152 
of light. Those leaves also, which intercept the sun's 
light, delineate on the fruit beneath the bounds which 
they prescribe to its action ; and if a portion of fruit 
be covered with a piece of tinfoil, the uncovered por- 
tion will become perfectly red, while the covered part 
will exhibit only a pale or straw colour. So, like- 
wise, if grapes, which would have become violet by 
exposure, be inclosed in black paper or glass, which 
excludes the light, they assume only a grey colour. 
Those green fruits which do not redden, lose also 
their green colour in ripening, and become yellow. 
This change is quickened by the action of light, but 
it also takes place without it ; for many fruits pass 
from green to yellow, although they are secluded 
from light *. 
409. The red juices of many fruits are extracted 
by water and alcohol ; and both the solutions, and 
the juices themselves, says Dr Lewis, are sometimes 
made more florid by acids, and generally turned purple 
by alkalis t The skins of fruits, likewise, yield their 
colourable matter to water and alcohol. The red 
skin of the peach imparts a red tinge to water and 
alcohol, but the white skin of the same fruit renders 
alcohol green. When the red skin has been thus de- 
prived of its colour, it again assumes it, like the pe- 
tals of roses, by exposure to light and air. The skins 
of different green, red, and yellow fruits imparted 
their respective tints to alcohol, and some, in a small 
degree, to water J ; and the red tinctures of these 
* Mem. Phys. Chim. t. iii. p. 146. 7. 
f Newmann's Chemistry, p. 432. 
I Mem, Phys, Chim. torn, iii. p. 148. p. 
