The Sun.
London, England, 1867-08-20 00:00:00

EXPERIMENTS TVITII SAFETY LAMPS.

Several experiments have recently been made
with different.kinds of safety lamps for the purpose
of proving how far they may be depended upon for
safety when burning in fire-damp atmospheres in
coal mines ; and these experiments all seem to
prove that after a time these lamps will explode
a mixture of atmospheric air with carburetted
hydrogen gas if allowed to stand in currents of
the mixture travelling at the rate of from seven
to ten feet per second. In the account we gave
last week of the experiments at the Barnsley
Gasworks, a box twelve feet long and eleven inches
by four inches inside measurement seems to have
been attached to the flue of the retort house
andytthe th e gas was made to travel through
this chimney,
boxn
rate of 7.3 feet per second, when,
of five different lamps tried in the box, it was
ce,
a
found that they all exploded the gas after remain-
ing in the current in times varying from 3 to 75
seconds, the Davy exploded first, and the Stephen-
son last. Now, these experiments, so far as they
show the relative merits of the lamps in continuing
in gas before exploding, are doubtless of value, but
it must be borne in mind that the gas from the re-
tort of a gas works is somewhat different to the
fire-damp met with in coal mines. The former
contains a certain portion of olefiant or heavy
carburetted hydrogen gas, while the presence
of such in the latter was never found by
Sir Humphrey Davy in all the specimens of
fire-damp he ever examined. This justly-cele-
brated chemist, after finding that " the mixture
which seemed to possess the greatest explosive
power was seven or eight parts of air to one of gas,"
goes on to say, "it was very important to ascer-
tain the degree of heat required to explode the fire-
damp mixed with its proper proportion of air." It
was, indeed, the difference in the temperature at
which gases explode, and the high temperature re-
quired to explode fire-damp, as compared with
other gaseis, whiz,.ll mainly led to the discovery of
the lamp. Olefiant gas, he found, exploded
when mixed in equal proportion with air,
and is fired by both charcoal and iron
heated to dull redness ; carbonic oxide explodes
at the same temperature when mixed with double
its volume of air. With fire-damp there can be no
explosion until there is orie-of gas to four parts of
air ; but well-burned eharcoal ignited to the strongest
red heat, nor charcoal blown to whiteness by an
explosive mixture of the fire-damp, did not explode
it. Iron at the highest red heat, and even at the
common degree of white heat, will not explode fire-
damp ; it must be increased to brilliant combustion
before producing the effect. When, therefore,
these lamps tried at the Barnsley Gas Works
exploded, the gas passing through the wooden
box, such explosions arose in part from the
low temperature at which olefiant and car-
bonic oxide gases are ignited ; And if pure
hydrogen were present it would in no small
degree assist the explosion, as this gas explodes
at the lowest visible heat of iron and charcoal ; the
lamps were in fact placed in an atmospheric condi-
tion never known to exist in coal mines. If it can
be proved that heavy carburetted hydrogen, car-
bonic oxide, or pure hydrogen gases are at times
given off in the ordinary way from coal in situ in
mines, then indeed there is no such thing as a safety
lamp. There can be no doubt, however, that a
highly heated gauze will pass flame more readily
than a cold one ; and, moreover, when strong cur-
rents are made to play upon the flame of an ordi-
nary Davy lamp, especially if the flame be burning
in fire-damp, the flame will eventually be forced
through the gauze and ignite the exterior gas.
Although Sir H. Davy says, when speaking about
the numerous experiments he made with a view to
the power of flame to pass through small tubes,
" I did not perceive any difference in these expe-
riments when the metals of the apertures were
warmed by repeated explosions," he nevertheless
adds, "It is probable, however, that considerable
elevation of temperature would increase the power
of the aperture to pass the explosion.—Colliery
Guardian.

THE TEA TRADE.—August 19.—The 'deliveries
in London made up for the week were 1,257,6971b5., being
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