renates of peroxide of iron and of oxide of manganese
are but very slightly soluble; crenate of alumina is insoluble. The
apocrenates of iron and manganese are slightly soluble; those of lime,
magnesia, and alumina are insoluble. All the insoluble crenates and
apocrenates, are soluble in solutions of the corresponding salts of the
alkalies.

Application of these facts will be given in subsequent paragraphs. It
may be here remarked, that the crenate of protoxide of iron is not
unfrequently formed in considerable quantity in peat-bogs, and
dissolving in the water of springs gives them a chalybeate character.
Copious springs of this kind occur at the edge of a peat-bed at
Woodstock, Conn., which are in no small repute for their medicinal
qualities, having a tonic effect from the iron they contain. Such
waters, on exposure to the air, shortly absorb oxygen, and the substance
is thereby converted into crenate and afterwards into apocrenate of
peroxide of iron, which, being but slightly soluble, or insoluble,
separates as a yellow or brown ochreous deposit along the course of the
water. By further exposure to air the organic acid is oxidized to
carbonic acid, and hydrated oxide of iron remains. Bog-iron ore appears
often to have originated in this way.

_Gein and Geic acid._--Mulder formerly believed another substance to
exist in peat which he called _Gein_, and from this by the action of
alkalies he supposed geic acid to be formed. In his later writings,
however, he expresses doubt as to the existence of such a substance,
and we may omit further notice of it, especially since, if it really
do occur, its properties are not distinct from those of humic acid.

We should not neglect to remark, however, that the word gein has been
employed by some writers in the sense in which we use humus, viz.: to
denote the brown or black products of the decomposition of vegetable
matters.

It is scarcely to be doubted that other organic compounds exist in peat.
As yet, however, we have no knowledge of any other ingredients, while it
appears certain that those we have described are its chief constituents,
and give it its peculiar properties. With regard to them it must
nevertheless be admitted, that our chemical knowledge is not entirely
satisfactory, and new investigations are urgently demanded to supply the
deficiencies of the researches so ably made by Mulder, more than twenty
years ago.

_Elementary Composition of Peat._

After thi