‘ 
6 Definite Proportions. 
niteness of proportion has been observed also among gaseous 
bodies, whether the combining quantities are estimated by 
weight or by volume. ater, for example, is constituted of 
just two measures of hydrogen and one of oxygen ; and a 
remarkable instance of the-same kind occurs in the combina- 
tions of nitrogen with different quantities of oxygen, which 
are to each other, respectively, as the numbers 1, 2, 3, 4, 
and 5. Nor in all the foregoing cases, is it known that any 
intermediate compound exists to destroy the Bermnay of these 
proportions. The only question which can arise here, is 
whether the same definiteness governs all thomas! combina- 
tions, or whether some constituents of a compound do not 
unite in every proportion, without observing such distinct 
gradations as are apparent in other cases? If we hold-melt- 
ed lead on the fire in a ladle, a yellow oxide will form on its 
surface. By augmenting the heat, this yellow oxide will pass 
through a great number of shades of colour, by apace 
ble gradations, until it becomes a t red. these 
shades of colour arise, from the different quantities af oxygen 
which successively combine with the lead, and the question 
occurs, do not these gradual changes of colour oppose the 
idea of distinct stages or gradations in the process ? Accord- 
ing to the doctrine of definite proportions, ought not the lead 
to combine with one dose of oxygen, und then to refuse any 
more until it can receive as much more all at once? All 
these insinuations against the doctrine, may be set aside, by 
observing (what undoubtedly happens) that only a part of 
= — is reduced to the next stage of oxidation at each 
ssive moment; Sal the red and yellow oxides being 
blended together, the mixture assumes diflerent shades of co- 
lour according as one or the other predominates. A number 
of cases of this kind occur in chemical combinations, where 
it is difficult, at the first view, to see the operation of the law 
of definite Oa geass But more attention will frequently 
lead to the detection of some circumstance, which shows that 
the case is not an exception to that law—its operation was 
merely concealed. Still, the foregoing law of definite pro- 
portions is most apparent in cases where the strongest affinity 
fer vails, and is hardly discernible in combinations of a fee- 
Definite Proportions and Atomic Theory, are phrases used 
by some some writers with little discrimination, as though both 
implied the same thing. But they differ widely from each 
