MECHANICS AND USEFUL ARTS. 27 



cylinder, 66 per cent of the steam formed in the boiler was condensed in 

 the cylinder; and when both the cylinder and valve-chest were immersed 

 in steam of the boiler temperature, 30 per cent of the steam was condensed 

 in the cylinder. The process by which this large amount of condensation 

 takes place is supposed to be this. When the steam is cut off and begins 

 to expand, a portion of its heat is consumed in the performance of work ; 

 or, if the expression is preferred, it is cooled by expanding. This cooling 

 causes a portion of the steam to be condensed into water, which is depos- 

 ited in a fine dew all over the inner surface of the cylinder. It will be 

 borne in mind that this condensation takes place under pressure. There 

 is not heat enough in the cylinder to keep all of the water evaporated un- 

 der the pressure that is actually exerted. When the piston has, finished 

 its stroke the exhaust port is opened, and the pressure upon the watei 

 clinging to the interior surface of the cylinder the pressure that held it 

 in the liquid .state is removed, and this water immediately flashes into 

 steam. In this change a portion of the heat required to convert the steam 

 into water is absorbed from the walls of the cylinder, thus cooling the 

 walls, and preparing them to repeat the process of condensation at the 

 next stroke. 



The proof of this condensation is found in the indicator cards, where 

 the line of pressure falls below, not merely the curve of the Marriotte 

 law, but also below this curve when corrected for the heat consumed in 

 the performance of work. And that the same process takes place in 

 engines generally ma) be learned by a careful examination of the numer- 

 ous cards taken from those engines. 



It will be observed that the condensation takes place on the steam 

 side of the piston and thus diminishes the working pressure, while the 

 re- evaporation occurs when the exhaust port is open, and when the 

 steam formed in the cylinder, if it exerts any pressure at all, exerts a 

 back pressure on the piston. Thus the condensation and the re-evapo- 

 ration are b >th injurious in their operation. 



It is manifest that if the inner surface of the walls of the cylinder 

 could be kept sufficiently heated, no water could be deposited upon 

 them, and thus this process of condensation and re-evaporation would be 

 prevented. The plan devised by Mr. Waterman to keep the inner sur- 

 face of the cylinder hot, is to make the walls very thin, and to surround 

 them with steam of the boiler temperature. In the experimental en- 

 gine the walls are of steel one-tenth of an inch in thickness, and the en- 

 gine is being tried first with hot steam around the cylinder, and then 

 under the same conditions with only a jacket of confined air. 



Should i he fact of the large condensation above referred to, be estab- 

 lished, it will prove a very important matter in the construction and 

 working of engines. 



STEAM ENGINE ECONOMY. 



" A patent case has been recently tried at Washington, U. S., 

 which has elicited certain statements so remarkable in their bearing 

 on the system of steam engine construction adopted of late in the 

 American Xavy, that we cannot pass it without notice. The case in 

 question is simple enough in itself. A Mr. Mattingly, of Washing- 

 ton, sued a steamboat company for a share of the savings effected by 

 a peculiar form of cut-off valve, the patent right in which he held, 



