chemical compound of the metal calcium with carbon, containing one
chemical "part," or atomic weight, of the former united to two chemical
parts, or atomic weights, of the latter; its composition expressed in
symbols being CaC_2. Similarly, water is a compound of two chemical parts
of hydrogen with one of oxygen, its formula being H_2O. When those two
substances are mixed together the hydrogen of the water leaves its
original partner, oxygen, and the carbon of the calcium carbide leaves
the calcium, uniting together to form that particular compound of
hydrogen and carbon, or hydrocarbon, which is known as acetylene, whose
formula is C_2H_2; while the residual calcium and oxygen join together to
produce calcium oxide or lime, CaO. Put into the usual form of an
equation, the reaction proceeds thus--

(1) CaC_2 + H_2O = C_2H_2 + CaO.

This equation not only means that calcium carbide and water combine to
yield acetylene and lime, it also means that one chemical part of carbide
reacts with one chemical part of water to produce one chemical part of
acetylene and one of lime. But these four chemical parts, or molecules,
which are all equal chemically, are not equal in weight; although,
according to a common law of chemistry, they each bear a fixed proportion
to one another. Reference to the table of "Atomic Weights" contained in
any text-book of chemistry will show that while the symbol Ca is used,
for convenience, as a contraction or sign for the element calcium simply,
it bears a more important quantitative significance, for to it will be
found assigned the number 40. Against carbon will be seen the number 12;
against oxygen, 16; and against hydrogen, 1. These numbers indicate that
if the smallest weight of hydrogen ever found in a chemical compound is
called 1 as a unit of comparison, the smallest weights of calcium,
carbon, and oxygen, similarly taking part in chemical reactions are 40,