New Improvements on Sfeajn-Engines. 127 



always acts on the upper side of the piston. For single en- 

 gines, oil, or wax, or fat of animals, or similar substances, 

 in sutficient quantity, will answer the purpose, if another 

 improvement, which constitutes part of my said invention, 

 be applied to the engine, namely, to take care that in either 

 the double or single engine so to be worked, the outlet that 

 conveys the steam to the condenser shall be so posited, and 

 of such a size, that the steam may pass without forcincr 

 before it or carrying with it any of the metal or other sub- 

 stance employed, that may have passed by the piston ; takino- 

 care at the same time to provide another exit for the metal or 

 other substance collected at the bottom of the steam vessel 

 or working cylinder to convey the same into a reservoir 

 kept at a proper heat, whence it is to be conveyed to the 

 upper side of the piston by a small pump worked by the 

 engine or by any other contrivance. In order that the fluid 

 metal or metals used with the piston may not be oxidated, 

 I always keep some oil or other fluid substance on its sur- 

 face, to prevent its coming in contact with the atmospherej 

 and to prevent the necessity of employing a large quantity 

 ot fluid metal, I generally make my piston of the depth of 

 the colurau required, but of a diameter a little less than the 

 steam vessel or working cylinder, excepting where the pack- 

 ing or other fitting is neccssarv to be applied; so that, in 

 fact, the column of fluid metal forms only a thin body round 

 the piston. In some cases I make a hollow metallic' piston, 

 and apply an altitude of fluid metal in the inside of the 

 same, to press its outside into contact with the steam vessel 

 or working cylinder. 



" It may be necessary, however, to state, that in apply- 

 ing my improved method of ktcping the steam vessels of 

 steam-engines at any required temperature to the engine 

 known by the name of Savary's, in any of its improved 

 forms, in which a separate condenser has been iiitroduced, 

 I sometimes employ oil (or any other substance lighter than 

 %vater, and capable of being kept fluid in the temperature 

 employed, without being converted into vapour,) in the 

 upper part of the tube or pipe attached to the steam vessel; 

 by which means steam of any temperature may be used 

 without being exposed to the risk of paitial condensation 

 by the admission of any colder body into the steam vessel ; 

 for the oil, or other substance employed for this purpose, 

 soon acquires the requisite temperature; and t& prevent 

 unnecessary escape of heat, I construct of, or line with, an 

 nnperfect conductor of heal, that ]iart of the tube or pipe 

 attached to the steam ve.ssel which may not be heated cx- 

 3 tcriorly. 



