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XLVII. Note on the Temperature and Heating-powers of Flames. 

 By W. M. Watts, D.Sc* 



HPHE April Number of the Philosophical Magazine contains 

 -L a paper by Messrs. Silliman and Wurtz on the tempera- 

 tures of names, in which certain conclusions on some practical 

 points of importance are stated. 



The following numbers are correctly given as representing the 

 amounts of heat evolved by the complete combustion of equal 

 volumes of the following gases : — 



Hydrogen 34462 



Carbonic oxide . . . 33642 



Marsh-gas 104504 



Olefiant gas ... . 166012 



But the conclusion that the heating-power of olefiant gas is 

 greater than that of an equal volume of hydrogen is condemned 

 as erroneous, and the authors give as the result of their investi- 

 gations "that the powers of the names 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." 



There seems to be throughout the paper a confusion between 

 the heating-power of a gas and the temperature of its flame in air. 



It is quite true that, because the specific heat of steam, which 

 is one of the products of combustion of olefiant gas, is greater 

 than the specific heat of carbonic anhydride (the only product 

 of combustion of carbonic oxide), the calculated name-tempera- 

 ture of the latter gas is higher than that of the former ; but, for 

 the very same reason, if these gaseous products of combustion 

 expend their heat in raising the temperature of water, the great- 

 est effect will be produced by the olefiant gas, although the tem- 

 perature of its flame is not so high as that of the flame of car- 

 bonic oxide. If the gases give up the whole of their heat to the 

 water, it is obvious that the calorific effects must be precisely in 

 the ratio of the numbers already quoted ; and even if they escape 

 at a temperature considerably above 0° C, their relative effects 

 will be nearly the same. If we suppose the products of com- 

 bustion to have a temperature of 200° C. when they escape, the 

 following quantities of heat will still be available by the combus- 

 tion of equal volumes of carbonic oxide and olefiant gas : — 



^ , Pounds of water raised 

 Gas burnt ; from 0° C. to 100 c C. 

 14 lbs. Carbonic oxide .... 314 

 14 lbs. Olefiant gas 1546 



And these numbers are almost exactly in the same ratio as the 



* Communicated by the Author. 

 Phil. Mag. S.4. Vol. 39. No. 262. May 1870. Z 



