6P ^^^' HENRY ON COMBtJSTIlJLE GASHS. 



that from good fpermaceti oil. So efiential a difFerence in lH» 



combudion of thefe gafes, induced me at firft to believe, that 



the gas from coal owes its illuminating property to fomething 



mechanically lafpended in it j but I was afterwards fatisfied, 



that though it contains, when recently prepared, much that 



This bft gas is fubrequently depofited, vet that its qualily of burning with 

 burns with i_ • i . j r, n " \ \ . . , . , 



much (though ^ bright and compact (lame belongs to it, though certamly 



diminiihed) light with contiderable diminution, as a permanent gas, alter the 



fncd its conden'^P^''^^'^" "^ ^'' condenfible matter. It appeared, therefore,, 



fible matter. worthy oii invefligation to determine, on what the fuperior 



fitnefs of the gas from coal, for evolving lighl, depends ; and 



to conned the theory of its combuflion with that of other fub- 



llances, commonly employed as fources of artificial light. 



Products by With this view, numerous comparative experiments were 



from waf^witir '"^^^ ^" ^^^^ ^^P'^ combuftion of this gas with ovigenous gas 



oxigen and alfo in clofe veflels, and alfo on that of other inflammable gafes; 



other gafes. ^pj tj^gir compofition maybe inferred from the products of 



thefe experiments, the principal refults of which are contained 



ia. the following. table ; 



Oxigen Gas required 



to fat urate loo Carbonic Acid 



Kiad of Gas. Meafures. produced. 



Table of refults. Pure hydrogen, . 50 to 54 



Gas from moifr charcoal, 60 - - 35 



wood (oak). 54 - - 33 



dried peat, 68 - - 43 



■ — coal, or cannel, 170 - - 100 



-—lamp-oil, 190 - - 124 



wax, - 220 - - 137 



Pure olefiant gas, 284 - - 179 



Ifthc meafurc N-OW if it be afllimed (which I believe is as nearly as pof- 

 of carbonic acid ^j^le the ta(5l) that in the formation of each meafure of carbonic 

 dufted from the acitl» *" the above experiments, an equal volume of oxigen 



whole oxigen gas is employed*, we (hall learn, by deducing the numbers in 

 employed, the , 



remainder will ^"® 



exprefs the mea- 

 fure of oxigen * Mr. Cruickftiank takes It for granted, as the bafis of his cal.^ 

 which was em- culations, that in forming fix meafures of carbonic acid, fev.en 

 fr^^thehvdroeen""^^^"^^^ ^'^ oxigenous gas are employed. This proportion I be- 

 ef the gas |^ and lie ve to be over-eltimated. Dr. Prieftley obferves, (on Air, 2d 

 this laft doubled Edition, III. 377), " I heated 8|: grains of perfea charcoal in 70 

 m give the quqcc meafures of dephlogifticated air, when it ftill remained 70 or. 



