HO ON THE HEAT DETELOPED IN COMBUSTION, 



be sufficiently thin, and well dried, I have found, that any 



kind of wood may be burned cbmpletety* 



Management j u burning candles, wax tapers, or fat oils in lamps, 

 of candles and . , ,. ,, . . 



lamps. *be only precautions necessary are so to arrange the wick, 



* as to yield no smoke; to place the flame properly in the 

 aperture of the worm ; and to surround the apparatus on 

 all sides by screens, to prevent the flame from being 

 deranged by the wind. 

 Source of er- In these experiments there is one source of errour, too 

 ai^coolh' 11 the °kvious to escape the most superficial observer, and to 

 receiver, which it was important to attend. While the calorimeter 



is warmed by the heat developed in the combustion of the 

 inflammable substance, which is burning at the aperture 

 of the worm, it is continually cooled by the ambient air, 

 that surrounds it on all sides. It would be possible, 

 no doubt, by calculations founded on a knowledge of 

 the law of refrigeraticTi of the receiver, which might be 

 found by separate experiments, to ascertain the quantity 

 of the effect produced by the refrigeration in question ; and 

 this even with a certain degree of precision : but it would 

 have been impossible by this method, or by any other 

 known, to calculate the effects of another cause of errour, 

 less obvious perhaps, but certainly more weighty, than 

 that of the refiigeration of the external surface of the 

 receiver, 

 and from the The nitrogen, which is mixed with the oxigen of the 

 p^'j^" 02 " 1 " atmospheric air, is necessarily carried into the worm with 

 the proper products of the combustion ; and without a 

 precaution, which it occurred to me to employ to prevent 

 the effects of this cause of errour, by making a compen- 

 sation for them, all the experiments would have been of no 

 value. 



Fortunately the method 1 employed to obviate the effects 

 of this cause of errour was sufficient, to prevent at the 

 same time those, that might have arisen from the cooling 

 of the outer surface of the receiver. 

 Method of ob • As the receiver is cooled, whether by the atmospheric 

 viatmg ot . a j r j n cm ,t ac t vvith its external surface, or by the nitrogen 

 and other gasses traversing the worm with the products 

 of combustion, only so far as the worm is hotter than the 



surrounding 



