MECHANICS AND USEFUL ARTS. 11 



cylinder at a temperature of 580, and, passing through the water- 

 reservoir of a coil of pipe, heats that water to 202 before escaping 

 into the air or being reduced to water. This engine has been worked 

 for three months, and the result of various experiments are, an 

 economy of fuel of over 50 per cent., a reduction in the weight of the 

 machinery of the same amount, and security from explosion. 



MEANS OF PREVENTING THE CORROSION OF STEAM-BOILERS. 



A WRITER in the London Artisan for December, 1849, proposes to 

 effect the prevention of the corrosive action exerted by the water on 

 the interior of boilers, by applying over the whole of the inside a thin 

 coat of varnish, of such a nature that, while it would remain unaffect- 

 ed by the high temperature to which it would be exposed, it should 

 offer no serious resistance to the regular transmission of heat from the 

 iron to the water. To effect this object, he proposes to pour a small 

 quantity of coal-tar into the water just before the steam is to be got 

 up. This substance possesses the singular property, when thrown 

 into boiling water, of parting with its volatile portions, and diffusing 

 the remainder of its substance, as a hard insoluble pitch, all over the 

 interior of the vessel, thus accomplishing the object desired. 



NEW SALINOMETERS. 



THE importance of having some means of determining the exact 

 density of the water in the boilers of marine engines, at any moment, 

 is universally recognized. To effect this end various " salinometers " 

 have been invented, but a new one, by William Sewall, jr., U. S. N., 

 will probably be found the most efficient yet produced, from its con- 

 venience, little liability to clog, and the possibility of placing it in any 

 desired position. It consists of a cj^lindrical brass chamber, perma- 

 nently attached in a vertical position, having on its side near the 

 bottom two cocks, with pipes leading into the boiler, the one direct- 

 ly over the furnace-crown, the other near the bottom of one of the 

 " legs." . Either may be used, as desired, but the first is that gener- 

 ally employed. An outlet-pipe leads from the bottom of the chamber, 

 furnished with a cock, below which enters another pipe, whose mouth 

 or upper end is about half an inch below the top of the chamber ; this 

 forms an overflow. A Fahrenheit thermometer, attached securely to 

 the inner side of the chamber, and an hydrometer, graduated for saline 

 solutions containing from i to ?| (the latter being the point of satura- 

 tion), sliding freely in a guide for steadiness, complete the apparatus. 

 When in use the first cock to the boiler is always partly open, while 

 the overflow carries off the water as fast as it enters ; but when it is 

 desired to test the density, this cock is shut, until the water has cooled 

 to 200 F., when the hydrometer is read off and the current rees- 

 tablished, thus preventing saline deposits in the pipes. Journal of 

 Franklin Institute, July. 



MR. MATHER has introduced a self-acting and discharging salinome- 

 ter, which consists of a brass brine-receiving cylinder, fixed on the 



