THE VOLATILE PART OF PLANTS. 85 
that in the living plant cellulose passes into pectose and 
pectin. Without doubt, also, the reverse transformations 
may be readily accomplished. 
4. Tar Vuceraste Acips.—The Vegetable Acids are 
very numerous. Some of them are found in all classes of 
plants, and nearly every family of the vegetable kingdom 
contains one or several acids peculiar to itself. Those 
which concern us here are few in number, and though 
doubtless of: the highest: importance in the economy of 
vegetation, are of subordinate interest to the objects of 
this work, and will be noticed but briefly. They are 
oxalic, tartaric, malic, and citric acids. They occur in 
plants either in the free state, or as salts of lime, potash, 
etc. They are mostly found in fruits. 
Oxalic acid, C, H, O, 2 H, O, exists largely in the com- 
mon sorrel, and, according to the best 
observers, is found in greater or less \ 
quantity in nearly all plants. The pure Y 7 
acid presents itself in the form of color-_ \ 
less, brilliant, transparént crystals, not 
unlike Epsom salts in appearance, (Fig. 
15,) but having an intensely sour taste. 
Oxalic acid forms with lime a salt—the oxalate of lime 
—which is insoluble in pure water. It nevertheless exists 
dissolved in the cells of plants, so long as they are in active 
growth, (Schmidt, Ann. Chem. u. Pharm., 61,297.) To- 
wards the end of the period of growth, it often accumu- 
lates in such quantity as to separate in microscopic crystals. 
These are found in large quantity in the mature leaves and 
roots of the beet, in the root of garden rhubarb, and espe- 
cially in many lichens. 
Oxalate of potash is soluble in water, and exists in the 
juices of sorrel and garden rhubarb. It was formerly 
used for removing ink-stains from cloth and leather, under 
the name of salt of sorrel. Oxalic acid is now employed 
for this purpose. Oxalate of soda is soluble in water, and 
Fig. 15. 
