182 Mr. Charlton on the [Sept. 



employed in the correct separation of the former from one or 

 more of the three latter. 



4. That the gases evolved by heat from coal and from oil, 

 though extremely uncertain as to the proportions of their ingre- 

 dients, consist essentially of carburetted hydrogen, with variable 

 proportions of hydrogen and carbonic oxide : and that they owe, 

 moreover, much of their illuminating power to an elastic fluid, 

 which resembles defiant gas in the property of being speedily 

 condensed by chlorine. 



5. That the portion of oil gas and coal gas, which chlorine 

 thus converts into a liquid form, does not precisely agree with 

 defiant gas in its other properties ; but requires, for the combus- 

 tion of each volume, nearly two volumes of oxygen more than 

 are sufficient for saturating one volume of defiant gas, and 

 affords one additional volume of carbonic acid. It is probably, 

 therefore, either a mixture of defiant gas with a heavier and 

 more combustible gas or vapour, or a new gas mi generis, con- 

 sisting of hydrogen and charcoal, in proportions that remain to 

 be determined. 



Manchester, Jan. 1S21. 



Article III. 



On the Production of Colours by Mechanical Division. 

 By Mr. J. P. Charlton. 



(To the Editor of the Annals of Philosophy.) 



SIR, 



In the course of some experiments upon enamel colours, I 

 have been led to observe a fact which you may, perhaps, think 

 worth insertion in your Annals, as it is contrary to the state- 

 ments of approved chemical works, and as it must, I think, be 

 considered a remarkable instance of a complete change of colour 

 produced merely by mechanical comminution : the fact to which 

 I allude is, that oxygenation is not essential to tire rose colour 

 which gold imparts to enamels. 



It has long been known that silver has the property of staining 

 glass an opaque blue or green, when viewed by reflected light, 

 which becomes a fine transparent orange colour, when viewed 

 by transmitted light, a property generally attributed to the oxide, 

 but which I have found to belong equally to metallic silver, 

 which, when fired alone in contact with glass, is quite as effec- 

 tual as all the other preparations of it. From the above and some 

 other circumstances, 1 was led to suspect that the case might 

 be the same with respect to gold. Accordingly, I ground toge- 



1 



