and Attached Water. 57 



That the two salts are not independent of one another, 

 appears from their joint action as a cryogen ; for mixed in 

 the above equivalent ratio and stirred with snow, they give 

 ■—16°. Comparing the joint with the separate effects, 



The cryohydrate of (NH 4 ) 2 S0 4 solidifies at -17 

 NaS0 4 „_ - 0-7 



„ „ equiv. mixture solidifies at — 7 



and 



o 



As a cryogen, (NH 4 ) 2 S0 4 gives . — 17*5 

 „ Na 2> S0 4 / „ ; . - 0-7 



„ equiv. mixture gives —16 



It is manifest that the doubling of the salt is not taking 

 place during the solution of its two constituents when their 

 mixture is a cryogen, but that it takes place when from solu- 

 tion they unite together in partnership with water as a cryo- 

 hydrate. 



§ 117. Variation of both Constituents (AX + BY). — The fas- 

 cinating hypothesis of Berthollet that double decomposition 

 always partially ensues when two such salts as AX and BY 

 are mixed, even when no removal from the chemical field takes 

 place of any of the possible new bodies resulting from the re- 

 combination, may be critically approached from the side of the 

 cryohydrates with great profit. Let me put the question in 

 two concrete forms, and indeed in two of the forms which I 

 immediately propose to examine experimentally. 



Is a solution consisting of 



202 grms. of KN0 3 and 142 grms. of Na 2 S0 4 



dissolved in water, identical with a solution consisting of 



170 grms. of NaN0 3 and 174 of K 2 S0 4 



dissolved in the same amount of water ? 



If they are identical, does any one of the salts KN0 3 , 

 NaN0 3 , K 2 S0 4 , Na 2 S0 4 exist as such in either solution ? 



§ 118. Comparison beticeen a mixture of 2NaN0 3 and 

 K 2 S 4 and a mixture of 2 KN0 3 and Na 2 S0 4 as Cryohydrates 

 and Cryogens. 



33-666 grms. of KN"0 3 

 and 



23-666 grms. of Na 2 S0 4 , 



both anhydrous, were mixed, dissolved, and evaporated to satu- 

 ration. This gave solution (1). Again, 



28-333 grms. of NaN0 3 

 and 



29 grms. of K 2 S0 4 



