and Attached Wa ter. 211 



resulting from the union of the halogens with the alkali metals 

 has brought to light many points of interest. The two members 

 of this family which I had previously examined were Nad, 

 solidifying at —23° with 10*5 molecules of water, and NH 4 C1, 

 solidifying at —16° with 12 molecules of water. I have reexa- 

 mined the cryohydrate of chloride of ammonium ; and the mean 

 of several analyses gives 19*27 per cent of chloride, which brings 

 the ratio to NH 4 CI + 12*4 H 2 O. 



There is nothing particular to remark in the analysis of this 

 group. All, excepting the ammonium salts, bear heating to 300° 

 or 400° C. without decomposition or volatilization. The liquid 

 cryohydrates were weighed in covered basins of Bohemian glass, 

 evaporated to dryness, strongly heated, covered, and quickly 

 cooled. The ammonium salts were heated on the water-bath 

 till they ceased to lose weight. 



§ 57. Iodide of Potassium. — This salt, which at the ordinary 

 temperature is so abundantly soluble in water, yields a large 

 proportion of anhydrous salt when cooled. An ice-salt cryogen 

 fails to solidify it, but just brings it to the verge of solidification, 

 removing all the free salt in the same manner as it does with 

 NaCl solution, excepting that there does not appear to be any 

 intermediate cryohydrate corresponding with NaCl + 2H 2 0. 

 The KI solution appears to be homogeneous at —8° or —12°. 

 When subjected to solid C0 2 and ether, it at once begins to so- 

 lidify at —22° to —23°, and retains this temperature to dryness. 

 Of the four parts into which the substance was divided as it so- 

 lidified, two were analyzed — namely, the second crop of crystals, 

 and the finally solidified and remelted mother-liquor. Of the 

 first, 5*8240 grms. gave 3*0120 anhydrous KI, or 51*72 per 

 cent. ; of the second, 6*3960 grms. gave 3*331, or 52*07 per 

 cent. The latter corresponds to the molecular ratio 

 KI + 8*5H 2 0. 



§ 58. Bromide of Potassium. — This forms a cryohydrate of 

 great beauty. At -—13° the characteristic crystals are seen to 

 be produced. They have the fern-like shape of ice-crystals. 

 The fronds are studded with a fructification of opaque crystals, 

 whose opacity seems to spread through the at first transparent 

 fronds till the whole resembles frosted silver. The two portions 

 which were taken for analysis were the final part, or that which 

 solidified last, and the immediately preceding crop of crystals. 

 Of the former, 7*8285 grms. gave 2*5170 of KBr; of the latter, 

 9*4560 grms. gave 30070 dry salt. These correspond respec- 

 tively with 32*15 and 31*80 per cent. The first points to the 

 molecular relationship 



KBr + 13*94H 2 0. 

 P2 



