288 PHILIP DAWSON 



If superheaters are used in the boiler flues, economizers 

 are not much good. If a separate superheater is used the 

 cost of extra fuel, interest, maintenance, and sinking fund 

 must be taken into account in considering economy in steam 

 and coal. 



In Great Britain, superheated steam is generally only 

 used with the idea of getting absolutely dry steam at the 

 engines and doing away with the bother always caused by 

 steam traps and separators. Consequently economizers are 

 much used, and it is undoubtedly a fact that for compound 

 condensing plants, economizers, when used in connection 

 with mechanical stokers, give the best results. 



Cooling towers and cooling ponds for condensing water 

 are much in vogue on the continent. In America cooling 

 towers are also used as designed by Worthington-Wlieeler 

 Condenser company, and others, but with the difference 

 that mechanical draft is created by the use of fans, whereas 

 continentals build their towers of wood and of sufficient 

 height to create a sufficient draft. 



It is curious to note that in the case of the Berlin Elec- 

 tricity works, where the greatest care has been taken owing 

 to the cost of coal (over 20 shillings a ton) to reduce fuel 

 consumption, and where in view of the size of the plants 

 small economies would soon mount up, the engineers in 

 charge of these stations have stated to the writer that after 

 careful tests they find it cheaper to stoke by hand, which they 

 do in all their stations. British experience, which is con- 

 firmed by American practice, is to use mechanical coal and 

 ash conveyors, in conjunction with weighing machines over 

 each boiler, and to employ exclusively mechanical stoking. 



The waste heat engine being experimented with in Ber- 

 lin is an entirely novel departure, and as it is being taken 

 up by the AUgemeine Elektricitats Gesellschaft on a com- 

 mercial scale, I shall say a few words about it. Speaking 

 broadly, the principle of this engine is as follows: — The ex- 

 haust steam from a steam engine is condensed in a surface 

 condenser, which uses, instead of water as in the ordinary 

 way, some liquid of a very low boiling point. The heat of 

 the exhaust steam evaporates the cooling liquid and the vapor 



