of water = 337·44 = H⁶ O³
acetic acid = 643·20 = H⁶ C⁴ O³
Hence, in this formation of vinegar, 100 parts by weight of alcohol take
68·89 parts of oxygen; and there are produced 58·11 parts of water, and
110·78 of acetic acid.
These beautiful experiments prove, that when in a mere mixture of
alcohol and water, under the influence of the atmospheric air and heat,
some vinegar comes to be formed after a considerable time, the same
formation of vinegar takes place in a similar, but more effective,
manner, when a ferment is present, which acts here in a somewhat
analogous way to the platina powder in the preceding case. Several
azotized substances serve as re-agents towards the acetous
fermentation,--such as vinegar ready-made, vinegar-yeast, or lees,
barley bread, leaven, beer barm, and similar vegetable matters, which
contain gluten. The best and purest ferment is, however, vinegar itself.
With this ferment we must conjoin, as an essential condition of
acetification, the free access of atmospheric air.
It is a well-known fact, that spirituous liquors, as weak brandy, wine,
and beer, &c., may be preserved for years in close vessels, without
undergoing the acetous fermentation, even when they repose upon a layer
of lees. It is equally well known, that these very liquors, if they
stand for some time in open vessels, become readily sour, especially if
exposed, also, to a somewhat high temperature. If we fill a flask with
common brandy, and subject it, without a stopper, to the influence of
air and warmth, the contained liquor may, at the end of many weeks,
discover no sensible acidity: if we add to the same brandy a ferment,
and stop the flask air-tight, everything will still remain unchanged;
but if we leave a portion of air in the flask, or leave it uncorked,
vinegar will soon make its appearance in the brandy.
If we investigate the nature of the air which remains over brandy in the
act of acetification, we shall find that it consists entirely of
carbonic acid and azote, the oxygen being absorbed and combined in the
acetic acid and water formed.
Since this absorption of oxygen from the air can take place only at the
surface of the fermenting liquors, we thus see the necessity and the
practical importance of amplifying that surface, in order to accelerate
and complete the acetification, by multiplying the points of contact
between the alcohol and the oxygen. The essence of the new German method
of rapid acetification depends upon this principle.
Temperature has also a remarkable influence on the formation of vinegar.
The acid fermentation proceeds very feebly in the cold, but takes an
accelerated pace as the heat is raised. It would even appear that
spirituous vapours brought by themselves in contact with atmospheric
air, without the aid of any ferment, are capable of being converted into
acetic acid, since it has happened in the rectification of brandy, in a
still furnished with a large capital and adopter pipe into which air was
allowed to enter, that vinegar made its appearance. Hence, warmth does
not seem to act as a promoter of the combination of alcohol with oxygen
in a merely chemical point of view, but it acts, so to speak,
physically. Over the warm liquor a stratum of spirit vapour appears to
float, which, coming there into conflict with the atmospherical oxygen,
probably causes the generation of some acetic acid, and thus accelerates
the operation, much more than by the mere contact of the oxygen with the
liquid surface.
When we expose any spirituous liquors, as wine, beer, &c., with the
requisite ferment, to the external air, at a temperature of from 64° to
68° Fahr., the fluid, however clear before, becomes soon turbid;
filamentous slimy particles begin to appear moving in the middle and on
the sides of the vessel, and then form a scum on the top of the liquor.
When this scum has acquired a certain thickness and consistence, it
falls in a sediment to the bottom. The Germans call it the vinegar
_mother_, as it serves to excite acetification in fresh liquors.
Meanwhile, the liquor has become warmer than the surrounding air, and
the vinegar process betrays itself by diffusing a peculiar aroma in the
apartment. Whenever all the alcohol present has been converted into
acetic acid, the liquor comes into a state of repose; its temperature
sinks to the pitch of the atmosphere; it becomes bright, and is the
article well known by its taste and smell under the name of vinegar.
Genuine wine or raisin vinegar differs from that formed either from
apples, or sugar, beer, &c., in containing wine-stone or tartar; by
which peculiarity it may be distinguished, except in those cases where
crude tartar has been artificially added to the other vinegars, as a
disguise. Barley-malt vinegar contains some phosphoric acid, in the
state of phosphate of lime or magnesia, derived from the grain.
After these general observations upon acetification, we shall now
proceed to describe the processes for manufacturing vinegar on the
commercial scale.
1. _Wine vinegar._--The first consideration with a vinegar maker is a
good fermenting room, in which the wines may be exposed to a steady
temperature, with an adequate supply of atmospherical air. As this air
is soon deprived of its oxygenous constituent, facilities ought to be
provided for a renewal of it by moderate ventilation. The air holes for
this purpose ought to be so contrived that they may be shut up when the
temperature begins to fall too low, or in windy weather. The best mode
of communicating the proper warmth to a chamber of this kind is by means
of fire-flues or hot water pipes, running along its floor at the sides
and ends, as in a hothouse; the fireplace being on the outside, so that
no dust may be created by it within. The flue is best made of bricks,
and may have a cross section of 10 or 12 inches by 15 deep. The soot
deposited, even when coals are burned, will find ample space in the
bottom of the flue, without interfering essentially with the draught,
for a very long period, if it be made of the above dimensions.
Low-roofed apartments are preferable to high ones; and those built with
thick walls, of imperfectly conducting materials, such as bricks, lined
with lath and plaster work. Should the chamber, however, have a high
ceiling, the fermenting tuns must be raised to a suitable height on
scaffolding, so as to benefit by the warmest air. Sometimes the vinegar
vessels are placed at different levels; in which case the upper ones
acetify their contents much sooner than the under, unless they are
emptied and filled alternately, which is a good plan.
Orleans is the place most famous for vinegars. The building there
destined to their manufacture is called a _vinaigrerie_, and is placed,
indifferently, either on the ground floor or the floor above it; but it
has always a southern exposure, to receive the influence of the
sunbeams. The vessels employed for carrying on the fermentation are
casks, called _mothers_. Formerly they were of a large capacity,
containing about 460 litres (115 gallons, Eng.); but at the present day
they are barrels of half that capacity, or somewhat less than an old
English hogshead. It is now known that the wine passes sooner into
vinegar the smaller the mass operated upon, the more extensive its
contact with the air, and the more genial its warmth. These casks were
formerly arranged in three ranks by means of massive scaffolding; they
are now set in four ranks, but they rest on much smaller rafters,
sustained by uprights, and can be packed closer together. The casks,
which are laid horizontally, are pierced at the upper surface of their
front end with two holes: one, to which the name of _eye_ is given, is
two inches in diameter; it serves for putting in the charge, and drawing
off the vinegar when it is made; the other hole is much smaller, and is
placed immediately alongside; it is merely an air hole, and is necessary
to allow the air to escape, because the funnel completely fills the
other hole in the act of filling the cask.
When new vessels are mounted in a vinegar work, they must be one third
filled with the best vinegar that can be procured, which becomes the
true _mother_ of the vinegar to be made; because it is upon this portion
that the wine to be acidified is successively added. At the ordinary
rate of work, they put at first upon the _mother_, which occupies one
third of the vessel, a _broc_ of 10 litres of red or white wine; eight
days afterwards they add a second _broc_; then a third, and a fourth,
always observing the same interval of time, 8 days. After this last
charge, they draw off about 40 litres of vinegar, and then recommence
the successive additions.
It is necessary that the vessel be always one third empty if we wish the
acetification to go on steadily; but as a portion of the tartar and the
lees forms and accumulates in the lower part of the cask, so as
eventually to counteract the fermentation, the time arrives when it is
requisite to interrupt it, in order to remove this residuum, by clearing
out all the contents. The whole materials must be renovated every 10
years; but the casks, if well made and repaired, will serve for 25
years.
We have mentioned a definite period at which the vinegar may be drawn
off; but that was on the supposition that the process had all the
success we could wish: there are circumstances, difficult to appreciate,
which modify its progress, as we shall presently show. We ought,
therefore, before discharging the vinegar, to test and see if the
fermentation has been complete. We proceed as follows: we plunge into
the liquor a white stick or rod, bent at one end, and then draw it out
in a horizontal direction: if it be covered with a white thick froth, to
which is given the name of _work_ (_travail_), we judge that the
operation is terminated; but if the work, instead of being white and
pearly, be red, the manufacturers regard the fermentation to be
unfinished, and they endeavour to make it advance, by adding fresh wine,
or by increasing the heat of the apartment.
It is not always easy to explain why the fermentation does not go on as
rapidly in one case as in another. There are even certain things which
seem at present to be entirely inexplicable. It happens sometimes, for
example, that although all the vessels have been equally charged, and
with the same wine, yet the fermentation does not form in the same
manner in the whole; it will move rapidly in some, be languid, or
altogether inert, in others. This is a very puzzling anomaly; which has
been ascribed to electrical and other obscure causes, because it is not
owing to want of heat, the casks in the warmest positions being
frequently in fault; nor to the timber of the cask. It, however,
paralyses the process so completely that the most expert vinegar makers
have nothing else for it, when this accident happens, than to empty
entirely what they call the lazy cask, and to fill it with their best
vinegar. The fermentation now begins, and proceeds as well in it as in
the others. See FERMENTATION.
We must here make an important remark, relatively to the temperature
which should prevail in the fermentation room. In many chemical works we
find it stated, that the heat should not exceed 18° R., or 65° Fahr.,
for fear of obtaining bad products. But the vinegar makers constantly
keep up the heat at from 24° to 25° R., 75° to 77° F.; when the
acetification advances much more rapidly, and the vinegar is equally
strong. The best proof of this heat not being too high is, that under
it, the vessels in the upper part of the room, work best and quickest.
In Orleans, cast-iron stoves and wood fuel are used for communicating
the requisite warmth.
Before pouring the wine into the _mothers_, it is clarified in the
following manner. There are tuns which can contain from 12 to 15 pieces
of wine. Their upper end has at its centre an opening of four or five
inches diameter, which may be closed afterwards with a wooden cover;
this opening is for the purpose of receiving a large funnel. The inside
of the tun is filled with chips of beechwood, well pressed down. The
wine is poured upon these chips, allowed to remain for some time, and
then gently drawn off by a pipe in the lower part of the vessel. The
lees are deposited upon the chips, and the wine runs off quite clear.
However, it happens sometimes, notwithstanding this precaution, that the
vinegar, after it is made, requires to be clarified, more particularly
if the wine employed had been weak. The vinegar must be filtered in the
same way; and it derives an advantage from it, as the products of
different casks get thereby mixed and made uniform.
By this Orleans method several weeks elapse before the acetification is
finished; but a plan has been lately devised in Germany to quicken
greatly the acid fermentation by peculiar constructions. This system is
called, the _quick_ vinegar work, because it will complete the process
in the course of 2 or 3 days, or even in a shorter time. It depends,
chiefly, upon the peculiar construction of the fermenting vessels,
whereby the vinous liquor is exposed on a vastly expanded surface to the
action of the atmospheric air.
An oaken tub, somewhat narrower at the bottom than the top, from 6 to 7
feet high and 3 feet in diameter, is furnished with a well-fitted
grooved, but loose, cover. About half a foot from its mouth, the tub has
a strong oak or beech hoop fitted to its inside surface, sufficiently
firm to support a second cover, also well fitted, but moveable. The
space under this second cover is destined to contain the vinous liquor,
and in order to bring it very amply into contact with the atmosphere,
the following contrivances have been resorted to: This cover is
perforated, like a sieve, with small holes, of from 1 to 2 lines in
diameter, and about 1-1/2 inch apart. Through each of these holes a wick
of pack-thread or cotton is drawn, about 6 inches long, which is
prevented from falling through by a knot on its upper end, while its
under part hangs free in the lower space. The wicks must be just so
thick as to allow of the liquor poured above the cover passing through
the holes in drops. The edges of the lid must be packed with tow or hemp
to prevent the liquor running down through the interval.
The whole lower compartment is now to be filled with chips of beechwood
up to nearly the perforated cover. The liquor, as it trickles through
the holes, diffuses itself over the chips, and, sinking slowly, collects
at the bottom of the tub. The chips should be prepared for this purpose
by being repeatedly scalded in boiling water, then dried, and imbued
with hot vinegar. The same measures may also be adopted for the tub. To
provide for the renewal of the air, the tub is perforated at about a
foot from its bottom with eight holes, set equally apart round the
circumference, two thirds of an inch wide, and sloping down, through
which the air may enter into this lower compartment, without the
trickling liquor being allowed to flow out. In order that the foul air
which has become useless may escape, four large holes are pierced in
the sieve cover, at equal distances asunder and from the centre, whose
united areas are rather smaller than the total areas of the holes in the
side of the tub. Into these four holes open glass tubes must be
inserted, so as to stand some inches above the cover, and to prevent any
of the liquor from running through them. The proper circulation of the
air takes place through these draught holes. This air may afterwards
pass off through a hole of 2-1/2 inches diameter in the uppermost cover,
in which a funnel is placed for the supply of liquor as it is wanted to
keep up the percolation.
The temperature of the fermenting compartment is ascertained by means of
a thermometer, whose bulb is inserted in a hole through its side, and
fastened by a perforated cork. The liquor collected in the under vessel
runs off by a syphon inserted near its bottom, the leg of which turns up
to nearly the level of the ventilating air pipes before it is bent
outwards and downwards. Thus the liquor will begin to flow out of the
under compartment only when it stands in it a little below the sieve
cover, and then it will run slowly off at the inclined mouth of the
syphon, at a level of about 3 inches below the lower end of the glass
tubes. There is a vessel placed below, upon the ground, to receive it.
The tub itself is supported upon a wooden frame, or a pier of brickwork,
a foot or 18 inches high.
A tub constructed like the above is called a GRADUATION VESSEL, which
see. It is worked in the following way:--The vinegar room must be, in
the first place, heated to from 100° to 110° F., or till the thermometer
in the graduation vessel indicates at least 77°. The heat may then be
modified. We now pour through the uppermost cover of the tub a mixture,
warmed to 144° F., of 8 parts proof spirits, 25 parts soft water, 15
parts of good vinegar, and as much clear wine or beer. The water should
be first heated, and then the vinegar, spirits, and wine may be added to
it. Of this mixture, so much should be poured in as is necessary to
cover over the second lid, 2 or 3 inches deep, with the liquor; after
which, the rest may be poured slowly in, as it is wanted.
When the liquor has run for the first time through the graduation
vessel, it is not yet sufficiently acidified; but the weak vinegar
collected in the exterior receiving cistern must be a second time, and,
if need be, a third time, passed through the graduation tub, in order to
convert all the alcohol into acetic acid. In general, we may remark,
that the stronger the vinous liquor the more difficult and tedious is
its conversion into vinegar, but it is so much the stronger. To lessen
this difficulty somewhat, it would be well not to put all the spirits at
first into the wash, or mixed liquors, but to add a little more of it at
the second and the third running, especially when we desire to have very
strong vinegar.
After the graduation vessel has been some days at work, it is no longer
necessary to add vinegar to the mixture of spirits and water, since the
sides of the graduation tub, the beech chips, and the packthreads, are
all impregnated with the ferment, and supply its place. The mixture
must, however, be always maintained at the temperature of 100°.
Instead of the above mixture of brandy, water, and wine, we may employ,
according to Dingler, a clear fermented wort of malt, mixed with a
little spirits. The perfect vinegar, which collects in the receiving
cistern, may be immediately racked off into the store casks for sale.
It has been objected to this process, that, in consequence of the
mixture of saccharine and glutinous materials, which are contained in
beer or worts, along with the acetous fermentation, there is also,
partially, a vinous fermentation, and much carbonic acid, thereby
disengaged, so as to obstruct the acetification. This obstruction may be
remedied by a freer circulation of air, or by the exposure of quicklime
in the chamber. It is a more substantial objection, that, from the
addition of beer, &c., more lees, or dregs, are deposited in the
graduation tub, whereby a more frequent cleansing of it, and of the
beech chips, with a loss of time and vinegar, becomes necessary. The
only mode of obviating this difficulty is, to take well-clarified
fermented wash.
Another evil attendant on the quick process is, the evaporation of the
spirituous liquors. Since, in the graduation tub, there is a temperature
of 110°, it is impossible to avoid a loss of spirit from the circulation
and efflux of the air. The air, indeed, that issues from the top hole in
the uppermost cover, might be conducted over an extensive surface of
fresh water, where its spirit would be condensed in a great measure.
But, after all, this fear of great loss is, I believe, groundless;
because the spirit is rapidly acidified by the oxygen of the air, and
thereby rapidly loses its volatility.
The supply of the warm wash should be drawn from a cistern placed near
the ceiling, where the temperature of the apartment is hottest; and it
may be replenished from the partly acetified liquor in the cistern on
the floor. With this view, two cisterns should be placed above, so that
one of them may always contain liquor sufficiently hot, and thus the
process will suffer no interruption.
When malt wash is used for this quick process, the resulting vinegar
must be clarified in a tun with beech chips, as above described. In two
or three days the impurities will be deposited, and the fine vinegar may
be racked off.
The following prescription, for preparing what he calls malt wine, is
given by Dr. Kastner. Eighty pounds of pale barley malt, and 40 pounds
of pale wheat malt, are to be crushed together. These 120 pounds are to
be infused with 150 quarts of water, at the temperature of 122° Fahr.,
afterwards with 300 quarts of boiling water, and the whole body is to be
mashed thoroughly, till all the lumps disappear. It is then to be left
at rest in a large covered tub, for two or three hours, to allow the
grains to settle down, from which the wort is to be drawn off. When it
has fallen to the temperature of 64° Fahr., 15 pounds of good yeast are
to be stirred in, and it must now be left for two or three days to
ferment, in a loosely covered tun. When the vinous fermentation has
taken place, the clear liquor must be drawn off by a tap hole, a little
above the bottom, so as to leave the lees and scum in the tun. This malt
wine, he adds, may be kept for a long time in close vessels, and is
always ready for making quick vinegar.
2. _Malt Vinegar._--The greater part of British vinegar is made from
malt, by the following process:--1 boll of good barley malt, properly
crushed, is to be mashed with water at 160° Fahr. The first water should
have that temperature; the second must be hotter than 160°, and the
third water, for the extraction of all the soluble matter, may be
boiling hot. Upon the whole, not more than 100 gallons of wort should be
extracted. After the liquor has cooled to 75° Fahr., 3 or 4 gallons of
beer yeast are poured in, and well mixed with a proper stirrer. In 36 or
40 hours, according to the temperature of the air, and the fermenting
quality of the wash, it is racked off into casks, which are laid upon
their sides in the fermenting apartment of the vinegar work, which
should be kept at a temperature of 70° at least; in summer partly by the
heat of the sun, but in general by the agency of proper stoves, as above
described. The bung-holes should be left open, and the casks should not
be full, in order that the air may act over an extensive surface of the
liquor. It would be proper to secure a freer circulation to the air, by
boring a hole in each end of the cask, near its upper edge. As the
liquor, by evaporation, would be generally a few degrees colder than the
air of the apartment, a circulation of air would be established in at
the bung-hole, and out by the end holes. By the ordinary methods, three
months are required to make this vinegar marketable, or fit for the
manufacture of sugar of lead.
In making vinegar for domestic purposes, the casks are usually set on
their ends; and they have, sometimes, a false bottom, pierced with
holes, placed about a foot above the true one. On this bottom, a
quantity of _rape_, or the refuse raisins, &c. from the making of
British wines, is laid. The malt liquor has a proper quantity of yeast
added to it. In about 24 hours it becomes warm, and is then racked off
into another similar cask. After some time, this racking process is
discontinued, and the vinegar is allowed to complete its fermentation
quietly. The proper temperature must always be kept up, by placing the
cask in a warm situation. A little wine-stone (_argal_) added to the
malt wash, would make the vinegar liker that made from wine. Sometimes a
little isinglass is employed to clarify vinegar. A portion of sulphuric
acid is often added to it.
3. _Sugar vinegar._--By pursuing the following plan, an excellent sugar
vinegar may be made. In 158 quarts of boiling water dissolve 10 pounds
of sugar, and 6 pounds of wine-stone; put the solution into a fermenting
cask, and when it is cooled to the temperature of from 75° to 80°, add 4
quarts of beer yeast to it. Stir the mixture well, then cover the vessel
loosely, and expose it for 6 or 8 days to the vinous fermentation, at a
temperature of from 70° to 75° Fahr. When it has become clear, draw off
the vinous liquor, and either acetify it in the graduation tub above
described, or by the common vinegar process. Before it is finished, we
should add to it 12 quarts of strong spirits (brandy), and 15 quarts of
good vinegar, to complete the acetous fermentation. With a graduation
tub which has been used, this addition of vinegar is unnecessary.
The following simpler prescription for making sugar vinegar deserves
attention. For every gallon of hot water take 18 ounces of sugar; and
when the syrup has cooled to 75°, add 4 per cent., by measure, of yeast.
When the vinous fermentation is pretty well advanced, in the course of 2
or 3 days, rack off the clear wash from the lees into a proper cask, and
add 1 ounce of wine-stone, and 1 of crushed raisins, for every gallon of
water. Expose it in a proper manner, and for a proper time, to the
acetifying process; and then rack off the vinegar, and fine it upon
beech chips. It should be afterwards put into bottles, which are to be
well corked.
Vinegar obtained by the preceding methods has always a yellowish or
brownish colour. It may be rendered colourless by distillation. For
nicer chemical purposes, this is done in a glass retort; but on a large
scale, it is usually performed in a clean copper still, furnished with a
capital and worm-refrigeratory, either of silver or block tin. It is
volatile at the boiling temperature of water; and if the process be
carried on briskly, it will not sensibly corrode the copper. But we can
never obtain, in this way, a strong article; for, as soon as the vinegar
gets concentrated to a certain degree, we cannot force off the
remainder by heat, for fear of giving it an empyreumatic odour; because
the gluten, colouring matter, &c. begin to adhere to the bottom of the
still. We are, therefore, obliged to suspend the operation at the very
time when the acid is acquiring strength. It has been also proposed to
concentrate vinegar by the process of congelation; but much of it
remains entangled among the frozen water; and common distilled vinegar
is so weak, that it congeals in one mass.
[Illustration: _Fig._ 1.]
Before the process for pyrolignous acid, or wood vinegar, was known,
there was only one method of obtaining strong vinegar practised by
chemists; and it is still followed by some operators, to prepare what is
called radical or aromatic vinegar. This consists in decomposing, by
heat alone, the crystallised binacetate of copper, commonly, but
improperly, called distilled verdigris. With this view, we take a
stoneware retort, (_fig._ 1.) of a size suited to the quantity we wish
to operate upon; and coat it with a mixture of fire clay and horsedung,
to make it stand the heat better. When this coating is dry, we introduce
into the retort the crystallised acetate slightly bruised, but very dry;
we fill it as far as it will hold without spilling when the beak is
considerably inclined. We then set it in a proper furnace. We attach to
its neck an adopter pipe, and two or three globes with opposite
tubulures, and a last globe with a vertical tubulure. The apparatus is
terminated by a Welter’s tube, with a double branch; the shorter issues
from the last globe, and the other dips into a flask filled with
distilled vinegar. Every thing being thus arranged, we lute the joinings
with a putty made of pipeclay and linseed oil, and cover them with glue
paper. Each globe is placed in a separate basin of cold water, or the
whole may be put into an oblong trough, through which a constant stream
of cold water is made to flow. The tubes must be allowed a day to dry.
Next day we proceed to the distillation, tempering the heat very nicely
at the beginning, and increasing it by very slow degrees till we see the
drops follow each other pretty rapidly from the neck of the retort, or
the end of the adopter tube. The vapours which pass over are very hot,
whence a series of globes are necessary to condense them. We should
renew, from time to time, the water of the basins, and keep moist pieces
of cloth upon the globes; but this demands great care, especially if the
fire be a little too brisk, for the vessels become, in that case, so
hot, that they would infallibly be broken, if touched suddenly with cold
water. It is always easy for us to regulate this operation, according to
the emission of gas from the extremity of the apparatus. When the air
bubbles succeed each other with great rapidity, we must damp the fire.
The liquor which passes in the first half hour is weakest; it proceeds,
in some measure, from a little water sometimes left in the crystals,
which when well made, however, ought to be anhydrous. A period arrives
towards the middle of the process when we see the extremity of the beak
of the retort, and of the adopter, covered with crystals of a lamellar
or needle shape, and of a pale green tint. By degrees these crystals are
carried into the condensed liquid by the acid vapours, and give a colour
to the product. These crystals are merely some of the cupreous salt
forced over by the heat. As the process approaches its conclusion, we
find more difficulty in raising the vapours; and we must then augment
the intensity of the heat, in order to continue their disengagement.
Finally, we judge that the process is altogether finished, when the
globes become cold, notwithstanding the furnace is at the hottest, and
when no more vapours are evolved. The fire may then be allowed to go
out, and the retort to cool.
As the acid thus obtained is slightly tinged with copper, it must be
rectified before bringing it into the market. For this purpose we may
make use of the same apparatus, only substituting for the stoneware
retort a glass one, placed in a sand bath. All the globes ought to be
perfectly clean and dry. The distillation is to be conducted in the
usual way. If we divide the product into thirds, the first yields the
feeblest acid, and the third the strongest. We should not push the
process quite to dryness, because there remains in the last portions
certain impurities, which would injure the flavour of the acid.
The total acid thus obtained forms nearly one half of the weight of the
acetate employed, and the residuum forms three tenths; so that about two
tenths of the acid have been decomposed by the heat, and are lost. As
the oxide of copper is readily reduced to the metallic state, its oxygen
goes to the elements of one part of the acid, and forms water, which
mingles with the products of carbonic acid, carburetted hydrogen, and
carbonic oxide gases which are disengaged; and there remains in the
retort some charcoal mixed with metallic copper. These two combustibles
are in such a state of division, that the residuum is pyrophoric. Hence
it often takes fire the moment of its being removed from the cold
retort. The very considerable loss experienced in this operation has
induced chemists to try different methods to obtain all the acid
contained in the acetate. Thus, for example, a certain addition of
sulphuric acid has been prescribed; but, besides that the radical
vinegar obtained in this way always contains sulphurous acid, from which
it is difficult to free it, it is thereby deprived of that spirit called
the _pyro-acetic_, which tempers the sharpness of its smell, and gives
it an agreeable aroma. It is to be presumed, therefore, that the
preceding process will continue to be preferred for making aromatic
vinegar. Its odour is often further modified by essential oils, such as
those of rosemary, lavender, &c.
4. _Pyrolignous Acid, or Wood Vinegar._--The process for making this
acid is founded upon the general property of heat, to separate the
elements of vegetable substances, and to unite them anew in another
order, with the production of compounds which did not exist in the
bodies subjected to its action. The respective proportion of these
products varies, not only in the different substances, but also in the
same substance, according as the degree of heat has been greater or
less, or conducted with more or less skill. When we distil a vegetable
body in a close vessel, we obtain at first the included water, or that
of vegetation; there is next formed another portion of water, at the
expense of the oxygen and hydrogen of the body; a proportional quantity
of charcoal is set free, and, with the successive increase of the heat,
a small portion of charcoal combines with the oxygen and hydrogen to
form acetic acid. This was considered, for some time, as a peculiar
acid, and was accordingly called _pyrolignous_ acid. As the proportion
of carbon becomes preponderant, it combines with the other principles,
and then some empyreumatic oil is volatilised, of little colour, but
which becomes thicker, and of a darker tint, always getting more loaded
with carbon.
Several elastic fluids accompany these different products. Carbonic acid
comes over, but in small quantity, much carburetted hydrogen, and,
towards the end, a considerable proportion of carbonic oxide. The
remainder of the charcoal, which could not be carried off in these
several combinations, is found in the retort, and preserves, usually,
the form of the vegetable body which furnished it. Since mankind have
begun to reason on the different operations of the arts, and to raise
them to a level with scientific researches they have introduced into
several branches of manufacture a multitude of improvements, of which,
formerly, they would hardly have deemed them susceptible. Thus, in
particular, the process for carbonising wood has been singularly
meliorated, and in reference to the preceding observations, advantage
has been derived from several products that formerly were not even
collected.
[Illustration: _Fig._ 2.]
The apparatus employed for obtaining crude vinegar from wood, by the
agency of heat, are large iron cylinders. In this country they are made
of cast iron, and are laid horizontally in the furnace; in France, they
are made of sheet iron riveted together, and they are set upright in the
fire. _Fig._ 2. will give an accurate idea of the British plan, which is
much the same as that adopted for decomposing pit coal in gas works,
only that the cylinders for the pyrolignous acid manufacture are
generally larger, being frequently 4 feet in diameter, and 6 or 8 feet
long, and built horizontally in brickwork, so that the flame of one
furnace may play around two of them. It would, probably, answer better,
if their size were brought nearer the dimensions of the gas-light
retorts, and if the whole system of working them were assimilated to
that of coal gas.
The following arrangement is adopted in an excellent establishment in
Glasgow, where the above large cylinders are 6 feet long, and both ends
of them project a very little beyond the brickwork. One end has a disc
or round plate of cast iron, well fitted, and firmly bolted to it, from
the centre of which disc an iron tube, about 6 inches diameter, proceeds
and enters, at a right angle, the main tube of refrigeration. The
diameter of this tube may be from 9 to 14 inches, according to the
number of cylinders. The other end of the cylinder is called the mouth
of the retort; this is closed by a disc of iron, smeared round its edge
by clay lute, and secured in its place by fir wedges. The charge of wood
for such a cylinder is about 8 cwt. The hard woods--oak, ash, birch, and
beech--are alone used; fir does not answer. The heat is kept up during
the day-time, and the furnace is allowed to cool during the night. Next
morning, the door is opened, the charcoal removed, and a new charge of
wood is introduced. The average product of crude vinegar called
pyrolignous acid, is 35 gallons. It is much contaminated with tar, is of
a deep brown colour, and has a sp. gr. of 1·025. Its total weight is
therefore about 300 lbs., but the residuary charcoal is found to weigh
no more than one fifth of the wood employed; hence nearly one half of
the ponderable matter of the wood is dissipated in incondensable gases.
Count Rumford states, that the charcoal is equal in weight to more than
four tenths of the wood from which it is made. The count’s error seems
to have arisen from the slight heat of an oven to which his wood was
exposed in a glass cylinder. The result now given, is the experience of
an eminent manufacturing chemist.
The crude pyrolignous acid is rectified by a second distillation in a
copper still, in the body of which about 20 gallons of viscid tarry
matter are left from every 100. It has now become a transparent brown
vinegar, having a considerably empyreumatic smell, and a sp. gr. of
1·013. Its acid powers are superior to those of the best household
vinegar, in the proportion of three to two. By redistillation,
saturation with quicklime, evaporation of the liquid acetate to dryness,
and conversion into acetate of soda by sulphate of soda, the
empyreumatic matter is so completely dissipated, that on decomposing the
pure acetate of soda by sulphuric acid, a perfectly colourless and
grateful vinegar rises in distillation. Its strength will be
proportionable to the concentration of the decomposing acid.
The acetic acid of the chemist may be prepared also in the following
modes:--1. Two parts of fused acetate of potash, with one of the
strongest oil of vitriol, yield, by slow distillation from a glass
retort into a refrigerated receiver, concentrated acetic acid. A small
portion of sulphurous acid, which contaminates it, may be removed by
redistillation from a little acetate of lead. 2. Or four parts of good
sugar of lead, with one part of sulphuric acid, treated in the same way,
afford a slightly weaker acetic acid. 3. Gently calcined sulphate of
iron, or green vitriol, mixed with sugar of lead, in the proportion of 1
of the former to 2-1/2 of the latter, or with acetate of copper, and
carefully distilled from a porcelain retort into a cool receiver, may be
also considered an economical process. But that with binacetate of
copper above described, is preferable to any of these.
[Illustration: _Fig._ 3.]
The manufacture of pyrolignous acid is conducted in the following way in
France. Into large cylindrical vessels (_fig._ 3.) made of rivetted
sheet iron, and having at their top and side a small sheet iron
cylinder, the wood intended for making charcoal is introduced. To the
upper part of this vessel a cover of sheet iron, B, is adapted, which is
fixed with bolts. This vessel, thus closed, represents, as we see, a
vast retort. When it is prepared, as we have said, it is lifted by means
of a swing crane, C, and placed in a furnace, D, (_fig._ 4.) of a form
relative to that of the vessel, and the opening of the furnace is
covered with a dome, E, made of masonry or brickwork. The whole being
thus arranged, heat is applied in the furnace at the bottom. The
moisture of the wood is first dissipated, but by degrees the liquor
ceases to be transparent, and becomes sooty. An adopter tube, A, is then
fitted to the lateral cylinder. This adopter enters into another tube at
the same degree of inclination which commences the condensing apparatus.
The means of condensation vary according to the localities. In certain
works they cool by means of air, by making the vapour pass through a
long series of cylinders, or sometimes, even, through a series of casks
connected together; but most usually water is used for condensing, when
it can be easily procured in abundance. The most simple apparatus
employed for this purpose consists of two cylinders, F, F, (_fig._ 4.)
the one within the other, and which leave between them a sufficient
space to allow a considerable body of water to circulate along and cool
the vapours. This double cylinder is adapted to the distilling vessel,
and placed at a certain inclination. To the first double tube, F, F, a
second, and sometimes a third, entirely similar, are connected, which,
to save space, return upon themselves in a zigzag fashion. The water is
set in circulation by an ingenious means now adopted in many different
manufactories. From the lower extremity, G, of the system of condensers,
a perpendicular tube rises, whose length should be a little more than
the most elevated point of the system. The water, furnished by a
reservoir, L, enters by means of the perpendicular tube through the
lower part of the system, and fills the whole space between the double
cylinders. When the apparatus is in action, the vapours, as they
condense, raise the temperature of the water, which, by the column in L
G, is pressed to the upper part of the cylinders, and runs over by the
spout K. To this point a very short tube is attached, which is bent
towards the ground, and serves as an overflow.
[Illustration: _Fig._ 4.]
The condensing apparatus is terminated by a conduit in bricks covered
and sunk in the ground. At the extremity of this species of gutter is a
bent tube, E, which discharges the liquid product into the first
cistern. When it is full, it empties itself, by means of an overflow
pipe, into a great reservoir; the tube which terminates the gutter
plunges into the liquid, and thus intercepts communication with the
inside of the apparatus. The disengaged gas is brought back by means of
pipes M L, from one of the sides of the conduit to the under part of the
ash pit of the furnace. These pipes are furnished with stopcocks M, at
some distance in front of the furnace, for the purpose of regulating the
jet of the gas, and interrupting, at pleasure, communication with the
inside of the apparatus. The part of the pipes which terminates in the
furnace rises perpendicularly several inches above the ground, and is
expanded like the rose of a watering can, N. The gas, by means of this
disposition, can distribute itself uniformly under the vessel, without
suffering the pipe which conducts it to be obstructed by the fuel or the
ashes.
The temperature necessary to effect the carbonisation is not
considerable: however, at the last it is raised so high as to make the
vessels red hot; and the duration of the process is necessarily
proportional to the quantity of wood carbonised. For a vessel which
shall contain about 5 meters cube (nearly 6 cubic yds.), 8 hours of fire
is sufficient. It is known that the carbonisation is complete by the
colour of the flame of the gas: it is first of a yellowish red; it
becomes afterwards blue, when more carbonic oxide than carbonic hydrogen
is evolved; and towards the end it becomes entirely white,--a
circumstance owing, probably, to the furnace being more heated at this
period, and the combustion being more complete. There is still another
means of knowing the state of the process, to which recourse is more
frequently had; that is the cooling of the first tubes, which are not
surrounded with water: a few drops of this fluid are thrown upon their
surface, and if they evaporate quietly, it is judged that the
calcination is sufficient. The adopter tube is then unluted, and is slid
into its junction pipe; the orifices are immediately stopped with plates
of iron and plaster loam. The brick cover, E, of the furnace is first
removed by means of the swing crane, then the cylinder itself is lifted
out and replaced immediately by another one previously charged. When the
cylinder which has been taken out of the furnace is entirely cooled, its
cover is removed, and the charcoal is emptied. Five cubic meters of wood
furnish about 7 chaldrons (voies) and a half of charcoal. (For
modifications of the wood-vinegar apparatus, see CHARCOAL and
PYROLIGNOUS ACID.)
The different qualities of wood employed in this operation give nearly
similar product in reference to the acid; but this is not the case with
the charcoal, for it is better the harder the wood; and it has been
remarked, that wood long exposed to the air furnishes a charcoal of a
worse quality than wood carbonised soon after it is cut.
Having described the kind of apparatus employed to obtain pyrolignous
acid, I shall now detail the best mode of purifying it. This acid has a
reddish brown colour; it holds in solution a portion of empyreumatic oil
and of the tar which were formed at the same time; another portion of
these products is in the state of a simple mixture; the latter may be
separated by repose alone. It is stated, above, that the distilling
apparatus terminates in a subterranean reservoir, where the products of
all the vessels are mixed. A common pump communicates with the
reservoir, and sinks to its very bottom, in order that it may draw off
only the stratum of tar, which, according to its greater density,
occupies the lower part. From time to time the pump is worked to remove
the tar as it is deposited. The reservoir has at its top an overflow
pipe, which discharges the clearest acid into a cistern, from which it
is taken by means of a second pump.
The pyrolignous acid thus separated from the undissolved tar is
transferred from this cistern into large sheet iron boilers, where its
saturation is effected either by quicklime or by chalk; the latter of
which is preferable, as the lime is apt to take some of the tar into
combination. The acid parts by saturation with a new portion of the tar,
which is removed by skimmers. The neutral solution is then allowed to
rest for a sufficient time to let its clear parts be drawn off by
decantation.
The acetate of lime thus obtained indicates by the hydrometer, before
being mixed with the waters of edulcoration, a degree corresponding to
the acidimetric degree of the acid employed. This solution must be
evaporated till it reaches a specific gravity of 1·114 (15° Baumé),
after which there is added to it a saturated solution of sulphate of
soda. The acids exchange bases; sulphate of lime precipitates, and
acetate of soda remains in solution. In some manufactures, instead of
pursuing the above plan, the sulphate of soda is dissolved in the hot
pyrolignous acid, which is afterwards saturated with chalk or lime. By
this means no water need be employed to dissolve the sulphate, and
accordingly the liquor is obtained in a concentrated form without
evaporation. In both modes the sulphate of lime is allowed to settle,
and the solution of acetate of soda is decanted. The residuum is set
aside to be edulcorated, and the last waters are employed for washing
fresh portions.
The acetate of soda which results from this double decomposition is
afterwards evaporated till it attains to the density of 1·225 or 1·23,
according to the season. This solution is poured into large
crystallising vessels, from which, at the end of 3 or 4 days, according
to their capacity, the mother waters are decanted, and a first
crystallisation is obtained of rhomboidal prisms, which are highly
coloured and very bulky. Their facettes are finely polished, and their
edges very sharp. The mother waters are submitted to successive
evaporations and crystallisations till they refuse to crystallise, and
they are then burnt to convert them into carbonate of soda.
To avoid guesswork proportions, which are always injurious, by the loss
of time which they occasion, and by the bad results to which they often
lead, we should determine experimentally, beforehand, the quantities
absolutely necessary for the reciprocal decomposition, especially when
we change the acid or the sulphate. But it may be remarked that,
notwithstanding all the precautions we can take, there is always a
notable quantity of sulphate of soda and acetic acid, which disappear
totally in this decomposition. This arises from the circumstance that
sulphate of soda and acetate of lime do not completely decompose each
other, as I have ascertained by experiments on a very considerable
scale; and thus a portion of each of them is always lost with the mother
waters. It might be supposed that by calcining the acetate of lime we
could completely destroy its empyreumatic oil; but, though I have made
many experiments, with this view I never could obtain an acetate capable
of affording a tolerable acid. Some manufacturers prefer to make the
acetate of soda by direct saturation of the acid with the alkali, and
think that the higher price of this substance is compensated by the
economy of time and fuel which it produces.
The acetate of soda is easily purified by crystallisations and
torrefaction; the latter process, when well conducted, freeing it
completely from every particle of tar. This torrefaction, to which the
name of fusion may be given, requires great care and dexterity. It is
usually done in shallow cast iron boilers of a hemispherical shape.
During all the time that the heat of about 500° Fahr. is applied, the
fused mass must be diligently worked with rakes; an operation which
continues about 24 hours for half a ton of materials. We must carefully
avoid raising the temperature so high as to decompose the acetate, and
be sure that the heat is equally distributed; for if any point of the
mass enters into decomposition, it is propagated with such rapidity, as
to be excessively difficult to stop its progress in destroying the
whole. The heat should never be so great as to disengage any smoke, even
when the whole acetate is liquefied. When there is no more frothing up,
and the mass flows like oil, the operation is finished. It is now
allowed to cool in a body, or it may be ladled out into moulds, which is
preferable.
When the acetate is dissolved in water, the charcoaly matter proceeding
from the decomposition of the tar must be separated by filtration, or by
boiling up the liquor to the specific gravity 1·114, when the
carbonaceous matter falls to the bottom. On evaporating the clear
liquor, we obtain an acetate perfectly fine, which yields beautiful
crystals on cooling. In this state of purity it is decomposed by
sulphuric acid, in order to separate its acetic acid.
This last operation, however simple it appears, requires no little care
and skill. The acetate of soda crystallised and ground is put into a
copper, and the necessary quantity of sulphuric acid of 1·842 (about 35
per cent. of the salt) to decompose almost, but not all, the acetate, is
poured on. The materials are left to act on each other; by degrees the
acetic acid quits its combination, and swims upon the surface; the
greater part of the resulting sulphate of soda falls in a pulverulent
form, or in small granular crystals, to the bottom. Another portion
remains dissolved in the liquid, which has a specific gravity of 1·08.
By distillation we separate this remainder of the sulphate, and finally
obtain acetic acid, having a specific gravity of 1·05, an agreeable
taste and smell, though towards the end it becomes a little
empyreumatic, and coloured; for which reason, the last portions must be
kept apart. The acid destined for table use ought to be distilled in an
alembic whose capital and condensing worm are of silver; and to make it
very fine, it may be afterwards infused over a little washed bone-black.
It is usually obtained in a pretty concentrated state; but when we wish
to give it the highest degree of concentration, we mix with it a
quantity of dry muriate of lime, and distil anew. This acid may be
afterwards exposed to congelation, when the strongest will crystallise.
It is decanted, and the crystals are melted by exposing them to a
temperature of from 60° to 70° Fahr.; this process is repeated till the
acid congeals without remainder, at the temperature of 55° Fahr. It has
then attained its maximum strength, and has a specific gravity of 1·063.
We shall add an observation on the above mode of decomposing the acetate
of soda by sulphuric acid. Many difficulties are experienced in this
process, if the sulphuric acid be poured on in small quantities at a
time; for then such acrid fumes of acetic acid are disengaged, that the
workmen are obliged to retire. This inconvenience may be saved by adding
all the sulphuric acid at once; it occupies the lower part of the
vessel, and decomposes only the portion of the acetate in contact with
it; the heat evolved in consequence of this reaction is diffused through
a great mass, and produces no sensible effect. When the sulphuric acid
forms an opening, or a species of little crater, the workman, by means
of a rake, depresses the acetate into it by degrees, and then the
decomposition proceeds as slowly as he desires.
The acetic acid, like the nitric, chloric, and some others, has not
hitherto been obtained free from water, and the greatest degree of
concentration which we have been able to give it is that in which it
contains only the quantity of water equivalent to the atomic weight of
another oxidized body; a quantity which amounts to 14·89 per cent. The
processes prescribed for preparing concentrated acetic acid sometimes
tend to deprive it of that water without which it could not exist:
hence, in all such cases, there is a part of the acid itself decomposed
to furnish the water necessary to the constitution of the remainder. The
constituent principles of the decomposed portion then form a peculiar,
intoxicating, highly inflammatory liquid, called the PYRO-ACETIC SPIRIT.
The most highly concentrated acid of 1·063 becomes denser by the
addition of a certain quantity of water up to a certain point. According
to Berzelius, the prime equivalent of this acid is 643·189, oxygen being
reckoned 100. Now, the above strongest acid consists of one prime of
acid, and one of water = 1124·79. When it contains three atoms of water,
that is, 337·437 parts to 643·189, or 34·41 to 65·59 in 100, it then has
taken its maximum density of 1·075; after which the further addition of
water diminishes its specific gravity, as the following table of
Mollerat shows. His supposed anhydrous or dry acid contains, at 1·0630,
0·114 parts of water.
_Table of Acetic Acid._
+----------+--------+
| Water in |Specific|
|100 parts.|gravity.|
+----------+--------+
| 0·00 | 1·0630 |
| 8·37 | 1·0742 |
| 17·00 | 1·0770 |
| 23·00 | 1·0791 |
| 28·10 | 1·0763 |
| 33·83 | 1·0742 |
| 37·60 | 1·0728 |
| 47·00 | 1·0658 |
| 50·00 | 1·0637 |
| 51·80 | 1·063 |
+----------+--------+
Acetic acid readily takes fire when it is heated in open vessels to the
boiling point, and it burns with a blue flame, nearly like alcohol. It
must be kept in close vessels, otherwise it loses its strength, by
attracting humidity from the air. When concentrated, it is used only as
a scent, or pungent exciter of the olfactory organs, in sickness and
fainting fits. Its anti-epidemic qualities are apocryphal. What is met
with in the shops under the name of salts of vinegar is nothing but
sulphate of potash, put up in small phials, and impregnated with acetic
acid, sometimes rendered aromatic with oil of rosemary or lavender.
Acetic acid, in its dry state, as it exists in fused acetate of potash
or soda, is composed of
47·536 carbon
5·822 hydrogen
46·642 oxygen
-------
100·000
And its symbol by Berzelius is H⁶ C⁴ O³ = A. We must bear in mind that
his atomic weight for hydrogen is only one half of the number usually
assigned to it by British chemists, in consequence of his making water a
compound of two atoms of hydrogen and one of oxygen.
When the vapour of acetic acid is made to traverse a red-hot tube of
iron, it is converted into water, carbonic acid, carburetted hydrogen,
but chiefly pyro-acetic spirit. Acetic acid is a solvent of several
organic products; such as camphor, gluten, gum-resins, resins, the
fibrine of blood, the white of egg, &c.
It is an important problem to ascertain the purity and strength of
vinegar. Spurious acidity is too often given to it by cheaper acids,
such as the sulphuric and the nitric. The former, may most surely be
detected by the nitrate of baryta, or even by acetate of lead, which
occasion a white precipitate in such adulterated vinegar. For the case
of nitric, which is more insidious, the proper test is, a bit of gold
leaf, wetted with a few drops of muriatic acid. If the leaf dissolves,
on heating the mixture in a watch glass, we may be sure that nitric acid
is present.
Specific gravity, if determined by a sensible hydrometer, is a good test
of the strength of the genuine vinegar; and the following table of
Messrs. Taylor is nearly correct, or sufficiently so for commercial
transactions.
Revenue proof vinegar, called by the English manufacturer No. 24., has a
specific gravity of
1·0085 and contains of real acid in 100-- 5
1·0170 10
1·0257 15
1·0320 20
1·0470 30
1·0580 40
An excise duty of 2_d._ is levied on every gallon of the above proof
vinegar. Its strength is not, however, estimated directly by its
specific gravity, but by the specific gravity which it assumes when
saturated with quicklime. The decimal fraction of the specific gravity
of the calcareous acetate is very nearly the double of that of the pure
vinegar; or, 1·009 in vinegar becomes 1·018 in acetate of lime. The
vinegar of malt contains so much mucilage or gluten, that when it has
only the same acid strength as the above, it has a density of 1·0014,
but it becomes only 1·023 when converted into acetate of lime: indeed,
0·005 of its density is due to mucilaginous matter. This fact shows the
fallacy of trusting to the hydrometer for determining the strength of
vinegars, which may be more or less loaded with vegetable gluten. The
proper test of this, as of all other acids, is, the quantity of alkaline
matter which a given weight or measure of it will saturate. For this
purpose the bicarbonate of potash, commonly called, in the London shops,
carbonate, may be employed very conveniently. As it is a very uniform
substance, and its atomic weight, by the hydrogen radix, is 100·584,
while the atomic weight of acetic acid, by the same radix, is 51·563, if
we estimate 2 grains of the bicarbonate as equivalent to 1 of the real
acid, we shall commit no appreciable error. Hence, a solution of the
carbonate containing 200 grains in 100 measures, will form an acetimeter
of the most perfect and convenient kind; for the measures of test liquid
expended in saturating any measure,--for instance, an ounce or 1000
grains of acid,--will indicate the number of grains of real acetic acid
in that quantity. Thus, 1000 grains of the above proof, would require 50
measures of the acetimetrical alkaline solution, showing that it
contains 50 grains of real acetic acid in 1000, or 5 per cent.
It is common to add to purified wood vinegar, a little acetic ether, or
caramelised (burnt) sugar to colour it, also, in France, even wine, to
flavour it. Its blanching effect upon red cabbage, which it has been
employed to pickle, is owing to a little sulphurous acid. This may be
removed by redistillation with peroxide of manganese. Indeed, Stoltze
professes to purify the pyrolignous acid solely by distilling it with
peroxide of manganese, and then digesting it with bruised wood charcoal;
or by distilling it with a mixture of sulphuric acid and manganese. But
much acid is lost in this case by the formation of acetate of that
metal.
Birch and beech afford most Pyrolignous acid, and pine the least. It is
exclusively employed in the arts, for most purposes of which it need not
be very highly purified. It is much used in calico printing, for
preparing acetate of iron called IRON LIQUOR, and acetate of alumina,
called RED LIQUOR; which see. It serves also to make sugar of lead; yet
when it contains its usual quantity, after rectification, of tarry
matter, the acetate of lead will hardly crystallise, but forms
cauliflower concretions. This evil may be remedied, I believe, by
boiling the saline solution with a very little nitric acid, which causes
the precipitation of a brown granular substance, and gives the liquor a
reddish tinge. The solution being afterwards treated with bruised
charcoal, becomes colourless, and furnishes regular crystals of acetate
or sugar of lead.
Pyrolignous acid possesses, in a very eminent degree, anti-putrescent
properties. Flesh steeped in it for a few hours may be afterwards dried
in the air without corrupting; but it becomes hard, and somewhat
leather-like: so that this mode of preservation does not answer well for
butcher’s meat. Fish are sometimes cured with it. See PYRO-ACETIC
SPIRIT; PYROXILIC ETHER; PYROXOLIC SPIRIT; PYROLIGNOUS ACID and
VINEGAR.
ACETIMETER. An apparatus for determining the strength of vinegar. See
the conclusion of the preceding article for a description of my simple
method of acetimetry.
ACETONE. The new chemical name of pyro-acetic spirit.