THEORY. 
937 
certain number of oxyds of each metal could be formed, in 
which the ratio of the metal to the oxygen is uniform. 
Many of the salts in the same way are formed by limited 
doses of acid. Some of the facts in the latter have been 
explained on Berthollett’s hypothesis, while its application 
to the former facts is totally insufficient. Long previous to 
the true cause of these limited closes, the facts were so con¬ 
spicuous, that a decided nomenclature was adopted for the 
purpose of expressing these different stages of combination. 
The oxyds have been distinguished by the Greek numerals 
prot, deut, trit, &c. The salts containing two doses of acid 
have been called super-salts ; and those containing an extra 
dose of base, have been called sub-salts. 
Although chemists have frequently used a language which 
appeared to shew their acquaintance with the real cause of 
the definite proportions, such as oue compound being forced 
by one proportion, dose, or particle of one of its elements, 
and another with two proportions, doses, of particles: on 
the other hand, we find expressions which would favour the 
idea of indefinite proportions; such as bodies losing a small 
portion of their oxygen, or absorbing a little oxygen from 
the atmosphere. Salts are sometimes said to contain a slight 
excess of acid, or a small excess of base. 
The most decided language used in any chemical work 
before the discoveries of Mr. John Dalton, giving any idea 
that the doses are limited by distinct atoms, will be found in 
a work by Mr. Higgins, entitled “ A Comparative View of 
the Phlogistic and Antiphlogistic Theories.” 
This work was written for the express purpose of com¬ 
batting the phlogistic theory, and principally, in answer to 
Mr, Kirwan’s treatise of phlogiston. In order to shew the 
contradictions and absurdities of the phlogistic doctrine, 
which, under the name of phlogiston, confounded a number 
of bodies which were very different, he exhibited by 
diagrams a number of chemical operations, in which he sup¬ 
posed the elementary bodies concerned to be ultimate par¬ 
ticles, and their immediate compounds molecules. He in 
the same diagrams also used numbers, which he supposed to 
be estimates of the strength of affinity of the combining par¬ 
ticles. By this means he very successfully shewed many of 
the inconsistencies which must be admitted to explain the 
phenomena on the phlogistic theory. In this mode of pro¬ 
ceeding, however, the numbersexpressing the relative attrac¬ 
tions, served his purpose much more than the consideration 
of the proportions being caused by distinct atoms; and the 
language which would induce the belief that he had such a 
conception of the nature of elementary matter, occurs only 
in a very few parts of his work. 
After concluding that it is unnecessary to admit the exist¬ 
ence of the imaginary substance of phlogiston in sulphur, he 
concludes, in page 36, that sulphurous acid is compounded 
of one ultimate particle of sulphur with one of oxygen, 
and that sulphuric acid consists of one of sulphur and two of 
oxygen. 
In the same page he also observes, that water is formed by 
one ultimate particle of water united to one of oxygen. 
In page 81, he supposes sulphuretted hydrogen to consist 
of nine ultimate particles of sulphur with five of hydrogen. 
Previous, however, to this conclusion, he believes that the 
sulphur and hydrogen are not chemically combined, but 
that the sulphur is dissolved in hydrogen, as a salt dissolves 
in water. 
After using arguments to shew, in answer to Mr. Kirwan, 
that the nitric acid does not contain what was thought to be 
phlogiston, he concludes, in page 132, with giving what he 
conceives to be its constituents, viz., that the nitrous oxyd 
consists of one ultimate particle of azote and one of oxygen ; 
nitrous gas, of one of azote and two of oxygen ; red nitrous 
vapour, one of azote and three of oxygen; straw-coloured 
nitrous acid, one of azote to four of oxygen; and lastly, that 
the nitric acid is contituted by one of azote and five of 
oxygen. These facts are certainly very remarkable, as 
they agree with the conclusions in the present time, and 
give a strong proof of Mr. Higgins’s genius at the time he 
wrote. 
Vol. XXni. No. 1619. 
He does not, however, lay any stress upon these remarks, 
and was not probably aware that they would be confirmed 
by future research. We are induced to think so, from the 
manner in which he expresses himself in other parts of his 
work, in which he frequently speaks of the absorption of 
small portions of oxygen, and of bodies having a small 
portion of oxygen more than they can retain. This vague 
manner of speaking is sufficient to shew that Mr. Higgins had 
no fixed notions of the cause of definite proportions, and 
that the language in which he has used the words ultimate 
particles and molecules, was employed rather with a view to 
illustrate his examples, than to broach any new theory to ex¬ 
plain indefinite proportions. Indeed it would have been in¬ 
consistent to have treated two subjects, so very different in 
their objects, in their same pages. 
It was not enough to know that compound bodies were 
formed of particles, to enable us to explain the cause of de¬ 
finite proportions; and we want no greater proof of this, 
than the fact of the true cause not being known till twenty- 
eight years after Mr. Higgins had told us that one particle of 
sulphur and one of oxygen formed sulphurous acid, and that 
one to two formed sulphuric acid. These loose expressions 
were but a small step indeed towards the discovery of the 
atomic theory in its present form, w'hich has placed chemistry 
on the same ground with that on which the discovery of 
the laws of gravity placed the science of astronomy. 
We are inclined to believe that the first step towards this 
important discovery was given by Richter. He found, in 
the double decomposition of salts, that the acid of one salt 
was always just sufficient to saturate the base of the other, 
and vice versa. He also ascertained, that when one metal 
was precipitated by another, the oxygen of the precipitated 
metal was just what was required by the precipitating 
metal. 
The inference to be drawn from these facts was, that if A 
combine with x to saturation, and B with y to the same; 
then, if A shouuld be found to saturate, y, B would also sa¬ 
turate x. This inference may be still further extended; for 
if A be a body capaple of combining with B, they will mu¬ 
tually saturate each other. 
It is the means of drawing these inferences arising from 
the mutual fitness of those parts of bodies which combine, 
that constitutes the importance of the atomic theory, and it 
is for the establishment of this new principle that we are in¬ 
debted to Mr. John Dalton. 
When Mr. Dalton’s book was first before the public, very few 
chemists understood the true spirit of the atomic theory; and 
those who conceived they did understand it, in general dis¬ 
carded it. All knew that he considered compounds to be 
formed of atoms united 1 to 1, 1 to 2, 1 to 3, &c.; but it 
was not till the reciprocral fitness of these atoms with each' 
other was found to agree with analysis, that it was generally 
received. When they saw that the numbers, which Dalton 
called the weights of the atoms, expressed the simple propor¬ 
tions in which bodies combine, they knew it could not be the 
effect of chance, and have willingly joined in the research. 
It is for this part of the discovery that Mr. Dalton justly 
merits the fame he has acquired. 
The French chemists have adopted the atomic theory 
under another form, which will be found to agree with the 
language given by Berzelius, who uses the word volume for 
atom. 
Gay Lussac several years ago published a new law respect¬ 
ing the combination of gaseous bodies. He held that gases 
which combine chemically, either unite in equal volumes, 
or 1 to 2, or some multiple of 1, by a whole number, 
Although a number of facts seemed to agree with this law, 
the truth of it was doubted by some chemists, and princi¬ 
pally because no apparent reason appeared for such a law. 
There is a curious coincidence between the specific gravity 
and the weight of atoms of the gases, which has since been 
taken notice of by Dr. Prout in Dr. Thompson’s Annals. In 
order that the weights of the atoms way be equal to their spe¬ 
cific gravities, it is there stated, that the number of particles in 
equal volumes of all gases must be equal, and the distance 
11 F between 
