realised by reference to the table which follows. Broadly speaking, however,
no illuminant which evolves light by combustion (oxidation), and which therefore
requires a supply of oxygen or air for its maintenance, affords light with so
little exhaustion of the air as acetylene. Hence in confined, ill-ventilated,
or crowded rooms, the air will suffer less exhaustion, and accordingly be better
for breathing, if acetylene is chosen rather than any other illuminant, except
electricity.
Next, in regard to vitiation of the air, by which is meant the alteration in
its composition resulting from the admixture of products of combustion with
it. Electric lighting is as superior to other modes of lighting in respect of
direct vitiation as of exhaustion of the air, because it does not depend on
combustion. Putting it aside, however, light is obtainable by means of acetylene
with less attendant vitiation of the air than by means of any other gas or of
oil or candles. The principal vitiating factor in all cases is the
