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The Acidimeter And Its Use








"The first instrument of this kind which came into general use, was one
invented by DR. OTTO, and consists of a glass tube, from ten to twelve
inches in length, half an inch in width, and closed at the lower end.
Fig. 33 shows OTTO'S Acidimeter.

"The tube is filled to the partition line _a_, with tincture of litmus.
The must to be examined, before it has begun to ferment is then poured
into the tube, until it reaches the line 0. The blue tincture of
litmus, which would still be blue, if water had been added, is turned
into rose-color by the action of the acids contained in the must.

"If a solution of 1,369 per cent, of caustic ammonia is added to this
red fluid, and the tube is turned around to effect the necessary
mixture, keeping its mouth closed with the thumb, after the addition of
more or less of the ammonical fluid, it will change into violet. This
tinge indicates the saturation of the acids, and the height of the
fluid in the tube now shows the quantity of acid in the must, by whole,
half and fourth parts per cent. The lines marked 1, 2, 3, 4, indicate
whole per cents.; the short intermediate lines, one-fourth per cents."

When DR. GALL, shortly before the vintage of 1850, first publicly
recommended the dilution of the acids, he was obliged to refer to this
instrument, as already known, and everywhere at hand, which was at the
same time cheap, and simple in its use. "It is true, however, that if
must is examined by this instrument, the quantity of acids contained in
it, is really somewhat larger than indicated by the instrument; because
the acids contained in the must require for their saturation a weaker
solution of ammonia than acetic acid." As however, OTTO'S acidimeter
shows about one eighth of the acids less than the must actually
contains, and about as much acids combined with earths is removed
during fermentation, DR. GALL recommends that the quantity of acids be
reduced to 6-1/2, or at most 7 thousandths of OTTO'S acidimeter, and
the results have shown that this was about the right proportion; as the
wines in which the acids were thus diluted were in favor with all
consumers.

"The acidimeter referred to was afterwards improved, by making the tube
longer and more narrow, and dividing it into tenths of per cents,
instead of fourths; thus dividing the whole above 0 into thousandths.
But although by this improved acidimeter the quantity of acids could be
ascertained with more nicety, there remained one defect, that in often
turning the glass tube for mixing the fluids, some of the contents
adhered to the thumb in closing its mouth. This defect was remedied in
a new acidimeter, invented by Mr. GEISLER, who also invented the new
vaporimeter for the determination of the quantity of alcohol contained
in wine. It is based on the same principle as OTTO'S, but differs
altogether in its construction. It is composed of three parts, all made
of glass; the mixing bottle, Fig. 34; the Pipette, Fig. 35; and the
burette, Fig 36. Besides, there should be ready three small
glasses--one filled with tincture of litmus, the second with a solution
of 1,369 per ammonia, and the third with the must or wine to be tested;
also, a taller glass, or vessel, having its bottom covered with cotton,
in which glass the burette, after it has been filled with the solution
of ammonia, is to be placed in an upright position until wanted.

"To use this instrument the must and the tincture of litmus, having
first received the normal temperature of 14 deg. Reaumer, are brought into
the mixing bottle by means of the pipette, which is a hollow tube of
glass, open on both ends. To fill it, place its lower end into the
tincture or must, apply the mouth to the upper end, and by means of
suction fill it with the tincture of litmus to above the line indicated
at A. The opening of the top is then quickly closed with the thumb; by
alternately raising the thumb, and pressing it down again, so much of
the tincture is then allowed to flow back into the glass so as to lower
the fluid to the line indicated at A. The remainder is then brought
into the bottle, and the last drops forced out by blowing into the
pipette.

"In filling it with must, raise the fluid in the same way, until it
comes up to the line indicated at B, and then empty into the mixing
bottle.

"The burette consists of two hollow tubes of glass. In filling it, hold
the smaller tube with the right hand into the glass containing the
solution of ammonia, apply the mouth to the larger one, and by drawing
in the fluid the tube is filled exactly to the line indicated at 0 of
the tube.

"Holding the mixing bottle by the neck between the thumb and forefinger
of the left hand, place the smaller tube of the burette into the mouth
of the mixing bottle, which must be constantly shaken; let enough of
the solution of ammonia be brought drop by drop, into the mixture in
the bottle, till the red has been changed into the deep reddish blue of
the purple onion. This is the sign of the proper saturation of the
acids. To distinguish still better, turn the mixing bottle upside down,
by closing its mouth with the thumb, and examine the color of the fluid
in the tube-shaped neck of the bottle, and afterwards, should it be
required, add another drop of the ammonia. Repeat this until the proper
tone of color has been reached, neither red nor blue. After thus fixing
the precise point of the saturation of the acids, the burette is held
upright, and the quantity of the solution of ammonia consumed is
accurately determined,--that is, to what line on the scale the burette
has been emptied. The quantity of the solution so used corresponds with
the quantity of acids contained in the must--the larger division lines
opposite the numbers indicating the thousandths part, and the smaller
lines or dots the ten thousandths part.

"Until the eye has learned by practice to recognize the points of
saturation by the tone of color, it can be proven by means of litmus
paper. When the mixture in the bottle begins to turn blue, put in the
end of a slip of litmus paper about half an inch deep, and then draw
this end through your fingers, moistened with water. So long as the
ends of the blue litmus paper become more or less reddened, the acids
have not been completely saturated. Only when it remains blue, has the
point of saturation been reached.

"In examining _red_ must, the method should be modified as
follows:--Instead of first filling the pipette with tincture of litmus,
fill it with water to the line A, and transfer it into the bottle.
After the quantity of must has been added, drop six-thousandths of the
solution of ammonia into the mixture, constantly shaking it while
dropping, then test it, and so on, until, after every further addition
required with litmus paper, it is no longer reddened after having been
wiped off."

DR. GALL further gives the following directions, as a guide, to
distinguish and determine the proportion of acids which a must should
contain, to be still agreeable to the palate, and good:

"Chemists distinguish the acid contained in the grape as the vinous,
malic, grape, citric, tannic, gelatinous and para-citric acids. Whether
all these are contained in the must, or which of them, is of small
moment for us to know. For the practical wine-maker, it is sufficient
to know, with full certainty, that, as the grape ripens, while the
proportion of sugar increases, the quantity of acids continually
diminishes; and hence, by leaving the grapes on the vines as long as
possible, we have a double means of improving their products--the must
or wine.

"All wines, without exception, to be of good and of agreeable taste,
must contain from 4-1/2 to 7 thousandths parts of free acids, and each
must containing more than seven thousandths parts of free acids may be
considered as having too little water and sugar in proportion to its
quantity of acids.

"In all wine-growing countries of Germany, for a number of years past,
experience has proved that a corresponding addition of sugar and water
is the means of converting the sourest must, not only into a good
drinkable wine, but also into as good a wine as can be produced in
favorable years, _except_ in that peculiar and delicate aroma found
only in the must of well-ripened grapes, and which must and will always
distinguish the wines made in the best seasons from those made in poor
seasons.

"The saccharometer and acidimeter, properly used, will give us the
exact knowledge of what the must contains, and what it lacks; and we
have the means at hand, by adding water, to reduce the acids to their
proper proportion; and by adding sugar, to increase the amount of sugar
the must should contain; in other words, we can change the poor must of
indifferent seasons into the normal must of the best seasons in
_everything_, _except_ its bouquet or aroma, thereby converting an
unwholesome and disagreeable drink into an agreeable and healthy one."





Next: The Change Of The Must By Fermentation Into Wine

Previous: The Must Scale Or Saccharometer



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