and Attached Water. 37 



Employed as a cryogen, — o, 18 was the lowest temperature 

 reached. The only data I can find of the solubility of lime at 

 different temperatures are those of Dalton ; from whose expe- 

 riments it appeared that lime-water saturated at 



100° C. contains O1050 per cent, of CaO H 2 

 54-4 „ 0-1371 



15-5 „ 0-1712 



From my results it appears that, the mean CaO being 0*275 per 

 cent, (the mean of two analyses of the cryohydrate at — o, 15 

 gave 0-3634 per cent, of CaO H 2 O), lime is 3| times more 

 soluble in water at — 0°'15 C. than at 100 C. 

 With regard to these water-worths, 



W.W. 



Hydrate of barium .... 565 

 „ strontium . . . 1463 



„ calcium .... 1116 



it is not only noteworthy, but imperatively demands notice, 

 that here calcium lies between barium and strontium. They 

 who are engaged with the spectra of these metals will scarcely 

 need a further hint. 



The melted cryohydrates of SrO H 2 and CaO H 2 O, which 

 had been solidified in an ice and NaCl freezing-mixture, did 

 not exhibit the characteristic opacity of cryohydrates. They 

 became milky in a carbonic acid and ether cryogen, but did 

 not seem even then to assume the characteristic opacity. A 

 trace of this true opacity appeared with BaO H 2 O. 



§ 170. Hydrate of Potassium. — A concentrated solution, 

 namely a solution resulting from the deliquescence of the 

 solid hydrate in moist air free from carbonic acid, did not 

 solidify on being subjected to a cryogen of C0 2 and ether: it, 

 however, became syrupy. A dilute solution (indefinite) soli- 

 dified wholly within the range of an ice-and-JSFaCl cryogen. 

 The solid was transparent and resembled ice ; it sank in water 

 at 0° C. 



As a cryogen, caustic potash gave a temperature of — 19°'2 C. 

 But, as will appear subsequently (and this is an important 

 point), a salt which evolves heat on mixing with water makes 

 a more powerful cryogen with ice if previously cooled ; not 

 so those which do not. 



§ 171. Permanganate of Potassium. — On cooling a saturated 

 solution of this salt, crystals of the permanganate separated 

 out down to 0° C. The cryohydrate was formed at — 0°*57; 

 and the temperature then ceased to sink. The estimation of 

 the water was by evaporation at 100°. The samples are from 



