ually contains a portion of lime, originating from hard water
being used instead of soft, in the preparation of this medicine.

To ascertain the purity of magnesia, add to a portion of it a little
sulphuric acid, diluted with ten times its bulk of water. If the
magnesia be completely soluble, and the solution remains transparent, it
may be pronounced _pure_; but not otherwise. Or, dissolve a portion of
the magnesia in muriatic acid, and add a solution of sub-carbonate of
ammonia. If any lime be present, it will form a precipitate; whereas
pure magnesia will remain in solution.

Calcined magnesia is seldom met with in a pure state. It may be assayed
by the same tests as the common magnesia. It ought not to effervesce at
all, with dilute sulphuric acid; and, if the magnesia and acid be put
together into one scale of a balance, no diminution of weight should
ensue on mixing them together. Calcined magnesia, however, is very
seldom so pure as to be totally dissolved by diluted sulphuric acid;
for a small insoluble residue generally remains, consisting chiefly of
silicious earth, derived from the alkali employed in the preparation of
it. The solution in sulphuric acid, when largely diluted, ought not to
afford any precipitation by the addition of oxalate of ammonia.

The genuineness of calomel may be ascertained by boiling, for a few
minutes, one part, with 1/32 part of muriate of ammonia in ten parts of
distilled water. When carbonate of potash is added to the filtered
solution, no precipitation will ensue if the calomel be pure.

Indeed, some of the most common and cheap drugs do not escape the
adulterating hand of the unprincipled druggist. Syrup of buckthorn, for
example, instead of being prepared from the juice of buckthorn berries,
(_rhamnus catharticus_,) is made from the fruit of the blackberry
bearing alder, and the dogberry tree. A mixture of the berries of the
buckthorn and blackberry bearing alder, and of the dogberry tree, may be
seen publicly exposed for sale by some of the venders of medicinal
herbs. This abuse may be discovered by opening the berries: those of
buckthorn have almost always four seeds; of the alder, two; and of the
dogberry, only one. Buckthorn berries, bruised on white paper, stain it
of a green colour, which the others do not.

Instead of worm-seed (_artemisia santonica_,) the seeds of tansy are
frequently offered for sale, or a mixture of both.

A great many of the essential oils obtain