on the Nature of certain Bodies. 87 
fluoric acid gas, the intensity of the heat was such, as to fuse 
the bottom of the retort, and destroy the results. 
In a very thick plate glass retort, containing about nineteen 
cubical inches of gas, I once succeeded in making a decisive 
experiment on ten grains and a half of potassium, and I found 
that about fourteen cubical inches of fluoric acid disappeared, 
and about two and a quarter of hydrogene gas were evolved. 
The barometer stood at 30.3, and the thermometer at 61* 
Fahrenheit ; the gas had not been artifically dried. In this 
experiment there was very little sublimate ; but the whole of 
the bottom of the retort was covered with a brown crust, and 
near the point of contact with the bottom, the substance was 
darker coloured, and approaching in its tint to black. 
When the product was examined by a magnifier, it evi- 
dently appeared consisting of different kinds of matter ; a 
blackish substance, a white, apparently saline substance, and 
a substance having different shades of brown and fawn 
colour. 
The mass did not conduct electricity, and none of its parts 
could be separated, so as to be examined as to this pro- 
perty. 
When a portion of it was thrown into water, it effervesced 
violently, and the gas evolved had some resemblance in smell 
to phosphuretted hydrogene, and was inflammable. 
When a part of the mass was heated in contact with air, it 
burnt slowly, lost its brown colour, and became a white saline 
mass. 
When heated in oxygene gas, in a retort of plate glass, it 
absorbed a portion of oxygene, but burnt with difficulty, and 
required to be heated nearly to redness ; and the light given 
