NEWCASTLE UPON TYNE. 
by any means different from aCHve inflammation, pro¬ 
ceeded to make experiments on the fire-damp itfelf, in 
order to difcover whether any of its properties might pre- 
fe it the means of defending it from the danger of explofion. 
The pureft fire-damp which he obtained was from a blower 
in the Hepburn coalery; it contained only T \-th of atmo- 
fpheric air, with no other contamination whatever. The 
moft impure or the weakeft fire-damp contained ^ths of 
atmofpheric air: a hundred cubic inches of the firlt-men- 
tioned fpecimen weighed exactly 19^- grains : one meafure 
of it required to its complete combuftion by the eleCtric 
fpark, nearly two meafnres of oxygen ; and they formed 
about one meafure of carbonic acid. From a number of 
other experiments he concluded, that the opinion ge¬ 
nerally entertained by chemifts refpe&ing the fire-damp 
is perfectly correct ; and that it is the lame fubftance with 
the inflammable gas of marlhes, the true nature of which 
was firft found out by Mr. Dalton, who (bowed, that it 
confifts of four parts of hydrogen in weight 4, and one of 
charcoal in weight 11-5. 
The next inquiry was into the combuftibility or ex- 
plofive power of the fire-damp, when diluted with different 
proportions of atmofpheric air. When mixed in equal 
parts, they burnt by the approach of a lighted taper, but 
did not explode. The refults of a number of other ex¬ 
periments of the fame kind made it appear, that the mix¬ 
ture which poflefled the greateft force was one of 7 or S 
parts of air to 1 of gas; but, neverthelefs, the report pro¬ 
duced by fifty cubical inches of that mixture, was lefs 
than was produced by five cubical inches of a mixture of 
2 parts of atmofpheric air with 1 of hydrogen. 
It then occurred, that it was very material to determine 
the degree of heat required to explode the fire-damp when 
it was mixed with the due proportion of it. It was found 
that a common electrical fpark would not explode five 
parts of air and one of fire-damp, though it was able to 
explode fix parts of the former with one of the latter. 
Very ftrong fparks from the difcharge of a Leyden jar, 
feemed, however, to have the fame power of exploding 
different mixtures of thofe fluids as the flame of a candle. 
Well-burnt charcoal, ignited to the ftrongeft red heat, 
did not explode any mixture of air and fire-damp; and 
charcoal could even be blown np to whitenefs by an ex¬ 
plofive mixture of air and fire-damp, without producing 
inflammation. An iron rod at the higheft red heat, and 
even at the common degree of white heat, was equally 
inefficient; but, when in brilliant combuftion, it produced 
explofion. Thus, in refpeCt of combuftibility, it was 
found that the fire-damp differs materially from the other 
inflammable gafes. Olefiant gas, mixed with fuch a pro¬ 
portion of air as to render it explofive, is fired both by 
charcoal and iron heated to a dull red heat. Gafeous 
oxyd of carbon, which explodes when mixed with two 
parts of air, is likewife inflammable by red-hot iron and 
charcoal; and the cafe is the fame with fulphuretted hy¬ 
drogen. 
The next obje& of fir Humphry’s experiments, was the 
degree of expanfion of mixtures of air and fire-damp during 
their explofions, and likewife their power of communi¬ 
cating flame through given apertures to other explofive 
mixtures. He found, that in explofions, at the moment 
when the expanfion was greateft, the volume of the gas 
was not increafed in a greater ratio than that of 3 to 2. 
This, we muft obferve, is a much fmaller expanlion than 
is produced by the heat of ignition in other elaftic fluids. 
In the firing of gunpowder, the expanfion of the air is 
eftimated by Robins at four times its bulk in the common 
temperature of the atmofphere; and there is reafon to 
think that he has confiderably under-rated the quantity 
of it. 
Thefe experiments were connected with the propagation 
of the flame: thofe that followed were more immediately 
directed to that objeCt. In the conveyance of flame from 
one explofive mixture to another, he found, that the nar¬ 
rowness of the tube of communication formed a great 
obftacle ; infomuch, that a mixture of 1 part of gas from 
the diftillation of coal, and 8 parts of air, could not be 
made to explode in a glafs tube -J-th of an inch in dia¬ 
meter; although the above mixture, by containing fome 
olefiant gas, was more inflammable than the common 
fire-damp. In like manner, when he exploded mixtures 
of fire-damp and air in a jar, communicating with the 
atmofphere through an aperture of half an inch, and with 
a bladder having in it an exploding mixture, through an 
aperture of £th of an inch ; the flame palled into the at¬ 
mofphere, but did not communicate with the mixture in 
the bladder. Here, therefore, was a limit certainly de¬ 
termined to the width of the apertures by which flame 
could be communicated from one explofive mixture to 
another. This was a difcovery of great importance, and 
obvioufly pointed at a method by which the flame might 
be reftrained within certain bounds, without the com¬ 
munication between the gafes themfelves being entirely 
cut off. Sir Humphry concluded, and indeed with great 
probability, that this phenomenon depended on the heat 
loft during the explofion, by the contact of a large cooling 
furface, which brought the temperature of the firft por¬ 
tions exploded below that required for the firing of the 
contiguous portions. Thus he found, that metallic tubes 
refitted the paflage of the flame better than glafs tubes of 
the fame diameter, metal being a better conductor of heat 
than glafs. In this way, the high temperature required 
to the inflammation of the fire-damp furnilhed the means 
of confining the flame within certain bounds, notwith- 
ftanding the material of the combuftion was diffufed all 
round, and the parts every-where in contact with one 
another. A more difficult problem than to prevent the 
communication of flame in fuch a cafe, and one more 
unlikely to be refolved, cannot eafily be imagined. A 
covering for the flame was to be provided, penetrable to 
light, and penetrated by the inflammable fubftance that 
was on fire within, and yet impenetrable to the flame, 
which it muft not permit to efcape. By pufhing the 
fame experiments farther, fuch a covering was actually 
found; and it was difcovered that the flame of the fire¬ 
damp would not pafs through very fine wire-fieves or 
wire-gauze. It was alfo obferved that mixtures of azot 
and carbonic acid, thrown into an explofive mixture of 
air and fire-damp, deprived the latter of its power of 
explofion. Carbonic acid more effectually allayed the 
exploding power than the azot, probably on account of 
its greater capacity for heat, as well as its better conduct¬ 
ing power proceeding from its greater denfity. 
The fafety-lamps and fire-fieves conftruCted from thefe 
experiments, were very properly fubjeCted to the fevereft 
trials; to trials, indeed, much more fevere than they 
could ever meet with in the mines. “ I fubmitted the 
fafe-canals, tubes, and wire-gauze fire-fieves,” fays fir 
Humphry, “ to much more fevere tefts. I made them the 
medium of communication between a large glafs veflel 
filled with the llrongeft explofive mixture of carburated 
hydrogen and' air, and a bladder half full of the lame 
mixture, both infulated from the atmofphere. By means 
of wires pafling near the flop-cock of the glafs veflel, I 
fired the explofive mixture in it by the difcharge of a 
Leyden jar. The bladder a] ways expanded at the moment 
the explofion was made, a contraction as rapidly took 
place, and a lambent flame played round the mouths of 
the fafety-apertures, upon the glafs veflel, but the mixture 
in the bladder did not explode ; and, by prefling fome of 
it into the glafs veflel, fo as to make it replace the foul 
air, and fubjeCting it to the eleCtric fpark, repeated ex- 
plofions were produced, proving the perfeft fecurity of 
the fafety-apertures, even when aCted on by a much 
more powerful explofion than could poflibly occur from 
the introduction of air from the mines.” 
Thefe experiments led to feveral excellent contrivances, 
which fimplified themfelves as they proceeded, and ended 
at laft in the Jafety-lamp, made of wire-gauze, in the 
fhape of a cage or cylinder. The apertures in the gauze 
lhould 
