120 
Gluten and albumen differ from the other 
vegetable products, principally by containing azote. 
When gluten is kept long in water, it undergoes 
fermentation ; ammonia (which contains its azote) 
is given off with acetic acid ; and a fatty matter 
and a substance analogous to woody fibre remain. 
Extract, tannin, and gallic acid, when their 
solutions are long exposed to air, deposit a matter 
similar to woody fibre ; and the solid substances 
are rendered analogous to woody fibre, by slight 
roasting ; and in these cases it is probable that 
part of their oxygene and hydrogene is separated 
as water. 
All the other vegetable principles differ from the 
vegetable acids in containing more hydrogene and 
carbon, or less oxygene ; many of them, there- 
fore, are easily converted into vegetable acids by a 
mere subtraction of some proportions of hydro- 
gene. The vegetable acids, for the most part, 
are convertible into each other by easy processes. 
The oxalic contains most oxygene; the acetic 
the least : and this last substance is easily formed 
by the distillation of other vegetable substances, or 
by the action of the atmosphere on such of them 
as are soluble in water; probably by the mere 
combination of oxygene with hydrogene and car- 
bon, or in some cases by the subtraction of a 
portion of hydrogene. 
Alcohol, or spirits of wine, has been often men- 
tioned in the course of these Lectures. This sub- 
stance was not described amongst the vegetable 
principles, because it has never been found ready 
formed in the organs of plants. It is procured by 
