ill not be eight
measures of proof spirit; in consequence of the _contraction_ which
ensues, there will be a deficiency of about [Symbol: oz.]iv in each
gallon. This must be borne in mind in preparing tinctures.

During a long series of experiments on the preparation of ethers, it
appeared a desideratum to find a ready method of ascertaining how much
spirit of any density would be equal to one chemical equivalent of
absolute alcohol. By a modification of a rule employed by the Excise,
this question may be easily solved. The Excise rule is as follows:--

To reduce from any given strength to any required strength, _add_ the
_overproof_ per centage _to_ 100, or _subtract_ the _underproof_ per
centage _from_ 100. Multiply the result by the quantity of spirit, and
divide the product by the number obtained by _adding_ the _required_ per
centage overproof, or _subtracting_ the _required_ per centage
underproof, to or from 100, as the case may be. The result will give the
measure of the spirit at the strength required.

Thus, suppose you wished to reduce 10 gallons of spirit, at 54
overproof, down to proof, add 54 to 100 = 154; multiply by the quantity,
10 gallons (154 x 10) = 1540. The required strength being proof, of
course there is nothing either to add to or take from 100; therefore,
1540 divided by 100 = 15.4 gallons at proof; showing that 10 gallons
must be made to measure 15 gallons, 3 pints, 4 fl. oz., by the addition
of water.

To ascertain what quantity of spirit of any given strength will contain
one equivalent of absolute alcohol. Add the overproof per centage of the
given spirit to 100, as before; and with the number thus obtained divide
4062.183. The result gives in gallons the quantity equal to four
equivalents (46 x 4).

_Example._--How much spirit at 54 per cent. overproof is equal to 1
equivalent of absolute alcohol?

Here,

54 + 100 = 154 and 4062.183 = 26.3778 galls., or 26 galls. 3 pts.
--------
154

which, divided by 4, gives 6 gallons, 4 pints, 15 oz.

Suppose the spirit to be 60 overproof,--

4062.183 {one-fourth of which is equal
then ---------- = 25.388 gallons, {to 6 gallons, 2 pints,
(100 + 60) {15-1/2 oz.

This rule is founded on the following data. As a gallon of water weighs
10 lbs., it is obvious that the specific gravity of any liquid
multiplied by 10 will give the weight of one gallon. The sp