12, and 16 respectively. Thus the symbol CaC_2, comes to convoy three
separate ideas: (_a_) that the substance referred to is a compound
of calcium and carbon only, and that it is therefore a carbide of
calcium; (_b_) that it is composed of one chemical part or atom of
calcium and two atoms of carbon; and (_c_) that it contains 40 parts
by weight of calcium combined with twice twelve, or 24, parts of carbon.
It follows from (_c_) that the weight of one chemical part, now
termed a molecule as the substance is a compound, of calcium carbide is
(40 + 2 x 12) = 64. By identical methods of calculation it will be found
that the weight of one molecule of water is 18; that of acetylene, 26;
and that of lime, 56. The general equation (1) given above, therefore,
states in chemical shorthand that 64 parts by weight of calcium carbide
react with 18 parts of water to give 26 parts by weight of acetylene and
56 parts of lime; and it is very important to observe that just as there
are the same number of chemical parts, viz., 2, on each side, so there
are the same number of parts by weight, for 64 + 18 = 56 + 26 = 82. Put
into other words equation (1) shows that if 64 grammes, lb., or cwts. of
calcium carbide are treated with 18 grammes, lb., or cwts. of water, the
whole mass will be converted into acetylene and lime, and the residue
will not contain any unaltered calcium carbide or any water; whence it
may be inferred, as is the fact, that if the weights of carbide and water
originally taken do not stand to one another in the ratio 64 : 18, both
substances cannot be entirely decomposed, but a certain quantity of the
one which was in excess will be left unattacked, and that quantity will
be in exact accordance with the amount of the said excess--indifferently
whether the superabundant substance be carbide or water.

Hitherto, for the sake of simplicity, the by-product in the preparation
of acetylene has been described as calcium oxide or quicklime. It is,
however, one of the leading characteristics of this body to be