decompounding fixed Air. 293 
and phosphoric acid, that the question, whether carbonic acid 
united to clay will be decompounded by phosphorus ; can only 
be answered by future experiments. 
As I presume that I have made experiments which enable 
us to draw conclusions concerning the above cases of com- 
pound attraction, and which also shew, in several instances, 
that carbonic acid is decompounded, and affords respirable air, 
and charcoal ; I think it my duty, on a subject so very in- 
teresting in the present state of chemistry, to submit them to 
the consideration of this Society. 
Experiments with Phosphorus, applied to mild fossil Alkali. 
I began with attempting to decompound carbonic acid in 
union with fossil alkali, in preference to the same substance 
combined with quick-lime, because the proportion of this 
elastic fluid is much greater in mild fossil alkali than in cal- 
careous earth, because the affinity is not so strong between 
carbonic acid and fixed alkalies, as between carbonic acid and 
quick-lime, and because the mechanical separation of char- 
coal from alkalies, and phosphorated alkalies, may be more 
easily made than of charcoal from calcareous earth and 
phosphoric selenite. The purest fossil alkali I could procure 
was employed, from which I had expelled °f ^ ts we >ght 
of water, but none of its carbonic acid. 
Into a thick white glass tube, almost one inch wide, three 
feet and a half in length, coated within nine or ten inches of 
the open end, were introduced two hundred grains of trans- 
parent phosphorus, and eight hundred grains of the above de- 
aquated alkali were pressed down upon them. The tube, thus 
MDCCXCII. Qq 
