on and
fraud. It is also a curious fact, that from the decomposition of these
artificial camphors by lime, volatile oils may be obtained by
distillation, isomeric with the original oils from which the camphors
were formed; but in neither case has the new product any action on
polarized light.

In conclusion, I would recommend that this oil, as well as all other
essential oils, be kept in a cool, dark place, where no very great
changes of temperature occur.

* * * * *

BENZOIC ACID, AND TESTS FOR ITS PURITY.

BY W. BASTICK.

Dr. Mohr's process for obtaining benzoic acid, which is adopted by the
Prussian Pharmacopoeia, unquestionably has the reputation of being the
best. According to this process, coarsely-powdered gum benzoin is to be
strewed on the flat bottom of a round iron pot which has a diameter of
nine inches, and a height of about two inches. On the surface of the pot
is spread a piece of filtering paper, which is fastened to its rim by
starch paste. A cylinder of very thick paper is attached by means of a
string to the top of the iron pot. Heat is then applied by placing the
pot on a plate covered with sand, over the mouth of a furnace. It must
remain exposed to a gentle fire from four to six hours. Mohr usually
obtains about an ounce and a half of benzoic acid from twelve ounces of
gum benzoin by the first sublimation. As the gum is not exhausted by the
first operation, it may be bruised when cold and again submitted to the
action of heat, when a fresh portion of benzoic acid will sublime from
it. This acid thus obtained, is not perfectly pure and white, and Mohr
states that it is a question, in a medicinal and perfumery point of
view, whether it is so valuable when perfectly pure, as when it contains
a small portion of a fragrant volatile oil, which rises with it from the
gum in the process of sublimation.

The London Pharmacopoeia directs that it shall be prepared by
sublimation, and does not prescribe that it shall be free from this oil,
to which it principally owes its agreeable odor.

By the second sublimation the whole of the benzoic acid is not
volatilized. What remains in the resin may be separated by boiling it
with caustic lime, and precipitating the acid from the resulting
benzoate of lime with hydrochloric acid. Benzoic acid can be obtained
also in the wet way, and the resin yields a greater product in this
process than in the former; yet it has a less perfu