OF THE AREOMETER, OR PROOF BOTTLE.
This instrument is indispensable to the distiller: it ascertains the
value of his spirits, since it shows the result of their different
degrees of concentration. I will give the theory of this useful
instrument, as it may be acceptable to those who do not know it.
Bodies sink in fluids, in a _compound ratio_ to the volume and the
density of those fluids, which they displace. It is from that law of
nature, that a ship sinks 20 feet in fresh water, while it sinks only
about 18 feet in sea water, which has more density on account of the
salt dissolved therein.
The reverse of this effect takes place in fluids lighter than water, as
bodies floating in them sink the more, as the liquor has less density.
Upon those principles are made two kinds of areometers--one for fluids
denser than water; the other for those that are lighter: the first are
called _salt proof_; the second _spirit proof_. Distilled water is the
basis of those two scales: it is at the top for the _salt proof_, and at
the bottom for the _spirit proof_; because the first is ascending, and
the other descending; but by a useless singularity, the distilled water
has been graduated at 10° for the spirit proof bottle, and at 0 for the
_salt proof_. We shall only dwell upon the first, because it is the only
one interesting to the distiller.
Water being graduated at 10° in the areometer, it results from thence
that the spirit going to 20°, is in reality only 10° lighter than water;
and the alcohol gaaduated [TR: graduated] at 35°, is only 25° above
distilled water.
The areometer can only be just, when the atmosphere is temperate; that
is, at 55° Fahrenheit, or 10° Reaumur. The variations in cold or heat
influence liquors; they acquire density in the cold, and lose it in the
heat: hence follows that the areometer does not sink enough in the
winter, and sinks too much in the summer.
Naturalists have observed that variation, and regulated it. They have
ascertained that 1° of heat above temperate, according to the scale of
Reaumur, sinks the areometer 1/8 of a degree more; and that 1° less of
heat, had the contrary effect: thus the heat being at 18° of Reaumur,
the spirit marking 21° by the areometer, is really only at 20°. The cold
being at 8° below temperate, the spirit marking only 19° by the
areometer, is in reality at 20°. 2-1/4 of Fahrenheit corresponding to 1°
of Reaumur, occasion in like manner a variation of 1/8 of a degree:
thus, the heat being at 78-1/2°, the spirit thus marking 21°, is only at
20; and the cold being at 87°, the spirit marking only 19° by the
areometer, is in reality at 20°.
It is easily conceived, that extreme cold or extreme heat occasion
important variations. For that reason, there are in Europe inspectors,
whose duty it is to weigh spirits, particularly _brandy_: for that
purpose they make use of the areometer and the thermometer. An
areometer, to be good, must be proved with distilled water, at the
temperature of 55°. Areometers, being made of glass, are brittle, and
must be used with great care. This inconvenience might be remedied, by
making them of silver; I have seen several of this metal. A good
silversmith could easily make them; I invite those artists to attend to
that branch of business; it might become valuable, as the distillers
will be more enlightened.