THE CONQUEST OF TIME AND SPACE 



*'It is not claimed for compound locomotives that a 

 heavier train can be hauled at a given speed than with 

 a single-expansion locomotive of similar weight and 

 class; but the compound will, at very slow speed, on 

 heavy grades, keep a train moving where a single-ex- 

 pansion will slip and stall. This is due to the pressure 

 on the crank-pins of the compound being more uni- 

 form throughout the stroke than in the case of the 

 single-expansion locomotive, and also to the fact that, 

 when needed, live steam can be admitted to the low- 

 pressure cylinders." 



Of course, the principal reason for compounding the 

 locomotive is to economize steam, and this is unques- 

 tionably accomplished; but nevertheless the compara- 

 tive economy of compound and single-expansion loco- 

 motives was for some time a mooted question. Nu- 

 merous tests have been made with these two classes of 

 engines, and the widest ranges of differences were 

 shown in many instances. In some cases the com- 

 pounds seem to show a saving of some forty per cent, 

 in fuel; but this is by no means a determinative factor 

 in the daily use of an engine. It is found that repairs 

 on the compound are more difficult to make, and con- 

 sequently more expensive than on the single-expansion 

 engines ; but on the whole it is very generally conceded 

 that the compound saves its owners from ten to twenty- 

 five per cent, over the older type. 



The rapid increase of the size, and consequent coal- 

 consuming capacity, of the modem locomotive has 

 added another problem to engineering — that of keep- 

 ing the yawning maw of the fire-box supplied with coal. 



[140] 



