70 REPORT—1858. 
substances; if a definite combination at all, its constitution is probably 3AsO? Cl 
AsCl. 
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 por- 
tions of water to the chloride, the proportion of chlorine in the undissolved quantity 
gradually diminishes, until the last globules consist chiefly of the compound acid. 
3. Hydrated Chloro-arsenious Acid.—Chloride of arsenic is dissolved in the smallest 
possible quantity of water (about 16 equivalents), and the solution set aside in a closed 
flask. In two or three days minute nucleated crystals begin to form; and these gra- 
dually 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 pla- 
tinum spatula, and then dried by pressure between numerous folds of blotting-paper. 
A portion was analysed which had been completely dried by powerful pressure, and 
the following results were obtained :— 
Arsenic . « « e« 91°80 1=75 51°90 
Chlorine . « » »« 24:97 1=35°5 24°57 
Oxygen « 6 «© © oe 2=16 11:07 
Water « « «© «© « 12°35 2=18 12°46 
144°5 100°00 
The crystallized acid contains, therefore, two equivalents of water, and is repre- 
sented by the formula 2HO, AsClO*. It becomes anhydrous over oil of vitriol, but 
at the same time loses 2 or 3 per cent. of chlorine, The crystals are exceedingly 
minute, and form in mammillated masses resembling the mineral Prehnite, ‘The 
slowly-formed crystals are acicular, and collect in stellate 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 equivalents 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 equivalents of alkaline chloride; so that these compounds 
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 immediately throws 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 solu- 
tion 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 aqueous 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 sufficient quantity to prevent the form- 
ation of chloro-arsenious acid, and a small lump of chloride of ammonium is intro- 
duced. At first, small, hard, reddish-coloured, cubical crystals, consisting of almost 
pure chloride 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-paper. The following results were 
obtained with the salt dried over oil of vitriol :— 
Arsenic . . + « 82:23 I= 75 32°12 
Ammonium . . . 15:23 2= 36 15°42 
Chlorine «. . . . 44°78 3=106°5 45°61 
Oxygen « « « + os 2= 16 6°85 
233°5 100-00 
