Synthetic Inorganic Chemistry

NOTES AND PROBLEMS^49

table a few typical examples are selected from the data for all
gaseous or volatile oxygen compounds.
The smallest number in the next to the last column is 16, and
this must be the atomic weight of oxygen because it represents
the smallest weight of oxygen in the molecular weight of any of its
compounds. It is extremely unlikely that there would not be at
least some compounds whose molecules contained but a single
atom. But if such could be the case and 16 were for example
twice the atomic weight, we should expect that 8 would be the
greatest common divisor and that numbers equal to 3 X 8 or
5X8 and therefore not divisible by 16 would be found in the
next to the last column. We can therefore be reasonably certain
that 16 is the actual atomic weight and not a multiple of the atomic
weight of oxygen.
A similar study of other elements, for example of chlorine, hy-
drogen, sulphur, mercury, shows that in all the gaseous or volatile
compounds of these elements the smallest weight ever found in
the molal volume is 35.46 grams of chlorine, 1.008 grams of hydro-
gen, 32.06 grams of sulphur, and 200.6 grams of mercury; further-
more, when the molal volume contains a greater weight of these
elements, the weight is invariably a small even multiple of these
smallest weights. Thus the atomic weights of these elements
as given in the table are verified.

The following table shows selected examples from the col-
lection of the data for all gaseous or volatile chlorine compounds.

Substance

Hydrogen chloride
Chlorine
Mercuric chloride
Arsenic trichloride
Silicon tetrachloride
Phosphorus penta-
chloride

Weight in

grams of 1

mole

36 5

70 9

270 9

182 1

170 2

208 3

Percentage

by weight

of chlorine

97 22

100

26 19

57 7

83 4

85 2

Weight of

chlorine in

1 mole

35 5

70 9

70 9

107 0

142

177 5

Greatest

common

divisor

1X355

2X355

2X35 5

3X355

4X355

5X355

Derivation of a Formula. Let us take for example ethyl ether.
This substance is a liquid at ordinary temperature and pressure
but it is easily vaporized. We must first find its molecular weight.