MECHANICS AND USEFUL ARTS. 45 



the boilers, and in its turn into the steam-chest, after becoming super- 

 heated. When the two portions reunite, the combined steam is at a very 

 high temperature some four hundred degrees higher than usual. The 

 movement is given to the engine in the ordinary way, but with a vastly 

 increased force. 



A series of experiments, made under the direction of Mr. Collins, is 

 said to have established the economy of this process, in respect to fuel the 

 savings in which is said to be about 70 per cent. By burning six hundred 

 and sixty-six pounds of coal an hour, the simple steam gives nineteen and 

 three-tenths double strokes of the piston per minute ; whereas the combined 

 steam gives twenty and one-tenth, with four hundred and forty pounds of 

 coal only. 



The Journal of the FranJdin Institute for April, 18-54, contains a 

 report from Mr. Isherwood, Chief Engineer United States Navy, on the 

 proposed new plan of Messrs. Wethered. The claim in the patent obtained 

 by them, reads as follows : " What ice claim as new is, the combining steam, 

 and super-heated^ or surcharged steam for actuating engines, token generated^ 

 the elasticity increased, and operated as set forth." From this claim, says 

 Mr. Isherwood, it will be seen, that the patent does not intend the use of 

 steam simply surcharged by heat ; that is to say, having a higher tempera- 

 ture than is normal to the same pressure of saturated, or ordinary steam ; 

 but it intends the use of a mixture of saturated and surcharged steam. I 

 prefer these terms of saturated and surcharged steam to those of hydrous 

 and anhydrous steam, or to those of steam and stame, because they are 

 proper and their meaning already understood ; ordinary steam being 

 saturated with water, or of maximum density for the pressure ; and sur- 

 charged steam being ordinary steam surcharged with heat, having less than 

 the maximum density for the pressure, and therefore not being saturated 

 with water. 



The idea of the patentee is, that if a certain quantity of saturated steam 

 be withdrawn from the boiler, and heated (out of contact with water) to 

 a high abnormal temperature, then mixed with a certain quantity of satu- 

 rated steam, and this mixture used to actuate the engine, a greater power 

 can be derived from it with a given weight of fuel than could be derived 

 from the use of saturated steam alone, generated by the same weight of 

 fuel. 



The mode of obtaining the "mixture" for practical use is very simple, 

 and as follows, viz. : from the steam- chimney, or drum of the boiler, an 

 usual steam-pipe, furnished with the necessary stop-valves, conveys exter- 

 nally from the boiler, the saturated steam to the valve- chest ; another similar 

 pipe, with stop-valves, etc., from, the same steam- chimney or drum, but 

 starting within the smoke- chimney, conveys saturated steam down the 

 smoke- chimney, through the flues and through the furnaces, passing 

 immediately over the incandescent fuel, and then having become highly 

 surcharged in its passage, it is led out of the front of the boiler to the same 

 valve- chest, where it is mixed with the saturated steam. From the valve- 



