206 On the Decomposition of certain Hydro-carbons. 



from the surface of the valve past which it rushed, or of the 

 interior of the air- way against which it was thrown, and that 

 that metal had caused the stain upon the paper ; but upon exa- 

 mination, this proved not to be the case ; for the black deposit 

 upon a card, when subjected to acids, remained insoluble, and 

 when burnt and tested chemically, gave no traces of copper. 



Further examination of the substance showed that it was not 

 a pure carbon, but one of those compounds, containing a very 

 large proportion of carbon, combined with a small quantity of 

 hydrogen analogous to tar, pitch, or asphaltum, for it dissolved 

 readily in the fluid^hydro-carbons obtained by the compression of 

 oil-gas. As these black carbonaceous compounds are formed in 

 the process of making oil-gas, a suspicion cannot but arise, that 

 the effect observed may have been produced by the current of 

 gas having swept off small portions of such substances pre- 

 viously deposited, or slowly formed in the interior of the vessels 

 at former periods ; and have left them upon the wall in the acci- 

 dental result, or upon the paper placed in the current of the 

 gas, when the effect has been purposely shown. 



It may, however, be remarked that, in experiments made in 

 the laboratory of the Royal Institution, upon the fluid product 

 obtained by condensing oil-gas at high pressures, it was observed 

 that, after rectifying the products arid separating the more fixed 

 from the more volatile, that although they were perfectly clear 

 and transparent at first, yet by spontaneous evaporation 

 through the corks which closed the vessels, and after a lapse of 

 time, chemical changes were produced; for, ultimately, there 

 remained nothing in several of the receivers but a broAvn sub- 

 stance, heavy, adhesive, like honey or treacle, and in certain 

 cases even almost solid. From the circumstances of the experi- 

 ments, no hesitation could arise in concluding that a sponta- 

 neous chemical change had taken place ; and it does not seem 

 at all unlikely that a similar change, or one to a much greater 

 extent, may have occurred suddenly during the rapid alteration 

 in the mechanical condition of the gas in Mr. Gordon's experi- 

 ment ; the most condensible of the substances in the mixture of 

 elastic matters which constitute oil-gas, being perhaps those 

 which are most altered, and in that case Mr. Gordon's account 

 of the plienomena would be correct. 



