72 Professors Ayrton and Perry on the 



the cylinder. This is largely expended in heating the cylinder 

 itself, in friction at bends in the exhaust-valve, ccc. ; so that it 

 disappears as radiated heat, and as heat given to the water- 

 jacket during the remaining parts of the cycle. Now we may 

 safely take it that the expenditure of gas is about 22 cubic 

 feet per hour per indicated horse-power; so that, using the 

 heat of combustion calculated in Table I., the total energy of 

 combustion of the gas used is 5*91 W ; and we are now in a 

 position to make the following table. Of the 5*91 W, the 

 total energy of combustion of a charge, we have : — 



1*38 W. Work of forward working-stroke till exhaust- 

 valve opens. 



0*14 W. Work of forward working- stroke after exhaust- 

 valve opens. 



2*31 W. Heat given to the cylinder during forward work- 

 ing stroke by radiation before exhaust-valve 

 opens*. 



0*14 W. Heat of combustion after exhaust-valve opens 

 and which is radiated to the cylinder. 



1*57 W. Heat carried off by gases in exhaust-pipe. 



0*37 W. Given to the cylinder as heat after the exhaust- 

 valve opens, partly by friction at the exhaust- 

 valve, partly during the succeeding three fourths 

 or non-working parts of the cycle. 



It is found by experiment that the water from the water- 

 jacket carries off somewhat more than 50 per cent, of the total 

 heat of combustion, or 2*96 W; but it is almost impossible to 

 make this measurement accurately for one cycle. It is some- 

 times as much as 62 per cent, and sometimes as little as 35 

 per cent. We have not employed such a measurement here, 

 partly for this reason, and partly on account of the rate of loss 

 during three fourths of the cycle being indeterminate. Again, 

 the cylinder loses heat by radiation as well as by the water- 

 jacket; so that, even if we could assume that such a number as 



* It may be well to state here that we do not know with certainty the 

 amount of gas used per indicated horse-power when the particular diagram 

 which we are discussing was being taken, nor are we quite sure that 

 Mr. Clerk is right in saying that the exhaust-gases show complete 

 combustion when the engine is working to its full power. Our 

 arrangements for determining this latter point are now nearly complete. 

 We consider that there was no possibility of the expenditure having been 

 less than 20 cubic feet per hour per indicated horse-power when our dia- 

 gram was taken ; and if we take 24 as a higher limit, and assume with 

 Mr. Clerk that combustion is complete in the exhaust-pipe, we find the 

 amount of heat given to the cyliDder during the forward-working stroke 

 by radiation before the exhaust-valve opens could not have been less than 

 1-77 W, the higher limit giving 2-85 W. 



