Cuar. VIL, § 3.] 
which had chemically combined with the other; and 
if it happen that fresh compounds are formed pos- 
sessing new qualities, then the varying ingredient 
reaches 3, 4, or 5 times the amount which it had in 
the first combination ; or more generally the propor- 
tions by weight of the combining elements may be 
exactly represented by whole numbers. 3. “If two 
bodies combine in certain proportions with a third, 
they combine in the very same proportions with 
each other.”” This is called the law of reciprocal pro- 
portion. Thus, suppose that one ounce of a body A, 
saturates or forms a chemical combination with two 
ounces of B, 5 of C, and 11 of D; then if B, C, and D 
are capable of combining, it will be in the exact pro- 
portions of the numbers 2,5,and11. Hence a single 
number being determined for each body, determines 
all its possible combinations with other known bo- 
dies. 4. It may perhaps be added as an indepen- 
dent fact, that when complex bodies combine with 
other bodies, no matter whether simple or compound, 
the combining number of the complex body is the 
sum of the numbers representing the constituents. 
Thus the combining number of lime is 28; but lime 
consists of calcium 20 and oxygen 8. So also the 
combining number of water is 9; but water consists 
of hydrogen 1 and oxygen 8: and the combining 
number of hydrate of lime is 37, the sum of the 28 
parts of lime and 9 of water of which it is composed. 
(622.) The discovery of these laws has been termed by 
Partial an- Sir John Herschel the most important, after the laws 
HEAT (ATOMIC CHEMISTRY).—DALTON. 
937 
ness portions of these laws twenty or thirty years 
before, addressed a scientific public by no means pre- 
pared to appreciate their value, or to feel a conviction 
of their generality. Had Wenzel,! Higgins,? and 
Richter* individually apprehended the great impor- 
tance of the definite and multiple combining pro- 
portions which they announced,—had they felt the 
theory of them to constitute the very foundations of 
chemistry,—they would not have rested until they 
had verified it in numerous details, and applied it to 
the various purposes of speculation and practice, as 
Dalton did. But whether from want of energy, or 
from ill fortune, their ideas sunk into entire oblivion; 
and the ingenuity and social position of Berthollet 
were giving a currency to opinions respecting chemi- 
cal forces which tended to undo even the far more 
elementary notions of the constancy of elective affi- 
nities, at the time when Dalton’s researches were 
unostentatiously brought before the world. His first 
insight into the theory of chemical combinations 
dates from the year 1803. It was expounded by 
him both in conversation and by lectures in 1804, 
at which date Dr Thomas Thomson recorded the 
results of a conversation held with him at Manches- 
ter, which, three years later (evidently with Dalton’s 
approbation), he published in his work on Chemistry. 
Finally, Dalton himself, in 1808, announced the prin- 
Wenzel, 
Higgins, 
and Rich- 
ter. 
ciples of his theory at no greater length than five ~ 
pages “on Chemical Synthesis” in his Chemical 
Philosophy. 
yaaa of mechanies, which the study of nature has yet dis- | Now, it is to be observed, that Dalton’s views were (623.) 
these laws. closed. No slight or transient reputation is due all along expressed in the language of a strictly Ato- pS ree 
to him who first clearlyapprehended and taught them. ‘mic theory. Compounds are only chemically com-¢);, Theory 
Nor must we be surprised to find several claimants to plete, when one or several atoms of an element com- to the pro- 
a share of the honour. It is the invariable history of 
all great generalizations, that they have been partly 
anticipated; and it may serve to moderate the self- 
esteem of even the greatest discoverers, that however 
high may be their individual merits, they are in some 
sense the mere exponents of the aggregate know- 
ledge of their contemporaries. The laws of motion 
were partially anticipated before the time of Galileo, 
and could not have remained much longer undefined ; 
and even the unparalleled discoveries of Newton 
must, in all probability, have ere long been made 
piecemeal by the united energy of his contemporaries 
and immediate successors. The steam-engine was 
not the sole creation of Watt, nor was Davy the first 
to apply the voltaic battery to chemistry. In like 
manner, Dalton’s laws of chemical combination were 
published at a happy moment, which gave them 
speedy acceptance with the active chemists of his 
day; whilst those who had seen with sufficient clear- 
bine with one, two, or more atoms of another. Any 
superfluity of either element remains uncombined, or 
mechanically mixed. All the other parts of the laws 
of combination readily lead to the same idea, and, in 
fact, find in it their simplest expression. 
no wonder, then, that Dalton firmly believed in the 
physical existence of his/atoms, and that the new 
properties of compounds are due to the peculiar mo- 
dification of the most elementary parts into which 
bodies can be divided without a loss of those proper- 
ties, that is, without decomposition. He figured 
these elementary molecules by uniting the symbols 
of their constituents, and by so doing, may be said 
to have laid the foundation of those algebraic sys- 
tems of technical notation, which speak to the eye 
only in another way from Dalton’s diagrams, and 
which have been of such eminent service to the 
chemist. Nor must we think too lightly of a hypo- 
thesis which served so materially to aid in realizing 
1 Lehre von der Verwandschaft der Kérper, 1777. He shows that in a double decomposition the new compounds are chemi- 
cally perfect. 
2 A Comparative View of the Phlogistic and Antiphlogistic Theories, 1789, by Mr William Higgins, points out the multiple com- 
bining proportions of sulphur and oxygen, and of nitrogen and oxygen, but only incidentally. Dr Bryan Higgins, a relative of 
Mr W. H., had published, in 1786, a work said to contain the idea of definite atomic combinations. 
% Anfangsgriinde der Stéchyometrie, 1792. He gavea series of numbers representing the combining proportions of different 
elements. 
VOL. I. 
6c 
gress of 
chemistry. 
There is - 
