250 Mr. G. J. Parks on Heat Evolved or 



the term -=-' which appears in the foregoing theoretical 



investigation. The same powder was used throughout, and 

 the results are tabulated in calories per gramme as well as in 

 calories per sq. cm., so that the data should be equally useful 

 whatever be the hypothesis advanced. 



The thermometers used in these experiments gave a range 

 of temperature from 5° C. to 25° C; hence the range over 

 which experiments could be made was rather less than 20° C. 



It was found necessary to modify the apparatus so that the 

 calorimeter could be kept for some hours at constant tempe- 

 rature above that of the atmosphere. The cylindrical copper 

 vessel in which the calorimeter was suspended was closed by 

 a tightly fitting copper lid, under the rim of which was tightly 

 packed an indiarubber ring which had previously been 

 stretched around the top of the vessel. Into the copper lid, 

 two copper tubes about two inches long were soldered ; 

 through one of these tubes the bulb of the thermometer 

 could be put into the calorimeter, and through the other passed 

 the handle of the crushing instrument. Thus the bulb could 

 be crushed and the liquid stirred and the temperature observed 

 without opening the vessel. The copper vessel was now 

 immersed in several gallons of water, the top of the lid being 

 about an inch below the surface. This water was kept at 

 approximately constant temperature for several hours, during 

 which time the bulb containing the powder was immersed in 

 the water in the calorimeter, so that there could be no doubt 

 about the powder and the water being at the same temperature. 



This apparatus proved so satisfactory that it was finally 

 adopted in the later experiments at the lower temperature, 

 instead of the arrangement previously described. 



In the first eight experiments the mean temperature was 

 about 7°*1 C. and the mean heat evolved was 7*18 calories per 

 gramme, or '00105 calorie per sq. cm. In the last eight 

 experiments, the mean temperature was about 24°* 3 C. and 

 the mean heat evolved was 7*55 calories per gramme or 

 •00111 calorie per sq. cm. 



Tl 1 ' f djk 'Q 0006 .rWWV^ 



The mean value of -7- = , „ ,» — 000003 1>. 

 at It I 



The mean value of - = ^^ = '0000037. 



T loO I 



Hence, roughly speaking, ^ = -.and h varies as t, that is 



the heat evolved is roughly proportional to the absolute 

 temperature. 



