14 CALORIFIC POWER OF FUELS. 



EVALUATION OF THE CALORIMETER IN WATER. 



Before using a calorimeter its equivalent in water must be 

 determined; that is, we must calculate to what quantity of 

 water it corresponds in terms of specific heat. This is to 

 be added to the weight of water employed and includes the 

 combustion-chamber, cylinder, and the immersed pieces, 

 thermometer, supports, etc. 



Below is given an example showing the calculation of the 

 value in water of a Favre and Silbermann's calorimeter: 



Copper, 1145.651 grams at 0.09516 specific heat = 109.008 grams. 



Platinum, 22.810 " "0.0324 " " = 0.706 



Value in water of the chamber and accessories = 109.714 " 

 Thermometer, weight of glass immersed, 12 grams at 0.198 = 2.400 " 

 Mercury, 63 " " 0.332 = 2.070 " 



Total equivalent of water = 114.184 " 



which added to the 2 kilograms of water in the bath makes a 

 total of 2114.184 grams of water. 



The calorimetric weight for the Berthelot bomb at the 

 College of France in 1888 was 398.7 grams for bomb and 

 accessories. 



The water value of the calorimeter used by Lord and Haas 

 at the Ohio State University, Columbus, O., was determined 

 as 465 grams. Mahler's apparatus had a water equivalent 

 of 481 grams. Still, it is better to determine this equivalent 

 by actual experiment, as we are not sure of the specific heat 

 of the metal of the bomb, which might, however, be deter- 

 mined by a sample taken from the original block of which it 

 was made. 



Several methods may be employed for this. 



When we use the calorimetric bomb, we burn in the obus, 

 using 2000 grams of water, a known quantity of a substance 

 of fixed composition, and of which the heat .of combustion 

 is known, as sugar, or naphthalin. We then use less water 

 and burn a smaller quantity of the substance. If I gram of 

 substance was taken the first time, we may take 0.8 gram with 

 1800 grams of water the second time. We then have two 



