REVIEW OF FEED-WATER TESTS. 271 



per hour was 2%. Both of these are cases where the ratio 

 of area of the two cylinders was unusually large, and the 

 re-heating surface in the receiver was also unusually large, 

 being sufficient to superheat the steam that passed into the 

 low-pressure cylinder. Whatever value jacketing and re-heating 

 may have in a compound engine, it may be reasonably expected 

 that it would show to the best advantage where the expansion 

 is carried to the greatest extent ; and . consequently the condi- 

 tions of these two cases are as favorable to a good showing for 

 the jackets as they could be in most engines of the compound 

 type. It would appear then, that 2% is the most that can be 

 expected for the saving of steam due to jackets and re-heaters 

 in ordinary compound engines of the types referred to. 



There are none of the tests of the other compound engines 

 which furnish much actual data on the subject ; but it may be 

 said that the superficial indications of the results of the tests 

 where the engines are jacketed, furnish little ground for the 

 belief that jacketing had much effect upon the economy. Take 

 the case of Engine No 58 A, which had no jackets, but which 

 was fitted with a re-heating receiver. The consumption of 

 feed- water was 13.21 Ibs. per I. H. P. per hour, and this is 

 lower than any result given where the engine was provided 

 with jackets. No doubt the unusually tight condition of the 

 valves and pistons in this case had a favorable effect; but if 

 jacketing is necessary for good economical results and the 

 advantage it produces is a marked one, its absence in Engine 

 No. 58 should have produced a much more noticeable effect. 



Beyond the saving in steam consumption produced by jack- 

 ets, which in Engines No. 47 and 53 amounted to 2%, there 

 is a further saving in fuel which cannot be overlooked, which 

 may be obtained by returning the hot water condensed in the 

 jackets to the boilers. The temperature of this water is 

 ordinarily about 300, and its quantity on the tests noted 

 was 7.7% in one case, and 11% in the other, averaging 

 9.3% for the two. If the temperature of the main supply 

 of feed- water is 100, the return of this water to the boilers 

 would add about 19 to the temperature of the feed-water, 



