45, CORNHILL, E.G., AND 122, EEGENT STREET, W., LONDON. 



175 



417 Negretti and Zambra's Saturometre or Thermometrical Salinometer for 

 determining the amount of Salt held in solution in the water of Marine Boilers. 



It is well known that pure water boils at 212 Fahr. at the level of the sea, and 

 if water is impregnated with salt, the point of ebullition is materially raised ; hence 

 the water in a marine boiler can be accurately tested as to its saline properties by 

 observing at what temperature the ebullition is taking place within the boiler. The 

 apparatus consists of a metal reservoir attached to the boiler by a stopcock, R, and 

 union joint, B ; this reservoir carries a thermometer. T, whose bulb, A, reaches nearly 

 to the bottom of the chamber ; the graduations on the scale commence at 212, the 

 boiling point of pure water. At the bottom of the reservoir is an outlet tap, S, and 

 there is also a tap, X, inserted a little above the bottom of the reservoir, with a tube 

 connected with it reaching nearly to the top of the interior of the reservoir. 



The apparatus is used as follows : the reservoir having been emptied by the 

 tap S, it should be closed, and the taps R and X opened ; the water from the boiler 

 will then flow into the chamber A, partly fill it, and pass out by the pipe and tap X. 

 After the water has been allowed to escape for a few seconds, the thermometer is to 

 be examined, and according to the temperature indicated so will be the specific 

 gravity of the water in the boiler, or, in other words, the percentage of salt dis- 

 solved in it. This fact is quickly and conveniently ascertained by simply opening 

 three taps and reading the thermometer (fig. 416) . . . . 440 



Our table in connection with the description and use of Salinometers (page 189) 

 will give the relative degrees of Saltness and Temperature. 



Messrs. Negretti and Zambra very strongly advise the use of the Thermonietric 

 Pressure Gauges (No. 409) in conjunction with the Mercurial and Spring Gauges 

 as a comparative and precautionary measure of safety. When steam is generated 

 and confined in a boiler, the pressure upon the boiling water may be twice or thrice 

 that of the atmosphere. Experimentally it has been found, that if the pressure in 

 the boiler be 251bs. on the square inch, the temperature of the boiling water, and of 

 the steam likewise, is raised to 241 ; and under the exhausted receiver of an air- 

 pump, water will boil at 185, when the pressure is reduced to 17 inches of mercury. 

 The following table, compiled by Dr. A. S. Taylor, gives the relative temperatures 

 and pressures up to 12 atmospheres or 180 Ibs. pressure. 



Water boils. Barometer 30 inches. 

 320 degrees Fahr. 6 Atmospheres. 

 327 6'5 



Water boils. Barometer 30 inches. 



212 degrees Fahr. 1 Atmosphere. 



234 1-5 



251 2 332 7 ' 



267 2-5 337 7'5 



275 3 342 8 



285 3-5 



295 4 ., 359 10 



300 4-5 368 11 



307 5 374 12 



315 5-5 



ON COMBINED STEAM. By the Hon. J. WETHERED. 



" In its passage through the super-heating apparatus a portion of steam is raised by the 

 waste heat to a temperature of 500 or 600 Fahrenheit. The heat thus arrested is conveyed 

 to and utilised in the cylinders by its action on the other portion of the steam from the 

 boiler, which is more or less saturated, according to circumstances. The combined steam is 

 used in the cylinder at from 300 to 450 Fahrenheit, at which steam is generally employed, 

 The effect of using the two kinds of steam is, that the super-heated steam yields a portion of 

 its excess of temperature to the ordinary steam, converting the vesicular water which it 

 always contains into steam, and expanding it several hundred-fold ; whilst at the same time, 

 the ordinary steam yields a portion of its excess of moisture, converting the steam gas into 

 a highly rarefied elastic vapour in other words, into pure steam at a high temperature." 



