52 Frederick Guthrie on Salt Solutions 



formed, and the temperature remains constant for a consider- 

 able time. The opaque crystals, on being remelted, showed 

 the following composition. By a silver-determination 6*6835 

 contained 2*3365 of CaCl 2 . This shows 36*45 of CaCl 2 , and 

 exhibits the molecular ratio 



CaCl 2 + ll*8H 2 0. 



Mixed Salts, as Cryogens and Cryohydrates. 



§ 109. Still bearing in mind the problem of sea-water, we 

 may next consider the behaviour of mixtures of soluble salts, 

 both as cryogens and cryohydrates. Even regarding salts as 

 preserving the individuality of their metallic and non-metallic 

 parts when mixed together, there is a variety of recomposition 

 possible. Thus taking the typical salts AX and BY, we may 

 have A=B or X=Y. No double recomposition is possible 

 in either of the latter cases. But there may still be formed 

 double salts in which each metal is engaged with both non- 

 metallic constituents. I suppose that in the present state of 

 chemical knowledge it would be unwise to assert that any 

 double salt is impossible, especially after the evidence which 

 has been so abundantly given above that the body water is 

 virtually pantameric. 



On the other hand, remembering the liberal margin of ratio 

 between ice and a salt for the production of the normal or 

 maximum cold, we shall get by examining the temperature of 

 the cryogen of a mixture of salts and the temperature of their 

 common cryohydrate, if they have one, a valuable and indeed 

 unique insight into their molecular relation, in the sense of de- 

 termining whether double salts or double recomposition ensues. 

 At present I have confined my examination to the various cases 

 of two salts. Of these a few typical examples are taken ; and 

 in the first place a pair of salts are examined which differ only 

 in their metals. 



§ 110. Mixed Nitrates of Potassium and Sodium as Cryo- 

 hydrate. — The salts were just fused, poured on a slab, crushed 

 while hot, and bottled. The two salts were weighed in mono- 

 molecular ratio ; namely, of 



KN0 3 there were 33*666 grms. 

 NaN0 3 „ 28*333 „ 



These quantities were mixed, completely dissolved in water, 

 and allowed to evaporate at 13° C. till crystallization began. 

 The mixture was then cooled in an ice-salt cryogen. At about 

 + 12° to +10° C. transparent crystals resembling KNT0 3 

 began to form, and continued to do so as the temperature fell. 

 At about —7° an opaque cryohydrate appeared. This went 



