CHEMICAL NOTATION AND ATOMIC WEIGHTS. 
58 L 
tives is said to consist of one atom, because it can be substituted only bv one 
operation. 
O 
Water. 
H 
I 
ITypoehlorous Acid. 
'Cl 
II 
o 
{ 
o 
Caustic Potash. 
K 
O 
I 
H 
Oxide of Silver. 
A<; 
O 
‘ (H 
I 
Alcohol, 
w ^ Et 
H w 
Oxygen, therefore, combines with two atoms of hydrogen or its represen¬ 
tatives ; but it can also take the place of II 2 as shown by the formula of 
acetic acid, and innumerable analogous compounds. 
Let alcohol 
acetic acid, O 
(C 2 H 6 OorO|f) 
CCJLO" , 
j H ’ * rom As 
be represented thus :—O | ^^ 3^2 5 then 
mode of formation and other circumstances 
is plainly that compound in which the place of the H„ is occupied by O. 
The simplest combinations into which carbon enters, all proclaim this ele- . 
inent to have a replacing or combining value equal to four atoms of hydrogen ; 
it is quadrivalent. Marsh gas exhibits this element in the full vigour of its 
combining capacity ; in this compound twelve parts or one atom of carbon are 
united with four parts or atoms of hydrogen, CH 4 . 
It might be disputed if we had not already settled the atomic weights that 
this formula might be simplified by dividing it by two or four. That this is 
impossible is proved by studying the products generated by the direct action 
of chlorine. These products, if the theory of substitution is based upon 
sound principles, are represented by the following formulas:— 
fH 
(Cl 
[Cl 
f 
c - 
II 
H 
1 TT 
°-jH °- 
Cl 
H 
c - 
II 
Ui 
[R 
V 
Cl 
Cl 
Cl 
II 
c • 
Cl 
Cl 
(Cl 
l Cl 
In the first we have the carbon apportioning its affinity to the four atoms 
of hydrogen ; the first effect of chlorine is to produce the compound CII 3 C1, 
the composition of which, it is clear, cannot be represented by any simpler ex¬ 
pression, since it contains a single atom of chlorine, which, of course, cannot 
be subdivided. So also with the third substitution product, chloroform, 
CHC1. V 
Enough has been said to indicate the manner in which the several combin¬ 
ing capacities of the elements are discovered. Chlorine, iodine, bromine, 
jiotassium, sodium, etc., are the representatives in combination of one atom 
of hydrogen; their atomic coincides with their equivalent weight, and they 
are denominated monatomic or univalent. Oxygen, barium, calcium, etc., 
possess the substituting power of two atoms of hydrogen; they are therefore 
diatomic, and their equivalent numbers equal their atomic weights divided 
by two. 
Triatomic elements have equivalents which are one-third of their atomic 
weights ; and so throughout. 
Passing from the consideration of the atomicity of elementary atoms, we 
have next to examine those cases in which groups of atoms are concerned in 
processes of exchange and substitution. These groups, like the separate ele¬ 
ments of which they are made up, have different capacities of replacement. 
This can, in many instances, be found by inspection of the symbolic expres¬ 
sion. To take a simple instance ; ox} r gen is bivalent, hydrogen of course the 
unit of quantivalence; let O be conceived united with H, thus IIO; the ox 3 ^gen 
in such a compound would be only half satisfied, and must unite with another 
atom of a univalent element or grouping before it could form a molecule 
complete, or as the term is, saturated. Thus IIO can unite with K', produc¬ 
ing Iv 1TO (potash) or with (0 2 H 5 )' forming C„H 5 HO (alcohol), or with 
