﻿92 



Messrs. H. T. Tizard and D. P. Pye on the 



Since the total volume remains constant, this equation can be 

 written 



kg." 



f 



P-P, 



at 



(?) 



f 



if the simple gas laws hold. P max . is here the maximum 

 compression pressure, P the observed pressure t seconds after 

 the maximum compression pressure is reached, and P/- the 

 final pressure of the gas when its temperature is the same as 

 that of the walls. P/is therefore equal to rxPi, where r is 

 the compression ratio and P x the initial pressure (in these 

 experiments one atmosphere) before compression. 



Fig. 6 is a typical cooling curve obtained when air at an 

 initial pressure of 14*73 lb. sq. in. and temperature of 

 23° C. was compressed in the ratio of 7*02 to 1. The time of 

 compression was 0*08 second, and the values of the cooling 

 factor a, obtained from observations of the fall in pressure, 

 are given in the following table : — 



Table I. 



Time after 



Observed 





P -P* 



, -""max. *-f „ 



lo s p p* ~ s - 



2-3S 



max. pressure 



pressure = P 



P-fy 



a =~T' 



(seconds). 



lb./sq. in. 





r r f 









199-7 



96-3 







•173 



185-7 



82-3 



•068 



•90 



•347 



174-6 



71-2 



•131 



•87 



•52 



165 



61 6 



•194 



•86 



•695 



158-3 



54-9 



•244 



•81 



•87 



152-4 



49 



•294 



•78 



Me? 



m=-85 





6 (initial temp.) = 





Pi = 14-73 lb./ 



23° C. 



Pf=PiX 702 =103-4. 



sq. in. 



Max. temp, (calc.) = 





299° C. 





It was found as a rule that the calculated cooling factor 

 tends to diminish as " t' 3 increases. This may be due in part 

 to errors of observation, for the errors are big when the time 

 interval after the attainment of maximum pressure is small : 

 but experimental error will not wholly account for it, and it 

 may be explained on the reasonable assumption that there is 

 a fair degree of turbulence in the gas just after a sudden 

 compression, which dies down after a short time. Potation 

 of the fan at a high speed increases the rate of cooling con- 

 siderably ; experiments with air gave a cooling factor about 



