56 Frederick Guthrie on Salt Solutions 



lowers the temperature to — 16°*7. Comparing as before, 



o 



The cryohydrate of Sr Cl 2 solidifies at . . —17 



„ „ BaCl 2 „ . . — 8 

 „ M equiv. mixture solidifies at —18 



and 



As a cryogen, SrCl 2 gives . . . —17 



BaClj, „ . : . - 7-2 



„ equiv. mixture gives — 16*7 



As it is almost impossible to separate barium and strontium 

 with very great precision, and as it was highly desirable to 

 compare the relative quantities in the cryohydrate in at least 

 one other case besides that of § 113, I chose in the right place 

 the— 



§ 116. Mixed Sulphates of Sodium and Ammonium as Cryo- 

 hydrates and Cryogens. 



6-6 grms. of (NH 4 ) 2 S0 4 

 and 



7-1 grms. of Na s S(V 



were dissolved, mixed, and allowed to evaporate to saturation. 

 On cooling to 0°, acicular crystals were deposited (of sulphate 

 of sodium). At — 4°*5 a cryohydrate began to form; the 

 whole was solid and dry at —7°. On analysis, by evaporation 

 to dryness and subsequent strong heating, the portion last to 

 solidify was found in two specimens to have the following com- 

 position : — 



a. b. Mean. 



(NH 4 ) 2 S0 4 . 12-23 12 25 12-24 



Na 2 S0 4 . . 4-82 4-86 4-84 



H 2 . . . 82-95 82-89 82-92 



The molecular ratios are accordingly 



Na 2 S0 4 1 



(NH 4 ) 2 S0 4 .... 2-72 



H 2 135-2 



or nearly 



4Na 2 S0 4 + 11(NH 4 ) 2 S0 4 + 541H 2 0. 



As (§ 88) the water-worth of Na 2 S0 4 is 165'6, and that of 

 (NH 4 ) 2 S0 4 is 10*2, this cryohydrate can neither be regarded 

 as a substitutive cryohydrate like that suggested in § 113 for 

 the cryohydrate of the chlorides of potassium and ammonium, 

 nor as a simply additive cryohydrate ; for the joint water- 

 worth is less than that of the ammonium salt alone. The double 

 sulphate of sodium and ammonium is formed ; and this has the 

 specific water-worth of 135*2 or (taking the higher molecule) 

 of 541. 



