decompounding fixed Air. 301 
water present, at least when no inflammable air is extricated. 
3dly. The greatest quantity of regulus of lead was obtained 
in those parts of the alkaline matter which contained the 
smallest quantity of charcoal, and therefore, I conceive, the 
charcoal, formed in those parts, had united to the air of the 
calx after the phosphorus had been driven through the alkali, 
so that the carbonic acid thus composed could not be decom- 
pounded, but was combined with the alkali, which was al- 
ways redundant. In calculating the proportion of carbonic 
acid decomposed, it will be necessary to consider the reduction 
which here takes place. 
If the air-apparatus be not affixed to the tube, containing a 
charge of phosphorus and alkali, charcoal and respirable air 
will be formed ; but the phosphorus will take fire at the open 
end of the tube, and burn with splendour, as in dephlogisti- 
cated air. 
Porcelain, or w r ell glazed Wedgwood tubes, answer in 
these experiments better than glass ones, the insides of which 
are apt to melt ; but unglazed vessels allow the phosphorus to 
pass through their pores, though part of the carbonic acid 
may be decompounded. 
The heat applied must be greater than the white glass now 
made can endure without melting ; for, I passed phosphorus 
through a tube containing mild fossil alkali, heated so that it 
appeared red hot in the dark, and no charcoal was formed, 
though the inside of the tube was blackened. 
MDCCXCII. 
Rr 
