In arranging sites for the fire companies, the principle pursued is to distribute small companies with different appliances over as wide an area as possible, instead of concentrating men and appliances at certain central points. By thus placing companies separately, it is believed that a larger area is served in the same time than by concentrating them together. On the occurrence of large fires, when many companies are called out, distant companies are called from various points, like reserves, to take the places of some of those in action, to meet calls that may arise in the same districts; while at some stations, or company houses, the men are divided into two sections with duplicate apparatus, so that, while one responds instantly to the first call, the second at once prepares to answer any subsequent alarm. Among the apparatus used is the jumping-sheet, designed as a last attempt to save life; circular rope nets some 15 feet in diameter being carried on the tenders and trucks in New York; while their canvas sheets have rope handles. Light chemical fire-engines are also largely used in small places and in the suburbs of large cities, the lightness of the machine being, no doubt, a great recommendation. An efficient pattern is the double-tank engine, one tank of which can be replenished while the other is being discharged. The tanks contain a mixture producing carbonic acid gas, which is a great foe to fire. The gas is absorbed by water, and as it expands causes a great pressure, sufficient to force the fluid through hose, and throw it a distance of about a hundred and fifty feet. When the water reaches the flames, the gas held in solution is liberated by the heat and chokes the fire. The mixture will not freeze, even when the temperature falls to zero; it is thus always ready. The machine is light, and contains its own propulsive force for the water; so that we cannot wonder it is widely adopted. Similar apparatus throws hydrochloric acid and ammoniacal gases, but opinions differ as to their utility; for though efficient fire-quenchers, yet a small portion only of the gas appears to be carried by the fluid and actually reaches the flames. Another piece of apparatus is a hose-hoister. For using hose on very high buildings, and also, indeed, for hoisting ladders to great heights, a simple appliance has been devised, consisting essentially of a couple of rollers in a frame; the rope, of course, runs over the rollers to hoist the hose, but the frame is shaped to adjust itself to the coping or cornice of the wall.