August Dupré John Louis William Thudichum.

A treatise on the origin, nature, and varieties of wine: being a complete ... online

. (page 18 of 64)
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dish, evaporated on a water-bath, and heated for about
half an hour after the evaporation has apparently ceased.
The residue, which is generally a thick viscid fluid, is redis-
solved in water, and the amount of free acid left is estimated
as before described* This free acid represents the total free
fixed acid of the wine* and the difference between this and
the first determination gives of course the total volatile acids
present, as measured by their neutralia^ing power.

In case the wine contains much sugar or extractive matter,
it may be of advantage to mix some pure powdered quartz
with the wine previous to the evaporation, and so stir the
mass well towards the end to facilitate the escape of the
volatile acid. This will, however, but rarely be found necessary
if the wine is evaporated in a shallow dish and upon an open
water-bath. Too long heating of the residue should also be
avoided^ as it gradually loses in acidity, by changes which are
not due to any escape of volatile acid. Thus, in two samples of
Rhine wine, 20 c. c. of the wine itself required 156 c. c. and
13*8 c. c. d. n. soda. After evaporation and heating for one
hour, ir6 a c. and ico C c. were respectively required, but
the same samples required but 5*1 c. c. and 48 c. c. d. n.
soda when the evaporated residue had been heated on a
water-bath till its weight remained constant, which took about
forty-eight hours. The acidity of the residue was still further
diminished on drying the residue in an air-bath to 110° till
the weight remained constant, when the residue from 20 c. c.
of the above two wines required only i 2 and i 9 c. c. soda.
The residues which had been heated for forty-eight hours on
the water-bath took still twenty-four hours in the air-bath to
become constant in weight.

It is almost impossible accurately to estimate the volatile acid
by distillation and estimation of the acidity of the distillate,
as even repeated distillation to dryness, and filling up again
with water, fail to drive over all the volatile acid. The estima-



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192 ESTIMATION OF TARTARIC ACID [chap.

tion of the fixed acid in the residue left in the retort would be
still more unsatisfactory ; for the acidity of the residue, when
added to the acidity of the distillate, even after very careful
distillation, never quite comes up to the total acidity of the
wine, and may even fall very far short of it if the distillation
has been continued a little too far. The latter accident is,
however, almost unavoidable, if anything like the greater
quantity of the volatile acid is to be distilled over.

In good sound wines the total amount of free acid ranges
from 0'3 to 67 per cent. ; wines with more than the latter
amount of free acid are neither pleasant nor wholesome. Of
the total acidity not more than about 015 per cent, should be
due to volatile acid.

ESTIMATION OF TARTARIC ACID AND BITARTRATE OF
POTASH IN WINE.

The bitartrate of potash, although slightly soluble in water,
is almost absolutely insoluble in strong alcohol or a mixture
of alcohol and ether. Upon this insolubility two methods for
the estimation of the tartaric acid and bitartrate have been
based. The first, proposed by Berthelot, and giving on the
whole the most accurate results, is as follows : — 20 c. c. of
wine are mixed in a well-stoppered bottle or flask with 100 c c
of a mixture of equal volumes of alcohol and ether; to another
20 c. c. of the wine a quantity of potash (sufficient to neutralize
about one-fifth of the free acid of the wine) is added, together
with 100 c. c. of the alcohol and ether mixture. Both bottles
are then set aside for two or three days in a cool place ; at
the end of this time almost all the bitartrate of potash present
in both bottles will have been deposited, sometimes in well-
defined crystals. These precipitates are then collected on
a filter, washed with alcohol-ether, introduced with the
paper into a flask or bottle, and dissolved in distilled water, if
necessary, with the aid of heat. The free acid present in these
solutions is then estimated by a. decinormal solution of soda
as previously described.

These precipitates of bitartrate do not, however, represent
the total amount of bitartrate present, because a small



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VI.] AND BI TARTRATE OF POTASH, 193

quantity remains in solution, amounting to about 0004 grm.,
equivalent to 0*02 per cent, of bitartrate in the wine. These
0CX)4 grm. bitartrate of potash require 0'2i c. c, d. n, soda,
which have to be added to the amount found. With this
correction, the precipitate from the first 20 c. c. represents
the bitartrate present in the wine ; the precipitate from the
second 20 c. c. contains the whole amount of the tartaric acid
present. We have then simply to multiply the number of
c ۥ d. n. soda required to neutralize the precipitates, plus the
necessary correction of 02 1 c. c, by 0094 and 0*075 respec-
tively, to obtain the percentage of bitartrate and of tartaric
acid in the wine.

The second method, which also yields very satisfactory
results, has been described by Nessler. The total free acid
present is first estimated in 20 c. c. of the wine ; 40 c. c. of the
wine are then put into a flask and mixed with a sufficient
quantity of absolute alcohol to amount to 150 c. c. The flask
is then set aside for forty-eight hours ; at the end of this time
nearly all the bitartrate present will have been precipitated ;
75 c. c. of the clear liquor are then taken off with a pipette,
put into a beaker, and the free acid still present is estimated
as usual. If no bitartrate had been precipitated, the amount
of free acid in these 75 c. c. should of course be one-half of the
free acid in the 40 c. c. of wine employed, and any deficiency
in its acidity, in the case where bitartrate had been deposited,
is the measure of the bitartrate present in 20 c. c. of the wine.
The total amount of tartaric acid present is estimated thus :
to 40 c. c. of wine enough of decinormal alcoholic potash is
added exactly to neutralize 10 c. c. of wine, and the whole
is then made up to 1 50 c. c by absolute alcohol. After the
lapse of forty-eight hours 75 c. c. of the clear liquid are
taken off and their free acid is estimated ; the amount of the
deficiency, taking into consideration the 10 c. c. d. n. potash
added, corresponds to the bitartrate present in the 20 c. c. of
wine, or to half the amount of tartaric acid in 20 c. c. of
wine.

A solution containing 05 per cent, of crj'^stallized tartaric
acid was made; 20 c. c. of it required 13*3 c c. d. n. soda;

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194 ESTIMATION OF TARTARIC ACID [chap.

40 c. c. of this were then measured into a flask, 13*3 c c d. n.
alcoholic potash was added, and the whole made up to 150 c c ;
after two days' standing, 75 c. c of the clear liquid required, as
the mean of several experiments, 0-15 c. c d. n. soda, which
represents the solubility of the bitartrate in the alcoholic liquid.
To 50 c. c of this same solution i grm. citric acid was
added, and then water up to 200 c. c. ; 20 c. c. of this mix-
ture required 17 c. c. d. n. soda. 40 c. c. of this solution were
now mixed with 8*5 c. c. d. n. potash, and then with alcohol up
to 150 c. c; after two days' standing, 75 c. c. of the clear
solution required in c. c. d. n. soda, or subtracting the above-
stated correction for the solubility of the bitartrate (0*15 c. c),
10*95 c. c, there should have been required 1275. Deducting
from this iO'9S, there remain i-8, which multiplied by two
gives 3*6 c. c,, the amount of d. n. soda required to neutralize
the tartaric acid in 20 c. c. of the mixture. The rest of the
17 c c. required to neutralize 20 c. c of mixture is, therefore,
due to citric acid. We have thus —

d. n. soda required to neutralize the T, of 20 mixture,

Calculated : 3*32 c c.= 0*124 P^r cent.

Found : 3*6 c.c =0*135 »»
d. n. soda required to neutralize the C,

Calculated : 13*68 c. c.

Found I 13*4 c. c.

showing that even in presence of a considerable excess of
citric acid this process gives tolerable results.

(The tartaric acid solution first employed required 13 "3 c. c.
d. n. soda per 20 c. c, solution ; 50 c. c. of this were diluted up
to 200 c. c, and if no citric acid had been added 20 c. c would
now require only yiz c. c, d. n. soda; enough citric acid had,
however, been added to bring the strength up to 17 c c. d. n.
soda, of which 3*32 c c. being due to tartaric acid, 13*68 c. c
must have been due to citric acid.)

Both methods give rather accurate results, if the amount
of tartaric acid present does not fall short of 0*05 per cent. ;
below this amount the results are inaccurate, inasmuch as the
acidity of either the precipitate, or the 50 c. c of alcoholic
mixture, or of the wine itself, cannot be estimated to within
less than O'l c. c. d. n. soda.



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VI,] AND BITARTRATE OF POTASH, 195

In Berthelot's method, however, the precipitate bitartrate
is collected and its acidity directly estimated, and this can be
done, as above stated, to within 0"i c. c.,- whilst in Nessler's pro-
cess the acidity of the precipitate is found from the difference
in the acidity of the wine before and after the addition of
alcohol ; it is thus liable, even with the greatest care, to an
error of 02 a c: if, for example, the acidity of the wine has
been estimated 0"i c. c too high, whilst, after the addition of
the alcohol, it has been estimated o'l c c. too low.

Both Berthelot and Nessler have, in their estimation, used
half the quantities of wine only which are here recommended ;
we have found that the accuracy obtainable by working with
the quantities proposed by these authors is not sufficient,
except in the case of wines tolerably rich in tartaric acid.

If the wine contains less bitartrate than corresponds to the
solubility of this salt in the quantity of ether alcohol or alcohol
employed, no tartaric acid at all will be found by these pro-
cesses. This quantity is, however, only about 002 per cent.
If it is, nevertheless, desired to estimate this small amount,
or, if the presence or absence of any tartaric acid in a wine
is to be demonstrated, the following plan may be adopted
A quantity of wine, say 100 c. c, is precipitated by a small
excess of acetate of lead ; the precipitate is collected, washed,
suspended in water, and decomposed by a current of sulphur-
retted hydrogen. The excess of Hg S is then driven off by
boiling, and the sulphide of lead removed by filtration. The
dear solution thus obtained is evaporated to a small bulk,
about one-quarter of its acid neutralized by potash, and a con-
siderable excess of ether-alcohol mixed with it. After the
lapse of forty-eight hours, the precipitate, if any be produced,
may be examined as above described. Or, 100 c. c. of wine
are precipitated by lime-water ; the precipitate is washed and
boiled with carbonate of potash. The carbonate of lime
formed being removed by filtration, the alkaline filtrate is
acidulated by acetic acid, and also mixed with a considerable
excess of ether-alcohol or absolute alcohol. Any precipitate
thereby produced must then be examined for tartaric acid.

In the majority of cases all the tartaric acid of the wine

o 2



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196 ESTIMATION OF TARTARIC [cHAP.

is present as bitartrate ; that is to say, there is a sufficient
amount of potash present to enable the whole of the tartaric
acid to be precipitated in this form on the addition of ether-
alcohol ; the wines, in fact, frequently correspond to a solution
of bitartrate, saturated at the lowest temperature to which
the wine may have been exposed for a certain length of
time.

As a geneijil rule, all pure natural wine contains more or
less of tartaric acid, and the quantity is probably the higher
the riper the grapes from which it is produced. There is
not, however, any apparent connection between the amount
of tartaric acid present, and the quality of the wine. On
the other hand, strongly fortified wines contain little or no
tartaric acid, and this acid is almost entirely absent from all
such wines during the production of which plaster of Paris
has been employed.

In looking over the tables giving the results of our nume-
rous wine-analyses the reader will see that in the great
majority of cases, if not in all, the amount of tartaric acid
corresponds to only a fraction of the total free fixed acid of
the wine, the rest of which is, according to our researches,
made up mostly of malic acid. Indeed, a very small error
only will be committed if all the free fixed acidity not due to
tartaric acid is put down to malic.

It must, however, be borne in mind that a part of the total
amount of tartaric acid found is neutralized by potash, and
is thus not included in the alkalimetric estimation of the total
fixed acidity ; and, on the other hand, that even the direct
estimation of the bitartrate of the wine, by one of the above
methods, does not give us the exact amount of that acid
which in the wine contributes to the acidity. All wines con-
tain more or less sulphate and chloride of potassium (found
in the ash), and both salts are decomposed by tartaric acid
under the above conditions, i.e, addition of ether-alcohol in
which the bitartrate is insoluble. As long, however, as
acids and bases are in solution, by far the greater portion
of the alkali is in combination with the sulphuric and hydro-
chloric acid.



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VI.] AND MALIC ACID, 197

If, however, there is more alkali present than is capable
of combining with the sulphuric and hydrochloric acid, it
will be left in the ash as carbonate. The amount of tartaric
acid, which can be neutralized by the amount of alkali
found as carbonate in the ash being subtracted from the
total amount of tartaric acid found, leaves the rest of the
tartaric acid present in the wine as free fixed acid ; and
this, when subtracted from the total free fixed acid found,
leaves the amount of malic acid present, expressed in its
equivalent of tartaric acid. In this calculation, however,
several acids, as succinic acid and part of the phosphoric
acid, &c, present, are left out of consideration, and the
amount of malic acid thus found can, therefore, be taken only
as an approximation to reality.

Malic acid may, however, also be obtained in a somewhat
more direct manner. A certain quantity of wine (say 50 c. c.
or 100 c. c) is precipitated with a slight excess of lime-water,
the precipitate formed filtered off, washed, and the clear
filtrate evaporated to about 25 c. c or 50 c. c, to which
is then added a considerable excess of absolute alcohol.
The precipitate thereby produced consists chiefly of malate
and sulphate of lime; it is collected on a weighed filter,
washed, dried at lex)"*, and weighed. The sulphuric acid
must then be estimated in a second quantity, and the
amount of sulphate of lime thus shown to be present in
the above precipitate being subtracted, the rest represents
the malate of lime.

The other acids in the wine, with the exception of the
mineral acids, of which we shall treat when describing the
ash of wine, cannot at present be estimated with any degree of
exactness.



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CHAPTER VII.

THE ETHERS IN WINE.

Aceto-ethylic ether. — Aceto-propylic, butylic, amylic, caproylic, &c. ethers. —
Butyro-ethylic, caprylo-ethylic, &c. ethers. —CEnantho-ethylic ether. — Tartaric
ethers. — Berthelot's estimation of the ethers in wine. — New process for the
determination of ethers in wine. — General principles. — General description of
the process. — Determination of alcohol as acetic acid. — Determination of the^
fixed ethers. — Modification of the foregoing process. — Controlling experiments
with wines. — Controlling experiments with tartaric ether. — Determination
of the ethers in a variety of wines. — Results. — Consideration of Berthelot's
theory of the limitation of ethers in wine. — Smell, bouquet, and aroma of wine.

ACETO-ETHYLIC ETHER.

If alcohol and acetic acid are mixed and left to stand,
aceto-ethylic* ether, commonly called acetic ether, —
Ca H3 (Ca H5) Oj — is gradually formed; the process is
very slow, and is never complete, owing to the simul-
taneous formation of water, the presence of which prevents
complete etherification. The more diluted the acid and alcohol
are, the smaller will be the proportion of acid ultimately con-
verted into ether. The formation of the compound ether
in this case is much facilitated by the addition o( sulphuric
acid. The ether may, however, be prepared much more
readily by distilling ten parts of anhydrous acetate of soda,
eight parts of alcohol of 90 per cent, and fourteen parts of
sulphuric acid. The distillation is continued as long as the
distillate is not completely miscible with a small quantity of
water. The product at first obtained is washed with about
its own bulk of water; the ether remaining on the top of
the water is taken off, agitated with carbonate of soda, once



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CHAP, vii.] ACETO'ETHYLlCy ETC ETHERS, 199

more washed with water, and lastly dried over fused chloride
of calcium. The dry ether is again distilled, once more dried
over chloride of calcium, with which it now generally enters
into a crystalline combination, easily decomposed, however,
on application of heat. The ether distilled off from this com-
pound is finally submitted to fractional distillation ; those
portions only which come over at a temperature of 74° C. are
pure acetic ether.

Acetic ether is a colourless, transparent, very mobile liquid,
possessing a very agreeable ethereal refreshing smell, and
burning taste ; it is neutral to test paper. It boils at a tem-
perature of 74'3*' C, but evaporates rapidly even at the ordi-
nary temperature; its specific gravity is 0*9 104, and it is
miscible with alcohol and ether in every proportion. One part
of ether requires about seven parts of water for its solution.
On the other hand, the ether dissolves water, and the solution
gradually becomes acid, owing to the decomposition of some of
the ether into acetic acid and alcohol. When heated with an
alkali, it readily breaks up into an acetate and alcohol, which
reaction is used as a means of estimating the amount of com**
pound ether present in a solution.

By far the greater part of the volatile ethers found in wine
is acetic ether, and being volatile and possessing ^tty decided
smell, it doubtless contributes much to the general flavour of
the wine, although neither the characteristic wine flavour nor
the peculiar bouquet of wines is due to it. In wine the ether
is formed by the action of acetic acid on alcohol, perhaps
facilitated by the presence of other acids, but kept within
certain limits by the presence of water. As the formation of
a compound ether under these conditions takes place gradually,
the amount of it present at a given time is, to a certain extent,
a measure of the age of the wine.

ACETO-PROPYLIC, BUTYLIC, AMYLIC, CAPROYLIC, ETC.
ETHERS.

Just as acetic acid forms acetate of ethyl, or acetic ether»
with ordinary (ethylic) alcohol, so it forms compound ethers
with the alcohols of the above radicles. Th6se ethers are



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200 BUTYRO-ETHYLIC, ETC, ETHERS. [CHAP.

formed and may be prepared by processes analogous to that
given under acetic ether. They correspond in their general
characters to acetic ether, and are all volatile, their boiling-
point rising as the atomic weight of the alcohol from which
they are formed increases. They have all an agreeable
etherial smell, greatly resembling the smell of fruit, more
particularly when much diluted ; thus acetate of amyl has the
smell of pears. All these ethers, when heated with an alkali,
are decomposed into acetate and the relative alcohols.

As the alcohols corresponding to all the above-named
radicles are found in wine, in minute quantity, some of the
above ethers are undoubtedly present, particularly in old wine,
and contribute to its flavour and bouquet.

BUTYRO-ETHYLIC, CAPRYLO-ETHYLIC, CAPRO-ETHYLIC,
AND PELARGO-ETHYLIC ETHERS.

Just as acetic acid forms a series of ethers with the radicles
of the alcohol series enumerated in the foregoing, so the other
acids of the fatty acid series form each a series of ethers with
the same series of alcohol radicles. In wine, we may expect
these acids always to combine with the prevailing, namely
ethylic, alcohol. The etherification is apparently facilitated by
the presence of tartaric acid. Many of these ethers have a
very powerful and characteristic odour. Very frequently this
odour IS rather disagreeable in the pure ether, but becomes
agreeable, and resembles the aroma of fruit or flowers when
greatly diluted. Thus butyric ether (C4 H7 (C, H5) Oi)
resembles the smell of pine-apples ; caprylic ether (Cg H^
(Ca Ho) Oj) has much the same smell ; caproic ether (Q H,i
(C2 Hfi) Oj) has the smell of melons; and to pelargonic
ether (C, H 1 (C, H5) O,) is probably due a portion of the
characteristic wine-flavour.

CENANTHIC ETHER.

When large quantities of wine are distilled, a small amount
of an oily liquid passes over towards the end of the distilla-
tion. Forty thousand parts of wine yield about one part of
the oil. The same oil may also be obtained from wine yeast.



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VII.] TARTARIC ETHER. 201

For this purpose the yeast is diluted with its own volume of
water, and carefully distilled over an. open fire. The first
distillate is rectified when, towards the end of the rectification,
the oil distils over. This oil is oenanthic ether mixed with a
variable proportion of acid. To obtain the pure ether this
crude oil is again distilled, and the first quarter coming over
is collected separately.. This is now shaken, and gently
heated with a solution of sodium carbonate. The carbonate
removes the free acid, but leaves the ether unaffected. In the
cold the ether and carbonate form a sort of emulsion, from
which the ether does not separate even after long standing.
However, when the mixture is heated to boiling, the ether
readily rises to the top. It is taken off and digested for some
time over lumps of chloride of calcium, by which the last
traces of moisture and of alcohol are removed.

The pure ether thus obtained is a colourless, thin, oily
liquid, like oil of peppermint, with an overpowering vinous
smell and a sharp, disagreeable taste. It has a specific
gravity of 0862, a vapour density of 10508, and boils be-
tween 225- — 230"* C. Its elementary composition is Cig Hgj O^
= Ci4 H„ O"* 2 Ca He. It is very soluble in ether, alcohol,
or even very diluted spirit, but almost insoluble in water.
The fixed caustic alkalies readily decompose it into alcohol
and cenanthic acid ; the alkaline carbonates, and aqueous
ammonia are, however, without action on it.

The characteristic vinous smell which distinguishes all kinds
of wine from every other fermented liquid, is due to the
presence of this oenanthic ether. The flavour or bouquet,
however, by which the wines of different vineyards and vines
are distinguishable from each other, is produced by substances
of different nature and composition.

TARTARIC ETHER.

As a dibasic acid, tartaric acid is capable of forming two
varieties of ethers, namely neutral and acid ones. Only the
latter kind is met with in wine, or formed by the mere
digestion of tartaric acid with alcohol. Tartro-ethylic ether —
C4 H, (C, Hb) Of-is a solid, crystallizable, but deliquescent



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202 ESTIMA TION OF ETHERS. [chap.

body, which behaves like an acid, inasmuch as it can combine
with an atom of base, and form neutral salts. Its calcium,
lead, and silversalt are rather insoluble in an excess of the
acid ether. It cannot be distilled without breaking up into
various products.

By the influence upon each other of the alcohols and
acids shown to be present in wine, a considerable number of
compound ethers may be produced. For, supposing five
acids and five alcohols to be present, they might produce
twenty-five compoand ethers, some or all of which might
be present and contribute their share to the flavour, such
flavour altering as one or the other ether predominated. All
these ethers occur in wine in extremely minute quantity
only, and almost entirely elude ordinary analysis. However,
in the manufacture of brandy enormous quantities of wine
are distilled and a considerable amount of so-called fousel
oil obtained, in which a number of the above-named volatile



Online LibraryAugust Dupré John Louis William ThudichumA treatise on the origin, nature, and varieties of wine: being a complete ... → online text (page 18 of 64)