The invention of soda-water, in the state in which it is now known,
as an effervescing beverage impregnated with three or four times its
volume of carbonic acid gas, is of very modern date. There are, indeed,
to be found in most of the old works on chemistry descriptions of
Nooth's apparatus for impregnating liquids with carbonic acid; but
all that was attempted to be done by that apparatus was to produce an
impregnation of the water with little more than the quantity of gas it
will naturally absorb under the pressure of the atmosphere. It was not
until about the year 1815 that mechanical pressure was applied to force
a larger quantity of gas into combination with water, to imitate the
briskly effervescing medicinal waters of Germany.
Mr. Schweppe and Mr. Paul were the first who introduced the manufacture
of artificial effervescing waters into England, and soda-water was then
considered, as tea was on its first introduction, entirely medicinal.
Indeed, the quantity of soda which was at that time usually dissolved
in the water gave it a disagreeable taste; but when the manufacturers
diminished the quantity of alkali, and increased the volume of gas
forced into the water, they produced a pleasant beverage, which soon
became in request for its refreshing, wholesome qualities.
The apparatus for the manufacture of soda-water, as it is usually
made on a large scale, consists of a strong vessel, furnished with a
safety valve, in which the water is impregnated with gas. This vessel,
containing about nine gallons, is made of thick wood, well seasoned and
nicely fitted, and bound round with strong iron hoops, the heads of the
cask being well secured by means of iron bolts and screw nuts. It is
requisite that the receiver should be capable of bearing a pressure of
at least six atmospheres, which is equal to 90 lbs. to the square inch.
The carbonic acid gas is generated from chalk or whiting and diluted
sulphuric acid. The materials are mixed together in a small closed
wooden or leaden vessel, provided with an agitator, that can be
worked by a handle fixed to a projecting axis at the top. The gas, as
generated, enters by a bent tube into a gas-holder, the opening of the
tube being under water. By this means the gas is freed from the fumes
of sulphuric acid vapour, and from the fine particles of chalk that
become mingled with it during its sudden liberation. The gas sometimes
undergoes a further purification, by passing through a gas washer,
before it is forced into the water.
A small force-pump, worked by a crank, with the assistance of a
fly-wheel, draws the carbonic acid from the gas-holder, and forces it
into the water. The combination of the gas and water is facilitated by
an agitator, the axle of which projects through a stuffing box, and it
is worked either by hand, or is turned by means of a small cog-wheel,
that works into the teeth of a larger one fixed to the crank axle, so
as to produce rapid rotation.
It is found requisite, in the first place, to expel the atmospheric air
in the receiver; for which purpose the safety valve is left open for a
short time after the gas is being forced in, otherwise it would retard
the impregnation of the water by the gas. When the gas and water are
well incorporated, the liquid will contain as many volumes of gas as
there are atmospheres of pressure in the air-space above it in a state
ready to effervesce, and one other volume, with water absorbs under
the pressure of the atmosphere. Thus, when there are three atmospheres
of gas under pressure, each bottle of soda-water contains four bottles
full of gas, which are absorbed without perceptibly increasing its
bulk. The perfect impregnation of the water with gas, however,
requires time. The water will, indeed, become brisk almost as soon as
two or three atmospheres of gas have been forced in, but it will not
acquire the flavour of good soda-water until the gas and water have
been allowed at least half an hour to digest; and it is improved by
remaining in contact for several hours.
The temperature has considerable influence in the process of
impregnation, for in hot weather the gas will not combine so readily,
nor will the water absorb an equal volume of gas. In summer time,
therefore, soda-water should be made before the heat of the day, and
ice should be added to the water.
When the receiver is fully charged, and the operation of bottling
begins, every bottle-full that is drawn off diminishes the pressure on
the water that remains; and if no means were taken to add more gas, the
soda-water would gradually become weaker and weaker as each bottle was
drawn off. It is usual, in the best arranged apparatus, to have two
tubes connected with the force-pump, one of which feeds it with water,
the other with gas, by which contrivance water and gas, in their proper
proportions, are continually forced into the receiver, which may thus
be always kept nearly full.
The process of bottling requires great manual dexterity. The neck of
the bottle is pressed by a lever against a collar of leather fixed to
a flange on the tap, so that, when the soda-water rushes in, no air
nor gas can escape. The pressure inside the bottle therefore quickly
becomes equal to that of the receiver, and the water ceases to flow
through the tap, until some of the air is allowed to escape. When the
bottle is nearly full, the operator quickly withdraws it with one hand,
and having a cork ready in the other, he puts it in before the water
can rush out. The cork is then forced in further by pressure, and
fastened down by wires or strings.
A bottling apparatus has been invented for facilitating the process;
but a man accustomed to bottle by hand can do it more quickly, and with
as little waste of gas and water as with a machine. Much depends,
however, upon the state of the soda-water in the receiver; for if the
gas be well digested, and the temperature low, it rushes into the
bottle with much less force, though the water may contain a greater
quantity of gas, than when it is newly made, and apparently more brisk.
The bottles very frequently burst during the operation with great
violence, and unless they are enclosed in a guard, the men are liable
to be severely injured. Glass bottles have now generally supplanted
those made of earthenware, which were formerly used; and though the
glass bottles are much stronger than the earthenware ones, the bursting
of them, when it does occur, is far more dangerous.
The process of forcing gas into the water by mechanical pressure,
in the manner described, requires great labour, for the pump has to
be worked against a pressure exceeding fifty pounds on the square
inch. With a view to remove that inconvenience, and to avoid the use
of costly machinery, so that private individuals might manufacture
soda-water, the author contrived a modification of Nooth's apparatus,
for which he obtained a patent in 1831. By that means, the gas is
generated in a closed vessel, and forces itself into the water by
its own elasticity. Any amount of pressure can thus be obtained by
chemical action alone. The accompanying woodcut represents a section
of the apparatus in its improved form. The vessel, A, is made of very
strong stone ware, inside which is the gas generator _b_. A few inches
from the bottom of the generator is the partition, _a_, perforated
with holes, and near the top there is inserted the small tube, _c_,
which conveys the gas down to a perforated expansion of the tube,
_d_, through the apertures of which the gas issues into the water
contained in A. Another tube, _e_, reaches near the bottom, and is
connected with a stop-cock for the purpose of drawing off the aerated
liquid. In charging the apparatus, the interior, A, is nearly filled
with water, or other liquid, through the opening, _f_, which is then
closed by cork, which is kept in its place by a screw nut. A few
ounces of carbonate of soda, mixed with water, are then poured into
the generator through the opening at _g_. The mixture flows through
the apertures in the partition, and occupies the lower part of the
generator. A proportionate quantity (about three-fourths of the weight
of the soda) of tartaric acid in crystals is then introduced through
_g_, which lodge on the top of the partition without touching the soda.
The opening being then closed by a screw-nut, the apparatus, which is
mounted on pivots, with an appropriate stand, is swung backwards and
forwards like a pendulum. The effect of this agitation is to force
a portion of the water saturated with carbonate of soda through the
apertures at _a_, where it comes in contact with the tartaric acid,
and instantly generates carbonic acid gas. The gas, having no other
escape than through the tube, _c_, is forced into the vessel A, and
becomes mingled with the water by the same act of vibration that brings
the soda and tartaric acid together. The continuance of the vibratory
action for a short time generates sufficient gas to aerate the water
or other liquid contained in the vessel, A. When the aeration is
completed, the soda-water may be drawn off, as required, through the
stop-cock. The apparatus is made of two sizes, to hold one and two
gallons.
[Illustration]
The tartaric acid and soda in the generator do not mingle with the
water, and the tartrate of soda, resulting from the combination, is
emptied after the soda-water is drawn off, before renewing the charge.
A French modification of this apparatus, in glass vessels protected by
cane netting, called a "gasogene," has recently been introduced, and is
extensively used. The materials for generating the carbonic acid gas
are put into the smaller vessels, and kept separate until the apparatus
is inverted, and then gas is rapidly generated, and forces itself
through the water.
The powders that are sold for making soda-water, by mixing them
together, consist of carbonate of soda and tartaric acid. When brought
together in solution, a violent effervescence ensues, but the gas is
not combined with the water in the same manner as when it is forced
in and allowed to remain for some time with the liquid to be aerated.
There is the further disadvantage attending such powders, that the
tartrate of soda, formed by the tartaric acid and the carbonate of
soda, employed to generate the gas, is drunk with the water.