BENEDICT. — DOUBLE HALOIDS. 225 



of SbCl 3 and KC1 with or without free acid ; preferably concentrated 

 solutions. This salt is the one most readily obtained of all the salts. 



The hjdrated salt III. (SbCl 3 . 2 KC1 . 2 H 2 0) crystallizes from 

 moderately dilute solutions by exposure to severe cold, — 10°. The 

 presence of free hydrochloric acid does not interfere in auy way, and 

 possibly assists in the crystallization, provided it is not in too great 

 an excess. 



Lastly, the monoclinic form of SbCl 3 . 2 KC1. The hexagonal salt 

 is readily obtained, and, if it is left in the mother liquor, after a few 

 days undergoes a transformation from the hexagonal to the mono- 

 clinic. This is apparently accomplished by the building up of the 

 hexagonal plates into a dumb-bell form, after which the planes of the 

 monoclinic form are assumed, accompanied by an entire reconstruction 

 of the crystal. 



The mutual relations of these salts require further considera 

 tion. If a solution is made up as directed for preparing salt I. 

 (SbCl 3 . SbOCl. 2 KC1), the addition of one drop of water beyond a 

 certain point will cause a white precipitate, which is soluble upon heat- 

 ing, but which reapjy-'ars on cooling. If, however, a crop of I. 

 crystals is taken from the solution, and the mother liquor be divided 

 in two portions, water can be added to one of them in considerable 

 quantity, till finally one drop produces a cloudiness, which disappears 

 on heating, but reappears on cooling. If now the second half of the 

 mother liquor be added to the dish, the precipitate will not redissolve 

 in the cold, but on heating it goes completely into solution, and is not 

 thrown out on cooling. If this solution was left to evaporate after 

 removing the cryst als of I., there would soon be a deposit of II. 

 (SbCl 3 .2KCl, hexagonal). But it is found that the addition of 

 water as above described will promote the crystallization of more I. 

 (SbCl 3 . SbOC1.2KCl). 



When a solution depositing I. is placed at a temperature of — 5° then 

 III. will immediately be deposited. 



When the salt I. is dissolved in hydrochloric acid just strong enough 

 to effect the solution, there is deposited chiefly II., together with a 

 few I. 



When the salt II. is dissolved under the same conditions, there is 

 dissociation, and the potassic chloride crystallizes out as cubes or cubo- 

 octahedrons at first. Later, the salt will crystallize out itself as II. 



As has been before stated, II. hexagonal goes into II. monoclinic 

 on long standing at a moderate temperature. Considerable difficulty 

 was experienced in attempting these crystallizations during rainy 



VOL. XXIX. (n. S. XXI.) 15 



