on the Nature of certain Bodies. 71 
the two volumes of elastic fluids were 1.8 cubical inches and 
1 .9 cubical inches ; and both gave the same diminution by de- 
tonation with oxygene, as pure hydrogene. Two grains of 
potassium, by acting upon water, would have produced two 
cubical inches and one eighth of hydrogene gas ; the defici- 
ency in the result, in which potassium alone was used, must 
be ascribed to the loss of a small quantity of metal, which 
must have been carried off in solution in the hydrogene, and 
perhaps, likewise, to the action of the minute quantity of 
metallic oxides in the plate glass. The difference in the 
quantity of hydrogene given off in the two results, is however 
too slight to ascribe it to the existence of oxygene in the 
plumbago. 
I repeated this experiment several times with like results, 
and in two or three instances examined the compound form- 
ed. It was infusible at a red heat, had the lustre of plumbago. 
It inflamed spontaneously, when exposed to air, generated 
potash, and left a black powdery residuum. It effervesced 
most violently in water, and produced a gas, which burnt 
like pure hydrogene. 
When small pieces of charcoal from the willow, that had 
been intensely ignited, were acted upon by Voltaic electri- 
city in a Torricellian vacuum, every precaution being taken to 
exclude moisture from the mercury and the charcoal, the re- 
sults were very different from those occuring in the case of 
plumbago. 
When plumbago was used, after the first spark, which ge- 
nerally passed through a distance of about one eighth of an 
inch, there was no continuation of light, without a contact or 
an approach to the same distance ; but from the charcoal a 
