en hours. The residue in the retorts is removed while still
red-hot to air-tight vessels in which it is allowed to cool. It is
then passed through grinding mills, and is subsequently riddled by
revolving cylindrical sieves. The yield is from 55 to 60% of the bones
carbonized, and the product contains about 10% of carbon and about 75%
of calcium phosphate, the remainder being various inorganic salts and
moisture (6-7%). Animal charcoal has a deep black colour, and is much
used as a filtering and clarifying material. The vapours evolved
during carbonization are condensed in vertical air condensers. The
liquid separates into two layers: the upper tarry layer is floated off
and redistilled; the distillate is termed "bone oil,"[1] and mainly
consists of many fatty amines and pyridine derivatives, characterized
by a most disgusting odour; the residue is "bone pitch," and finds
application in the manufacture of black varnishes and like
compositions. The lower layer is ammoniacal liquor; it is transferred
to stills, distilled with steam, and the ammonia received in sulphuric
acid; the ammonium sulphate, which separates, is removed, drained and
dried, and is principally used as a manure. Both during the
carbonization of the bones and the distillation of the tar inflammable
gases are evolved; these are generally used, after purification, for
motive or illuminating purposes. (C. E.*)

FOOTNOTE:

[1] Bone oil, also known as Dippel's oil, was originally produced by
the distillation of stags' horns; it is of interest in the history of
chemistry, since from it were isolated in 1846 by T. Anderson
pyridine and some of its homologues.

BONE BED, a term loosely used by geologists when speaking generally of
any stratum or deposit which contains bones of whatever kind. It is also
applied to those brecciated and stalagmitic deposits on the floor of
caves, which frequently contain osseous remains. In a more restricted
sense it is used to connote certain thin layers of bony fragments, which
occur upon well-defined geological horizons. One of the best-known of
these is the Ludlow Bone Bed, which is found at the base of the Downton
Sandstone in the Upper Ludlow series. At Ludlow itself, two such beds
are actually known, separated by about 14 ft. of strata. Although quite
thin, the Ludlow Bone Bed can be followed from that town into
Gloucestershire for a distance of 45 m. It is