184 Mr. Tennant on the Decompofition of fixed Sir. 
ting a little of it in a fmall retort with nitre, fixed air was im- 
mediately reproduced.— Since, therefore, charcoal, by its repa- 
ration from fixed air, is proved to be one of its confhtuent prin- 
ciples, it can hardly be doubted, that this fubftance is prefent 
whenever fixed air is produced ; and that thofe experiments, 
from which it is fuppofed that this acid may be formed without 
the aid of charcoal, have not been conduced with the requifite 
caution. 
As vital air is attraded by a compound of phofphorus and 
calcareous earth more powerfully than by charcoal, I was defi- 
rous of trying their efficacy upon thefe acids, which may from 
analogy be fuppofed to contain vital air, but which are not 
affeded by the application of charcoal. With this intention I 
made phofphorus pafs through a compound of marine acid and 
calcareous earth, and alfo of fluoracid and calcareous earth, but 
without producing in either of them any alteration. Since 
the ftrong attradion which thefe acids have for calcareous earth 
tends to prevent their decompofition, it might be thought that 
in this manner they were not more difpofed to part with vital 
air than by the attraction of charcoal. But this, however, 
does not appear to be the fad. I have found, that phofphorus 
cannot be obtained by paffing marine acid through a compound 
of bones and charcoal, when red-hot. The attraction, there- 
fore, of phofphorus and lime for vital air exceeds the attradion 
of charcoal by a greater force than that arifing from the attrac- 
tion of marine acid for lime. 
