MECHANICS AND USEFUL ARTS. 61 



The result is a rapid production of steam, stead}" increase of 

 pressure, in a boiler containing steam free from water and water 

 free from steam. Should a rupture take place, the result is a 

 simple relief of pressure, without any explosive or disastrous re- 

 sults. This arrangement is favorable to economy of fuel and pre- 

 vents injury to the boiler, as all the heat is at once absorbed by 

 the thin stratum of water. To prevent loss of heat from the sub- 

 sidence of sediments from the water, he introduces into cylindrical 

 and flue boilers a curved, trough-like apparatus, which gives di- 

 rection to the circulating currents and arrests the sediments. 



The Hicks Boiler. In this boiler, Mr. James M. Hicks claims 

 to overcome the objections to the ordinary form of tubular boilers, 

 namely, that for want of a proper circulation the sediment collects 

 upon the most important heating surfaces, and the water is not 

 returned to the bottom in a continuous. and stead} 7 current. The 

 boiler is cylindrical, upright, in the common form, with the usual 

 outer shell, supported on hollow legs, forming the sides of the 

 fire-box; from the lower tube-sheet rise the tubes, connected 

 above with the upper tube-sheet, and opening directly into the 

 smoke-pipe. Within the shell, and separated by a narrow space, 

 is a circular iron drum surrounding all the tubes, and extending 

 from near the lower tube-sheet to just below the proper water- 

 line, and kept in place by stays ; this divides the water among the 

 tubes from the water near the shell of the boiler. Over this, ex- 

 tending from just above the water-line to within half an inch of 

 the upper tube-sheet, is an iron cone, fitting at its lower edge the 

 inside shell of the boiler, to which it is fastened : this forms a 

 steam-chamber, into which the steam can pass only by going over 

 the top of the cone. 



The water directly over the fire is of course first heated, and 

 rises inside over the top of the drum, delivering its steam, its 

 place being supplied by the descending colder water on the out- 

 side of the drum, thus establishing a current up the middle and 

 down the sides, rapid in proportion to the intensity of the heat. 

 This circulation secures an even temperature in the water, and' 

 carries upward all the bubbles of steam which tend to adhere to 

 the steam-making surfaces. The steam rises pure into the cone 

 and is there further dried, without being superheated, and is 

 collected in the steam space outside of the cone pure, whence it is 

 conveyed by the steam-pipe to the engine. By this circulation all 

 the heat is utilized, with great economy of fuel, and all dirt and 

 sediments are deposited in the legs of the fire-box where the 

 water is the most quiet, and whence it may be blown off by a 

 tube below the surface of the grate ; this effectually prevents in- 

 crustation, as ample experience with salt and very dirty water 

 proves. It also prevents foaming, and generates steam rapidly. 

 He has applied this principle of construction to horizontal and 

 locomotive boilers. 



GAS STEAM-GENERATOR. 



The trial of Mr. Jackson's system of generating steam by gas, 

 6 



