dissolves are’ separated by water; 
gum water holds in solution, is precipitated by alec 
dissolves the same principles as alcohol ; it fastber diss 
the elastic gum of some vegetables, and it precipitates the extractive 
matter from water. The alkalies discover several of the acids con- 
‘tained in vegetable substances, and the acids are sometimes used - ; 
tests. ’ 
Lastily, in the analysis of vegetables, we are often able to procure 
several of their proximate principles by mechanical gscers! easel es 
larly by expression: Sometimes, also, they exude spontan | 
from the growing vegetable, or are obtained. from it | 
made in the hes or trunk. - ; 
~ After we have discovered the proximate principles of ve 
the next step is to ascertain their composition. This, with respect 
to their ultimate principles, is nearly uniform; the. differences in 
their chemical properties and sensible qualities arising principally 
from differences in the proportions of these principles, and in the 
modes in which they are combined. . These differences are too sub- 
tile to be very accurately determined by analysis, and henee this 
species of investigation is now. acknowledged to convey no 
tion on the medicinal powers of vegetables. Besides ¢: 
gen, and oxygen, which are their principal cons 
of them contain azotand phosphorus, which mod 
Various metals, too, particularly iron and mangan 
three alkalies, either pure, or in combination with ’ 
are not unfrequently constituents of vegetable matter, tho 
in any considerable proportion, nor is “it certain but. that 
these are formed during the analysis by which they are obtaii 
The proximate principles of vegetables are sometimes analyzed Rot 
by mere exposure to heat; their elements enter into new combina- 
tions, and from the products we discover what the principles were, 
and even, to a certain extent, in what proportions they had been uni- 
ted. — Sometimes the atmospheric air is admitted when they a 
sed to the temperature of ignition, and by collecting the 
formed by their combustion, we form a similar judgn 
composition. Others of them are capable of undergoing 
tion; and from the products of this process, the constituent princi- 
ple: “of the. ‘substance operated on are determined. Lastily their 
analysis may often be effected by the agency of the nitric acid, which 
communicates to them oxygen, and by the resulting compound « as- 
certains the nature of their acidifiable base. 
The proximate principles of vegetables are : poner, and of very 
different kinds. They are not all to. be 1 ae very plant, or — 
in every period of vegetation, but each them = to be found : 
some plants, at certain periods of their growth. 
a) are all the products of vegetation from a common jui 
‘Sap which circulates Ae bh through every part of the vegetable 
. 
: 4 a : 3 Seog ‘into contact, in the: vessels. 
