When this gas is mixed with atmospheric air, it inflames by a lighted taper; but unless the quantities are duly proportioned, the inflammation is too slow to be accompanied with sound. The combustion appeared to be most sudden when there were about 7 or 8 parts of air to 1 of the gas. When 1 of the gas is mixed with 15 or 16 of air, the candle burns with an enlarged flame, which does not extend to the whole quantity, and the same phenomenon occurs when the gas constitutes no more than 130th part of the mixture.
The author next made trial of the degree of heat necessary for the combustion of this gas, which in fact is difficult to ignite, for even the electric spark will not explode a mixture containing 5 parts of air to 1 of the gas; but when the air is increased as far as 6 to 1 , or nearer to the most explosive proportion, then it does take fire by the electric spark. Even the most explosive mixture will not take fire from well burned charcoal, nor by iron heated to any degree short of actual combustion. But on the contrary, hydrogen whether simple or sulphuretted, olefiant gas, or carbonic oxide, may each be set on fire very readily by all these means; and hence the gas procured by distillation from coal is liable to be fired by ignited iron or charcoal, in consequence of the olefiant gas which it contains along with the carburetted hydrogen in the first stage of the process of distillation, and on account of the carbonic oxide and hydrogen which it contains in the latter stages of its production.
Since the fire-damp of coal mines is free from these admixtures, it might be possible to light a mine by means of a charcoal fire, if free from flame, which is necessary for the ignition of the gas. The method, however, which the author proposes, is not dependent on this property, but upon the supply of air to a lamp employed for that purpose being limited, in such a manner that the lamp will be extinguished by impurity of the air before an explosion can take place.
If a lighted lantern, in the bottom of which there is only a small aperture just sufficient for its supply, be inserted in a mixture of common air, with about 112th of fire-damp, the flame first appears feeble, next enlarges, and then is uniformly extinguished. In the lantern here proposed for coal mines, a chimney is added of such length as to prevent any communication from the enlarged flame upwards with the external air; and the opening below is designed to be at a fixed distance from the flame, by using oil lamps instead of candles. As an additional security in some cases, the author conceives it may be useful to add valves at the apertures, which may be made to shut by a thermometric spring when the heat is increased by enlargement of the flame.
Beside the foregoing, which the author terms the safe lantern, he has constructed two others on the same principle with that proposed by Dr. Clanny, and described in a late volume of our Transactions: but as that of Dr. Clanny has been found objectionable, not only on account of manual labour and constant attention necessary in working the bellows, but also on account of its size, those now proposed
