496 



FUEL 



1001 



mercury would have equal capacities, since the same quantity of heat would produce 

 in an equal mass of these two substances equal changes of temperature, viz., an eleva- 

 tion of 90 in the water and a depression of 90 in the mercury. But in reality, the 

 mixture is found to have a temperature of only 37$, showing that while the mercury 

 loses 17H , the water gains only 5i; two numbers in the ratio of about 32 to 1 ; 

 whence it is concluded, that the capacity of mercury is ^ of that of water. Correc- 

 tions must be made for the influence of the vessel and for the heat dissipated during 

 the time of the experiment. 



If our object be to ascertain the relative heating powers of different kinds of fuel, we 

 need not care so much about the total waste of heat in the experiments, provided it be 

 the same in all ; and therefore they should be burned in the same furnace, and in the 

 same way. But the more economically the heat is applied, the greater certainty will 



there bo in the results. The apparatus, fig. 

 1004, is simple and well adapted to make such 

 comparative trials of fuel. The little furnace 

 is covered at top, and transmits its burned air 

 by c, through a spiral tube immersed in a cis- 

 tern of water, having a thermometer inserted 

 near its top, and another near its bottom, into 

 little side orifices, a a, while the effluent air 

 escapes from the upright end of the tube b. 

 Here also a thermometer -bulb may be placed. 

 The average indication of the two thermo- 

 meters gives the mean temperature of the 

 water. As the water evaporates from the cis- 

 tern, it is supplied from a vessel placed along- 

 side of it. The experiment should be begun 

 when the furnace has acquired an equability 

 of temperature. A throttle valve at c serves 

 to regulate the draught, and to equalise it in the different experiments by means of 

 the temperature of the effluent air. When the water has been heated the given 

 number of degrees, which should be the same in the different experiments, the fire may 

 be extinguished, the remaining fuel weighed, and compared with the original quan- 

 tity. Care should be taken to make the combustion as vivid and free from smoke as 

 possible. 



The following calorimeter, founded upon the same principle as that of Count Kum- 

 ford, but with certain improvements, may be considered as an equally correct instru- 

 ment for measuring heat with any of the preceding, but one of much more general 



1005 



, 2 





Scale about \ inch to the square foot. 



application, since it can determine the quantity of heat disengaged in combustion, as 

 well as the latent heat of steam and other vapours. 



It consists of a large copper bath, c,f(fig. 1005), capable of holding 100 gallons of 

 water. It is traversed four times, backwards and forwards, in four different levels, 



