ht it vitiates the air and exhausts the oxygen to a
less degree than the others. Of course, in these respects the gas-mantle
is superior.

The reaction which takes place when water and calcium carbide are
brought together is a double decomposition and is represented by,

CaC_{2} + H_{2}O = C_{2}H_{2} + CaO

It will be seen that the products are acetylene gas and calcium oxide or
lime. The lime, being hydroscopic and being in the presence of water or
water-vapor in the acetylene generator, really becomes calcium hydroxide
Ca(OH)_{2}, commonly called slaked lime. If there are impurities in the
calcium carbide, it is sometimes necessary to purify the gas before it
may be safely used for interior lighting.

The burners and mantles used in acetylene lighting are essentially the
same as those for other gas-lighting, excepting, of course, that they
are especially adapted for it in minor details.

The chief source of calcium carbide in this country is the electric
furnace. Cheap electrical energy from hydro-electric developments, such
as the Niagara plants, have done much to make the earth yield its
elements. Aluminum is very prevalent in the soil of the earth's surface,
because its oxide, alumina, is a chief constituent of ordinary clay. But
the elements, aluminum and oxygen, cling tenaciously to each other and
only the electric furnace with its excessively high temperatures has
been able to separate them on a large commercial scale. Similarly,
calcium is found in various compounds over the earth's surface.
Limestone abounds widely, hence the oxide and carbonate of lime are
wide-spread. But calcium clings tightly to the other elements of its
compounds and it has taken the electric furnace to bring it to
submission. The cheapness of calcium carbide is due to the development
of cheap electric power. It is said that calcium carbide was discovered
as a by-product of the electric furnace by accidentally throwing water
upon the waste materials of a furnace process. The discovery of a
commercial scale of manufacture of calcium carbide has been a boon to
isolated lighting. Electric lighting has usurped its place on the
automobile and is making inroads in country-home lighting. Doubtless,
acetylene will continue to serve for many years, but its future does not
appear as bright as it did many years ago.

The Pintsch gas, used to some extent in railroad passenger-cars in this
country, is an oil-gas produced by the destructive