LECT. iv.] HISTORY OF CHEMISTRY 55
taiued confirmation of the law. The law is to this effect:—If
two substances, A and B, form several compounds, of which
the compositions are all calculated with respect to the same
quantity of A, then the quantities of B combined with this,
stand to each other in a simple ratio.20 Dalton sought in the
atomic theory an explanation of this law, which was simply
an expression of the observed facts.
According to the atomic theory, chemical compounds are
formed by the arrangement, in juxtaposition, of atoms of the
elements, these latter being incapable of undergoing any
further decomposition. With regard to this Dalton says :—21
" Chemical analysis and synthesis go no further than to the
separation of particles one from another, and to their reunion.
No new creation or destruction of matter is within the reach
of chemical agency." By the fact that Dalton assigns a
definite unalterable weight to the atom of every element, and
admits the possibility of the combination of several atoms,
his theory is brought into harmony with experiment, and
becomes, indeed, a necessary consequence of it. According
to the number of atoms which enter into combination, the
resulting atom may belong to a different order.
The atoms of elements are simple atoms, or atoms of the
first order.
When i atom of an element A combines with i atom of
an element By i atom of the second order is produced.
When 2 atoms of an element A combine with i atom of
an element B, i atom of the third order is produced.
When i atom of an element A combines with 2 atoms of
an element B, i atom of the third order is produced.
When i atom of an element A combines with 3 atoms of
an element B, i atom of the fourth order is produced.
When 3 atoms of an element A combine with i atom of
an element J3, i atom of the fourth order is produced, etc.
30 It appears that Dalton never stated the law in this general form.
Compare Memoirs of John Dalton, by W. Henry, 79 et seq* 2l
System. I, 212; A.C.R. 2, 20,.