[ 2IO ] 



The following are my reafons for fuppofing that the iron was in 

 the ftate of an oxyd, and that the principal colouring matter was 

 compofed of carbon and bitumen. 



With a view of difcovering whether the iron was in its metallic 

 ftate, or otherwife, in the ftone, a large quantity of it, amount- 

 ing to feveral hundred grains, was treated with muriatic acid, and 

 the gas which was extricated was paffed through water, and 

 caught in a pneumatic apparatus. 



The fame procefs was repeated, with the fubftitution of the 

 fiilphuric for the muriatic acid. In both cafes the refult was the 

 fame. — No hydrogen gas could be colleded ; but, when the whole 

 of the carbonic acid had been imbibed by the water, there re- 

 mained, in the veflel, a fmall quantity of azotic gas. 



That the dark colour of the ftone could not be produced mere- 

 ly by the oxyd of iron, I was naturally led to fufped from the 

 change produced in it by calcination. I therefore fatisfied myfelf 

 on that point, by carefully feparating from a portion of the ftone 

 every particle of the metal, a procefs which produced no change in 

 lis colour. 



As it appeared now pretty evident that the calp contained fome- 

 inflammable matter, to which it was indebted for its dark colour, 

 I e:ndeavoured to eftimate its proportion by the following procefs: 



Thirty 



