On Chloro-arsenious Acid, and some of its Compounds. 359 



solid, according to the temperature to wliich it is exposed. It is 

 transparent, but has a brown colour, which does not appear to 

 be owing to the presence of any impurity. It fumes slightly in 

 the air, parting with a small portion of its chlorine as hydro- 

 chloric acid, and absorbing oxygen. When strongly heated, 

 it boils up with considerable frothing, and affords a distillate of 

 pure chloride of arsenic. When brought up to about the tem- 

 perature at which arsenious acid sublimes, it leaves a glassy, 

 hard, transparent substance, which was found to contain lO'Oi 

 per cent, of chlorine, agreeing with the formula 2AsO^, AsClO^. 



The fluid poured off from the chloro-arsenious acid was found, 

 on analj'-sis, to contain an amount of chlorine which corresponds 

 with the formula AsCP, AsO^. It is therefore similar to the 

 solution prepared by adding arsenious acid to heated chloride of 

 arsenic. I do not believe, however, that this liquid is a com- 

 pound of these two substances ; if a definite combination at all, 

 its constitution is probably SAsClO^, AsCF. 



Chloro-arsenious acid is also formed when chloride of arsenic 

 is treated with a quantity of water not quite sufficient to dissolve 

 it. On adding small successive portions of water to the chloride, 

 the proportion of chlorine in the undissolved quantity gradually 

 diminishes, until the last globules consist chiefly of the com- 

 pound acid. 



3. Hydrated Chloro-arseniotts Acid. 



Chloride of arsenic is dissolved in the smallest possible quan- 

 tity of water (about 16 equivalents), and the solution set aside 

 in a closed flask. In two or three days minute nucleated cry- 

 stals begin to form ; and these gradually increase until about one- 

 half of the liquid is occupied by them. A second crop of crystals 

 may be obtained by placing a fragment of rock-salt in the mother- 

 liquor : these take a long time to form, and are much larger and 

 better defined than those which result from the first operation. 

 The crystals may be well pressed with a platinum spatula, and 

 then dried by pressure between numerous folds of blotting-paper, 

 A portion was analysed which had been completely dried by pow- 

 erful pressure, aiid the following results were obtained : — 



144-5 100-00 



Tiie crystallized acid contains, therefore, two equivalents of 

 water, and is represented by the formula 2II0, AsClO-. It 

 becomes anhydrous over oil of vitriol, but at the same time loses 



