123 
fact, that the colour which is discharged, when the 
green solution is exposed to light and air, is again 
restored, according to M. Senebier, by the addition 
of an alkali * ; and we found, by experiment, the 
same restoration of colour to be made when an alkali 
was added to the solution which had been deprived 
of colour by the direct application of carbonic acid. 
The green colour, however, did not resume its former 
intensity ; and M. Berthollet remarks, that when the 
green solution has undergone all the discolouration 
from exposure which it is able to exhibit, alkali then 
produces in it no change f. 
370. The phenomena afforded by these solutions 
of the colourable matter of vegetables in alcohol, 
agree with those which are presented by infusions of 
the same substances in water. The flowers of most 
plants, and also the leaves of many, yield to water 
materials which become red or green, according as 
acid or alkaline matter is made to predominate in 
them ; but if the acid and alkali be furnished in cer- 
tain proportions, the colour disappears altogether. 
371. Not only, however, is the green colour of 
vegetable infusions destroyed by the direct application 
of acids, but, like that of the green solurions, it is 
gradually discharged by exposure to the air. M. 
Becker remarked, that if a vegetable infusion, that 
has been made green by alkali, be exposed to the 
air, it gradually passes to a yellow colour J. This, 
* Mem. Pbys. Chim. torn. ii. p. lj'2. and torn. iii. p. 4-7 
f Klem. de la Teinture, vol. i. p. 54. 
* Berthollct's Elem. de la Teinture, vol. i. p. ()4. 
