212 
Dr. Thomson on some of 
6. Arseniate of chromium. 
Arseniate of soda, when dropt into a solution of muriate of 
chromium, though very dilute, occasions a green flocky pre- 
cipitate, at first dissolving in the liquid, but becoming perma- 
nent after the addition of a certain quantity of arseniate. 
This precipitate is an arseniate of chromium. When dry, it 
has a fine green colour, is tasteless, and insoluble in water. 
I dissolved in muriatic acid a quantity of hydrated green 
oxide of chromium, containing 10 grains of oxide, evaporated 
the solution to dryness, and re-dissolved the salt in water. 
This solution was mixed with a solution of 41*5 grains of 
arseniate of soda (containing 15*5 grains of arsenic acid). 
This mixture was evaporated to dryness in a porcelain dish, 
and the saline residue digested in water till nothing more 
could be taken up. The water did not contain any trace of 
arsenic acid ; but it still retained a green colour, and was 
found to contain 1*125 grain of green oxide of chromium. 
The arseniate formed was a compound of 
Arsenic acid - 15*5 - - 8* 73 - atom. 
Green oxide - 8*8 75 - or 5 -1 atom. 
An accident prevented me from weighing the arseniate. It 
was very nearly, though not quite neutral. 
There exists also a binarseniate of chromium, which was 
obtained in the following manner. A quantity of liquid arsenic 
acid was digested over hydrated oxide of chromium till it re- 
fused to take up any more. A dark green liquid was obtained, 
which was evaporated to dryness. There remained a dark 
green matter, which being digested in water gave out arsenic 
acid, and a dark green insoluble salt remained, which was 
