44 CALORIFIC POWER OF FUELS. 



The fuze is lighted, and the whole quickly put in the jar of 

 water. The mixture of combustible and potassium chlorate 

 soon ignites and burns, all the gases generated being forced 

 out at the bottom of the bell through the perforations, and 

 bubble up through the liquid. After the combustion is finished 

 the temperature is taken and the heat-units calculated. 



From 8 to 10 parts of oxidizing mixture is recommended 

 for one of coal; but if the coal is very rich this must be 

 increased to 1 1 parts, calculated on the crude coal. With 

 pure coal, cinders out, the extreme limits are 1 1 and 14 parts. 

 It would probably increase the accuracy of the method, if 

 the same quantity of oxidizing mixture was employed, what- 

 ever the kind of coal used, and to mix with it inert substances, 

 as silica or ground porcelain, in quantity varying with the 

 richness of the coal. 



Scheurer-Kestner tested this apparatus very carefully, 

 using a great variety of fuels whose heats had been previously 

 ascertained by means of Favre and Silbermann's calorimeter. 

 He found some 15 per cent deficit in the figures, and after 

 correcting by this amount the results varied only a few per 

 cent from those actually obtained. In thirty different kinds 

 of coal tested the average was 1.8 per cent too low. 



The use of this calorimeter requires some skill. Its imper- 

 fect insulation requires prompt reading and rapid combustion. 

 Care must be taken to work at temperatures very close to 

 that of the room, as the calorimetric bath is not protected. 

 The proportions of the mixture used vary, not only with each 

 kind of coal, but for each sample, on account of the propor- 

 tions of cinders. Fat coals require more oxidizer than lean 

 coals, as it is evident an increase in quantity of cinders should 

 require a decrease in oxidizer. But in changing the propor- 

 tions of oxidizer a certain difference in elevation of tempera- 

 ture is necessarily produced by the heat of solution of the 

 salts left after the combustion. These various causes render 

 its working rather delicate, and always uncertain. 



