121 
discharge of colour to the simple combination of 
oxygen. 
366. But, if it thus appear, that the muriatic acid 
discharges vegetable colours, like other acids, al- 
though its oxygen cannot be separated, may we not 
presume that these other acids act not in virtue of 
the oxygen which they contain, but by reason of 
their acid properties alone ? And since we also know 
that oxygen gas readily combines with the carbon of 
vegetables, and forms an acid substance, may we not 
farther presume, that the oxygen, employed in these 
experiments, really entered into such a combination, 
and that the acid, thereby formed, contributed to 
the discharge of the vegetable colour ? 
367. That carbonic acid is really formed, when 
oxygen gas is placed in contact with this green solu- 
tion, seems almost certain from the following fact. 
If, says M. Senebier, sulphuric acid be poured into a 
green solution, which has been previously discolour- 
ed by light, it occasions a strong effervescence, the 
mixture then reddens, and a white precipitate is 
thrown down, similar to that which the green tinc- 
ture affords, when, in its coloured state, it is made 
to combine with the same acid*. There can, we 
think, remain little doubt, but that the elastic matter, 
which is thus driven off by sulphuric acid, is carbo- 
nic acid gas ; and hence, when oxygen gas disappears 
in these experiments, and combines with the colour- 
able matter, the discharge of colour that ensues is 
not properly to be ascribed, as M. Senebier supposes, 
* Mem, Phvs. Chim. vol. iii. p. 44. 
