194 
Dr. Thomson on some of 
When the protohydrate of acetic acid, in the liquid state, 
which it always has during the summer, is mixed with the 
red liquid, no immediate decomposition takes place ; the 
mixture continues red and opaque, and as liquid as ever. The 
smell of the chlorine was much weakened, or overpowered 
by the acetic acid. No alteration in this mixture had taken 
place in a week ; but in a fortnight the chloro-chromic acid 
was decomposed, and a quantity of reddish brown matter had 
precipitated. 
A quantity of the red liquid was put into a receiver, and a 
current of ammoniacal gas was made to pass into the receiver 
from a small retort filled with a mixture of sal ammoniac and 
quick lime, to which the flame of a spirit lamp was applied. 
When the receiver was filled with ammoniacal gas, it was 
turned round so as to bring the red liquid in contact with it. 
A brilliant combustion took place, the red liquid assumed the 
form of a dark brown solid, and glowed for some time with 
an intense red heat. The residual matter being digested in 
water left a quantity of green-coloured muriate of chromium, 
or chloride of chromium, which would neither dissolve in 
water, nor nitric acid ; but I ascertained the presence of 
muriatic acid by heating it with caustic potash. By this pro- 
cess much sal ammoniac is formed, and a quantity of muriate 
of chromium. 
It is obvious from the preceding facts, that the property of 
supporting combustion, which this liquid possesses to so great 
a degree, is not owing solely to the chlorine which it contains, 
but likewise to the oxygen of the chromic acid ; which, as 
we shall see afterwards, constitutes so considerable a portion 
of it. So that chromic acid is a supporter of combustion, as 
