AMERICAN INSTITUTE. 485 



Jittlc difference whether the steam be more or less dense within the limits 

 found in practice. Hence an increase of pressure will allow a reduction of 

 steam room and water-levol. 



Thus we see considerable changes in the proportions of boilers. The 

 standard boiler, that succeeded the early boilers, has a small grate, and 

 little fire-box surface, and much flue-surface. The recent boilers, more 

 like the early ones, have a large grate, large fire-box surface, and moderate 

 Sue-surface, It must be observed that a high pressure is used in the new 

 boilers — double that of the early ones ; the effect of which is to keep the 

 steam comparatively dry. 



Dryness of steam is acknowledged to be highly important; and, within 

 a few years, in locomotives aind marine engines, means have been applied 

 to dry it, or superheat it. Penn & Sons, of Greenwich, claim that they 

 have saved thirty per cent, of the fuel by it ; and the Allaire works claim 

 that twenty per cent, is saved by their steam chimneys. Sharp, Stewart & 

 Co., of Manchester, have used the steam chimney, and McConnell has 

 used a water-heater, both with a saving of fuel. 



Let us now consider the upright multiflue boiler, in reference to these 

 changes. It has a large grate — much larger than the standard locomotive 

 boiler, but not larger than the recent examples. It has a large flue area, 

 to pass the smoke, which is advantageous ; and its flues pass through the 

 steam room, and serve to dry steam, which is claimed to be advantageous ; 

 and a large fire-box is got, without much inconvenience, simply by making 

 it as deep as is required. The fire-box in this boiler has usually beeu 

 made shallow, so that there has not been sufficient room for combustion, 

 and the fire has been too near the tube-joints, and burned them, especially 

 when the crownsheet becomes foul; but a depth of thirty to thirty-six 

 inches, instead of twelve to eighteen, will make a proportion more like 

 that of the recent locomotive boilers, and will place the crownsheet farther 

 from the fire, and a greater depth may be adopted if expedient. 



It has been objected that the flues passing through the steam room, will 

 be burned at the upper ends. I have inquired as to the fact, and have not 

 found direct evidence of it ; on the contrary, Mr. Secor states that the 

 steam chimney lasts as long as the fire-boxes. And Mr. Smith, of the New 

 Jersey Locomotive Works, says that they repaired an old locomotive boiler, 

 whose flues had become imbedded in a solid crust, so that no water could 

 reach them, and yet they were in tolerable condition. From all that I can 

 learn, this objection is not sustained by facts. The only fact unfavorable 

 to this boiler, which I have found is, that the incrustation upon the crovrn- 

 sheet, when the water is foul, soon causes it to burn out. It is, therefore, 

 necessary to keep it clean. 



The height of this boiler has sometimes been too great for locomotive 

 purposes — eight feet is not unfrequent. Six feet is as high as is allowable 

 for carriages, and five -and a half is better. In recent examples, the tubes 

 have been made two feet long, and in some cases fifteen inches. The steam 

 fire-engine boilers, built in Lawrence and Manchester, have 199 tubes, two 



