"I find it will not explode, if mixed with less than six times, or more than fourteen times its volume of atmospheric air. Air, when rendered impure by the combustion of a candle, but in which the candle will still burn, will not explode the gas from the mines; and when a lamp or candle is made to burn in a close vessel having apertures only above and below, an _explosive mixture_ of gas admitted _merely enlarges_ the light, and then gradually extinguishes it without explosion. Again,--the gas mixed in any proportion with common air, I have discovered, _will not explode_ in a _small tube_, the diameter of which is less than 1/8th of an inch, or even a larger tube, if there is a mechanical force urging the gas through this tube. "Explosive mixtures of this gas with air require much stronger heat for their explosion than mixtures of common inflammable gas.[29] Red-hot charcoal, made so as not to flame, if blown up by a mixture of the mine gas and common air, does not explode it, but gives light in it; and iron, to cause the explosion of mixtures of this gas with air, must be made _white_-hot. "The discovery of these curious and unexpected properties of the gas, leads to several practical methods of lighting the mines without any danger of explosion. "The first and simplest is what I shall call the _Safe lamp_, in which a candle or a lamp burns in a safe lantern which is air-tight in the sides, which has tubes below for admitting air, a chamber above, and a chimney for the foul air to pass through; and this is as portable as a common lantern, and not much more expensive. In this, the light never burns in its full quantity of air, and therefore is more feeble than that of the common candle. "The second is the _Blowing lamp_. In this, the candle or lamp burns in a close lantern, having a tube below of small diameter for admitting air, which is thrown in by a small pair of bellows, and a tube above of the same diameter, furnished with a cup filled with oil. This burns brighter than the simple safe lamp, and is extinguished by explosive mixtures of the fire-damp. In this apparatus the candle may be made to burn as bright as in the air; and supposing an explosion to be made in it, it cannot reach to the external air. "The third is the _Piston lamp_, in which the candle is made to burn in a small glass lantern furnished with a piston, so constructed as to admit of air being supplied and thrown into it without any communication between the burner and the external air: this apparatus is not larger than the steel-mill, but it is more expensive than the other, costing from twenty-two to twenty-four shillings. "These lamps are all extinguished when the air becomes so polluted with fire-damp as to be explosive.