414 
THE CONSTITUTION OF MATTER. 
Then came Gay-Lussac’s discovery of the laws of chemical combination .of 
gases by volume or measure. The observation made by that illustrious chemist 
that gases combine in volume, which are either equal or are even multiples one 
of the other, was a discovery equally important with that of combination by 
weight. . - 
This simplicity arises from the peculiar circumstance that equal measures ot 
gaseous elements consist of weights (their specific gravities) which stand to each 
other in the same ratio as their combining quantities. , 
Thus hydrogen combines with chlorine in equal measures to form hydrochloric 
acid, because, to take concrete quantities, 11 litres of hydrogen weigh 1 gramme, 
and 11 litres of chlorine weigh 35| grammes; and these are the proportions 
in which these elements combine by weight. . . 
On stating it conversely, weights of solid or liquid elements proportional to 
their combining weights assume the same volume when converted into vapour 
and measured at the same temperature and under the same amount of pressure. 
Thus 127 grammes of iodine, when heated so as to change it into a gas, occupy 
the same space that 1 gramme of hydrogen fills. 
Another and a different kind of phenomenon is exhibited in the deportment 
of different bodies under the influence of heat. When different substances are 
made to receive heat at a uniform rate from one and the same source, it is found 
that their temperatures rise with very different degrees of rapidity. Or the ex¬ 
periment may be made by taking equal weights of the same substances and 
allowing them to lose a certain number of degrees of temperature, carefully 
noting the time occupied by both in undergoing this change. That body which 
changes in temperature most rapidly, whether to become hotter or colder, is said 
to have the smallest “specific heat/’ From experiments of this kind upon the 
different elements a series of numbers has been obtained,* which represent their 
respective specific heats, and the chief peculiarity of which is that when multi¬ 
plied by the combining weights, they give nearly the same number in each .in¬ 
stance ; this is equivalent to saying that the capacity for heat of each element 
is inversely as its combining weight. 
It has been said that elements, when examined in the state of perfect gas, are 
found to contain, in equal volumes, ponderable quantities which are identical 
with those of their combining quantities. This observation applies equally to 
compound bodies. 
The formula— 
HC1 represents 36^ parts of hydrochloric acid. 
18 parts of water. 
34 parts of sulphuretted hydrogen. 
16 parts of marsh gas. 
46 parts of alcohol. 
74 parts of ether. 
C 
C 
Id 2 0 
Id 2 S 
h 4 c 
,u e o 
4H.0O 
>1 
71 
All these, measured at such temperatures that they are in the gaseous condi¬ 
tion fill the same space, and they are the quantities which represent the “ units 
of chemical action ” in the instances given. These are the proportions in which 
it is easy to prove by other methods, these compounds enter into combinations, 
or are produced by chemical decompositions. They represent what are known 
as the molecules of these compounds. 
“ There are, also, crystalline compounds, which chemistry has found to be 
closely analogous, which oecupy, in the crystalline state, equal or nearly equal 
volumes. . 
“Among other physical properties which confirm the truth of the atomic views 
*■ See a paper by the author in the Phann. Journ. N. s. Vol. IX. p. 532. 
