Another cause of fire which may come under this head is the use of pipes for conveying away the products of combustion. Every one is acquainted with the danger of stove pipes, but all are not perhaps aware that pipes for conveying away the heat and effluvia from gas-burners are also very dangerous when placed near timber. It is not an uncommon practice to convey such pipes between the ceiling and the flooring of the floor above. This is highly dangerous. Gas-burners are also dangerous when placed near a ceiling. A remarkable instance of this took place lately, where a gas-burner set fire to a ceiling 28-1/2 inches from it. Another evil of furnaces is, that the original fireplace is sometimes not large enough to contain the apparatus, and the party wall is cut into. Perhaps it may be necessary to notice at this point the use of gas, as it is becoming so very general. Gas, if carefully laid on, and properly used, is safer than any other light, so far as actually setting fire to anything goes, but the greater heat given out so dries up any combustibles within its reach, that it prepares them for burning, and when a fire does take place, the destruction is much more rapid than in a building lighted by other means. Gas-stoves, also, from the great heat given out, sometimes cause serious accidents; in one instance, a gas-stove set fire to a beam through a two-and-half inch York landing, well bedded in mortar, although the lights were five or six inches above the stone. This is mentioned to show that gas-stoves require quite as much care as common fires. _Spontaneous ignition_ is believed to be a very fruitful cause of fires; but, unless the fire is discovered almost at the commencement, it is difficult to ascertain positively that this has been the cause. Spontaneous ignition is generally accelerated by natural or artificial heat. For instance, where substances liable to spontaneous ignition are exposed to the heat of the sun, to furnace flues, heated pipes, or are placed over apartments lighted by gas, the process of ignition proceeds much more rapidly than when in a cooler atmosphere. Sawdust in contact with vegetable oil is very likely to take fire. Cotton, cotton waste, hemp, and most other vegetable substances are alike dangerous. In one case oil and sawdust took fire within sixteen hours; in others, the same materials have lain for years, until some external heat has been applied to them. The greater number of the serious fires which have taken place in railroad stations in and near London have commenced in the paint stores. In a very large fire in an oil warehouse, a quantity of oil was spilt the day before and wiped up, the wipings being thrown aside. This was believed to have been the cause of the fire, but direct proof could not be obtained. Dust-bins also very often cause serious accidents. In one instance, 30,000_l._ to 40,000_l._ were lost, apparently from hot ashes being thrown into a dust-bin.