On H^drogtne. — Bitumens and illincra/ Coal. 487 



In the dicompofithn vffat aiidsil by Jin; Is'c] The difference between the leading aflump- 

 tion in Profcflbr iVlitcbill's letter, .an4 the theory formerly maintained by Mr. Kirwan, and 

 ftated by him in the Introdu£lion to his Work upon 1 lilogifton, appears to be, that the 

 former does not fuppofe his phlogiftou, or principle which affords flame, to be eflential to 

 the metallic (late, but merely, as I conceive it, accidental in that clafs of combuflible fub- 

 ftances. He follows Mr. Kirwan, by firft direcling his attention to the univerfality of hy- 

 drogene in organized bodiesj and then endeavouring to fliew that it exifts in fulphur, phof- 

 phorus, zinc, and iron, in their ordinary combuflible ftate. It has not yet been fliewn 

 that aqueous fulphuric acid can be produced by the combination of fulphur and oxigene, 

 without the prefence of water ready formed. The fame obfervation more ftrongly applies 

 to phofphorus, which LavolCer coiiverted into the folid acid by the burning glafs in a 

 veffel of oxigene gas over mercury. In the obfervations on zinc and on iron, we look in 

 vain for the experimentum cruets, vvliich mull be exhibited before the fupjiofed faft tliat 

 metals contain hydrogene can be admitted. 



I have ventured to make tliefe remarks on the Profeffoi's ingenious communication, with- 

 out aiming at the eftabliflnnent of pofitions contrary to thofe he has offered. The queftions 

 he treats mud be decided by plain fa£ls, if fuch can be found. Till this be done, they re- 

 main among the mafs of unknown propofitions, concerning which, we ought neither to 

 affirm nor deny. 



II. 



Experiments on the Compofttion and Proportion of Carbon in Bitumens and Mineral Coal. 

 By Richard Kirwan, Efq. F. R.S.L.bf E. M. R. I. A. l^c. 



x\N exa£l knowledge of the component parts of the different fpecles of mineral coal, and 

 alfo of bitumens (fubftances which mofl of them contain) forms an obje£l of fome im- 

 portance, not only to the naturalift whofe views are merely fpeculative, but to the practical 

 occotiomift, who wlflies to extract from each fpecles all the advantages it is capable of yield- 

 ing, and to be enabled to compare the various kinds afforded by different countries, in order 

 to obtain and employ that which fliall on the comparifon appear to him bed fuited to his 

 intentions. 



In effe£t, coals are not only applicable to the more ufual purpofes of combuftion — an ufe, 

 fimple as it may appear, attended, according to Jieir various fpccies, with a confiderable dif- 

 ference of calefadlive power both in intenfity and duration, but alfo to the produ£lion of 

 varnifhes, much more advantageoufly applicable in many inflances than thofe extratled from 

 the Vegetable Kingdom, as Lord Dundonald lias difcovcrcd, and abundantly proved*, and 

 alfo of that charred refiduum called coak, the only one that can be reforted to in many 

 cafes, and, in mofl, fuperior to vegetable charcoal. 



• Upon the moft minute enquiry why coal-varnifli is not more commonly employed in paying the bottoms 

 of Oiipt, r have been informed the priucipil riafon is, that it fuccccds too well ; the Ifaips not requiring fuch 

 frequent repair. K. 



Coals 



