HE VIEW OF FEED-WATER TESTS. 261 



IV. ECONOMY OF CONDENSING. 



It is held, in the popular mind, that the economy of con- 

 densing is, in round numbers, 25%. This percentage usually 

 relates to simple engines, and it refers to the economy as meas- 

 ured by the difference in the coal consumption produced by 

 a condenser. The evidence of some of the tests here given 

 shows that this belief is not well founded, unless it be in 

 special cases. The economy due to condensing ought to be 

 reckoned on the basis of coal consumption, and not alone on 

 the basis of feed-wator consumption; because a non-condensing 

 engine is usually accompanied by a feed- water heater, and some 

 of the loss of economy produced by running non-condensing is 

 made up by the saving of coal due to warming the feed-water. 

 If the feed-water is heated by the exhaust steam of the non-con- 

 densing engine from a temperature of 100, which is that of the 

 ordinary hot well, to a temperature of 210, the non-condensing 

 engine can be credited with about 11% less coal consumption. 

 This matter should properly be taken into account when con- 

 sidering the economy produced by a condenser. 



In the list of simple engines, a number of comparisons are 

 made on the same engine when carrying the same load, one 

 test being made with the engine condensing and the other 

 non-condensing. In the case of Engine No. 10, where such a 

 comparison was made, the feed-water consumed when running 

 non-condensing was 25.64 Ibs. per I. H. P. per hour, and when 

 running condensing, 20.51 Ibs., the difference being 5.13 Ibs., 

 or 20% of the larger quantity. In Engine No. 17, which 

 was tried in the same manner, the consumption running non- 

 condensing was 28.93 Ibs., and condensing, 22.08 Ibs., the 

 difference being 6.85, or 24% of the larger quantity. In 

 Engine No. 20, a similar test was made ; and the consumption 

 in one case was 30.16 Ibs., and in the other 23 Ibs., the dif- 

 ference being 7.16 Ibs., or 24% of the larger quantity. The 

 average of these three comparisons gives a saving produced 

 by condensing of 22.3%. If we allow for the steam or power 

 used by an economical condenser, it will be seen that the net 



