he latter about 2500
tons annually. Small as is the legacy of nitrogen bequeathed to us from
the Carboniferous period, we see that it sums up to a considerable annual
addition to our industrial resources.

The three products resulting from the distillation of coal--viz. the gas,
ammoniacal-liquor, and coke--having now been made to furnish their tale,
we have next to deal with the tar. In the early days of gas manufacture
this black, viscid, unsavoury substance was in every sense a waste
product. No use had been found for it, and it was burnt, or otherwise
disposed of. No demand for the tar existed which could enable the gas
manufacturers to get rid of their ever-increasing accumulation. Wood-tar
had previously been used as a cheap paint for wood and metal-work, and it
was but a natural suggestion that coal-tar should be applied to the same
purposes. It was found that the quality of the tar was improved by getting
rid of the more volatile portions by boiling it in open pans; but this
waste--to say nothing of the danger of fire--was checked by a suggestion
made by Accum in 1815, who showed that by boiling down the tar in a still
instead of in open pans the volatile portions could be condensed and
collected, thus furnishing an oil which could be used by the varnish maker
as a substitute for turpentine. A few years later, in 1822, the
distillation of tar was carried on at Leith by Drs. Longstaff and Dalston,
the "spirit" being used by Mackintosh of Glasgow for dissolving
india-rubber for the preparation of that waterproof fabric which to this
day bears the name of the original manufacturer. The residue in the still
was burnt for lamp-black. Of such little value was the tar at this time
that Dr. Longstaff tells us that the gas company gave them the tar on
condition that they removed it at their own expense. It appears also that
tar was distilled on a large scale near Manchester in 1834, the "spirit"
being used for dissolving the residual pitch so as to make a black
varnish.

But the production of gas went on increasing at a greater rate than the
demand for tar for the above-mentioned purposes, and it was not till 1838
that a new branch of industry was inaugurated, which converted the
distillation of this material from an insignificant into an important
manufacture. In that year a patent was taken out by Bethell for preserving
timber by impregnating it with the heavy oil from coal-tar. The use of tar
for this purpose had bee