furnaces, in like manner as carburetted hydrogen gas was purified. The
ironmaster supposed that it was the presence of sulphur in the air that
caused blast-furnaces to work irregularly, and to make bad iron in the
summer months. Mr. Neilson was of opinion that this was not the true
cause, and he was rather disposed to think it attributable to the want
of a due proportion of oxygen in summer, when the air was more
rarefied, besides containing more aqueous vapour than in winter. He
therefore thought the true remedy was in some way or other to throw in
a greater proportion of oxygen; and he suggested that, in order to dry
the air, it should be passed, on its way to the furnace, through two
long tunnels containing calcined lime. But further inquiry served to
correct his views, and eventually led him to the true theory of
blasting.

Shortly after, his attention was directed by Mr. James Ewing to a
defect in one of the Muirkirk blast-furnaces, situated about half a
mile distant from the blowing-engine, which was found not to work so
well as others which were situated close to it. The circumstances of
the case led Mr. Neilson to form the opinion that, as air increases in
volume according to temperature, if he were to heat it by passing it
through a red-hot vessel, its volume would be increased, according to
the well-known law, and the blast might thus be enabled to do more duty
in the distant furnace. He proceeded to make a series of experiments
at the Gas-works, trying the effect of heated air on the illuminating
power of gas, by bringing up a stream of it in a tube so as to surround
the gas-burner. He found that by this means the combustion of the gas
was rendered more intense, and its illuminating power greatly
increased. He proceeded to try a similar experiment on a common
smith's fire, by blowing the fire with heated air, and the effect was
the same; the fire was much more brilliant, and accompanied by an
unusually intense degree of heat.

Having obtained such marked results by these small experiments, it
naturally occurred to him that a similar increase in intensity of
combustion and temperature would attend the application of the process
to the blast-furnace on a large scale; but being only a gas-maker, he
had the greatest difficulty in persuading any ironmaster to permit him
to make the necessary experiment's with blast-furnaces actually at
work. Besides, his theory was altogether at variance with the
establ