Mr. Tennant on the Decompofition of fixed Air. igj 
attracted by charcoal than by phofphorus, yet in this com- 
pound it is retained by two attractions, by that which it has 
for phofphorus, and by that which the phofphoric acid has for 
lime, fince the vital air cannot be difengaged unlefs both thefe 
attractions are overcome. As thefe attractions are more power- 
ful than that which charcoal has for vital air, if phofphorus is 
applied to fixed air and calcareous earth, the vital air will unite 
with the phofphorus, and the charcoal will be obtained pure. 
Thefe fubftances, in order to aCt upon each other, muft be 
brought into contaCt when red-hot ; and this may be eafily 
effected in the following manner. Into a glafs tube, clofed at 
one end, and coated with fand and clay to prevent the fudden 
aCtion of the heat, a little phofphorus fhould be firft intro- 
duced, and afterwards fome powdered marble. The experi- 
ment fucceeds more readily if the marble is (lightly calcined, 
probably becaufe that part which is reduced to lime, by imme- 
diately uniting with the phofphorus, detains it to aCt upon the 
fixed air in the other part. After the ingredients are intro- 
duced, the tube (hould be nearly, but not entirely, clofed up ; 
by which means fo free a circulation of air as might inflame 
the phofphorus is prevented, whilft the heated air within the 
tube is fuffered to efcape. When the tube has remained red- 
hot for fome minutes, it may be taken from the fire, and muft 
be fuffered to grow cold before it is broken. It will be found 
to contain a black powder, confiding of charcoal intermixed 
with a compound of lime and phofphoric acid, and of lime 
united with phofphorus. The lime and phofphoric acid may 
be feparated by folution in an acid and by filtration, and the 
phofphorus by fublimation. 
Charcoal, thus obtained from fixed air, appears in no refpeCt 
to differ from the charcoal of vegetable matters. On deflagra- 
ting 
