Nutrition of Vegetables. 297 
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'of almost all its oxygen, and a small quantity of its hydrogen, by 
exposing it to a certain temperature, the result will be a hydro- 
guretted charcoal, partly soluble in potash, as I have found by 
experience. 
That part of the mould, which had resisted the action of pot 
lash, weighed when dried 5 gr. It had no longer the physical 
Icharacters of mould ; was in pieces that were tolerably hard and 
brittle; and had a striking resemblance to pitcoal, which led me 
to produce it in larger quantity. In this way it had still such a 
resemblance to coal, that I could compare it to nothing else. 
From this examination of mould it appears, that it cannot sup- 
ply plants with any soluble matter for their nutrition, since boil- 
ing water has no action on it. It would be superfluous to say, 
that seeds sowed in it vegetated with extraordinary vigour; but 
I must not omit to mention the presence of a large quantity of 
potash in the plants, though I could not detect any in the mould 
in which they grew, by the most strict researches. 
These observations appear to corroborate the opinion of Tibet 
and Parmentier, who consider manure as useful only by retain- 
ing moisture, and keeping strong soils open for some time, so as 
to allow the roots of plants to penetrate them. But if water and 
air be the only sources of the food of plants, any insoluble mat- 
ter, sufficient in quantity, and duly watered, must be adequate to 
the purpose of their growth. This I endeavoured to ascertain 
by experiments. 
Exp. I. In a box filled with pure litharge I sowed 400 seeds 
of white mustard, weighing 2-2 gr. These I watered frequently 
and carefully with distilled water. The box was placed in a 
good aspect, and a glass was hung over it to keep out the dust 
The plants throve very well, and produced perfect pods. 1 col- 
lected all the seminal leaves as well as the rest that dropped off ; 
and when the vegetation was at its height, pulled up the plants. 
Having well washed the roots, to remove any portions of oxyde of 
lead, and wiped them dry, the whole weighed 264 gr. After they 
were dried, the weight was 34-2 gr. 
These yielded 12 gr. of coal, which by incineration were redu- 
ced to 4-2 gr. of ashes. These lost by lixiviation 2*2 gr. ; of 
which ’59 gr. were sulphate of potash, *69 gr. potash. The inso- 
luble residuum afforded *4 gr. of silex; -45 gr. of oxyde of iron, 
alumine, and phosphate of lime, the proportions of which were 
P p 
