53. The acid at 0° was poured in various proportions upon 

 ice at 0°. Fifty grms. of ice were used in each experiment. The 

 Table shows within what small limits of ratio the minimum 

 temperature is reached. In the Table the weight of the ice is 

 taken as unity. 



Weight of ice 



Weight of HC1+»H 2 



Resulting 



at 0° C. 



at 0° C. 





Temperature. 



1 



1-5 





- 3 



1 



0-4 





-26 



1 



0-3 





-23 



1 



0-2 





-19 



We are therefore, when dealing with 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. 



§ 54. Accordingly, in examining the eiFect of the alteration in 

 the temperature of one or both of the constituents, it is necessary 

 always to use the same ratio. In the Table below, the ratio used 

 was that which gave the maximum cold when both were at 0° C, 

 namely 1 of ice to 0*4 of the saturated solution of HC1. It must 

 be understood that in those cases where the hydrochloric solution 

 was used below 0° C, it is not meant that the saturation with 

 HC1 took place at that lower temperature, but that, having been 

 saturated at 0°, the solution was subsequently cooled to the lower 

 temperature. 



Phil. Mag. S. 4. Vol. 49. No. 324. March 1875. P 



