64 Professors Ayrton and Perry on the 



Table VI. — Dowson Gas after Combustion, 





2- 



o p . 



0„. 



qCP. 



qC v . 



Water-vapour . . . 

 Carbon dioxide ... 

 Nitrogen 



0-2019 

 03279 

 1-3845 



•2984 

 •3307 

 •2870 



1-36 x '168 

 1*55 „ 

 1 



•0602 

 •1084 

 •3281 

 •4967 



•2746 x -168 

 •5083 „ 

 1-3845 „ 

 2-1674 „ 





Total 



1-9143 







•2594 



L-1323X-168 

 or -1902 







Ratio 





1-3637. 









The specific heats here given are those of the constituents 

 in the cold state. Seeing, however, that there is no great 

 change due to combustion, we may for many practical pur- 

 poses assume that the specific heats remain the same at all 

 temperatures. We have less right when using Dowson gas 

 than when using cool-gas to make our assumption, which is 

 that the fluid in the gas-engine, from the beginning of its 

 compression until it is allowed to escape, behaves like a perfect 

 gas, receiving heat from an outside source. 



4. Study of the Shapes of the Compression and Expansion 

 parts of the Diagram. — The first problem which comes before 

 us is the determination of the shape of the indicator diagram. 

 For the sake of illustration we mean to investigate the series 

 of diagrams shown in fig. 1, diagrams taken from a 6-horse 

 power Otto engine at the Finsbury College^ using coal-gas. 

 It will be observed that, although the ignition parts of the 

 various diagrams differ greatly, on account of differences in the 

 amounts of gas supplied, the curves agree in their compression 

 and expansion parts. It is known to us that the clearance- 

 space is 0*4 of the whole space occupied by fluid when the 

 piston is fully at the end of its stroke. If X is the distance in 

 feet passed through by the piston from the end of its stroke, 

 the stroke being 1J foot, the clearance is 0*889 foot, and 

 X-r-0'889,, or I feet expresses the volume of the fluid at 

 any instant. Measurements of I and p were made on the 

 expansion-curves of the indicator-diagrams, and tabulated 

 with log I and log p. 



We are making arrangements for measuring the clearance- 

 space with accuracy. The above assumption is made from 

 statements of the manufacturers, and may possibly be slightly 

 in error. Such an error is of but small importance to us at 

 present, as our object is to teach a method of study rather 

 than to give results of the use of the method. 



