The smoke-stack g is placed over the forward cud of the furnace, as shown in Fig. 17, causing the products of combustion, after passing through the spaces 10, to travel in the opposite direction toward the forward end of the furnace, as indicated by the dotted arrows in Fig. 17, the tubes being thus exposed to the action of the heat. This arrangement is another important feature of the invention, A baffle-plate or deflector, 71, is placed across the upper portion of the furnace, just in the rear of the smoke-stack, as shown in Fig. 17, which causes the products of combustion to take a downward course, as indicated by the dotted arrows, before reaching the smoke-staek, and prevents the too direct escape of the products of combustion, and causing the same to act more fully upon the water in the tubes. The products of combustion pass to the stack through the openings formed between the tubes .fand the latter being raised above t he tubes f forward of the deflector h, as shown in Fig. 17, leav ing spaces between the hor izontal portions of the tubes f and fs of sufficient width to permit the passage of the smoke and gases to the stack. The ends of the steam-drums arc connected with the ends of the water drums by the pipes i for the return of water from the Me:lin-drums to the water drums. These return pipes are loeated outside of the easing s, is is shown in Fig. 15, and are not subjected to the heat within the easing ; hence the descent of water through the return pipes to the water-drums is facilitated. Baffle-plates shown in Fig.
10, are attached to the upper portions of the steam-drums at opposite sides of the perforated dry-pipes which extend through the drums, and are connected outside of the drums with pipes which conelnet the steam to the engine. The water-drums are protected from contact with the fuel by the fire-brick linings ne, and the transverse eonneet Mg pipes a'' are protected by similar• linings. ne. The water-drums net also as mml-drums. and have suitable blow-off cocks and hand-holes to allow the removal of the deposits. The f', 111'0 expancb•d in the drums and pipes by special tools devised for this purimse. The adoption
of Iwo Sh'11111-11111111,4, not only makes the boiler syinmetrieal. but it gives a greater height of ['trump in proportion to the total height of boiler than could be obtained with one 41111111; and the water eapaeity is increased so that. as sudden lowering of water-level in the boiler when the supply of feed-water is interrupted is prevented, Non-rowthrriing Coverings for Boilers, ete.—W, Hepworth Collins, in Engineering, Sept. 4, 1891, deseribes some experiments he made on different non-conducting coverings for steam boilers. A mass of each material to he experimented upim. 1 in. thick, was carefully prepared and placed on a perfeetly flat iron plate or tray. whitili was then carefully maintained at a constant temperature of 310' P. The heat transmitted through each non-conducting 111555 was calculated in pounds of wider heated 10° P. per hour. The following table gives the results : Horse-Power of Boilers.—The committee on standard boiler trials of the American Society of Mechanical Engineers, in their report made in 1884, adopted as the unit of boiler horse power the same that had been previously adopted by the Committee of Judges of Steam-Boilers at the Centennial Exhibition, in 1870, viz., an evaporation 30 lbs. of water per hour from a feed-water temperature of 100' F. into steam at 70 lbs. gauge pressure, "which shall be con sidered to be equal to 344 units of evaporation—that is. to 34/ lbs. of water evaporated from a feed-water temperature of 212° F. into steam at the same temperature. This standard is equal to 33,305 thermal units per hour." code of Rules for Boiler-'lests.—In 1884 a committee of the American Society of Mechan ical Engineers, consisting of Prof. 1L II. Thurston and Messrs. J. C. Iloadley, Charles T. Por ter. Charles E. Emery, and William Kent, presented an elaborate report on a Standard Method of Steam-Boiler Trials, in which they included the following code of rules and system of re porting the results of a trial, which have met with general acceptance among engineers in the United States :