A few other unsuspected causes of fire may be mentioned. A common habit with some people, when ironing, is to rub the hot iron clean with a piece of stuff, paper, or “anything” at hand, and then throw the same aside without further thought. The small piece of stuff, usually more or less scorched, may lie smouldering for hours unsuspected in some corner, especially if shut up in a cupboard or drawer. The danger here alluded to applies equally to the careless throwing aside of anything likely to smoulder, such as cloths caught up at random for holding hot baking tins, kitchener handles, &c. No room ought ever to be left unoccupied without a guard being placed on the fire. Most of us have had experience of sudden small explosions of the coals, and holes being burnt in the hearthrug, even when there is some one at hand to stamp out the fire at once; and we can imagine what the consequences would be if the hearthrug had been left to smoulder. In the case of steam-pipes, after wood has remained a long time in contact with steam, hot-water, or hot-air pipes, the surface becomes carbonised. During the warm season, the charcoal absorbs moisture. When again heated, the moisture is driven off, leaving a vacuum, into which the fresh air current circulating around the pipes rapidly penetrates, and imparts its oxygen to the charcoal, causing a gradual heating and eventually combustion. The rusting of the pipes contributes also to this result, inasmuch as the rust formed during the hot season may be reduced by the heat of the pipes to a condition in which it will absorb oxygen to the point of red heat.