10 ON THE HEAT EVOLVED 



introduced after its first construction, to provide a space for tht 

 purpose of heating the air as much as possible before coming 

 in contact with the burning body, by which the quantity 

 remaining unconsumed is reduced from two ounces to less than 

 half an ounce. That portion which remains unconsumed after 

 an experiment, including the small particles which drop through 

 the apertures of the chambers into the ash pit, are washed Upon 

 a sieve to remove the ashes and any other foreign matter, and 

 when thoroughly dried in a crucible, are weighed and deducted 

 from the original weight. 



In making up the results of experiments in which charcoal 

 is used to ignite the body, from the resulting time is deducted 

 so much as is known by previous experiment to have arisen from 

 a portion of charcoal equal in weight to that used. Those 

 bituminous coals which fuse and cake in the process of coaking. 

 are the most troublesome to manage in small quantities, from 

 the inconstant manner in which the bituminous part burns, and 

 its tendency to become extinguished the moment that portion 

 is consumed ; the combustion of the bitumen not producing 

 the heat of ignition required by the carbonaceous part to con- 

 tinue the process of combustion, and the surface being partially 

 covered with the deposite from the pyrites, becomes more dif- 

 ficult to ignite, and requires to be broken asunder to present a 

 fresh surface. To overcome this difficulty, it was found neces- 

 sary to use the coal in very small pieces, and occasionally to 

 take from the stove such parts as had coaked, break them in 

 pieces, and return them to the stove as required, which, when 

 ignited, will burn permanently, and the heat required to coak 

 the remaining part of the coal is thereby produced. During 

 tedious experiments, the operator is sometimes under the ne- 

 cessity of passing from the interior to the exterior room, but if 

 done with proper caution, the differential thermometer is never 

 affected thereby. 



The animal heat imparted to the air of the room by the 

 operator, must be noticed. This, under ordinary exertion of 

 the muscles, being equal both in temperature and quantity, as 

 determined by Dr. Crawford, and being the same during the 



