EADIATIO??' or HEAT BY GASEOUS MATTEE. 
69 
absorption of ammonia is over seven thousand times, the absorption of olefiant gas seven 
thousand nine hundred and fifty times, ivhile the action of sulphurous acid is eight 
thousand eight hundred times that of air. 
It is impossible not to be struck by the position of chlorine and bromine in this 
Table. They are elements, and notwithstanding their colour and density, they take rank 
after the transparent elementary gases. The perfectly transparent olefiant gas absorbs 
more than one hundred and thirty times the amount absorbed by the untransparent 
chlorine, and nearly fifty times the quantity absorbed by the intensely brown vapour of 
bromine. I cannot think this fact insignificant. Hitherto chemists have spoken to us 
of elements, and we have helped ourselves to conceptions regarding them and their 
compounds in the only way possible to our mental constitution. But our conceptions 
remained purely subjective, nor were we acquainted with any physical trait which would 
in any degree justify these conceptions. Here, however, we seem to touch the ultimate 
particles of matter. Starting from the idea that a gas absorbs such vibrations as are iso- 
chronic wfith its own, in all cases the compound gas reveals itself to the mind’s eye with 
its molecules on the whole sufinging more slowly than the uncombined atoms of which 
it is composed. Their absorption of the longer undulations proves their general coinci- 
dence in period with those undulations. We load the atom by the act of chemical union, 
and thereby render its Hb rations more sluggish, that is to say, more fit to synchronise 
with the slowly recurrent waves of obscure heat. 
In the foregoing Table I have given the absorption of nitric oxide as 1590, which is 
less than that of nitrous oxide, though the molecule of the former contains a greater 
number of atoms than that of the latter. It will be noticed that those gases which on 
combining suffei' no condensation are less energetic absorbers than those which suffer a 
reduction of volume. Whether this rule is universal I am as yet unable to say. 
It is ver)' difficult to operate with nitric oxide ; the affinity of the gas for oxygen is so 
enormous that the slightest trace of this substance gives rise to the brown fumes of 
nitrous acid. On first sending this gas into the experimental tube, 1 inch of it gave an 
absorption of 2040 ; but the needle slowly went up afterwards, until it finally indicated 
an absorption of 5100. On looking across the tube at this time, the brown hue of 
nitrous acid was discernible. 
In a second experiment I made the vacuum as perfect as possible ; on allowing nitric 
oxide to enter, the absorption was 1860, but the needle soon afterwards declared an 
absorption of 3060, the brown fumes appearing as before. 
On filling the experimental tube with nitrogen, then exhausting, and allowing nitric 
oxide to enter, the absorption of 1 inch of the gas was 1680. On filling the experi- 
mental tube previously with hydrogen the absorption was 1590, which is that given in 
the Table. On letting in a mixture of air and nitric oxide till the tube was filled, the 
action last mentioned was augmented nearly twentyfold. Nitrous acid is therefore an 
extremely energetic gas. The difference between it and bromine is enormous when the 
colours of both are equally dense. 
