serve as a Substitute for Oak Bark . 429 
parts there exists in these substances an unctuous balsamic 
oleosa-, or vaporoso-spirituoso-ethereous principle. The 
volatile parts become soon disengaged from the rest, by 
the heat of the tanning ley, and evaporate, so that it is 
not at all times possible to discover any specific remains 
of them in the leather. 
If we examine next what the fixed terreo-gurmmj or 
terreo-resinoso-gummy substance consists of, we shall ob- 
tain a very clear knowledge of it, either from considering 
the manner in which it is naturally produced, or by means 
of chemical experiments. This terreous matter is some- 
times coarser, sometimes finer, sometimes in a greater and 
sometimes in a smaller quantity ; and it contains an oily 
substance, or inflammable principle, attached to a light 
acid, of the nature of vegetable acid, but not caustic, like 
mineral acid. In analysing the fixed substance of coria- 
ceous plants, we get by the alembie, out of a pound medi- 
cal weight, nearly the following parts, in a proportion 
more or less different: 1. About an ounce and two 
drachms of a clear, empyreumatic, but not astringent 
phlegm; 2. About two ounces and five drachms of an 
acid yellowish liquor ; 3. An ounce and somewhat more 
than six drachms of an empyreumatic oil. The caput 
mortuum often constitutes one half, or even more, and 
sometimes contains a portion of fixed alkaline salt. In 
dry fruits, juices, and bulbous roots, this proportion suf- 
fers some exceptions. It is easy to conceive that the 
knowledge of these component parts, of their respective 
quantities, and of their properties, which are well known 
to chemists, may lead to that of their effects, and of 
the manner in which they produce them. We shall 
be able then to distinguish a false tanning plant from 
a real one, or to lay aside such as are too weak for 
that purpose. There are some, for example, that are 
