All About Engines

336 All About Engines combustion takes place mainly in the first third of the length of the tube, and so much heat is abstracted from the gases by the material with which the tube is packed in the last two-thirds, that the temperature at the point of exit is only 300 higher than that of the steam in the boiler. More than 92 per cent, of the total heat produced is communicated to the water, as compared with 75 per cent, in the case of the best type of ordinary boiler, and it can be made in sizes to compete with the largest of them. The Bonecourt Boiler Co., moreover, claim that it occu- pies less than one-ninth of the space required by Lancashire boilers evaporating the same quantity of water per hour, though this does not allow for the space required if producers had to be installed. A single tube only 6 inches in diameter will burn over 900 cubic feet of town’s gas per hour and produce 400 lb. of steam from and at 2120 F. in the same time. The saving, as compared with ordinary boilers, depends upon the nature of the fuel used. Town’s gas is generally expensive, gas from blast furnaces and coke ovens is cheap and would otherwise run to waste, and Mond gas is cheap if the bye-products are recovered. So that there are many cases in which the full advantage of 15 per cent, to 18 per cent, in the efficiency of these boilers would be gained. It is not possible, however, for manufacturers to scrap their plant every time an improvement is placed on the market, and these boilers will be more readily adopted in iron and steel works which have an ample