360 On Chloro-arsenious Acid, and some of its Comjwunds. 



2 or 3 per cent, of chlorine. The crystals are exceedingly minute, 

 and form in mammillatcd masses resembling the mineral Preh- 

 nite. The slowly-formed ciystals are acicular, and collect in stel- 

 late groups, presenting, while in the liquid, a very beautiful 

 appearance. The smaller crystals have a dazzling white colour, 

 and emit a little hydrochloric acid on exposure to the air. 



Chloro-arsenious acid combines with chlorides, as arsenious 

 acid does with oxides. It appears to be bibasic, the two equiva- 

 lents of water being capable of being replaced by two equivalents 

 of an alkaline chloride. The ammonia-salt is the only one which 

 I have as yet succeeded in obtaining in a distinctly crystalline 

 form, and of definite composition. Potash and lime compounds 

 have been obtained as white powders which contain much less 

 than two ecjuivalents of alkaline chloride ; so that these com- 

 pounds have probably only one equivalent of alkaline chloride, 

 and one equivalent of basic water. 



Two interesting reactions of the solution of terchloride of 

 arsenic in water may here be mentioned : oil of vitriol immedi- 

 ately throvt^s down the anhydrous compound, while chloride of 

 calcium causes the separation of the chloride mixed with a small 

 proportion of chloro-arsenious acid. The same reactions occur 

 with a saturated solution of arsenious acid in concentrated aqueous 

 hydrochloric acid : indeed, an ounce or two of chloride of arsenic 

 may readily be prepared by adding an equal bulk of strong oil 

 of vitriol to such a solution. It is not so pure, however, as that 

 obtained from the aq\ieous solution of chloride of arsenic, and 

 must be rectified if required in a state of purity. 



4. Chloro-arsenite of Ammonia. 



The aqueous solution of chloride of arsenic is mixed with 

 strong liquid hydrochloric acid in sufiicient quantity to prevent 

 the formation of chloro-arsenious acid, and a small lump of 

 chloride of ammonium is introduced. At first small, hard, red- 

 dish-coloured, cubical crystals, consisting of almost pure chlo- 

 ride of ammonium, make their appearance ; but after some days, 

 long fibrous needles of snow-white colour and pearly lustre 

 begin to form, and gradually fill up the liquid. These consist 

 of the salt under consideration. They are well drained, and dried 

 by pressure between folds of blotting-pai)er. The following 

 results were obtained with the salt dried over oil of vitriol : — 



233-5 100-00 



