in their Relations to Composition and Luminosity. 293 



is actually the fact, that, within certain limits, the waste of heat 

 due to this cause alone counterbalances altogether the advantage 

 that would be supposed to result from the crowding of combus- 

 tible matter into so condensed a form as in the illuminating hy- 

 drocarbons. An inevitable result of our investigations of this 

 matter is, that the powers of the flames of pure hydrogen 

 and pure olefiant gas, even when used to the greatest advantage, 

 to heat water below its boiling-point are almost or quite identical. 

 In this discussion we have occasion to use the numbers repre- 

 senting the specific heats of but three gases (the three, namely, 

 which remain after complete combustion) — steam, carbonic acid, 

 and nitrogen — as we must assume that in the hottest and most lu- 

 minous zone or shell of the flame there is no oxygen in excess to be 

 heated. These three numbers are, according to Regnault's latest 

 determinations, for equal weights of 



Steam 0-4805 



Carbonic acid . . . 0*2163 



Nitrogen 0-2438 



[Liquid water being . . 1-0000) 

 This means that the amounts of heat which would raise one 

 pound of water and steam to the same degree are in the ratio of 

 0*4805 for the pound of steam, and 1 for the pound of water. 



Calculation of the Calorific Effect of Hydrogen burning in Air, 



Let us take, first, the simplest case possible, that of hydrogen 

 with exactly the right admixture of pure oxygen to burn it, 

 which, by Table I., developes a total heat of 34462° C. ; that is, 

 would heat a certain weight of liquid water to this temperature. 

 In order to find the actual amount of heat contained in the pro- 

 ducts of combustion, we must first take into account the fact that 

 one pound of hydrogen burns to nine pounds of steam, and then 

 obtain the ratio between the above number (34462), and the 

 amount of heat necessary to heat nine times the weight of steam — 

 that is, nine times the specific heat of steam. Calling the total 

 residual heat in the produced steam x, we have the simple pro- 

 portion : — 



9 x (specific heat of steam = 0-4805) : 34462 : : (specific heat of 



water =1) \x, 

 or 



^= 34462° = 7969° C.* = 14376° F. ; 

 4-3245 



* Bunsen, in his 'Gasometry' (English edition of 1857, p. 242), gives 

 this number as 8061° C, the difference being due to the use by him of a 

 different number for the specific heat of steam, namely 0'475, apparently 

 an earlier determination of Regnault. Bunsen makes here the singular 



