3 30 Experiments relative to Coals and Cokes 



probable that this takes place to a certain extent, and that 

 all carbonaceous matter prepared in contact with atmosphe- 

 ric air is inferior in point of purity, or, in other wopds, is 

 not so highly de-oxygenated as that prepared in close vessels, 

 I do not rind, however, that, by having recourse to close 

 vessels where there is no contact of atmospheric air, the re- 

 sulting product is materially altered as to colour and general 

 appearance, or thai the oxide of diamond apparently exists 

 in a state of diminution. Its carbonating effects, however, 

 become wonderfully changed by such a plan of procedure j 

 and subsequent experiment, in various stages, develops many . 

 characteristics not unworthy of an approach to the stale of 

 diamond. 



This change of quality may arise from another source than 

 simple distillation in- close vessels, and the prevention of the 

 contact of external air. 



If the Tieat of the distillation is urged beyond a dull red 

 colour, or even continued longer at the usual temperature, 

 the oxide begujs 10 de-oxidate itself, and the product will be 

 found materially changed as to its usual affinities. It will he 

 found more difficult to ignite in common open air. Its com- 

 bustion unless impelled with mechanical violence will move- 

 on sluggishly, and under every circumstance a higher tem- 

 perature and longer contact will be requisite, to effect an 

 union uyilh its usual relations. The extent of carbonaceous 

 principle arising from a given weight will, however, be in- 

 creased in the same proportion as the substance has been 

 de-oxidated. A greater quantity of carbonic acid gas will 

 Be obtained from the same weight of oxide, and of course a 

 greater quantity of carbon set free. 



It is cliiiicult to say to what extent this de-oxidizing prin- 

 ciple might be carried. In heats of 160 and 170° of Wedg- 

 wood,- the increased density of the carbon, particularly if in 

 the state of powder, and the uncommon depth of lustre 

 which the black assumes, are evidences that some material 

 bang,e has passed upon the arrangement of its constituent 

 here can, however, be no doubt that there exist 



pa; is. 



r 



certain fixed limits, unless a third affinity be interposed) be- 

 yond which carbonaceous matter ceases lo de-oxidate it-? 

 3 self: 



