and Attached Water. 



51 



Here the lowest temperature is reached at the ratio 1 : 4, or 

 about CaCl 2 + 15 H 2 0. We must not attach too much import- 

 ance to the numbers of this Table, because, as before remarked, 

 the liberation of heat when the anhydrous salt dissolves in, or 

 rather combines with water, largely supplies heat for the lique- 

 iaction of the solid ice and salt. And accordingly, though the 

 leat-quantity concerned may be deduced from knowledge of 

 the quantity due to such combination and the specific heat of 

 the solution and the heat of liquefaction of the ice, yet the tem- 

 perature or heat-tension, being a function of the time or rate of 

 iquefaction, cannot be so deduced. The caking of the chlo- 

 ride is also a source of experimental difficulty. 



§ 107. Monohydrated Chloride of Calcium as a Cryogen.— 

 On baking the terhydrate of chloride of calcium a porous mass 

 is left, which is used for the absorption of water in gases. 

 This, though called anhydrous in commerce, contains about 

 one molecule of water. And the presence of the water is be- 

 trayed when the body is used as a cryogen. The chloride, 

 finely powdered, was weighed upon snow or ice and stirred 

 with the thermometer unceasingly. The higher ratios of frozen 

 water were ice, the lower ones were snow ; the two are con- 

 nected together at the 50 per cent, ratios, marked #. 



Table XIV. 



CaC^+^O, 



Snow or ice, 



CaCl 2 H 2 0, 



Snow or ice, 



Temperature, 



grammes. 



grammes. 



per cent. 



per cent. 



Centigrade. 



100 



33 snow- 



75 



25 







+ 5 



100 



SO „ 



667 



33-3 



- 4 



75 



50 „ 



60 



40 



-10 



*50 



50 ,, 



50 



50 



-17 



*50 



50 ice 



50 



50 



-17 



50 



100 „ 



33-3 



667 



-17 



50 



150 „ 



25 



75 



-16 



50 



200 „ 



20 



80 



-16 



50 



300 „ 



14-3 



857 



-16 



50 



400 „ 



111 



88-9 



— 12 



50 



600 „ 



7-7 



92-3 



-10 



The margin of ratio for minimum temperature is consider- 

 able. The minimum temperature itself is intermediate between 

 the minima for CaCl 2 and CaCl 2 + 3 H 2 O. 



§ 108. The Cryohydrate of Chloride of Calcium. — A solution 

 of CaCl 2 3 H 2 O, saturated at the temperature of the air (10° C), 

 was cooled to —20° in snow and ice. The mother-liquor was 

 then exposed to the carbonic-acid-and-ether cryogen. The 

 temperature sank to —37° C. under continual separation of a 

 transparent hydrate. At —37° C. an opaque cryohydrate is 



E2 



