328 /. LeConte on the Injiuence of Sola?' Light on Combustion. 



imental researclies of Mr. David Waldie, in relation to the mix- 

 ture of various gases with air, led him to the general law, that, 

 *' Of incombustible gases which remain undecomposed, the power 

 of preventing combustion is in the order of their density : ' and 

 that, *' This effect of density in cooling the flame depencb on the 

 excessive diffusion of the flame in the denser gas."^ Under or- 

 dinary circumstances, the density of the aqueous vapor existing 

 in the air is comparatively small^ so that, according to Mr. Wal- 

 die's law, its influence on combustion ought not to be very stri- 

 king. It is very desirable that this point should be submitted to 

 a more rio;orous experimental investimtion. 



CJ JL Civ f 



Having discussed the probable influence of the three external 

 conditions on the rate of combustion, we are, in a measure, pre- 

 pared to investigate their adequacy to explain the variations in 

 the rapidity of hurning^ as indicated by the experiments which I 

 have brought forward. In none of them, have we the observa- 

 tions necessary for ascertaining the hygrometric condition of the 

 atmosphere: this must, therefore, be thrown out of considera- 

 tion. In Dr. M'Keever\s experiments, the larometric indications 

 are not given ; neither is it known how many of them were per- 

 formed on any one day. In my experiments, as well as in those 

 of Mr. Mitcliell, we are furnished with the data requisite for es- 



As- 



m 



timating the combined influence of pressure and temperature 

 suming, with Sir H. Davy, that the rapidity of combustion is i 

 the direct ratio of the density of the air^ we may submit these two 

 effects to a quantitative estimation, by using Mariotte's law and 

 Regnaulf s coefficient of expansion for air, 



1. Presuming that each set of experiments made by Dr. M'Kee- 

 ver, alternately in the dark and in the sunshine, were performed 

 on the same day^ and therefore under identical barometric condi- 

 tions, we may form some estimate of the adequacy of tempera- 

 ture to account for the difference in the rate of burning observed 

 by him. The subjoined table, w^hich I have constructed from 

 the data previously given, will place this in a clear light. 



Expt. 



Temp. 

 Dark. 



67^ F. 



^ ■ ^ ' »■ ^ ■ ■ ■ "Ml ^ ^MM Ml III ^^W ^^i^^^^^L-l^^^^^^^P^M^^l-^^^^ 



Consiimetl in 10 minutes, 



in Dark. 



in Sun. 



18-50 grs. 

 15-72 " 



17-00 grs. 

 14*29 " 



Ratio of Amr. 

 in Sun <fe Dark. 



1 ; 1 088 



1:M00 

 1 : 1 053 

 1:1111 



nnHooi Den. Air 

 in Sun & Dark. 



1:1021 

 1 : 1 021 



1:1023 



1 : 1023 





The remarkable discrepancies indicated by the numbers in the 

 first column of ratios, afford a striking illustration of the exist- 

 ence of some disturbing cause, tending to vitiate the accuracy 

 of these experiments. But a glance at the numbers contained 

 m the two columns of ratios, is sufficient to show, that icmpera- 



* 



ahne is entirely inadeauate to account for the dimini 



Philosophical 



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