1. An excellent acetic acid, of considerable strength, may be made by
soaking fresh-burnt and perfectly dry charcoal in common vinegar, and then
subjecting it to distillation. The water comes over first, and on
increasing the heat, the acid follows. Vinegar-bottoms and waste vinegar
may be used.
2. By exposing vinegar, or dilute acetic acid, to the air in very cold
weather, or to freezing mixtures, the water separates in the form of ice,
and the strong acetic acid may be obtained by draining it into suitable
glass vessels, observing to do so at a temperature sufficiently low to
keep the water solid. Said to answer well in cold climates.
3. Acetic acid containing 20% of water may be deprived of a good deal of
its superfluous water by standing over dry sulphate of soda. (Liebig.) It
may then be used either with or without distillation.
4. Acetic acid, of ordinary strength, may be concentrated to any degree,
by rectification once, or oftener, from dry acetate of potash or soda,
rejecting the first and last portions. The same acetate may be used
repeatedly. The temperature need not exceed 400°, and must not rise above
570° Fahr.
ACETIC ACID. (B. P.) _Syn._ ACIDUM ACETICUM. Water mixed with 33% of
hydrated acetic acid. Prepared by distilling acetate of soda with
sulphuric acid. Colourless sour liquid. Sp. gr. 1·044.
_Prop._ Pure hydrated acetic acid is a thin, colourless liquid above 62
Fahr.; at 50° to 55° it crystallises in large, brilliant, colourless,
transparent needles and plates, and even at 60° if a crystal of the acid
be dropped in; at 40° it is a solid crystalline mass. Sp. gr.--liquid,
1·063 (Mollerat) to 1·0635 (Mohr);[3]--crystallised, 1·135 at 55° Fahr.
(Ure). Odour, intensely pungent when concentrated, but grateful, fragrant,
and refreshing, when diffused; taste, intensely sour and acrid, becoming
agreeable and refreshing, on sufficient dilution with water; volatile;
inflammable, burning with a white flame; vapour of boiling acid highly
combustible; dissolves camphor, resins, gum resins, volatile oils,
gelatin, gliadin, coagulated albumen, and fibrin (as muscle or the
crassamentum of the blood); it coagulates casein, but not liquid albumen
(as the serum of the blood and white of egg): miscible with alcohol,
ether, and water in all proportions; boils at 248° Fahr.;[4] and is
decomposed at a red heat. Its salts are called ACETATES (which _see_).
[Footnote 3: 1·064--H. M. Witt (Ure's '_Dict., of Arts, M. & M._,' 5th
ed.); 1·063 to 1·065--Muspratt ('_Chemistry, Theor. & Prac._,' p. 2);
1·06296--Pereira (4th ed.); 1·0629--Brande; 1·062--Ure; 1·057--Berzelius
('_Jahr. ber._,' xvi, 192):--variations evidently arising from difference
of purity in the acid examined, or from difference of temperature. The sp.
gr. 1·080, with other numbers given by Prof. Lehmann ('_Chemistry_,' Day's
Transl.), is probably a misprint.]
[Footnote 4: This is the boiling-point given by the best authorities, and
confirmed by Gerhardt ('_Chimie Organique_,' i, 718). Ure made it 230°(an
error corrected in 5th ed.), Lehmann says 243·140, and others give it at
235°, 240°, &c. An acid of about 80% (sp. gr. 1·073 to 1·0743), its
maximum density, boils at 219° to 220° Fahr.]
_Char., Tests, &c._--1. Free acetic acid reddens litmus paper, like the
other acids; and may be readily recognised by its odour and
volatility:--2. Sesquichloride of iron being added, and the acid then
nearly saturated with ammonia, the fluid acquires a deep dark-red colour.
_Estim._ See ACETIMETRY. Organic mixtures that cannot be thus tested, or
from which the acid cannot be obtained by simple distillation, may be
neutralised, if acid, with carbonate of lime, boiled for a few minutes,
cooled, filtered, the lime precipitated with dilute sulphuric acid, and
the whole submitted to distillation, when the acid contents of the
distillate may be estimated as above.
_Pur._ By heat, it escapes (entirely) in vapour; nothing is precipitated
on the addition of either hydrosulphuric acid, nitrate of silver, or
chloride of barium. Sometimes it is contaminated with sulphurous acid,
which may be recognised by putting a fluid drachm of the acid, mixed with
an ounce of distilled water and half a drachm of pure hydrochloric acid,
also a few pieces of granulated zinc, into a flask. While effervescence
continues suspend a slip of white blotting-paper, moistened with solution
of sub-acetate of lead, in the upper part of the flask above the liquid,
for about five minutes. The paper should not be discoloured, and thus
indicate the absence of sulphurous acid.
_Adult._ The acetic acid of the shops is chiefly adulterated with water.
Sulphurous acid and lead are accidental contaminations; that of the latter
often reaches 2%, making the acid poisonous.
_Phys. eff., &c._ In its concentrated state it is a corrosive and an acrid
poison. Taken internally, it acts by dissolving the animal tissues, and by
thus destroying the organisation causes death, like the other acids. In
the dilute form it acts as a stimulant, rubefacient, alterative,
refrigerant, and escharotic.
_Uses._ Acetic acid is much employed by the chemist and pharmaceutist, in
the manufacture of various preparations, and in analysis; by the perfumer,
in the composition of several of his most refreshing and agreeable scents;
and in medicine, as an antiseptic, stimulant, rubefacient, alterative,
refrigerant, and escharotic. Acetic acid (B. P.) applied by means of a
piece of rag tied to the end of a small stick, is a nearly certain cure
for ring-worm and scaldhead--one or two applications generally effecting a
cure, and the severe smarting it causes is only of short duration; as a
caustic, it removes warts and corns; a piece of lint or blotting-paper
wetted with it and applied to the skin (evaporation being prevented),
forms a useful extemporaneous blister. It was once employed as a
disinfectant; but is now only used as a fumigation, to disguise the
unpleasant smell of the sickroom and crowded assemblies. It is a popular
refreshing scent in faintings, asphyxia, and nervous headache; and is a
valuable rubefacient, astringent, and local stimulant. It is also used as
a rubefacient and caustic in veterinary practice.
In the _arts_, the commercial acid (pure pyroligneous acid) is used by the
engraver to etch his plates; as an antiseptic in pickling and preserving
animal and vegetable substances used as food, and anatomical preparations;
in dyeing and calico printing, and in the manufacture of medicated
vinegars and other pharmaceutical preparations.
In the dilute state, its properties and applications are similar to those
of ordinary vinegar, and are noticed under that head.
_Poisoning_ from acetic acid is rare. When concentrated, it is capable, by
its corrosive and solvent action, of perforating the coats of the stomach
and digestive canal; and it colours the mucus of these organs by the
chemical action it exerts upon the blood. Vinegar in an excessive quantity
acts in a similar way, but in a slighter degree. The _treatment_ and
_antidotes_ are similar to those directed in cases of poisoning by the
other acids. See POISONS.
_Duty, Excise, &c._ See VINEGAR.
_Gen. commentary._ Acetic acid, on the large scale, is principally
prepared from acetate of soda, which yields by a comparatively
inexpensive, and not a difficult operation, an acid sufficiently strong
and pure for commercial purposes, without the necessity of rectification.
In this process shallow vessels of wood or of copper formed without rivets
or solder (except silver solder) in those parts exposed to the action of
the acid, are generally employed for the purpose of the distillation. A
coil of drawn copper pipe, heated by steam having a pressure of 30 to 40
lbs. to the inch, traverses the bottom of the apparatus, to impart the
necessary heat. The refrigerator consists of well-cooled earthenware,
Berlin ware, or glass vessels; and the adopter pipe is also of the same
materials. Another common form, which is even still more convenient, is a
stout copper still, furnished with a cast-iron jacket to hold
high-pressure steam, the usual refrigeratory being employed. In a few
instances the space between the still and jacket is filled with sand, oil,
tallow, or fusible metal; in which case the apparatus is set in brickwork,
and heated by a naked fire. Stills of earthenware are also frequently
employed; and even worms and condensers of silver, or silvered copper, are
sometimes used, and with advantage. With a leaden worm the product is
always contaminated with a little of that metal; the efforts of the
manufacturer to the contrary, by the exclusion of air, and by rejecting
the first and last portions of the distillate, only lessening and not
preventing this evil. A lute (if any) composed of linseed meal and water,
with or without a little powdered plaster of paris, may be employed; but
flat bands and short tubes of well-seasoned vulcanised india rubber are
infinitely more convenient and efficacious. The ingredients being placed
in the still, and well but hastily stirred together with a wooden spatula,
the head is luted on, and the distillation soon afterwards commenced. The
chief care now should be to increase the heat gradually as the
distillation proceeds; and when a steam-heat is not used, to carefully
avoid over-firing, particularly towards the close of the operation. A
little acetic ether is added by some manufacturers. In this way 4 lbs. of
acid of the sp. gr. 1·050, is obtained for every 3 lbs. of acetate of soda
employed. Should rectification be had recourse to, the addition of about 2
or 3% of bichromate of potash, peroxide of manganese, or red oxide of
lead, will remove empyreuma, if present. The first of these substances is
the most effective; the power of the others being in the order in which
they are printed. In distilling the weaker acids and vinegars, it is found
useful to add from 25 to 30% of chloride of sodium, which, by raising the
boiling-point of the liquid, allows the acid the more freely to pass over
(Stein); but this addition proves disadvantageous when any sulphuric acid
is present, in which case sulphate of soda may be employed instead. If
this addition be not made, the whole of the acid cannot be obtained
without distillation to dryness, and the generation of empyreuma.
On the small scale, glass retorts are usually directed to be used, but
glass alembics or flasks are more convenient and safe, as already noticed.
In the preparation of the pure acid, care should be taken that the acetate
of soda does not contain common salt, as the carbonate of soda prepared by
calcination, and frequently used to form the acetate, is generally
contaminated with it, and yields up its hydrochloric acid or chlorine
during the process of distillation, thus vitiating the product. In all the
methods given the product becomes more concentrated in proportion to the
dryness of the acetate and the strength of the oil of vitriol or muriatic
acid employed. By using the one dry, and the other concentrated, glacial
acid may always be obtained by collecting separately the last two fifths
that come over, and submitting this to refrigeration.
According to Melsens, pure GLACIAL ACETIC ACID is most advantageously
obtained by distilling pure and dry acetate of potash with an excess of
strong and moderately pure acetic acid, rejecting that which first passes
over.
Acetate of soda may be safely dried at a temperature of 400° to 450°,
provided care be taken to avoid ignition from contact with sparks. A less
heat is, however, quite sufficient to drive off the whole of its water of
crystallisation. It is known to be dry by its assuming the appearance of a
smooth oily liquid whilst hot. If, whilst heated, it emits fumes, it is
suffering decomposition. The same applies to the other commercial
acetates. Crystallised acetate of soda loses about 2/5ths of its weight by
thorough drying.
When acetate of soda and sulphuric acid are the ingredients employed in
the production of acetic acid, sulphate of soda is formed, which, in the
large way, the chemist returns to the manufacturer of acetate of soda (_i.
e._ to the pyroligneous acid maker), who employs it in the decomposition
of fresh acetate or pyrolignite of lime. In this way the same soda-salt is
employed over and over again, acting merely as the vehicle for the
separation of the crude acetic acid in the solid form, and its easy and
cheap transportation from one point to another. This ingenious method of
mutual assistance resulting from the application of chemical science to
provide for the wants of everyday life, offers some explanation of the
extraordinarily low price at which acetic acid may now be purchased.
The acetic acid of commerce (pure pyroligneous acid) is almost wholly
obtained from the acetates of soda and lime. The principal supply of crude
acetate (pyrolignite) of soda is from America, Norway, and Sweden; but
much is also obtained from our home manufactories. See ACETIFICATION,
ACETIMETRY, FERMENTATION, PYROLIGNEOUS ACID, SODIUM, (Acetate of),
VINEGAR, &c.
More recently, acetic acid has been obtained by decomposing with
hydrochloric acid the double salt of chloride of calcium and acetate of
lime, mentioned by Fritzsche ('Ann. de Poggend,' xxviii, 123). For this
purpose, solutions of acetate of lime and chloride of calcium are mixed
and evaporated, the combined salts readily crystallising in large needles.
These are freed from the mother-liquor and distilled with common muriatic
acid.
The acid furnished by this method requires redistillation, and is,
moreover, contaminated with some of the fatty products always present in
the crude pyrolignite.
=Anhydrous Acetic Acid.= _Syn._ ACETIC ANHYDRIDE. Acetic acid deprived of
the elements of water.
Acetic Acid. Water. Acetic Anhydride.
2C_{2}H_{4}O_{2} - H_{2}O = C_{4}H_{6}O_{3}.
=Aromat'ic Acetic Acid.= _Syn._ AROMATIC VINEGAR; A. SPIRIT OF V.; ACIDUM
ACE'TICUM AROMAT'ICUM, L.--_Prep._ 1. (Ph. E. 1839.) Dried rosemary and
origanum, of each 1 oz.; lavender flowers, 1/2 oz.; bruised cloves, 1/2
dr.; acetic acid (sp. gr. 1·068), 1-1/2 pint; macerate for 7 days,
express, and filter. A fragrant and refreshing perfume. Omitted in Ph. E.
1841 and P. B. 1867.
2. (Ph. E. 1817.) As the last, but using distilled vinegar instead of the
strong acid of the Pharmacop[oe]ia. Inferior.
3. (P. Cod. 1839) Camphor, 2 oz.; oil of lavender, 10 gr.; oil of
cinnamon, 20 gr.; oil of cloves, 30 gr.; concentrated acetic acid, 1 pint.
Very fragrant and refreshing.
4. (Ph. Bor. 1847; Cod. Med. Hamb. 1845.) Oil of cloves, 1 dr.; oils of
lavender and citron, of each 2 scrup.; oils of bergamot and thyme, of each
1 scrup.; oil of cinnamon, 10 drops; strongest acetic acid, 1 oz.; mix.
Limpid; yellow-brown; highly fragrant and refreshing. See ACETIC ACID
(Camphorated), and VINEGAR (Aromatic).
=Beaufoy's Acetic Acid.= A superior commercial acetic acid (_i. e._
purified pyroligneous acid), having a sp. gr. of about 1·044; or
containing about 28% of real acetic acid, or 32 to 33% of the hydrated
acid. Same strength, &c., as ACETIC ACID P. B.
=Cam'phorated Acetic Acid.= _Syn._ CAMPHORATED VINEGAR; ACIDUM ACE'TICUM
CAMPHORA'TUM, L.--_Prep._ 1. (Ph. E. 1841.) Camphor, 1/2 oz.; pulverise it
by means of a few drops of spirit of wine, and then dissolve it in acetic
acid (Ph. E.), 6-1/2 fl. oz.
2. (Ph. D. 1850.) Camphor, 1 oz.; rectified spirit, 1 fl. dr.; pulverise,
and dissolve in strong acetic acid (acid. acet. fort. Ph. D.), 10 fl. oz.
_Obs._ This preparation is intended as a substitute for the aromatic
acetic acid of the shops and previous pharmacop[oe]ias. It is also useful
as an embrocation, in rheumatism and neuralgia; as an extemporaneous
vesicant and counter-irritant; and as a fumigation in fevers, &c.
=Dilute' Acetic Acid.= _Syn._ ACIDUM ACETICUM DILU'TUM, L. Acetic acid, 1
pint; distilled water, 7 pints; mix, Sp. gr. 1·006. One fluid ounce
corresponds to 16 grains of anhydrous acid (3·63 per cent.).
=Glacial Acetic Acid.= _Syn._ ACIDUM ACETICUM GLACIALE. Acetate of soda,
20 oz., is liquefied by a gentle heat, stirred till it becomes
pulverulent, and then further heated until it fuses; it is at once removed
from the fire, and, when cool, the mass is broken up, placed in a 3-pint
stoppered retort connected with a Liebig's condenser, and then treated
with sulphuric acid, 8 fl. oz. When the distillation slackens heat is to
be applied, and the process continued until 6 fl. oz. of acetic acid have
passed over. If a little of the product strikes a blue colour when mixed
with a solution of iodate of potassium containing mucilage of starch, the
whole product must be agitated with perfectly dry black oxide of
manganese, 1/4 oz., and redistilled. Sp. gr. 1·065; contains 85% of
anhydrous acid.
=ACETIC ANHYDRIDE.= See ANHYDROUS ACETIC ACID.
=ACETICA.= [L.] Medicated vinegars.
=ACETIDUX, Dr DELFER'S.= Made by Döllinger, of Berlin. For the radical and
painless removal of warts, corns, hard skin, &c. A solution of 5 grms. of
chromic acid in 15 grms. of water. (Schädler.)
=ACETIFICATION.= _Syn._ ACETIFACIO, L.; ACETIFICATION, Fr.; ESSIGMACHEN,
EINSAÜERN, Ger. In _chemistry_, the act or process of converting into
vinegar; also the state of undergoing such conversion.
Acetic acid is produced either by the partial dehydrogenation and
subsequent oxidation of bodies containing its elements, or by their
destructive distillation. The first is effected--by their exposure, in a
finely divided state, to the action of air or atmospheric oxygen, as in
the quick process of making vinegar; or--by submitting them, in
combination with ferments, to contact with a free supply of atmospheric
air, as in the old field process of making vinegar; or--by exposure to the
direct action of chemical or mechanical oxidizing agents, as condensed air
(platinum-black process), chromic and nitric acid, &c. In general, it is
alcohol more or less dilute, particularly as it exists in fermented
liquors, which is thus converted into acetic acid. In the second process
(destructive distillation), wood is the substance usually employed, and
heat is the agent which develops the acid.
The conversion of alcohol into acetic acid is not immediate and direct.
The atmospheric oxygen first oxidises two atoms of its hydrogen, aldehyd
and water being formed; and this aldehyd uniting with one atom of oxygen
produces one molecule of ACETIC ACID. The changes are represented in the
following equations:--
Alcohol. Oxygen. Aldehyd. Water.
=1.= C_{2}H_{6}O + O = C_{2}H_{4}O + H_{2}O
Aldehyd. Oxygen. Acetic Acid.
=2.= C_{2}H_{4}O + O = HC_{2}H_{3}O_{2}
After the first formation of aldehyd, the two processes, unless
artificially checked, go on simultaneously, as long as any undecomposed
alcohol is present.
The conversion of alcohol into acetic acid, although greatly accelerated
by the presence of nitrogenised organic matter (according to Mulder, of a
fungus--the _Mycoderma Vini_ or Vinegar Plant), is rather a case of
eremacausis (slow combustion) than of fermentation. Acetification effects
combination, as shown by the foregoing equations, whereas fermentation
resolves complex bodies into simpler ones, _e.g._ sugar into alcohol and
carbonic anhydride. Moreover, the presence of ferments is not essential to
the change, since pure alcohol becomes acetified when exposed to the
oxidising agents already named.
Another remarkable distinction between acetification and fermentation is,
that the former requires the continued presence of atmospheric oxygen;
whilst the vinous fermentation after being once established, proceeds
perfectly without it.
During the oxidation of the alcohol of vegetable solutions, some of the
other organic matters present also suffer change. A white gelatinous mass
(_mother of vinegar_)[5] is commonly deposited; but this is a secondary
result of the process, and not, as formerly supposed, one essential to it.
In ordinary cases acetification occurs only at or near the surface of the
liquid; which accounts for the length of time required for the operation
under the old process of 'fielding,' and the shorter time in which it is
accomplished by the improved process of Mr Ham. It proceeds favorably at
temperatures ranging from 60° to 90° Fahr.; and most rapidly at 95° Fahr.
(Liebig). In the 'quick process' of making vinegar a temperature of 90° to
92° is generally aimed at; but it often rises to 100°, or even to 105°,
Fahr. As the temperature falls acetification proceeds more slowly, and at
46 to 50° Fahr. it ceases altogether (Liebig).
[Footnote 5: It has generally been asserted that this substance contains
vibriones, and other low forms of organised life; but Mulder describes it,
under the name _mycoderma aceti_, as a plant of the order 'fungi.' It is
formed at the expense of the constituents of the vinegar, and often causes
whole vats of it to pass into water.]
Aldehyd (see _above_) is an exceedingly volatile substance, and easily
dissipated by a slight heat. It is, therefore, of the highest importance
to duly regulate the temperature, as well as the supply of air, during
acetification. In the 'quick process' of making vinegar the loss from this
cause is always considerable, and often very great. This loss may be
diminished by passing the heated air, as it escapes from the acetifier,
through a porcelain or silvered copper worm or refrigerator, set in a
chamber containing water of a temperature not higher than 40° to 45°
Fahr.; the connection being made at the _lower_ end of the worm, whilst
the upper end is open to the air. On the small scale, as in the
platinum-black process, the loss may be almost entirely prevented by
causing the upper air tube to pass through a vessel containing ice or a
freezing mixture; or by uniting it with the lower end of a Liebig's
condenser.
In liquors undergoing the vinous fermentation, a portion of the newly
formed alcohol is invariably acetified whenever the temperature rises
above 51° Fahr.; and at a higher temperature, this proceeds with a
rapidity often highly injurious to the quality of the liquor. In this way
there is frequently a useless loss of the alcohol, which is rendered more
apparent by the incipient, and sometimes the actual, souring of the
liquor.
=ACETIM'ETRY=. _Syn._ ACETOM'ETRY; ACÉTOMÉTRIE, Fr.; ACETIME'TRIA, &c., L.
The art or process of determining the quantity of pure acetic acid in
vinegar, or in any other liquid. The plans generally adopted for this
purpose are--
I. From the saturating power of the acid, as in the common methods of
acidimetry:--
1. The molecular weight of commercially pure bicarbonate of potash, in
crystals, being 100, whilst that of absolute acetic acid is 60, it is
evident that every ten grains of the bicarbonate will exactly equal 6
grains of the acid. To apply this practically, we have only to exactly
neutralise 100 gr. of the vinegar or solution under examination with the
bicarbonate, observing the usual precautions; then, as 10 is to 6, so is
the number of grains used, to the per-centage strength required. In this,
as in other like cases, it is convenient to form a test-solution with the
bicarbonate, by dissolving it in sufficient water to fill the 100
divisions of any simple form of 'acidimeter,' as _a_, _b_, or _c_; when
the quantity of the solution, and, consequently, of the salt used, may be
read off at once from the graduated portion of the tube. Still greater
accuracy may be obtained by dissolving the bicarbonate in exactly 1000 gr.
of distilled water contained in a 'Schuster's alkalimeter,' previously
very carefully weighed; in which case each grain of the test-solution will
indicate 1/10th of a grain, or 0·1% of absolute acetic acid, whilst every
10 grains will be equal to 1 grain, or 1%.
[Illustration]
The test-solution may also be prepared from bicarbonate of soda, or from
the carbonates of soda or potash, care being taken that the quantity of
the salt dissolved be in proportion to its molecular weight.
2. (Brande.) A small piece of white marble, clean and dry, is weighed, and
then suspended by a silk thread in a weighed sample (say 100 or 1000 grs.)
of the vinegar or acid under examination; the action being promoted by
occasionally stirring the liquid with a glass rod, until the whole of the
acid is saturated, as shown by no further action on the marble being
observable on close inspection. The marble is then withdrawn, washed in
distilled water, dried and weighed. The loss in weight which it has
sustained will be nearly equal to the acetic acid present, or strictly, as
50 (marble) to 60 (absolute acetic acid). The only precautions required
are, to avoid striking the piece of marble with the rod whilst stirring
the solution, or causing loss of substance in it after its withdrawal; and
to allow ample time for the action of the acid on it. If the sample
consists of strong acid, it should be diluted with twice or thrice its
weight of water before suspending the marble in it.
3. (Ure.) 100 grains of the sample under examination is slightly reddened
with tincture of litmus, and ammonia of the sp. gr. 0·992 is added drop by
drop (from an acetimeter holding 1000 water-gr. measure, divided into 100
divisions) until precise neutralisation is effected, indicated by the blue
colour of the litmus being restored. The number of the divisions of the
acetimeter used, multiplied by 60, and the first two right-hand figures of
the product cut off as decimals, gives a number which represents the exact
quantity of absolute acetic acid in the sample. In practice, it is found
more convenient to keep the test-ammonia ready tinged with litmus.
The mode of estimating the per-centage of acetic acid in beers, when
finding their original gravities, is a slight modification of the above. A
test-solution of ammonia is prepared of such a strength that a given bulk
of it will exactly neutralise one per cent. of absolute acetic acid in an
equal bulk of beer, so that, if 100 fluid grains of the solution are
sufficient to neutralise the acid in 1000 fluid grains of beer, such beer
contains one tenth per cent. of acid. A solution of ammonia, diluted with
distilled water until it has the sp. gr. ·9986 at 60°, is of the exact
strength required.
An acetimeter holding 1000 grains, and graduated downwards to 100 equal
divisions, is filled to 0 of the scale with the test-ammonia, which is
then added, drop by drop, to 1000 measured grains of the beer, until
neutralisation takes place. Every division of the acetimeter
(corresponding to ten fluid grains), so emptied, indicates ·01 per cent.
of acetic acid in the beer. The progress of the neutralisation is tested
from time to time with a slip of reddened litmus paper, which should be
suffered to become faintly blue before ceasing to add the ammonia. By this
method the exact per-centage of absolute acetic acid in any sample may be
accurately determined. The only precaution necessary is to be certain that
the 'test-ammonia' has the required sp. gr. (·9986). Test-solutions may
also be prepared with pure potash or pure soda.
II. From the specific gravity of the liquid after it has been neutralised
with hydrate of lime:--
Common hydrate of lime (freshly slaked lime), in powder, is added
gradually to the sample under examination, until it is saturated, when the
sp. gr. of the resulting clear solution of acetate of lime is taken by
Taylor's ACETIMETER. This instrument is so adjusted and graduated as to
float at the mark on the stem called 'proof,' in a solution containing 5%
of absolute acetic acid (No. 24 vinegar). For vinegars stronger than proof
small weights are provided, each of which indicates an additional 5 per
cent. To ascertain the per-centage of real acid, 5% must therefore be
added to the acetimeter number. Thus, without being loaded, the
instrument, floating at the 'proof mark,' indicates a vinegar of 5%; with
one weight, a vinegar of 10%; with two weights, 15%, and so on. According
to this system of notation, each 5% is called a 'vinegar.' An acid of 10%
is said to contain two vinegars; one of 15%, three vinegars, &c. It is
also common to speak of the degrees of the acetimeter as proof or
over-proof. Thus, No. 24 vinegar is said to be proof; one of 5 acetimeter
degrees, 5 over-proof; one of 10 degrees, 10 over-proof, &c. For malt and
wine vinegars, which contain gluten and mucilage, this method is not
strictly accurate, as a portion of these substances escapes precipitation
by the lime, and consequently alters the specific gravity. A small weight
marked 'M' is generally supplied with the acetimeters for trying such
vinegars.