STEAM BOILER preserved in the collections of the Stevens in- stitute of technology, Hoboken. Walter Han- cock constructed boilers for his steam carriage of flat plates connected by stay bolts, several such sections composing the boiler ; and about the same time (1828) Sir Goldworthy Gurney constructed for a similar purpose boilers con- sisting of a steam and a water reservoir, placed one above the other, and connected by trian- gular water tubes exposed to the heat of the furnace gases. Jacob Perkins made many ex- periments looking to the employment of very high steam pressures, and in 1831 patented a boiler of this class, in which the heating sur- faces nearest the fire were composed of iron tubes, which tubes also served as grate bars. The steam and water space was principally comprised within a comparatively large cham- ber, of which the walls were secured by close- ly distributed stay bolts. For extremely high pressures boilers composed only of tubes were used. Dr. Ernest Alban about 1843 repro- duced the boiler described in the patent of John Stevens (1805), and published a work on " The High-Pressure Steam Engine," in which he described its construction and operation, and declared that he had experimented with pres- sures as high as 1,600 Ibs. to the square inch (which pressure Perkins also attained), at which point the temperature of the steam was suf- ficiently high to char slightly the hemp pack- ing of his engine. The Harrison steam boiler, which has been many years in use in the Uni- ted States, consists of several sections, each of which is made up of hollow globes of cast iron communicating with each other by necks cast upon the spheres, and fitted together with faced joints. .Long bolts, extending from end to end of each row, bind the spheres together. (See fig. 8.) An example of another modern type FIG. 8. Harrison's Sectional Boiler. in extensive use is given in fig. 9, which con- sists of a series of inclined wrought-iron tubes, connected by T heads, which form the vertical water channels, at each end. These tubes are "staggered," one row being placed immediate- ly above the space between two rows below it. The joints are faced by milling them, and then ground so perfectly tight that a pressure of 500 Ibs. to the square inch is insufficient to produce leakage. No packing is used. The fire is made under the front and higher end of the tubes, and the products of combustion pass FIG. 9. Babcock and "Wilcox's Sectional Boiler. up between the tubes into a combustion cham- ber under the steam and water drum ; hence they pass down between the tubes, then once more up through the space between the tubes, and off to the chimney. The steam is taken out at the top of the steam drum near the back end of the boiler. The rapid circulation pre- vents to some extent the formation of depos- its or incrustations upon the heating surfaces, sweeping them away and depositing them in the mud drum, whence they are blown out. Rap- id circulation of water, as has been shown by Prof. Trowbridge, also assists in the extraction of the heat from the gases, by the presentation of fresh water continually as well as by the prevention of incrustation. A sectional steam boiler like that illustrated in fig. 8 is one of the best examples of this class of steam generator. It is immensely stronger, is fairly economical of fuel, and is durable when properly managed. The sudden introduction of a large volume of cold water, which is liable to produce leaks from some of its numerous joints, is the most serious injury to be apprehended. It is almost absolutely safe from explosion, and should a globe explode, the danger to its surroundings is comparatively slight. The disadvantages of this type are the small amount of water and of steam room, which causes a difficulty in se- curing regularity of steam supply, and makes necessary very careful and skilful management. In the boiler illustrated in fig. 9 the last objec- tion is avoided by the use of the large steam and water drum. Some additional risk is thus incurred ; but, as the flames are inter- rupted by the numerous tubes interposed be- tween the drum and the fire, the liability of injury to the drum is too slight to be con- sidered. Attempts have been made to adapt sectional boilers to marine engines ; but very little progress has yet been made in their in- troduction. The Root sectional boiler, an American design, which is in extensive use in the United States and Europe, has been exper- imentally placed in service on shipboard. Its
