ibutions to Chemistry,
is to place it within easy reach of every student of Chemistry and of
the History of Chemistry.

The student's attention may be particularly called to Black's tacit
adoption of the quantitative method in a large number of his
experiments, and to the way in which he bases many of his conclusions
upon the results obtained in these experiments. Even yet it is very
frequently stated that the introduction of the quantitative method into
Chemistry (which did not by any means originate with Black) took place
at a considerably later date.

L. D.

EXPERIMENTS

UPON

MAGNESIA ALBA, QUICKLIME,

AND SOME OTHER

ALCALINE SUBSTANCES;

BY JOSEPH BLACK, M.D.[1]

PART I.

Hoffman, in one of his observations, gives the history of a powder
called _magnesia alba_, which had long been used and esteemed as a mild
and tasteless purgative; but the method of preparing it was not
generally known before he made it public.[2]

It was originally obtained from a liquor called the _mother of nitre_,
which is produced in the following manner:

Salt-petre is separated from the brine which first affords it, or from
the water with which it is washed out of nitrous earths, by the process
commonly used in crystallizing salts. In this process the brine is
gradually diminished, and at length reduced to a small quantity of an
unctuous bitter saline liquor, affording no more salt-petre by
evaporation; but, if urged with a brisk fire, drying up into a confused
mass which attracts water strongly, and becomes fluid again when exposed
to the open air.

To this liquor the workmen have given the name of the _mother of
nitre_; and _Hoffman_, finding it composed of the _magnesia_ united to
an acid, obtained a separation of these, either by exposing the compound
to a strong fire in which the acid was dissipated and the _magnesia_
remained behind, or by the addition of an alkali which attracted the
acid to itself: and this last method he recommends as the best. He
likewise makes an inquiry into the nature and virtues of the powder thus
prepared; and observes, that it is an absorbent earth which joins
readily with all acids, and must necessarily destroy any acidity it
meets in the stomach; but that its purgative power is uncertain, for
sometimes it has not the least effect of that kind. As it is a mere
insipid earth, he rationally concludes it to be purgative only when
converted into a sort of neutral salt by an acid in