of cerlain inflammable gaseous Compounds. 209 



Wiling point in similai- times, namely, 20' by each of the flames ; 

 50 that it would appear, that to raise a quart of water from 50** 

 to 212", at 30 inches barometrical pressure, requires 

 870 cubical inches of olefiant gas, 

 1300 - - oilgasj 



2190 - - coal gas. 



t^rom this experiment it may be inferred, that the air of a rOonri 

 equally lighted bv oil and coal gasj will be niufh less heated by 

 the former ihan the latter ; but that the actual heating power of 

 the flames is in the direct ratio of the quantity of olefiant gas. 



9. Having occasion in some of the foregoing experiments to 

 produce light of great brilliancv by the combustion of olefiant 

 gas, and finding it very difficult to measure its intensity by a com- 

 parison of shadows, in the manner pointed out by Count Rum- 

 ford, I endeavoured to avail m3'self of Mr. Leslie's photome- 

 ter ; for this purpose I concentrated the light by a plano-convex 

 lens, and placed the blackened ball of the instrument in the focusi 

 I found the effect, however, so great as to lead me to believe 

 that I had obtained a focus of considerable heating power, and 

 on substituting a delicate mercurial thermometer, it rose 4^,5 in 

 5'. In the focus thus obtained from the light of a large Argand 

 burner supplied with olefiant gas, the elevation of temperature 

 was very sensible to the hand ; and in depressing and elevating the 

 flame by means of a regulating stopcock, corresponding effects 

 were produced upon the thermometer : the lens itself, which was 

 a thick one, did not become heated. 



These experiments coincide in result with those of Dr. May- 

 cock, and of M. Delaroche*, and show that the calorific rays 

 emanating from common comljustibles, are capable of passing 

 through transparent media like those of the sun. 



10. There are certain substances, the chemical relations of 

 which are singularly affected by the influence of direct solar rays. 

 Among these, the mixture of chlorine and hydrogen is most re- 

 markable : if kept in common daylight, but out of direct sun- 

 shine, the gases do not act upon each other ; but the moment the 

 mixture is placed in the suuhhine, the muriatic acid begins to be 

 formed. 1 therefore hoped that this property might be appli- 

 cable in certain photometrical experiments. 1 exposed a mixture 

 of equal volumes <if chlorine and hydrogen, in a tube inverted 

 over water, capable of holding about four cubical inches, and 

 blown into a thin bulb at its upper extremity, to the brilliant 

 focus produced by a large olefian.t gas flame ; it was exposed for 1 5', 

 but underwent no other change than a slight increase of i)ulk, 

 acting as an air thermometer. 



1 1. It now occurred to me to try how far any efTect would be 



• Murray's System of Chemistry, vol. i. p. 336. 4th Edition. 

 Vol. 56. No. 2G9. SejA. 1820. D d pro- 



