BOTANIC PHYSICIAN. - 
mable, is sparingly soluble in cold water ; it is dissolved in 
considerable quantity by boiling water, and on cooling, crystallizes 
in white flakes. : . 
_ The last of the native vegetable acids is the gallic acid, hitherto 
distinguished as the principle of astringency. It exists in gallnuts, 
and in all those vegetables termed astringents. It is extracted either 
_ by maceration with water or by sublimation. It is distinguished 
_- from every other acid by the strong attraction which it has forthe 
oxyds of iron, and by forming with them a precipitate of a very deep 
black color. It contains a very large quantity of carbon, combined 
with an inferior proportion of oxygen, and with a very small quanti: 
A principle, which till lately was confounded with the gallie 
_-Rld}as TANNIN, or the tanning principle. It is distinguished from 
_ ‘every other principle by its power of combining with animal jelly, 
_ and forming a substance absolutely insoluble in water. It is ¢on- 
- tained in considerable quantity in the greater part of the vegetable 
astringents, and is generally mixed with the gallic aeid. ee 
Several of the native vegetable acids exist together in the same ve- 
getable. They are never contained in distinct vesicles, but are either 
mixed with the mucilaginous or saccharine juice, or are combined _ 
with the alkalies or earths. Combinations of these acids with lime _ 
or potash, arc, in particular, very abundant in the vegetable kingdom. 
Compounds formed by the union of the sulphuric, nitric, muriatic, — 
¢arbonic, and even phosphoric acids with the alkalies and earths, 
slap cxieh in many vegetables... che rs wy ests oe ae 
_ The last of these proximate principles is the Ligneous part, or — 
woody fibre. It is the basis to- which the others are attached, — 
and composes. the qpemies part of most vegetables, as it forms theit — : 
entire structure. It is insipid and insoluble in water or alcohol, 
and consequently remains as the residuum, after the active. princi= 
ples of any vegetable have been extracted by the action of these soe — 
vents. By the action of the nitrous acid, it affords the malic and 
oxalie acids; by distillation it yields the pyroligneous acid. Its — 
principal constituent part is carbon, combined with hydrogen and — 
oxygen. ; " 
ides those principles of vegetables which can be exhibited as 
listinct bodies, there are some of a more subtile kind, the existence 
of which has been maintained by many chemists; sach as the aroma 
or spiritous rector, the coloring principle, the bitter principle, the — 
narcotic principle, and several others. The existence of these, 
however, is very doubtful ; the properties of smell, taste color, &¢- — 
ge probably fhe result of posauar variations aie anor 
some of the known principles of vegetables, and hot depending 
on any peculiar pith = The odor of vegetables, for instance, 
generally depends on their essential oil ; and all the facts that haw! 
been stated In support of a distinct aroma, are explicable on t 
