212 



Frederick Guthrie on Salt Solutions 



I again found the temperature of the cryogen to be — 7°*3 

 ( — 7°*2, § 78), and the temperature of the cryohydrate to be 

 — 7°*5 to — 8°. But it is seen that as derived from a dilute 

 solution I now find the cryohydrate to contain only 21*83 per 

 cent, of BaCl 2 , while in § 78, where it was derived from a sa- 

 turated solution, I found 23*2. No doubt the smaller of these 

 numbers is the more correct. The composition of the cryohy- 

 drate was derived from the following data. 6*5151 of melted 

 cryohydrate gave 1*5225. The water-worth is accordingly 

 41*357. The solubility at 0° C. was derived from the fol- 



Mean. 



23*98 



§ 149. Separation of Ice fyc. from Solutions of Protosulphate 

 of Iron. 



Tabus XXX. 



ring :— 









1. 



2. 



Solution 



. 6*7830 



7*9470 



BaCl 2 . . 



. 1*6214 



1*9119 



Per cent. . 



. 23*90 



24*06 



FeS0 4 per cent, 

 by weight. 



H 2 O per cent, 

 by weight. 



Temperature 

 at which solidi- 

 fication begins. 



Nature of solid. 



5 

 10 

 14 5 

 14-9 



95 

 90 



85-5 

 851 



o 

 -0-2 

 -0-8 

 -20 



00 



Ice. 



>> 

 Cryohydrate. 

 FeS0 4 + 7H 2 0. 



As in § 148, I find the composition of the cryohydrate to 

 show somewhat less salt than previously (§ 82), where the 

 cryohydrate was obtained from a saturated solution, and where 

 the amount of salt was determined by simple evaporation. I 

 now find the melting-point of the cryohydrate to be — 2° C; 

 and the temperature of the cryogen is exactly the same. In 

 the above-given determinations of the cryohydrate and of the 

 solubility at 0° C. the solution was oxidized with nitric acid, 

 the sesquioxide was precipitated with ammonia and weighed ; 

 the amount of FeS0 4 was thence deduced. For the cryohy- 



4*8076 grms. gave 0*3676 Fe 2 3 , or 0*6984 Fe S0 4 . 

 The water-worth is therefore 49-8. For the solubility at 0° C. r 

 7*7890 grms. gave 0*6080 Fe 2 3 , or 1*1552 FeS0 4 . 

 § 150. Separation of Ice Sfc. from Solutions of Tribasie 

 Phosphate of Sodium and Hydrogen, Na 2 H P0 4 -j-2H 2 O. — 

 This, the most usual phosphate of sodium, when used as a cryo- 

 gen only reduces the temperature to — 1°*0 0. The cryohy- 



