EXTINCT VOLCANO IN BRITAIN. 237 



The experiments which we have had the honour of laying General con- 

 « „ , - r, l • • 4. elusions. 



before this Society prove several important points: 



]st. That the estimate given by Lavoisier, of 23 parts of Lavoisier's es* 

 carbon in every 1 00 parts of carbonic acid, is very nearly £0^**.°*^ 

 Correct; the mean of our experiments makes it 28*60. 



2dly. That the diamond is pure carbon; for had it con- Diamond pure 

 tained any notable proportion of hidrogen, it must have carbon. 

 been discovered, either by detonating with the oxigen, as in 

 the case of animal charcoal, or by diminishing the quantity 

 of oxigen gas. 



3clly. That well burnt charcoal contains no sensible quan- Fresh charcoal 

 tity of hidrogen ; but if exposed to the air for a few hours it contains no hi- 

 absorbs moisture, which venders the results uncertain. a 



4thly. That charcoal can no longer be considered as an Charcoal not 

 oxide of carbon, because, when properly prepared, it requires oxl ' le - 

 quite as much oxigen for its combustion as the diamond. 

 This is also the case with stone coal and plumbago. 



5thly. It appears that diamond and all carbonaceous sub- Carbonaceous 

 stances (as far as our present methods of analysis are capable f" r oSHntheir 

 of demonstrating their nature) differ principally from each aggregation. 

 other in the state of aggregation of their particles. Berthol- 

 let has well remarked, that in proportion as this is stronger, 

 decomposition is more difficult : and hence the variety of 

 temperatures required for the combustion of different inflam- 

 mable substances. 



IX. 



Account of an extinct Volcano in Britain. Communicated by 

 Mr. Donovan. 



_R. Donovan announces some particulars of an extraor- Cader Idris for^ 

 dinary nature to the scientific world respecting one of the |^ er y 

 Cambrian mountains; which, from the result of attentive 

 observation, and indubitable evidence, he endeavours to de- 

 monstrate must have been at some remote period a volcano 



of 



