268 ENGINE TESTS. 



with similar provisions in regard to jacketing. This method 

 may be interesting and valuable for scientific research ; but for 

 practically showing the advantages of compound engines, it is of 

 little importance, because one of the principal objects in com- 

 pounding is to enable the economy due to large expansions and 

 high pressures to be obtained without the sacrifice which such 

 expansions produce when carried on during the single stage 

 which occurs in one cylinder. The nearest approach to a com- 

 parison of this kind, derived from the tests reported, is that of 

 compound Engine No. 32, which w r as made with a boiler pres- 

 sure of 94.8 Ibs. Here the engine was unjacketed, and no 

 provision was made for re-heating between the cylinders. If 

 we compare this with the very best result obtained from a 

 simple condensing engine, that of No. 22, there appears, even 

 under these circumstances, a marked difference in favor of the 

 compound engine. These figures are 18.49 for the simple 

 engine, and 16.28 for the compound; and the difference is 2.21 

 Ibs., or about 12%. Comparing this, a^ain. with simple Kiiinnc 

 No. 28, which is running at 70 Ibs. pressure on a consumption 

 of 19.45 Ibs. of feed- water per I. H. P. per hour, the difference 

 is 3.17 Ibs., or 16.3%. 



A fairly satisfactory comparison between compound engines 

 and simple engines, where no jacketing or re-heating is pio- 

 vided, can be made by using compound Ku^ine NO. :-56. This 

 engine was jacketed; but the jackets were not drained, and 

 consequently, under the circumstances, they were ineffective. 

 In this engine the consumption of feed-water was 14.0"> Ibs. 

 per I. H. P. per hour when running at a pressure of 106. <S Ibs. 

 If we compare this Avith No. 28, simple engine, the difference 

 is 5.4 Ibs., or 27. S' , . 



A general comparison between the compound and simple 

 engines may be made Avithout regard to the matter of pressure 

 or the use of jackets and re-heaters, and without regard to the 

 quality of the steam, omitting the three engines which have an 

 excessively high ratio of cylinder areas. The engines selected 

 are those of the Corliss or other 4-valve type. Such a compari- 

 son is made in the following tables. 



