138 STEAM BOILERS 



Use of Trisodium Phosphate. For decomposing sulphate of 

 lime, tribasic sodium phosphate, more commonly known as 

 trisodium phosphate, is often used. This is claimed to act on 

 the sulphate of lime, forming sulphate of sodium and phos- 

 phate of lime, the former of which remains soluble and is 

 harmless, and the latter of which is a loose, easily removed 

 deposit. Trisodium phosphate also acts on carbonate of lime 

 and carbonate of magnesia, forming phosphate of lime and 

 phosphate of magnesia, at the same time neutralizing the car- 

 bonic acid released from the carbonate of lime and magnesia, 

 and the sulphuric acid released from the sulphates. 



Neutralization of Acids. Acid water can be neutralized by 

 means of an alkali, soda probably being the best one. The 

 amount of soda to be used can best be found by trial, adding 

 soda until the water will turn red litmus paper blue. 



Purification by Heat. Carbonate of lime and sulphate of 

 lime become insoluble if the water is heated, the former pre- 

 cipitating at about 212 P. and the latter at about 290 P. 

 This fact is taken advantage of in devices that may be called 

 combined feed water heaters and purifiers; as they generally 

 use live steam, they are also called live-steam feed-water heaters. 

 Since no feedwater heater can effect a direct saving on fuel 

 except when the heat is taken from a source of waste, it follows 

 that a live-steam feedwater heater can affect the fuel con- 

 sumption but indirectly. This it does by largely preventing 

 the accumulation of scale in the boiler and the attendant loss in 

 economy due to the lowering of the rate of heat transmission 

 through a plate heavily covered with incrustation. 



Economy of Heating Feedwater. The feedwater furnished 

 to steam boilers must of necessity be raised from its normal 

 temperature to that of steam before evaporation can commence, 

 and if not otherwise accomplished, it will be done at the expense 

 of fuel that should be utilized in making steam. At 75 

 Ib. gauge pressure the temperature of boiling water is about 

 320 P., and if 60 is taken as the average temperature of feed- 

 water, 320- (50 = 200 B. T. U. is required to raise 1 Ib. of water 

 from 60 to 320. It requires 1,151.5 B. T. U. to convert 

 1 Ib. of water at 60 into steam at 75 Ib. gauge pressure, so 

 that the 260 B. T. U. required for heating the water represents 



