. [ ,36 ] 
This obfervatlon of the conftancy of that cotour 
in glafs made of vegetable ajhest and it’s being 
caufed by irony led me to conjecture, that the colour 
of the intire vegetables arifes alfo from the iron, fo 
univerfally diffufed throughout their fubftance in 
their growth. 
Green is the colour which iron aflumes conftant- 
ly, when diilblved by the acid in the airy that metal 
thus diffolved being a true green vitriol of iron [/»]; 
and as this ferruginous or vitriolic matter is univer- 
fally difleminated through the leaves and branches 
of plants, thofe parts of it which are at the furface 
will, by their contaCt with the air, alTume the 
colour peculiar to its fait or vitriol. 
Mod: vegetables, when they grow in fuch a man- 
ner as to be defended from the contaCt of the air, 
are prevented from becoming green. 
This happens to the roots of trees, and as much 
of their flem as is covered with earth ; grafs grow- 
ing under ftones, or other bodies, that accidentally 
lie bn it, is white \ not having the lead green, but 
as the air has accefs to it : and it is a method 
commonly ufed by gardeners, to cover with earth 
thofe parts of plants which they would preferve 
white : by that means hindering them from being 
tinged green by the contaCt of the air, as the parts 
[/>] Shaw’s Notes to Boerbaave’s Chemiftry, vol. i. p. 94. 
Iron is eafily difl'olved in falts, dew, air, &c. By the a£Uon of 
any of thefe it contradis a ruff, which js nothing but the flowers 
,of iron, or iron difl'olved, and lorfakcn by it’s diilblvent ; for ircn 
examined with a microfcope when it full becomes rufly, fhews 
it’s furface covered with a number of pellucid vltrieik lamella:, 
or glebes, which, being afterwards dried by the fluid menftruum’s 
evaporating, become a ruddy caU. 
expofed 
