to a higher temperature to convert them into permanent gas, and this
causes an over-cracking of the most valuable illuminating
constituents; and this trouble cannot be avoided, as, if a lower
temperature is employed, easily condensible vapors are the result,
which, by their condensation in the pipes, give rise to much trouble.

The simplicity of the apparatus is a factor which causes a great
saving of time and expense, as it reduces to a minimum the risk of
stoppages for repairs, while the initial cost of the apparatus is, of
course, low, and the expense of keeping in order practically _nil_.

When I first made the acquaintance of this form of plant, a few years
ago, the promoters were confident that nothing could be used in it
but American anthracite, of the kind they had been in the habit of
using in America, and a light naphtha of about 0.689 specific gravity,
known commercially as 76 deg Baume.

A few weeks' work with the apparatus, however, quickly showed that,
with a slightly increased blow, and a rather higher column of fuel,
gas coke could be used just as well as anthracite, and that by
increasing the column of fuel, a lower grade of oil could be employed;
so that during a considerable portion of the experimental work nothing
but gas coke from the Horseferry Road Works and a petroleum of a
specific gravity of about 0.709 were employed.

Having had control of the apparatus for several months, and, with the
aid of a reliable assistant, having checked everything that went in
and came out of the generator, I am in a position to state
authoritatively that, using ordinary gas coke and a petroleum of
specific gravity ranging from 0.689 to 0.709, 1,000 cubic feet of gas,