On an artljiciul tmmlng Sulstance. 179 



a few of tlie experiments, with their results, because they 

 are intimately connected with the subject now under con- 

 sideration. 



In these experiments I have observed that concentrated 

 sulphuric acid, when poured upon any of the resinous sub- 

 stances reduced to powder, dissolved them in a few minutes; 

 at this period the solution was transparent, commonly pf a 

 yellowish-brown colour, and of the consistency of a viscid 

 oil. But if, after this, the vessel was placed on a sand- 

 bath, the colour of the solution became progressively darker, 

 sulphureous gas was evolved, and at length the whole ap- 

 peared like a very thick liquid of an intense black. I pur- 

 posely for the. present pass over many phaenomena, some 

 of which are peculiar to the different substances when thus 

 treated, whilst others are general, and n)ay be referred to those 

 attendant on etherification, for mv intention here is only to 

 notice, in a concise manner, such as immediately tend to 

 elucidate the subject of this paper. 



When concentrated sulphuric acid is poured on the com- 

 mon turpentine of the shops, it almost immediately dis- 

 solves it like the solid resins ; and if a portion of this solu- 

 tion be poured into cold water, the tuipentine is precipitated 

 in the solid brittle state of common yellow resin. But if a 

 second portion of the same solution, after the lapse of an 

 h(-ur or more, be in like manner poured into cold water, 

 the resin thus formed is not vellow, but dark brown.; and if 

 four or five hours are suffered to ciapse before a third portion 

 is poured into water, the resin is found to be completely 

 black. After this, supposing the digestion to be carried 

 on during several days, or until there is no longer any pro- 

 daction of sulphureous gas, the turpentine or resin will be 

 found converted mto a black porous coal, which, if the 

 operation has been properly conducted, does not contain 

 any resin, although a substance may frequently be separated 

 by digestion in alcohol, which T shall soon have occasion 

 to notice. 



When common rcsi.ji was thus treated, I obtained about 

 43 percent, of the coal, which, after being exposed to a 

 red heat in a loosely covered plalina crucible, still amounted 

 to 30 per cent., and by the slowness of its combustion and 

 other circumstances which need not here be related, ap- 

 proached very nearly to lj[je characters of some'of the mi- 

 neral coaU*. 



The 



• The dLTerence of the quanrity of carbon, which may bp obtnincd in 



tkr ii.itf of i-ual frjm roiinous auUtaiicei. by tiic humid and by the dry way, 



M li is 



