MECHANiCAL IMPROVEMENTS. 



495 



ordinary conditions the common safety-valve is 

 as effectual in relieving the pressure and clos- 

 ing quickly as any of the special forms. The 

 special devices were divided into six classes: 

 reactionary, having a lip or stricture, that the 

 reaction may push the valve farther from its 

 seat; disk safety-valves, having a disk of 

 greater area than the valve-opening ; annular, 

 with two seats and an annular opening ; double- 

 seated combination safety-valve, with small 

 secondary valves, or a combination of levers ; 

 piston safety-valves, with a piston to assist the 

 valve to rise. The rule adopted by the com- 

 mittee for calculating the evaporation per hour, 

 in pounds, was as follows : Multiply the num- 

 ber of square feet of grate-surface by 112 for 

 natural draught, and by 168 for forced draught. 

 The area of valve-opening required, according 

 to the rules of the committee, for a pressure 

 of 70 Ibs., is 10 inches. (Rankine's rule gives 

 12 inches; that of the English Board of Trade, 

 11.8; Molesworth's, 18.88; the French Gov- 

 ernment's rule, 6.75 ; Thurston's 1st rule, 8.3 ; 

 his 2d, 29.) Common valves should be of 

 sufficient size, but not to exceed 10 square 

 inches ; and when a greater area is required, 

 two or more should be used. In the experi- 

 ments with the common valves, the pressure 

 gradually increased to the maximum after the 

 valve had opened, and the valve promptly 

 closed when the pressure fell to the point at 

 which it was set. Several of the special forms, 

 of larger area than the common valves, allow 

 the pressure to increase as much as or more than 

 the common valves before opening ; and nearly 

 all of them allow the pressure to fall below the 

 opening point before closing again. Of the 

 special devices Ashcroft's, Crosby's, and Rich- 

 ardson's reactionary valves gave the best re- 

 sults. For marine engines in rough weather, 

 and for locomotives, some of the special forms 

 may be employed to advantage. 



Several devices for mechanical stoking are 

 now in use in England. The Frisbie feeder, 

 and Holroyd Smith's helix stoker, supply the 

 fuel upward from the bottom of the furnace, 

 the latter continuously. The advantages of 

 this method are, that the gases and smoke are 

 consumed in passing up through the burning 

 coal. Regan's stoker, for small coal, feeds the 

 furnace from a hopper above the bars, which 

 rotate slowly. Regan's joggle-bar furnace, for 

 marine engines, permits of a constant shaking 

 of the bars, which are placed transversely, and 

 are easily removable. Henderson's stoker has 

 a hopper from which the crushed coal is thrown 

 evenly upon the fire by fans, while the bars are 

 given an oscillating motion. In Dillwyn Smith's 

 stoker two grates are placed crosswise, one 

 above the other, in the same fire, so that the 

 gases escaping from the first are completely 

 consumed in the second. In some stokers even 

 the filling of the hopper is accomplished by me- 

 chanical means. 



No important improvements have been made 

 in mechanical appliances for street-car traction. 



The use of superheated water, tried by Mr. 

 Lamm, in America, and Mr. Bede, in Brussels, 

 is attended with some difficulties, which ren- 

 der it less practicable than the other methods; 

 fireless steam locomotives have, however, been 

 in use for many months in New Orleans. They 

 are built by Theodore Scheffler, of Paterson. 

 The hot water is held in a cylinder containing 

 300 gallons; the whole weight of the engine, 

 charged, is 8,700 Ibs. The driving-wheels are 39 

 inches in diameter, and the leading- wheels 20 

 inches. The cylinders are 4$ inches in diame- 

 ter and 10 inches long. The valve-gear con- 

 sists of the main valve, which always works at 

 full stroke and controls the exhaust, and a 

 steam-valve on top which controls the admis- 

 sion; a single link works both valves. The 

 tank is charged from a stationary sectional 

 boiler, the water having a temperature of 390, 

 which gives a pressure of 220 Ibs. per square inch. 

 The engines thus charged can draw a street-car 

 with an ordinary load six miles, the final press- 

 ure being 40 Ibs. per inch. The peculiar valve- 

 gear, patented by Mr. Scheffler, regulates the 

 supply of steam by the cut-off alone, the sep- 

 arate cut-off allowing a wider range of cut-off. 

 Scott-Moncrieff's car, driven by compressed 

 air, has a valve-gear which allows the com- 

 pressed air to escape from the reservoir at a 

 constantly uniform pressure, which can be va- 

 ried at the will of the driver. The air is al- 

 ways exhausted at the atmospheric pressure, 

 which prevents the production of excessive 

 cold in the exhaust, which prevents also all 

 noise, and utilizes the power to the utmost.) 

 The reservoir and machinery are by no means' 

 bulky. On the Vale of Clyde tramway the 

 Scott-Moncrieff car performs a journey of !$ 

 miles each way at every charge of air. Me- 

 karski's compressed-air tram-car allows the 

 pressure, at which the compressed air issues, 

 to be regulated by the driver. Hot water is 

 used to keep up the temperature of the ex- 

 hausted air. A special cylinder is employed 

 in starting, and the impetus acquired in de- 

 scending grades is turned to account in pro- 

 viding additional compressed air. Mr. Lamm 

 proposes a new kind of stored-up heat. A cyl- 

 inder on the top of the car, which is filled with 

 hot water, will inclose another cylinder con- 

 taining liquid ammoniacal gas, obtained from 

 sal-ammoniac heated by the action of the hot 

 water, with hydrate of lime. The gas, thus 

 generated, passes into working cylinders, and 

 then is conducted into the hot-water chamber, 

 imparting heat, as it is absorbed, to the water, 

 which rises in temperature, instead of falling, 

 during the trip. Steam propulsion, however, 

 has on the whole proved so far the most sat- 

 isfactory for street-cars. The Granthom car, 

 in which the boiler and condensers are placed 

 in the middle of the carriage, and the cylin- 

 ders and machinery underneath, is one of the 

 most successful form yet tried. It has two 

 pairs of wheels, one pair for driving and one 

 pair provided with a radial axle for preventing 



