Take a long narrow bottle, such as an old-fashioned Eau-de-Cologne
bottle, and put into it two and a half drachms of camphor, and eleven
drachms of spirit of wine; when the camphor is dissolved, which it
will readily do by slight agitation, add the following mixture:--Take
water, nine drachms; nitrate of potash (saltpetre), thirty-eight
grains; and muriate of ammonia (sal ammoniæ), thirty-eight grains.
Dissolve these salts in the water prior to mixing with the camphorated
spirit; then shake the whole well together. Cork the bottle well, and
wax the top, but afterwards make a very small aperture in the cork
with a red-hot needle. The bottle may then be hung up, or placed in
any stationary position. By observing the different appearances which
the materials assume, as the weather changes, it becomes an excellent
prognosticator of a coming storm or of fine weather.