ARTICLE 1. We parpose to present a few brief articles on this interesting and very important Bubject. They will contain considerable information that is new, and much which, although old, is useful, and known to but a limited number. In Vol. VI!., SCIENTIFIC AMERICAN, we published a series of articies illustrated with engravings of almost every kind of steam boiler and furnace. To go over the same ground again would be a work of supererogation. We intend principaily to present information not hitherto given, especially some new views which seem to be gaining countenance among engineers in relation to effective heating surfaces and the draft of furnaces. We will first give the substance of a very interesting paper which was rMently read before the Manchester (Eng.) Philosophical Society, by Mr. J. Graham, on the subject of evaporation in boilers, in which the results of several experiments were described. H@ first made a set of experiments with small vessels of equal size, the fire being placed under the first, and the fire-bed passing under all the others, The evaporative power of the first vessel was equal to 100, the second to 27, the third to 13, and the fourth to 8, A second set of similar experiments were made with like results upon larger boilers. He also made quite a number of experiments on evaporation with large working boilers, and these were extended over a period of several years, observations on them being made daily, and recorded, with remarks deduced from the results obtained. The boilers were all set and put in the best possible condition for securing superior working advantages as regards the admission of air, the draft of the chimney, the size of the fire place, the distance of furnace bars from the boiler, the thickness of the furnace bars, the form of the flame bed, flues and fire bridges, and the thickness of fire under the boiler. Each experiment was of twelve hours duration, and from thirty to forty were made with each boiler, one of which was altered and set thirty times to vary the experiments. A perfect command was maintained over the draft of each, and the temperature at the bottom of the chimney was generally 612 Fah., sufficient to melt lead. First—A "butterfly boiler," 25 feet long and 7 feet in diameter, under ordinary circumstances, evaporated with one pound of coal 8.29 pounds of steam, with feed water at 60; with warm water at 212, it evaporated 9.69 pounds. Second—A James Watt " wagon-shaped boiler," 25J feet long and 6J feet in diameter, under similar circumstances, and with the same weight of coal, evaporated 8.08 pounds of steam, with cold feed water, and 10.26 pounds with hot water feed. Third—The plain cylindrical boiler, 42 feet long and 6 feet in diameter, with fire-place underneath, uncer the same conditions, evaporated 6.20 pounds, and 7.23 pounds of steam. Fourth—The cylindrical boiler, with two internal fire places, joined in one internal flue, and called "the breeches boiler," 23 feet long and 8 feet in diameter, evaporated under like conditions 5.90 and 6.88 pounds of steam—all to one pound of coal. It was found that a supplementary boiler for heating the feed water, under favorable circumstances, effected a saving of 15 per cent in fuel. Flues round a boiler when cleaned out weekly, and the sides of the boiler scraped, effected a saving of 2 per cent. The difference betrsen a good shaped boiler ptoperly set, and a bad shaped boilei 1mproperly set, but both kept clean, amounted to 42 per cent. The difference between good and careful fireing and bad fireing amounted to 13 per cent. Neither wet coal, nor coal out of the mine for three years, were found to produce any different results. Windy weather was generally favorable ; a difference of atmospheric temperature from 40 to 70 did not produce different results. A comparatively thick hot fire, with a good draft, gave a much better result than a thin fire. Coals from the same mine were found to differ in evaporative quality to about 6 per per cent. When the steam was employed for heating water in such vessels as soapmaker's and dyer'S kettles, the higher the pressure of the steam, the greater was the effect. With the steam at a pressure of 2J pounds, considering (according to Mr. Graham) the effect equal to 100; with a pressure of 7 pounds, its effect was equal to 120; and with a pressure of 10 pounds, the effect was 130, the same quantity of coal being consumed in each case. This is a very surprising result, and if correct, it amounts to this :—When steam under pressure is employed, as it is very extensively in heating vessels, such as sugar pans, c. the same weight of coal consumed in the same number of hours will heat under 2J pounds pressure of steam, 10 vessels ; at 7 pounds pressure, 12 vessels ; at 10 pounds pressure, 13 vessels—all of equal size. Little or no saving is effected by great length of flue, especially if it is coated with soot, and no advantage of any consequence. is secured by very long boilers, one four times the length of the fire-box is more efficient than one longer. Considerable depends on the form of the boiler, and the genius of James Watt, even in his form of boiler, was shown— its evaporating power being superior to the ethers experimented with.
This article was originally published with the title "Steam Boilers and Furnaces"