95 



In the choice of motors for this work the steam engine has heretofore been 

 used, especially where the units are relatively large. An interesting example of 

 this is noted in the sugar refinery of Claus Spreckles, in Philadelphia, in which 

 there are some seventy live Westinghouse engines about the works, many of them 

 being of 75 and 100 horse-power. 



A similar subdivided plant involving forty-two engines was erected several 

 years ago at the print works of the Bunnell Company. Pawtucket, R. I. More 

 recently, however, the electric motor has superseded the steam engine for this 

 work, as its economy and convenience over the latter is now thoroughly recognized. 



For isolated machines and for heavy machines that may be in occasional use 

 the electric motor is particularly well adapted as a source of power, for such a 

 means of transmission consumes power only when the machine is in operation. 



This is true also of compressed air, and we tind numerous instances where it 

 has entirely replaced steam even in large work. Thus, at the steel works at 

 Terni, Italy, a 100-ton hammer is worked by compressed air, and also two large 

 cranes, one having a capacity of 100-tons and the other 150 tons. Compressed air 

 in some cases is also superseding steam for operating pumping machinery. 



In Paris, according to Prof. Unwin, compressed air motors are even used to 

 drive dynamos for electric lighting. At some of the newspaper offices there are 

 motors of 50 and 100 horse-power driving presses, and in shops and factories 

 these motors are used to run lathes, saws and various other machines. 



In the transmission of air, within reasonable limits, the loss in transmission 

 need not be considered, for although there is a slight loss in pressure due to the 

 frictional resistances of the pipes, yet there is a corresponding increase in vol- 

 ume due to fall in temperature, so that the loss is practically inappreciable. 



In the compression of air, with steam actuated compressors, there are various 

 sources of loss, which, in the aggregate, will vary from 25 to 45 per cent, of the 

 total power of the machine. 



The greatest loss of efficiency is that injhe air motor. It is usually imprac- 

 ticable to reheat the air with any degree of economy when employed intermit- 

 tently, and we find very generally that the air is used at normal temperature for 

 the various purposes to which it is applied. In small motors (1 to 2 horse-power) 

 the loss may be as much as 65 per cent, when the air is used without expansion. 

 With larger motors (75 horse-power), using a reheater and hot air jackets, the 

 motor loss has been kept within 20 per cent, at full load. 



These results and others would indicate that compressed air as now used is 

 not at all efficient as a source of motive power, since the combined efBciency of 

 compressor and motor, even under favorable conditions, is not more than 50 per 



