STEAM BOILER 331 duction in the modified form of sectional boil- ers. The earliest water-tubular boilers were those of Voight, Rumsey, and Fitch, and were invented and known as "pipe boilers" as ear- ly as 1785. One of these, consisting of a " col- lection of long pipes bent so as to cross each Longitudinal Section. Cross Section. FIGS. 5 and 6. Marine High-Pressure Boiler. other like the worm of a still," was used in one of John Fitch's boats in 1788 ; another form was adopted in the Babcock, built by John Babcock and R. L. Thurston in 1825. (See "American Journal of Science," March, 1827.) Where steam pressure exceeds about 30 Ibs. to the square inch in marine boilers, they are now usually given the form shown in sec- tion in figs. 5 and 6. This form of boiler is adopted where steam pressures of 60 Ibs. and upward are carried, as in steam vessels sup- plied with compound engines, cylindrical forms being considered the best with high pressures. The large cylindrical flues, therefore, form the furnaces as shown in the transverse sec- tional view. The gases rise, as shown in the longitudinal section, through the connection, and pass back to the end of the boiler through the tubes, and thence, instead of entering a steam chimney, they are conducted by a smoke connection, not shown in the sketch, to the smoke funnel or stack. In merchant steamers, a steam drum is often mounted horizontally above the boiler. In other cases a separator is attached to the steam pipe between boilers and engines. This usually consists of an iron tank, divided by a vertical partition extend- ing from the top nearly to the bottom. The steam, entering the top at one side of this partition, passes un- derneath it, and up to the top on the op- posite side, where it issues into a steam pipe leading directly to the engine. The sudden reversal of its course at the bottom vided into a large number of small compart- ments, and it becomes thus comparatively easy to secure a large "factor of safety," the tubes of ^ which such boilers are usually composed being capable of sustaining many times the pressure proposed to be carried within them. The boilers are composed either of a series of water tubes, of such tubes at- tached to larger reservoirs containing water or steam or both, or of a collec- tion of spherical vessels. The earliest real sectional steam boilers were proba- bly that used by Col. John Stevens of Hoboken, on the Hudson river, in 1804, and another which was patented in Great Britain in June, 1805, by his son John Cox Stevens. The first boiler is shown in fig. 7. The inventor says in his speci- fications: "The principle of this inven- tion consists of forming a boiler by means of a system or combination of small vessels, instead of using, as is the common mode, one large one ; the relative strength of the materials of which these vessels are com- posed increasing in proportion to the diminu- tion of capacity." The steamboat boiler of 1804 was built to bear a working pressure of over 50 Ibs. to the square inch, at a time when the usual pressures were from 4 to 7 Ibs. It consists of two sets of tubes, closed at one end by solid plugs, and at their opposite extremi- ties screwed into a stayed water and steam reservoir, which was strengthened by hoops. The whole of the lower portion was enclosed in a jacket of iron lined with non-conducting material. The fire was built at one end, in a furnace enclosed in this jacket. The furnace FIG. 7. John Stevens's Sectional Boiler, 1804. causes it to leave the suspended water in the bottom of the separator, whence it is drained off by pipes. Sectional steam boilers are a class of tubular boilers which differ from or- dinary forms in their peculiar arrangement of water and steam space. These spaces are di- gases passed among the tubes, down under the body of the boiler, up among the opposite set of tubes, and thence to the smoke pipe. In the second form, as applied to a locomotive in 1825, the tubes were set vertically in a double circle surrounding the fire. These boilers are
