Dr. Hare on Plumbago, Anthracite, ^-c. 455 



little more to the subject of polar contrast, which has as yet not 

 been sufficiently attended to ; and as they may also convince 

 those of the polarity of light, who will onlj' acknowledge the 

 contrast where that which on the one side is addition becomes 

 subtraction on the other. 



That this polar contrast in coloured light is also found in 

 the evolution of heat, all the preceding experiments, as well 

 as those of other philosophers, have sufficiently established. In 

 this function of light the polar contrast can only manifest it- 

 self in the greater and in the less ; and thus we found the heat 

 in one half of the spectrum greatest, and in the other least. 



LXVII. Strictures by Robert Hare, M.D. Professor of Che- 

 mistri), 8)X. S,-c., upon Professor Vanuxem's Memoir on Plum- 

 bago, Anthracite, Fused Carbon, Sfc. ptiblished in the Journal 

 of the Academy of Natural Sciences for June 1825 *. 



pROFESSOR VANUXEM, in a letter to Isaac Lea, Esq., 

 ■*- which has been lately read before the Academy of Natural 

 Sciences, endeavours to pi'ove that the fused products obtained 

 by Professor Silliman were none of them carbon; — first, by 

 analysing anthracite and plumbago ; and secondly, by expo- 

 sing those substances, or mahogany charcoal, severally to the 

 compound blowpipe, which he was obliged to use, not having 

 a deflagrator. 



The analyses thus given are interesting, so far as they may 

 afford correct views of the composition of anthracite and 

 plumbago. The only possible bearing which they can have 

 on Prolessor Silliman's experiments, is in showing, what every 

 chemist would have anticipated, especially in the case of plum- 

 bago, that there may be some ferruginous as well as earthy 

 matter in the minerals in (]uestion, and consequently that this 

 matter, when exj^osed to intense heat, may be fused into glo- 

 bules. This result is confirmed by the actual production of 

 globules from anthracite, and plumbago, on due exposuie un- 

 der the compound blowpipe. 



The fusion, however, of some ingredients in a comjiound 

 does not ])rovc the infusibility of others. If another ingre- 

 dient, subjected to ignition at the same time, be not fused, it 

 may show that it was not to be fused under the circumstances 

 of tiie experiment in question ; but it does not prove that un- 

 der other circumstances it would be insusceptible of fusion. 



The flame of the compound blowpipe, necessarily supported 



• Conmiunicated by the author. — See Professor Vanuxem's Memoir, 

 supra, i>. KJl. 



by 



