The Sun.
London, England, 1862-05-09 00:00:00

THE PIO(3BESS OF THE CHEJIICAL

ARTS.

Yesterday afternoon, Dr. Lyon Playfair com-
menced a short course of lectures at the Royal In-
stitution, "On some of the Chemical Arts, with
reference to their progress between the two Great
Exhibitions of 1851 and 1862." The lecture yes-
terday was on the distillation of coal, especially in
relation to the production of gas and to the forma-
tion of paraffin. The cause of his commencing with
the manufacture of gas, he observed, was not because
there has been much improvement in the process
itself during the last eleven years, but on account
of the important uses to which what were formerly
considered the waste products of the distillation of
coal have been applied. Dr. Playfair, in the first
instance, gave a slight sketch of the history of gas
lighting, noticing the experiments, at the close of
the last century, by Dr. Clayton, who confined what
was called "the spirit of coal in bladders, which
was ignited as it issued through small holes, to the
great astonishment of all; and then proceeded to
describe the efforts of Murdoch, Winser, and Clegg
to apply the gas produced from coal to the pur-
poses ofaillumination. The process as now con-
ducted in the gas-works was illustrated by large
diagrams, showing the successive stages the gas
passes through, commencing with its distillation in
the retorts, next the deposition of tar in the hydrau-
lic main, and in the condensers, the action of the
exhausters, by which it is drawn from the retorts,
its passage through the purifiers, whence it is
conveyed to the gasometer to be measured be-
fore it enters the gas-holder; and, finally, the regu-
lation of its distribution through the mains by a
" governor." There was also exhibited a model
apparatus in action, to exemplify the production
and purification of coal before it is fitted to be burned
in private houses. Dr. Playfair explained the che-
mical constituents of coal-gas, separating the prq-
aaata or coal into solid and ceriform. The illumi-
nating property of coal-gas, he observed, depends
on the quantity of olefiant gas it contains, for the
carburetted hydrogen and the carbonic oxide,
though very combustible, give scarcely any light,
and act only as diluents, whilst the carbonic acid
extinguished flame. Jets of carburetted hydrogen,
of carbonic oxide, of olefiant gas, and of common
coal-gas were inflamed for the purpose of showing
their comparative luminosities, when all appeared
dim compared with the olefiant gas, and the two
former flames were scarcely visible, The lumino-
sity of flame, Dr. Playfair explained, depends an
the quantity of matter that is contained in inflam-
mable gas, the particles being rendered incandescent
by heat, and thereby throwing out brilliant rays of
light. To exemplify this he passed a current of
pure hydrogen gas through a glass tube,into which
some peroxide of barium had been introduced, and
when it was heated and the gas ignited, it gave a
brilliant light. Dr. Playfair attempted to show
the effect of giving increased lighting power to
hydrogen gas by bringing it in contact with a fluid
hydro-carbon, on the same principle that is now
practised on many of the street lamps in
the City, of napthalising the gas before it
reaches the burners ; but, unfortunately, he
applied the light to the tube before all
the atmospheric air was expelled, and a
violent explosion took place, which shattered the
glass vessel, and threw particles of glass to all parts
of the lecture-room. -This accident, and the suf-
focating fumes produced, occasioned a serious inter-
ruption to the lecture, many ladies being obliged to
leave, and some of the audience being cut by the
pieces of glass. Dr. Play fair expressed great regret
at the accident, none such, he said, having occurred
during many years that he had lectured. In the
concluding portion of his lecture he explained the
chemical process of purifying gas from sulphuretted
hydrogen by lime and by the oxide of iron, the
latter plan having come into practical operation
since 1857, and is now generally adopted. The tar
produced by the distillation of coal yields paraffin
oil, which possesses the same illuminating proper.
ties as olefiant gas, and from that oil is extracted
the beautiful wax from which paraffin candles are
made. At the Great Exhibition of 1851 there was
a single paraffin candle exhibited which had been
made from peat ; the same substance has since been
manufactured abundantly from coal tar; and in the
present International Exhibition there are many
beautiful large blocks of paraffin wax and numerous
specimens of paraffin candles made from coal tar,
the manufacture having now become an important
branch of industry. In the next lecture, he said,
he should pursue the subject, and show still further
how the former waste products of gas works have
been economised ; and he assured his audience that
no similar accident should occur again to annoy
them.