and Attached Water. 213 



salt to a light-grey colour. Analysis showed that this colora- 

 tion did not sensibly affect the percentage composition of the 

 salt ; but still its power of assuming water might be seriously 

 affected. A saturated solution was exposed for some hours to 

 an ice-salt cryogen at —22°; it was then exposed to the car- 

 bonic-acid-and-ether cyanogen. It solidified wholly at from —27° 

 to —28°. While solidification is taking place, the cryohydrate 

 is nearly perfectly white. When dry and over-cooled, it as- 

 sumed a pinkish grey colour, resembling chloride of silver which 

 is beginning to be affected by light. 



The analysis of these portions is given, namely : — (1) the 

 last to solidify or remelted mother-liquor ; (2) the immediately 

 preceding crop of crystals ; and (3) the crop before (2) . As 

 the results are by no means in good accord, I give them 

 all:— 



Solution. NH 4 1. per cent. 



(1) . . . . 5-2935 gave 2-9375, or 55-49 



(2) . . . . 5-4960 „ 3-2120, „ 58*42 



(3) . . . . 8-4560 „ 4-8675, „ 57'56 



The portion (1), which, being the last, is in one sense likely 

 to be the most homogeneous, corresponds to the relationship 

 NH 4 I + 6-44H 2 0. 



The portions (2) and (3) would indicate as much as 0*7 mole- 

 cule less of water. 



§ 62. Bromide of Ammonium. — This salt separates as a cryo- 

 hydrate from a saturated solution at —17° C. Its formation is 

 well marked, and its analysis was satisfactory. Of the final 

 portion, 4'2591 grms. gave 1'3680 of NH 4 Br. Of the imme- 

 diately preceding crop of crystals, 5-5990 grms. gave 1*8010 

 of NH 4 Br. The percentages are 32*12 and 32*17 respect- 

 ively : these numbers correspond to the relationship 

 NH 4 Br + Il*15H 2 0. 



§ 63. Taking the value of the cryohydrate of chloride of am- 

 monium from § 56 as NH 4 C1 + 12*4H 2 0, we have for the 

 halogen salts of ammonium : — 



Number of 

 molecules of 

 Solidifying-temperature water to 1 

 of cryohydrate. of salt. 



NH 4 I. . . . -27-5 6-4 



NH 4 Br . . . -17 11*1 



NH 4 C1 ... -16 12*4 



whence it is gathered that the relative faculties of chlorine, 

 bromine, and iodine, in depressing the temperature at which the 

 cryohydrates are formed, are similar with ammonium to their 



