[ 35 3 
dilute yelloWf at the bottom, where it is thin ; 
and a little higher, where it is thicker, orange \ 
‘“where it is thicker Hill, it becomes red-, and 
“ where it is thickeft, the liquor is deepeji and dark- 
“ eft." Newton’s Opt. p. i6o. 
H AV I N G gone through thefe experiments and 
fadts, which feem to {hew that the metals mvzx'vdkAg 
exhibit colours in the order of their denfities, when 
melted with glajs^ under the circumftances above 
mentioned j and that the other preparations of the 
fame metals, for the moft part, aftume the fame 
colours', it feemed probable that the caufe, on 
which the colour of natural bodies depend, may 
fometimes be conjedlured from the chemical ana- 
lyfis of fuch fubllances. This I have attempted 
with regard to the colour of plants. 
It is known from the experiments of Lemery 
and others, that all earth is impregnated with iron ; 
that the ferruginous matter is received into the 
roots of plants in their growth, and makes part 
of their fubftance, and is univerfally diifeminated 
through them j and. that iron may be feparated by 
a magnet from the afhes of all vegetables [^]. 
It has been already obferved, that the green 
colour of thc^/<^ ufed in making bottles, is caufed 
by the iron contained in the materials of which it 
is made ; and I have cited Becher’s opinion, that 
the green or blue colour in glafs is an indelible 
mark of it’s vegetable origin. 
\^g'] Lemery’s Mem. cle I’Academ. anno 1706. 
Memoirs of the Acad, of Upfal and Stockholm, of the cafth 
found in vegetables, by J.G. Wallerius, 1760. 
F 2 This 
