r, or any other strong acid,
there separates a bulky brown or black substance, which, after a time,
subsides to the bottom of the vessel as a precipitate, to use a chemical
term, leaving the liquid of a more or less yellow tinge. This deposit,
if obtained from light brown peat, is _ulmic acid_; if from black peat,
it is _humic acid_. These acids, when in the precipitated state, are
insoluble in vinegar; but when this is washed away, they are
considerably soluble in water. They are, in fact, modified by the action
of the soda, so as to acquire much greater solubility in water than they
otherwise possess. On drying the bulky bodies thus obtained, brown or
black lustrous masses result, which have much the appearance of coal.

_Ulmin_ and _Humin_.--After extracting the peat with solution of
carbonate of soda, it still contains ulmin or humin. These bodies cannot
be obtained in the pure state from peat, since they are mixed with more
or less partially decomposed vegetable matters from which they cannot be
separated without suffering chemical change. They have been procured,
however, by the action of muriatic acid on sugar. They are indifferent
in their chemical characters, are insoluble in water and in solution of
carbonate of soda; but upon heating with solution of hydrate of soda
they give dark-colored liquids, being in fact converted by this
treatment into ulmic and humic acids, respectively, with which they are
identical in composition.

The terms ulmic and humic acids do not refer each to a single compound,
but rather to a group of bodies of closely similar appearance and
properties, which, however, do differ slightly in their characteristics,
and differ also in composition by containing more or less of oxygen and
hydrogen in equal equivalents.

After complete extraction with hydrate of soda, there remains more or
less undecomposed vegetable matter, together with sand and soil, were
these contained in the peat.

_Crenic_ and _apocrenic acids_.--From the usually yellowish liquid out
of which the ulmic and humic acids have been separated, may further be
procured by appropriate chemical means, not needful to be detailed
here, two other bodies which bear the names respectively of _Crenic
Acid_ and _Apocrenic Acid_. These acids were discovered by Berzelius,
the great Swedish chemist, in the water and sediment of the Porla
spring, in Sweden.

By the action upon peat of carbonate of ammonia, which is generated to
some ex