Part 16
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.
_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.]
_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
No. of gal. of proof-spirit = 11011 / 100 = 110·11
In like manner when a spirit is said to be 11 u. p., or under-proof, it means that 100 gal. of such spirit contains 11 gal. of water, and 89 gal. of 'proof spirit.' By deducting the per-centage under-proof from 100, we not only obtain the number of proof gal. contained in 100 gal. of such spirit, but, as in the last case, a factor which multiplied by any number of gal., and divided by 100, gives the exact number of 'proof gallons' contained in any quantity of the given strength. Thus:--An ullage brandy piece containing 45 gal. of spirit at 10 u. p., would have the proof value of--
Per cent. u. p. of sample 10, } subtracted from 100 } 90 No. of gall 45 --- 4050
Quantity of proof spirit = 4050 / 100 = 40·50
Or exactly 40-1/2 gallons.
The strength of absolute alcohol (sp. gr. ·7938) is estimated at 75-1/4% over-proof. It therefore contains 175-1/4% of 'proof spirit,' whilst proof spirit (sp. gr. ·91984) contains 57·06% of 'absolute alcohol,' both being by measure or volume. Thus--
(meas. of alc. × 175-1/4) / 100 = equiv. meas. of pf. spt.
And--
(meas. of pf. spt. × 57·06) / 100 = equiv. meas. of abs. alc.
From which we derive the 'constant multipliers' 1·7525 (or roughly 1-3/4), and ·5706, applicable to any number of volumes or gallons. For--
meas. of alc. × 1·7525 = equiv. meas. of pf. spt.
and--
meas. of pt. spt. × ·5706 = equiv. meas. of alc.
To ascertain what quantity of a spirit at any given strength is equiv. to or contains 100 lbs. of absolute alcohol, we have only to divide the constant number 2207·7 by the proof value per cent. of such spirit.[15] Thus--for a spirit 12 u. p.--this would be
[Footnote 15: This number is obtained thus:--
100 /·79381 = 12·6 (nearly),
12·6 × 175·25 = 2207·7.
]
100 - 12 = 88% of proof spirit;
and--
2207·7 / 88 = 25·1 gal. (nearly).
That is, 25-1/10 gal. of such spirit would contain 100 lbs. of absolute alcohol.
By removing the decimal point one place to the _right_, we have the equiv. measure of 1000 lbs. By removing it one, two, or three places to the _left_, we have it respectively for 10 lbs., 1 lb., and 1/10 lb.; from which the equiv. for all other weights may be easily obtained.