C 37 3 
cxpofed to it are ; though it appears from experi- 
ment that the prefence of light, as well as of air, is 
neceffary to the produ<fl;ion of the colour of plants. 
Befides the iron didblved at the Jurface of plants 
by the air, that which is contained in the injide of 
them, may be kept in a ftate of folution, when it 
meets with a proper quantity of acid', and it is 
remarkable that the inlide of moft fruits and other 
parts of plants remain green no longer than they 
continue in an acid ftate. 
The quantity of iron contained in plants will 
not appear too fniall to produce their colour, when 
it is known that one grain of vitriol, of which only 
a fmall part is iron, the reft being acid and water, 
is able fenftbly to communicate a green colour to 
ten thoufand grains of water. Lemery mentions 
this great divifibility of iron as an argument of it’s 
being able to pafs into the fmalleft parts of plants. 
Mem. Acad, anno 1706. 
A circumftance which ftrongly confirms that the 
colouring matter of vegetables ^ and a ferruginous 
vitriolic fubfance^ are of one and the fame kind, is, 
that the vitriol of irony which is greeny palfes 
through the fame colours, while it’s moifture is 
evaporating, which vegetables do, when by wither- 
ing they undergo the fame fort of change : the 
vitriol deprived of it’s water by calcination grows 
yellow and then red [/j ; and Sir Ifaac Newton 
[i] Boerhaave’s Chem. vol, ii. procefs 164. If this fecond 
calx (that is, grren vitriol reduced to powder by a moderate heat) 
be calcined in a crucible, in aii open rtrong fire, it grows yelloWy 
-rtidyAvA at length becomes a deep purple powder. 
has 
