1. _Methods based_ on the _specific gravity_, or _per-centage strength_,
by VOLUME:--
[Illustration]
_a._ With SYKES' HYDROMETER. _Revenue system._ The _engraving_ below
represents Sykes' hydrometer, as made by Mr Bate, under the directions of
the Commissioners of Inland Revenue and Customs. It consists of a
spherical ball or float, with an upper and lower stem, and is made of
brass, which (in the more expensive instruments) is usually coated with
gold, to prevent corrosion from damp, and the acidity so generally present
in spirituous liquors. The upper stem (A) is about four inches long, and
is divided into ten parts, each of which contains five subdivisions. There
are nine movable weights of the form _b_, of different sizes, numbered
respectively 10, 20, 30, &c., to 90, each of which represents so many of
the principal divisions of the stem, as its number indicates. In use, one
of these weights is slipped on to the lower stems; and thus, by means of
them, the instrument acquires a range of above 500 divisions, or degrees,
extending from the Revenue 'standard alcohol' (sp. gr. ·825) to water. It
is so formed as to give the sp. gr. with almost perfect accuracy, at 62°
Fahr. When loaded with the weight 60 it sinks in proof spirit to the line
marked (P) on the narrow edge of the stem at 51° Fahr.; and, by further
placing the square weight or cap (also supplied with the instr.) on the
top of the upper stem, it floats exactly at the same point in distilled
water. This weight or cap is found to weigh 43·66 grs., which is
practically 1-12th of the total observed weight of the instrument, and its
poise 60, and hence shows the difference between the gravity of proof
spirit and water, as explained hereafter. The whole is fitted up in a neat
mahogany case, accompanied with a thermometer, and a book of tables
containing corrections for temperature, &c.--_Process._ A glass tube of
the form of fig. _B_ is filled to about the mark (_a_) with the sample for
examination; the thermometer is then placed in the liquor, and stirred
about for two or three minutes (observing not to breathe upon the glass,
nor hold it in the hand), and the temperature noted. The hydrometer is
next immersed in a similar manner, and gently pressed down in the liquor
to the 0 on the stem with the finger; it having been previously loaded
with any one of the nine weights that will cause it to float with the
surface of the spirit at some point on the graduated part of the scale.
The indication at the point cut by the surface of the liquor, as seen from
below, added to the number of the weight with which the float is loaded,
gives a number which must be sought in the hook of Tables, which is always
sold with the instrument. In this book, at the page headed "Temperature as
observed by the Thermometer," and against the part of the column
appropriated to the given indication (weight), will be found the strength
per cent., expressed in degrees over or under proof, by VOLUME, in whole
numbers or decimal parts. In reading off the indication, to ensure
accuracy, it is necessary to allow for the convexity of the liquor at the
part where it immediately rests against the stem.
_Obs._ In an instrument requiring so much care and skill in its
manufacture the purchaser should be careful to procure a perfect one. A
very slight blow, friction from continual wiping with a rough cloth, and
other apparently trivial causes, tend to injure so delicate an instrument.
The shape of the weights occasionally vary; some being intended to be
attached to the hydrometer at the bottom of the spindle, and others to
rest on its top. The first plan is, perhaps, the best, as it tends to make
the instrument float with greater steadiness in the liquor; but, at the
same time, it renders its adjustment by the maker a matter of greater
difficulty.
In employing this instrument, the Revenue officers are instructed to take
the nearest degree above the surface of the mercury, when it stands
between any two degrees of the thermometer; and the division on the scale
of the hydrometer next below the surface of the liquid, when it cuts the
stem between any two lines; thus giving the difference in favour of the
trader in both cases.
By means of the _Table_ at page 64 the hydrometer indication, or the
degrees over or under proof, of the Revenue system, may be converted into
'real specific gravities,' by mere inspection; and the corresponding
'per-centage richness' in alcohol of any sample may be found, either by
WEIGHT or VOLUME.
The specific gravities in this table are such as, on being referred to
Gilpin's Tables, will give the expressions of proof strength answering to
the whole indications of the Revenue hydrometer. Intermediate values at
fifths of indications may be had by taking proportional differences
between the nearest tabular numbers. Thus, to find the specific gravity
that should stand opposite to Indication 70·6, we first obtain the
difference between the densities standing in a line with Indications 70
and 71 respectively, and then say, as 1 : 0·6 :: ·00192. 00·115, and
·94135 + ·00115 = ·94250, the specific gravity required.
_b._ With GLASS ALCOHOLOMETERS. That of Tralles, and most others of a like
description (as made in England), gave the per-centage strength, by
VOLUME, with tolerable accuracy, at the standard temperature of 60° Fahr.
Gay-Lussac's ALCOÖMETRE, which closely resembles that of Tralles, is
adjusted for the temperature of 59° Fahr. (15° Cent.). All of these, to
give at once accurate results, must, of course, be employed at the 'normal
temperature' of the instrument. As, however, in practice, the experiment
cannot be conveniently performed at any 'fixed' temperature but only at
that of the atmosphere, it is obvious that certain corrections are
constantly required in order to obtain results of any value. Perfect
accuracy requires that table for every variation of the thermometer,
founded on actual experiments, should accompany each instrument; as,
without them, tedious and difficult calculations are necessary, which, in
the hurry of the cellar and laboratory, or by persons inexpert at figures,
are not easily performed. A series of such Tables were prepared by
Gay-Lussac, and, with his instrument, are those which are almost
exclusively used in France. For rough purposes, in the absence of Tables
or nicer calculations, it may be useful to know that, for commercial
spirits, at ordinary temperatures, a variation of--
By VOLUME,
5° Fahr. is equal } 1·00% of Alcohol; } 1·794% of Proof
to (about) } or (about) } spirit.
1° " " 0·20% " 0·359% "
5° Cent. " 1·80% " 3·229% "
1° " " 0·36% " 0·646% "
By WEIGHT,
5° Fahr. is equal } 0·80% of Alcohol; } 1·62% "
to (about) } or (about) }
1° " " ·16% " ·32% "
5° Cent. " 1·43% " 2·9% "
1° " " ·28% " ·58% "
TABLE I.--_Showing the Densities and Values of Spirits
at 60° Fahr., corresponding to every Indication of
Sykes' Hydrometer._
+-----------+---------+----------+--------------------+
| | | | Per Cents. of |
| Sykes' | | | Absolute Alcohol. |
|Hydrometer |Strength | Specific +----------+---------+
|Indication.|per cent.| Gravity. | By | By |
| | | | Measure. | Weight. |
+-----------+---------+----------+----------+---------+
| | O.P. | | | |
| 0 | 67·0 | ·81520 | 95·28 | 92·78 |
| 1 | 66·1 | ·81715 | 94·78 | 92·08 |
| 2 | 65·3 | ·81889 | 94·31 | 91·42 |
| 3 | 64·5 | ·82061 | 93·84 | 90·78 |
| 4 | 63·6 | ·82251 | 93·33 | 90·07 |
| 5 | 62·7 | ·82441 | 92·80 | 89·36 |
| 6 | 61·8 | ·82622 | 92·29 | 88·67 |
| 7 | 60·9 | ·82800 | 91·77 | 87·99 |
| 8 | 60·0 | ·82978 | 91·25 | 87·30 |
| 9 | 59·1 | ·83151 | 90·74 | 86·63 |
| 10 | 58·2 | ·83323 | 90·23 | 85·96 |
| 11 | 57·3 | ·83494 | 89·72 | 85·30 |
| 12 | 56·4 | ·83661 | 89·21 | 84·65 |
| 13 | 55·5 | ·83827 | 88·70 | 84·00 |
| 14 | 54·6 | ·83993 | 88·17 | 83·33 |
| 15 | 53·7 | ·84153 | 87·67 | 82·70 |
| 16 | 52·7 | ·84331 | 87·10 | 81·99 |
| 17 | 51·7 | ·84509 | 86·51 | 81·26 |
| 18 | 50·7 | ·84680 | 85·95 | 80·58 |
| 19 | 49·7 | ·84851 | 85·39 | 79·89 |
| 20 | 48·7 | ·85022 | 84·81 | 79·19 |
| 21 | 47·6 | ·85205 | 84·19 | 78·44 |
| 22 | 46·6 | ·85372 | 83·61 | 77·74 |
| 23 | 45·6 | ·85537 | 83·04 | 77·07 |
| 24 | 44·6 | ·85700 | 82·47 | 76·39 |
| 25 | 43·5 | ·85878 | 81·85 | 75·66 |
| 26 | 42·4 | ·86055 | 81·21 | 74·92 |
| 27 | 41·3 | ·86229 | 80·59 | 74·19 |
| 28 | 40·2 | ·86402 | 79·97 | 73·47 |
| 29 | 39·1 | ·86574 | 79·34 | 72·75 |
| 30 | 38·0 | ·86745 | 78·71 | 72·03 |
| 31 | 36·9 | ·86915 | 78·08 | 71·32 |
| 32 | 35·7 | ·87099 | 77·40 | 70·54 |
| 33 | 34·5 | ·87282 | 76·71 | 69·77 |
| 34 | 33·4 | ·87450 | 76·08 | 69·06 |
| 35 | 32·2 | ·87627 | 75·41 | 68·32 |
| 36 | 31·0 | ·87809 | 74·72 | 67·55 |
| 37 | 29·8 | ·87988 | 74·03 | 66·79 |
| 38 | 28·5 | ·88179 | 73·29 | 65·98 |
| 39 | 27·3 | ·88355 | 72·60 | 65·23 |
| 40 | 26·0 | ·88544 | 71·86 | 64·43 |
| 41 | 24·8 | ·88716 | 71·17 | 63·68 |
| 42 | 23·5 | ·88901 | 70·43 | 62·89 |
| 43 | 22·2 | ·89086 | 69·69 | 62·10 |
| 44 | 20·9 | ·89268 | 68·95 | 61·32 |
| 45 | 19·6 | ·89451 | 68·21 | 60·53 |
| 46 | 18·3 | ·89629 | 67·47 | 59·76 |
| 47 | 16·9 | ·89822 | 66·67 | 58·92 |
| 48 | 15·6 | ·89997 | 65·93 | 58·15 |
| 49 | 14·2 | ·90182 | 65·14 | 57·34 |
| 50 | 12·8 | ·90367 | 64·34 | 56·52 |
| 51 | 11·4 | ·90551 | 63·54 | 55·70 |
| 52 | 10·0 | ·90732 | 62·74 | 54·89 |
| 53 | 8·6 | ·90913 | 61·94 | 54·09 |
| 54 | 7·1 | ·91107 | 61·09 | 53·23 |
| 55 | 5·6 | ·91299 | 60·24 | 52·38 |
| 56 | 4·2 | ·91479 | 59·43 | 51·57 |
| 57 | 2·7 | ·91666 | 58·58 | 50·73 |
| 58 | 1·3 | ·91839 | 57·78 | 49·94 |
| | U.P. | | | |
| 59 | 0·3 | ·92037 | 56·86 | 49·04 |
| 60 | 1·9 | ·92228 | 55·96 | 48·17 |
| 61 | 3·4 | ·92408 | 55·10 | 47·33 |
| 62 | 5·0 | ·92597 | 54·19 | 46·46 |
| 63 | 6·7 | ·92798 | 53·22 | 45·53 |
| 64 | 8·3 | ·92984 | 52·30 | 44·65 |
| 65 | 10·0 | ·93176 | 51·36 | 43·76 |
| 66 | 11·7 | ·93367 | 50·39 | 42·84 |
| 67 | 13·5 | ·93586 | 49·34 | 41·86 |
| 68 | 15·3 | ·93758 | 48·31 | 40·90 |
| 69 | 17·1 | ·93949 | 47·29 | 39·96 |
| 70 | 18·9 | ·94135 | 46·29 | 39·04 |
| 71 | 20·8 | ·94327 | 45·20 | 38·04 |
| 72 | 22·7 | ·94518 | 44·09 | 37·03 |
| 73 | 24·7 | ·94709 | 42·96 | 36·01 |
| 74 | 26·7 | ·94899 | 41·82 | 34·98 |
| 75 | 28·8 | ·95092 | 40·63 | 33·92 |
| 76 | 31·0 | ·95288 | 39·40 | 32·82 |
| 77 | 33·2 | ·95484 | 38·10 | 31·68 |
| 78 | 35·6 | ·95677 | 36·76 | 30·50 |
| 79 | 38·1 | ·95877 | 35·32 | 29·24 |
| 80 | 40·6 | ·96068 | 33·90 | 28·01 |
| 81 | 43·3 | ·96259 | 32·41 | 26·73 |
| 82 | 46·1 | ·96457 | 30·77 | 25·32 |
| 83 | 49·1 | ·96651 | 29·08 | 23·88 |
| 84 | 52·2 | ·96846 | 27·31 | 22·38 |
| 85 | 55·5 | ·97049 | 25·39 | 20·77 |
| 86 | 59·0 | ·97254 | 23·41 | 19·11 |
| 87 | 62·5 | ·97458 | 21·39 | 17·42 |
| 88 | 66·0 | ·97660 | 19·41 | 15·78 |
| 89 | 69·4 | ·97857 | 17·46 | 14·16 |
| 90 | 72·8 | ·98057 | 15·51 | 12·56 |
| 91 | 76·1 | ·98261 | 13·58 | 10·97 |
| 92 | 79·2 | ·98452 | 11·85 | 9·56 |
| 93 | 82·3 | ·98657 | 10·04 | 8·08 |
| 94 | 85·2 | ·98866 | 8·28 | 6·65 |
| 95 | 88·0 | ·99047 | 6·83 | 5·48 |
| 96 | 90·7 | ·99251 | 5·25 | 4·20 |
| 97 | 93·3 | ·99448 | 3·80 | 3·03 |
| 98 | 95·9 | ·99658 | 2·31 | 1·84 |
| 99 | 98·2 | ·99851 | ·997 | ·793 |
| 100 | ... | 1·00000 | ... | ... |
+-----------+---------+----------+----------+---------+
This Table {above} has been copied, by permission, from Loftus's 'Inland
Revenue Officer's Manual,' and its correctness verified by W. H. Johnston,
Esq., Surveying General Examiner.
TABLE II.--_Table for finding the Specific Gravity of
any Spirit at 60° Fahr., when the Specific Gravity at
any other Temperature is given._
Water taken as 1000.
+-----------------+----------+-----------------+----------+
| |Correction| |Correction|
|Specific gravity.| for each |Specific gravity.| for each |
| | degree. | | degree. |
+-----------------+----------+-----------------+----------+
| 810 to 820 | ± ·475 | 910 to 920 | ± ·434 |
+-----------------+----------+-----------------+----------+
| 820 " 830 | ± ·473 | 920 " 930 | ± ·424 |
+-----------------+----------+-----------------+----------+
| 830 " 840 | ± ·472 | 930 " 940 | ± ·406 |
+-----------------+----------+-----------------+----------+
| 840 " 850 | ± ·471 | 940 " 950 | ± ·381 |
+-----------------+----------+-----------------+----------+
| 850 " 860 | ± ·471 | 950 " 960 | ± ·340 |
+-----------------+----------+-----------------+----------+
| 860 " 870 | ± ·466 | 960 " 970 | ± ·269 |
+-----------------+----------+-----------------+----------+
| 870 " 880 | ± ·460 | 970 " 980 | ± ·165 |
+-----------------+----------+-----------------+----------+
| 880 " 890 | ± ·456 | 980 " 990 | ± ·090 |
+-----------------+----------+-----------------+----------+
| 890 " 900 | ± ·450 | 990 " 1000 | ± ·084 |
+-----------------+----------+-----------------+----------+
| 900 " 910 | ± ·442 | | |
+-----------------+----------+-----------------+----------+
Thus, by making the proper ADDITION to the apparent strength per cent.,
when the observed temperature is BELOW the normal temperature of the
instrument, or a corresponding SUBTRACTION, when it is ABOVE it, the
strength of the sample may be determined sufficiently near for all
practical purposes.
The following Table, taken from Loftus's 'Inland Revenue Officer's
Manual,' will be found of great value in making these corrections, and has
the merit of being easily applied.
An example will show how this Table is to be used.
_Example._--If a quantity of spirit is of the sp. gr. 894 at 73°, what
will be its sp. gr. at 60°?
Here the sp. gr. being between 890 and 900, we must add ·450 for each
degree of temperature between 73° and 60°. The sp. gr. at 60° would,
therefore, be 894 + (·450 × 13) = 899·85. When the temperature is below
60°, the correction for each degree must be subtracted. When, however,
very accurate results are desired, and the necessary Tables are not
accessible, the sample for trial must be brought to the normal temperature
of the instrument, in the manner explained under HYDROMETRY.
_c._ From the SPECIFIC GRAVITY. The temperature having been taken by a
thermometer, and the specific gravity ascertained by any of the usual
methods, but preferably by means of an accurate glass hydrometer, it
merely becomes necessary to refer to Table I, where, against the number
expressing the specific gravity, the alcoholic content per cent., by
volume, of the sample examined, will be found for 60° Fahr., subject to
the corrections just referred to, when the temperature is either above or
below this point.
If the precise specific gravity sought cannot be found in the _Table_, the
difference between it and the next greater specific gravity must be taken
for the numerator of a fraction, having for its denominator the difference
between the greater and the next less specific gravity in the table. This
fraction, added to the per-centage of alcohol in the fourth column of the
table, opposite the greater sp. gr., will give the true per-centage
sought. Thus, the sp. gr. ·96051 is not in the table, and the next greater
number is ·96068; the former must, therefore, be deducted from the latter,
and the difference (17) put as the numerator of the fraction, having for
its denominator 191, the difference between ·96068 and ·95877. The
fraction (17/191) ·089, so found, added to the per-centage strength
opposite ·96068 in the third column, gives 33·989 as the true per-centage
of alcohol in the given sample.
The per-centage by volume may be converted into per-centage by weight, by
multiplying the former by ·793811, the sp. gr. of absolute alcohol, and
dividing the product by the sp. gr. of the sample. The quotient is the
number of pounds of alcohol in 100 pounds of the given spirit.
Thus:--Suppose 1000 grains by measure of alcohol to weigh 950·92 grains,
and to contain (see Table I) 40·63 per cent. by volume of absolute
alcohol, what per cent. by weight does the sample contain?
·793811 × 40·63 = 32·25254093, and this product divided by ·95092 =
33·917, the true per-centage by weight of absolute alcohol in the sample.
2. Method based on the specific gravity, or per-centage strength by
WEIGHT:--
The specific gravity is ascertained and the Table used in precisely the
same manner as in the "method by volume," already described.
The per-centage by weight may be converted into per-centage by volume, by
multiplying the former by the sp. gr. of the sample, and dividing the
product by the sp. gr. of absolute alcohol. This is merely the reverse of
the operation described above.
_Obs._ The preceding methods of alcoholometry, as well as all others
depending on the sp. gr. refer to UNSWEETENED SPIRITS only; and are
inapplicable to those holding sugar in solution, or any other organic
matter capable of altering the sp. gr. For sweetened spirits, fermented
worts, wine, beer, &c., one or other of the following processes must be
adopted:--
3. Other methods, adapted to either SWEETENED or UNSWEETENED SPIRITS,
Tinctures, Fermented Liquors, &c.--
_a._ By DISTILLATION as originally proposed by M. Gay-Lussac. 300 parts of
the liquor under examination (measured in a graduated glass tube) are
placed in a retort or small still, and a quantity exactly equal to one
third (_i.e._, 100 parts), carefully drawn over; a graduated glass
tube[13] being used as a receiver, and the operation stopped as soon as
the distillate reaches the hundredth degree. The 'alcoholic strength' of
the distilled liquor is then ascertained by any of the usual methods, and
the result divided by three, when the per-centage of alcohol in the
original liquor is at once obtained. If, from want of attention, more than
100 parts should be distilled over, the number which expresses the
relation of the volume of the distilled product to the original bulk of
the liquor tested, must be employed as the divisor. Thus, if 106 parts of
liquor have distilled over (instead of 100), containing 33% of alcohol,
the 300 must be divided by 106, which gives 2·83, and the 33% by this
2·83, which gives 11·66%, the true proportion of alcohol in the original
liquor. The strength at 'proof' may be calculated from this in the usual
way.
[Footnote 13: Mulder, in his 'Chemistry of Wine' recommends this receiver
to be shaped like a bottle, with its neck, or tubular part, bent at right
angles above the line of its scale; and that it should be set in the
centre of a glass jar kept filled with very cold water.]
To ensure accurate results, the acidity (if any) of the liquor must be
neutralised with carbonate of sodium, prior to distillation. It is also
advisable to add 8% or 10% of common salt to the liquor in the retort or
still; this, by raising the boiling point, causes the whole of the spirit
to pass over into the receiver before the distillate has reached the
required measure. This applies more particularly to weak liquors. With
those of greater strength (as the stronger wines), it is better to distil
over 150 parts, and divide the result by 2 instead of 3. To liquors
stronger than 25% by volume of alcohol, or above 52% to 54% under proof,
add about an equal volume of water to the liquor in the still, and draw
over a quantity equal to that of the sample tested; when the alcoholic
strength of the distillate gives, without calculation, the true strength
sought. To liquors stronger than 48% to 50% (14 to 12 u. p.), add thrice
their bulk of water, and do not stop the process until the volume of the
distillate is double that of the sample tested, when the per-centage
obtained must also be doubled. In each case a proportionate quantity of
salt is employed.
REVENUE METHOD. The following is the method adopted in the Inland Revenue
and Customs Laboratories for the estimation of the per-centage of alcohol
in wines, liqueurs, &c. A measure flask is filled up to a mark on its
neck, with the wine, which is then carefully transferred to a distilling
flask or retort, the traces of wine remaining in the former vessel being
rinsed out with small quantities of distilled water, and the rinsings
added to the wine in the latter vessel. About two thirds of the contents
of the retort are then distilled over into the clean measure flask, and
made up to the original bulk with distilled water, at the same temperature
as the sample was previous to distillation. The strength is then taken by
Sykes' hydrometer, and this (if u. p.) deducted from 100, gives the
per-centage of proof spirit in the wine. Thus:--
Strength of distillate = 74·6 u. p. = 25·4 per cent. proof spirit.
_b._ From the TEMPERATURE of the VAPOUR, as originally proposed by
Gröning. The bulb of a thermometer is thrust through a cork into the head
of the still, or other vessel employed, and the temperature of the vapour
in which it is immersed being noted, is sought in the following table:--
TABLE III.--_Showing the Alcoholic Content, by_
VOLUME_, of Boiling Spirits, and of their Vapour, from
the Temperature of the latter, as observed by a
Thermometer._ By GRÖNING.
+---------------+-------------------+-------------------+----------------+-------------------+------------------+
|Temperature of | Alcoholic content | Alcoholic content | Temperature of | Alcoholic content | Alcoholic content|
| the Vapour. | of the Distillate | of the Boiling | the Vapour. | of the Distillate | of the Boiling |
| Fahr. | per cent. | Liquid per cent. | Fahr. | per cent. | Liquid per cent.|
+---------------+-------------------+-------------------+----------------+-------------------+------------------+
| 170·0 | 93 | 92 | 189·8 | 71 | 20 |
| 171·8 | 92 | 90 | 192·0 | 68 | 18 |
| 172·0 | 91 | 85 | 194·0 | 66 | 15 |
| 172·8 | 90-1/2 | 80 | 196·4 | 61 | 12 |
| 174·0 | 90 | 75 | 198·6 | 55 | 10 |
| 174·6 | 89 | 70 | 201·0 | 50 | 7 |
| 176·0 | 87 | 65 | 203·0 | 42 | 5 |
| 178·3 | 85 | 50 | 205·4 | 36 | 3 |
| 180·8 | 82 | 40 | 207·7 | 28 | 2 |
| 183·0 | 80 | 35 | 210·0 | 13 | 1 |
| 185·0 | 78 | 30 | 212·0 | 0 | 0 |
| 187·4 | 76 | 25 | | | |
+---------------+-------------------+-------------------+----------------+-------------------+------------------+
This method is admirably adapted to the purposes of the distiller and
rectifier, as it furnishes a ready means of approximately determining the
strength of the spirit passing over, at every part of the process of
distillation, as well as that of the wash left in the still.
_c._ From the BOILING POINT, as originally proposed by M. l'Abbé
Brossard-Vidal. This method is founded on the fact, that the boiling
points of mixtures of alcohol and water, unlike water alone, are scarcely
disturbed by the addition of saline, saccharine, or extractive matter
within certain limits. It hence offers a ready means of determining the
proportion of alcohol present in spirits, wines, fermented liquors, &c.,
with sufficient accuracy for all ordinary purposes. In applying it, a
thermometer, with a large bulb and a narrow bore, and a movable scale
graduated from 180° to 212° Fahr., is usually employed. Before using it as
an alcoholometer, it is set, with its bulb immersed, in a small metallic
boiler (brass or copper) containing distilled water, which is then raised
to the boiling-point, and the 212° of the scale accurately adjusted on a
level with the surface of the mercury, should it vary from that point.
This is necessary on account of variations of atmospheric pressure causing
corresponding variations of the boiling-points of liquids. It is then
ready for several hours' operations, and, generally, for an entire
business day, without further adjustment. The little boiler is next filled
with the liquor to be examined, and the lamp again lighted. The
temperature as shown by the scale of the instrument at the commencement of
full ebullition being ascertained, may be sought in one of the following
_Tables_, against which the alcoholic content of the liquor will be found
(nearly).
TABLE IV.--_Exhibiting the_ BOILING POINTS _of Mixtures
of Alcohol and Water of the given strengths._ By
GRÖNING.
---------------+------------+----------------+------------
| Alcohol | | Alcohol
Boiling point. | per cent. | Boiling point. | per cent.
Fahr. | by volume. | Fahr. | by volume.
---------------+------------+----------------+------------
205·34 | 5 | 179·96 | 55
199·22 | 10 | 179·42 | 60
195·8 | 15 | 178·7 | 65
192·38 | 20 | 177·62 | 70
189·50 | 25 | 176·54 | 75
187·16 | 30 | 175·46 | 80
185· | 35 | 174·92 | 85
183·38 | 40 | 174·2 | 90
182·12 | 45 | 173·14 | 95
181·58 | 50 | 172· | 100
---------------+------------+----------------+------------
TABLE V.--_Showing the_ BOILING POINTS _of 'under
proof' spirit._ By Dr URE.
----------------+-------------+---------------
Boiling points. | Per-centage | Corresponding
Fahr. | strength. | Sp. Gr.
----------------+-------------+---------------
178·5 | Proof. | ·9200
179·75 | 10· U.P. | ·9321
180·4 | 20· " | ·9420
182·1 | 30· " | ·9516
183·4 | 40· " | ·9600
185·6 | 50· " | ·9665
189· | 60· " | ·9729
191·8 | 70· " | ·9786
196·4 | 80· " | ·9850
202· | 90· " | ·9920
----------------+-------------+---------------
_Obs._ This method does not answer well with spiritous liquor above
'proof,' owing to the variations of their boiling point being so slight as
not to be easily observed with accuracy; but with liquors under 'proof,'
and particularly with wines, beer, and other fermented liquors, due care
being observed, it gives results closely approximating to those obtained
by distillation, and sufficiently accurate for all ordinary purposes. In
testing strong alcoholic solutions it is, therefore, proper to dilute them
with twice their bulk of water; and commercial spirits, with an equal bulk
of water; the results obtained being doubled or tripled as the case may
be.
[Illustration]
_d._ From the EXPANSION of the LIQUID when heated: Silbermann's
DILATATOMETER. The expansion of alcohol between 0° and 212° Fahr. is
triple that of water; and between 77° and 122° Fahr. it is much greater.
Between -14° and -98° Fahr. the rate of expansion is about the ·00047th
part in volume for every degree of Fahrenheit's scale. The measurement of
this expansion has been proposed as a new and ready method of
alcoholometry, adapted to nearly all spirituous and fermented liquors.
Silbermann's instrument, which is based on it (see _engr._), simply
consists of a flat brass or ivory plate (_A_), on which are fixed a
mercurial thermometer (_D_) graduated from 22° to 50° Cent. (= 77° to 122°
Fahr.); and the DILATATOMETER (_B_), which is a glass pipette open at both
ends. A valve of cork, or vulcanised india rubber, closes the tapering end
(_c_); this valve is attached to a movable rod (_C_) which is fastened to
the supporting-plate, and connected with a spring (_f_) and a handle
(_g_) bearing a four-threaded screw, by which the lower orifice of the
pipette can be opened or closed at will. In use, the pipette is filled
with the liquor under examination, to a little above the zero point (0) on
the scale. This is effected by suction, by means of a little piston of
leather (_i_), which fits tightly in the long and wider limb of the
pipette; the valve (_d_) being previously opened by turning the knob
(_h_). The proper quantity of liquor being introduced, and the lower end
closed, the piston is moved up and down two or three times, for the
purpose of drawing the air-bubbles and absorbed air out of the liquid, the
presence of which would vitiate the results of the trial. To allow the
piston to be withdrawn without any shock, or the danger of dividing the
column abruptly, the rod attached to it is made hollow throughout. In
using it the operator applies the ball of his forefinger to the top of the
piston-rod (_E_), in order to create a vacuum as he raises it; and then
withdraws it, to readmit the air when he thrusts it down or removes it
from the tube. The excess of liquid (if any) in the pipette is then run
off until its upper surface is exactly level with the zero (0) of the
scale, at 25° C., to which it is raised by immersion in a water bath of
that temperature, as observed by the thermometer; which is done by very
cautiously turning the rod which depresses the valve. The whole apparatus
is now again immersed in the water bath; and, held by the upper portion of
the plate, kept in gentle motion with the hand, until the temperature
rises to exactly 50° C., when the coefficient of expansion is obtained,
and hence also the proportion of alcohol--the scale of the instrument
being so graduated, from actual experiments previously made upon mixtures
of known composition, as to give, at once, the per-centage of alcohol by
VOLUME (nearly).[14]
[Footnote 14: 'Comptes Rendus,' xvii, 418.]
[Illustration]
_e._ From the TENSION of the VAPOUR:--Geissler's ALCOHOLOMETER. This
method, for which we are indebted to M. Geissler, of Bonn, depends on the
measurement of the tension or elastic force of the vapour of the liquid,
as indicated by the height to which it raises a small column of mercury.
The spirit, wine, or other liquor, of which it is desired to ascertain the
strength, is put into the little flask (_a_), which, when completely
filled, is screwed on to the curved glass-tube which contains the
mercurial column (which is inverted for the purpose), and is closed by the
stop-cock (_b_). The instrument (see _engr._) is then placed erect, and
the flask and lower part of the tube immersed in a water bath, as in the
previous method. The number, on the graduated scale of the instrument
corresponding to the height of the mercury, at the boiling point of the
liquor under examination, gives the per-centage of alcohol by VOLUME
(nearly).
This method furnishes approximative results with great facility and
expedition; and, with proper care, these do not vary more than 1/3 to 1/2
of 1%, from those obtained by distillation. We find, that by having the
diameter of the part of the tube at which the surface of the mercury is
acted on by the vapour a little larger than that of the longer limb, and
by previously abstracting the air from the sample, as in Silbermann's
method, or even by agitation and exposure in an open vessel, the two may
be made to correspond almost exactly.
_f._ From the DIFFERENCE between the sp. gr. BEFORE and AFTER
ebullitiom:--Taberié's method and [OE]NOMETER. The sp. gr. of the sample
is first accurately determined by any of the usual methods. It is next
carefully evaporated, in an open vessel, to one half its volume. The
residuum, when cold, is made up with pure water to exactly its original
measure at its original temperature, and the sp. gr. again ascertained.
The difference between the two being due to the spirit originally present,
furnishes the means of calculating a new sp. gr., from which the
per-centage richness of the sample may be obtained by mere inspection of
the Tables. The observed sp. gr. is the true one, whenever the liquor,
after ebullition and restoration to its original volume, has the same sp.
gr. as water (_i. e._, 1·000), at 60° Fahr. Taberié employs a peculiar
instrument, which he calls an [oe]nometer; but its use is not essential to
his method of alcoholometry. The results are, of course, only
approximative, though sufficient for all ordinary purposes. Prof. Mulder,
however, says that he prefers it to any of the previous methods; and that
the results, with care, are almost as accurate as those obtained by
distillation.
_g._ By means of CARBONATE OF POTASH:--
_g. a._ (Brande's Method.) The liquor for trial is poured into a long,
narrow glass tube (graduated centesimally), until the vessel is
half-filled, and, after the solution of about 12% or 15% of a strong
solution of subacetate of lead, or a little finely powdered litharge, is
agitated until the colour is entirely, or nearly removed. Anhydrous
carbonate of potash, in powder, is next added, until it sinks undissolved,
even after prolonged agitation of the liquid. The whole is now allowed to
repose for a short time, when the alcohol is seen floating on the top of
the aqueous portion of the liquid in a well-marked stratum. Its quantity,
read off by means of the graduations of the tube, and doubled, gives the
per-centage richness of the sample in alcohol, by volume.
This process answers well with cordials, wines, and the stronger ales; but
with very weak liquors it is not to be relied on. The whole operation may
be performed in two to five minutes, and (with these exceptions) furnishes
very reliable approximative results. In most cases the decolouring part of
the process may be omitted. The alcohol thus separated has a sp. gr. of
from ·8061 to ·8118, and contains 3% or 4% of water; but for ordinary
purposes it may be regarded as pure alcohol.
4. Alcoholometry of MINUTE QUANTITIES of liquid. When only a few drops, or
a quantity too small for the application of the preceding methods, can be
obtained, an organic analysis may be had recourse to, and the quantity of
absolute alcohol calculated from that of the resulting carbonic anhydride
and water; care being previously taken to free the sample from other
volatile bodies, if it contains any of them.
_Gen. commentary._ The duties on spirits in England are charged on the
number of proof gallons they contain, which is ascertained by gauging or
weighing the spirit, and then trying its strength by Sykes' hydrometer.
The per-centage of proof spirit multiplied by the number of gallons gives
the net amount of proof spirit to be charged.
'PROOF STRENGTH' is an arbitrary standard, adopted for the purpose of
facilitating calculations, for which it is well suited; although pure
alcohol would, for this purpose, be more simple. As defined by Act of
Parliament, 58 Geo. III, c. 28, "proof spirit" is such "as shall, at the
temperature of 51° of Fahrenheit's thermometer, weigh exactly twelve
thirteenth parts of an equal measure of distilled water."
Taking, therefore, water at 51° Fahr. as unity, the sp. gr. of "proof
spirit" at 51° Fahr. is 12/13 of 1·000 or ·92308. When such spirit is
raised to the temperature of 60° Fahr., its density is ·91984.
Spirit at "proof" contains very nearly equal weights of absolute alcohol
and water; the exact proportions according to recent experiments are:--
---------------------------------------------------------------------
| By VOLUME. | |
By WEIGHT. |---------------------------------------| Sp. gr. at |
| Bulk before | Bulk after admixture| 60° Fahr. |
| admixture. | and condensation. | |
----------------+-----------------+----------------------------------|
Alcohol. Water.| Alcohol. Water.| |
100·00 + 103·08 | 100·00 + 81·80 | 175·23 } ·91984 |
49·24 + 50·76 | 57·06 + 46·68 | 100·00 } |
---------------------------------------------------------------------
The standard alcohol of the Revenue authorities, and that on which
Gilpin's Tables are founded, is a spirit of the sp. gr. ·825 at 60° Fahr.,
which is said to contain, by weight, 89% of pure alcohol of ·796; and
92·6% of alcohol, by volume, which corresponds to about 62·5 o. p.
It is of great importance to the spirit dealer to be able to estimate
correctly the number of 'proof gallons' in any quantity of his
commodities, or in the whole or any portion of his stock, as disagreeable
errors frequently result from ignorance on this point. Calculations of
this kind are extremely simple. Thus, when we find, by the hydrometer,
that a given sample of spirit is 10 per cent. over-proof, it means, that
100 gallons of such spirit contain as much alcohol as 110 gallons of proof
spirit.
In over-proof spirit, the per-centage o. p. always represents the quantity
of water which the given spirit requires to reduce it to proof. By adding
this per-centage over-proof to 100, we obtain a number which, multiplied
by any number of gallons, and divided by 100, gives the exact number of
proof gallons which is contained in any quantity of the spirit referred
to. Thus:--A puncheon of rum gauged at 91 galls., and shown by the
hydrometer to be 21 o. p., contains--
21 o. p. of sample added to 100 121
No. of gallons of rum 91
------
11011