the compounds of chromium. 171 
acid weighs 6 5 ; and 6-5 — 1*5 = 5 = atomic weight of 
green oxide. 
The 5 atoms of sulphurous acid thus formed unite with 5 
atoms of sulphuretted hydrogen ; and these two bodies are 
mutually decomposed into 5 atoms hyposulphurous acid and 
5 atoms water. The 5 atoms of hyposulphurous acid uniting 
to the 10 atoms of potash constitute dihypo-sulphite of potash, 
composed of 1 atom hyposulphurous acid 5 
2 atoms potash - - 12 
17 
I conceive that this beautiful example of rather a compli- 
cated series of decompositions and new combinations, leaves 
no doubt that the atomic weight of green oxide of chromium 
is 5- 
When we take bichromate of potash instead of neutral 
chromate, and treat it with sulphuretted hydrogen gas, the 
precipitated hydrosulphuret has a buff colour instead of a 
green. This may perhaps be ascribed to a portion of undecom- 
posed chromic acid falling in combination with some part of 
the precipitate. For we shall see afterwards a similar coloured 
precipitate composed of chromic acid and green oxide. 
This buff coloured precipitate is tasteless, and insoluble in 
water. It is either a hydrosulphuret of chromium, or at least 
contains a hydrosulphuret ; for when it is heated sulphur 
sublimes, and sulphurous acid is given off. At a certain tem- 
perature it catches fire, and burns for some time with a yellow 
low flame. When digested in muriatic acid some sulphur 
precipitates. When digested in nitro-muriatic acid, a portion 
of the sulphur is converted into sulphuric acid. From 7-71 
grains of the buff coloured precipitate I obtained 
