and Attached Water, 217 



stops shortly below 0° C. ; and the solution may be cooled to 

 — 22° while the liquid remains quite clear. This possible de- 

 pression of the temperature in presence of one hydrate is clearly 

 a happy incident in the genesis of the cryohydrate as far as the 

 assurance of the freedom of the latter from the former is con- 

 cerned. On cooling by means of carbonic acid and ether, soli- 

 dification ensues shortly below —22°, and the temperature rises 

 to —17°, at which it remains constant. Of the portion last to 

 solidify, 7*0105 grms. on evaporation to dryness and heating to 

 130°, gave 29280 of 2NH 4 , S0 4 , or 41*7 per cent. Of the im- 

 mediately preceding portion, 4*0695 grms. gave 1*7195, or 

 42*2 per cent. The first of these corresponds to the relation 



2NH 4 ,S0 4 + 10-22 H 2 0. 



71. Sulphate of Potassium. — The saturated solution of this 

 salt solidifies at — 1°*2. Of the last portion, 3*9095 grms. 

 yielded 0*3075, or 7*8 per cent, of K 2 S0 4 . Of the immedi- 

 ately preceding part, 5*2905 grms. gave 0*3960, or 7*5 per 

 cent. The first of these shows the molecular relation 

 K 2 S0 4 + 114-2 H 2 0. 

 § 72. Sulphate of Sodium. — This was examined in § 26. Its 

 cryohydrate is formed at — 0°*7. The percentage of Na 2 S0 4 in 

 the last portion was found to be 4*55, and the water-worth 

 165*6. 



§ 73. Accordingly we have the sulphates of the alkalies 

 arranged as follows : — 



Temperature of 

 solidification of 

 cryohydrate. Water-worth. 



2NH 4 ,S0 4 . . -17 10*2 



K 2 S0 4 ... - 1-2 114*2 



Na 2 S0 4 ... - 0*7 165-6 



Once more, therefore, the lower the temperature of solidifica- 

 tion of the cryohydrate, the less is its water- worth. But the 

 order is different with S0 4 from the order with a halogen. 



Nitrates of the Alkalies. 

 § 74. Nitrate of Ammonium. — The nitrate of ammonium se- 

 parates as a cryohydrate from a saturated solution at — 17°*2 

 in exceedingly beautiful fern-like crystals. Dried at 100° C. 

 and heated to incipient fusion, 7*6100 grms. of the part last 

 to solidify gave 3*3265 of the anhydrous salt. Of the next 

 to the last, 7*2755 grms. gave 3*1475. The former therefore 

 contained 43*71 per cent, of NH 4 N0 3 , the latter 43-26. The 

 first indicates the relation 



NH 4 N0 3 -r5*72H 2 0. 



