b ON THE HEAT EVOLVED 



heat in its combustion, than an equal weight of dry char- 

 coal."* 



By the expression " dry vegetable flesh," the count means 

 to indicate that portion of dry wood which is inflammable, or 

 that part which is independent of the charcoal. Now I find, 

 by the most favourable comparison for this portion of the 

 wood, that an equal weight of dry charcoal, produces 286 

 per cent, more heat than the former, and by the least favour- 

 able comparison, 314 per cent, more, giving a mean difference 

 of 300 per cent, in favour of the charcoal. 



It will be proper to state what has been considered as 

 essential requisites to the perfection of the apparatus, that, as 

 the description proceeds, the degree of accuracy which it is 

 likely to possess, may, with greater facility be determined; 

 and this will be done under three heads, with explanatory 

 remarks. 



1st. That the apparatus in which the combustion is produced, 

 be so constructed, that all, or an equal proportion of all the 

 heat generated, may be measured by some unchanging standard. 



This is effected in a manner to be hereafter more particu- 

 larly described, but it may now be sufficiently understood, by 

 referring to the plate, in which the apparatus and the interior 

 of the room, constructed for performing the experiments, are 

 shown in perspective. At E is a thermometer, the bulb of 

 which is in the centre of the stove-pipe, and another, Fig. 6, 

 is suspended from the side wall of the room. 



When articles are submitted to combustion in the stove, the 

 heat is so completely given out by the pipe, that these two 

 thermometers, indicate exactly the same degree of tempera- 

 ture. 



Strictly speaking, we cannot say even in this case, that all 

 the heat generated is imparted to the air of the room. That 

 small portion which is included in the air of the pipe, and passes 

 off into the chimney, does not impart its heat to the air of the 

 room, both being of the same temperature, consequently, no 



• Nicholson's Journal, XXXV. 112. 



