Mr. F. Guthrie on Salt Solutions and Attached Water. 13 



§ 21. Cryohydrate of Chloride of Ammonium. — A saturated 

 solution of NH 4 C1 was cooled in ice and the liquid portion 

 transferred to a beaker surrounded by an ice-salt freezing- 

 mixture. The temperature fell continuously, and anhydrous 

 chloride of ammonium kept falling down. At — 15° the soli- 

 difying part presented a different appearance. It then took the 

 form of a brilliant white apparently flocculent mass lighter 

 than the unsolidified liquid. After standing, with stirring, for 

 a quarter of an hour, the temperature was still —15°. The 

 clear portion was poured off into a fresh beaker, to which the 

 cold was applied. The solidifying parts are now seen to be 

 minute crystals, very much resembling ice-flowers, but opaque. 

 The sides of the beaker become studded with transparent crys- 

 stals of four sides, which are striated parallel to the sides. By 

 and by these crystals become perfectly white and opaque, and a 

 third axis of crystallization is developed, which was at first sup- 

 pressed. The crystals are perfectly beautiful, resembling, where 

 opaque, frosted silver. On allowing a thick cup to freeze and 

 breaking it, an exquisite pearly appearance is presented. The 

 structure appears then quite fibrous, the fibres running perpen- 

 dicular to the axis of the cup ; and the appearance, as far as 

 structure is concerned, is similar to that of sublimed chloride of 

 ammonium. The temperature remains constant at —15° C, 

 even to perfect dryness. The first crops of crystals were rejected 

 as being possibly contaminated with NH 4 C1. The last crop and 

 the mother-liquor were analyzed by being weighed into glass 

 basins and evaporated at 100° C. 



grms. NH 4 C1. percent. 



I. . . 9-5360 gave 1*7573, or 18*43 

 M.L. II. . . 60890 „ 1-1895 „ 19-56 



The analysis II., which is of the mother-liquor, corresponds 

 nearly with the molecular relation NH 4 C1+ 12 H 2 O, which 

 requires 19*98 per cent, of NH 4 C1. 



§ 22. Cryohydrate of Sulphate of Zinc. — The hydrates of sul- 

 phate of zinc already known are very numerous. They are : — 



ZnS0 4 + H 2 0, 

 ZnS0 4 + 2H 2 0, 

 2ZnS0 4 + 7H 2 0, 

 ZnS0 4 + 5H 2 0, 

 ZnS0 4 + 6H 2 0, 

 ZnS0 4 +7H 2 0. 



The last, which is the ordinary form of zinc-vitriol, when satu- 

 rating water at 17-5° C, gives a solution, according to Karsten, 

 consisting of 52 per cent, of salt and 48 per cent, of water. On 

 cooling such a solution to and below 0° C, the heptahydrate 



