300 Dr. Pearson's Experiments for 
lighted wax taper. A charge of 95 grains of phosphorus, and 
540 grains of the above alkali, afforded 20 6 ounce measures of 
this inflammable air, which was of the same quality whether 
it was received over water or quicksilver. This air, I appre- 
hend, was produced by the decomposition of the water in the 
alkali, in consequence of the superior affinity between phos- 
phorus and respirable air, to the affinity betwixt respirable 
and inflammable air. Therefore when moist alkali is used, 
ccet. par. more phosphoric acid will be formed than when dry 
alkali is employed ; and in calculating the quantity of re- 
spirable air formed, regard must be paid to the decomposition 
of water. It appears also, that it requires less heat to decom- 
pound water by phosphorus, than to disunite carbonic acid 
from fixed alkali. 
In these experiments I frequently used thick white glass 
tubes, and applied heat for a long time, to the degree of ren- 
dering them flexible: when cold, I found the internal surface 
in contact with the black alkaline matter full of cells, or small 
cavities, and rough, to which small grains of lead adhered, con- 
sequently the respirable air of the calx of this metal in the 
glass had been attracted, and reduction effected. This re- 
duction might be produced by three substances here present, 
namely, phosphorus, inflammable air, and charcoal ; but I im- 
pute it to the charcoal ; 1st. because I obtained no particles 
of lead by passing phosphorus through a tube filled with 
powdered white glass, heated to the degree of rendering the 
tube soft, although on cooling, I found the internal surface of 
the tube was turned black, which colour could not be re- 
moved by rubbing, or by acids. This appearance I cannot 
explain. 2dly. This reduction is effected when there is no 
