ecific
gravity of absolute alcohol is 0.793811; hence, the weight of one gallon
will be 7.93811 lbs., and its strength is estimated at 75.25 overproof.

4 equivalents of alcohol = 46 x 4 = 184,

and

23.17936 gallons x 7.93811 lbs. per gallon, also = 184.0003094.

Hence it appears that 23.17936 gallons of absolute alcohol are equal to
4 equivalents. By adding the overproof per centage (75.25) to 100, and
multiplying by the quantity (23.17936 gallons) we get the constant
number 4062.183.

The rule might have been calculated so as to show _at once_ the
equivalent, without dividing by 4; but it would have required several
more places of decimals; it will give the required quantity to a
fraction of a fluid drachm.

* * * * *

PURIFICATION OF SPIRITS BY FILTRATION.

BY MR. W. SCHAEFFER.

Instead of resorting to repeated distillations for effecting the
purification of spirits, Mr. Schaeffer proposes the use of a filter. In
a suitable vessel, the form of which is not material, a filtering bed is
constructed in the following manner:--On a false perforated bottom,
covered with woollen or other fabric, a layer of about six inches of
well-washed and very clean river sand is placed; next about twelve
inches of granular charcoal, preferring that made from birch; on the
charcoal is placed a layer of about one inch of wheat, boiled to such an
extent as to cause it to swell as large as possible, and so that it will
readily crush between the fingers. Above this is laid about ten inches
of charcoal, then about one inch of broken oyster shells, and then about
two inches more of charcoal, over which is placed a layer of woollen or
other fabric, and over it a perforated partition, on to which the spirit
to be filtered is poured; the filter is kept covered, and in order that
the spirit may flow freely into the compartment of the filter below the
filtering materials, a tube connects such lower compartment with the
upper compartment of the filter, so that the air may pass freely
between the lower and upper compartments of the filter. On each, of the
several strata above described, it is desirable to place a layer of
filtering paper.

The charcoal suitable for the above purpose is not such as is obtained
in the ordinary mode of preparation. It is placed in a retort or oven,
and heated to a red heat until the blue flame has passed off, and the
flame become red. The charcoal is then cooled in water, i