Scientific American Suppl. No. 299

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On causing the mercury to rise into the space that it previously
occupied, the vapors are made to condense in the second test-tube at the
same temperature as that at which they were formed.

We immediately ascertain that the pressure-gauge shows an elevation
of pressure; moreover, the proof of the condensed alcohol has very
perceptibly risen.

If, instead of causing these vapors to condense in the second test-tube,
we leave the first communication open, the vapors recondense in the
first test-tube without any elevation of pressure; and we do not see the
least trace of liquid forming in the second test tube.

This difference of pressure in the two foregoing experiments must be
attributed, then, to the specific action of the water on the vapors of
alcohol. Now we can calculate the difference of the work of the pump,
and put at 1 kilogramme of condensed liquid the difference of mechanical
work represented in kilogrammeters. What is remarkable is that this
difference is absolutely the equivalent of the heat disengaged when the
condensed liquid and the old liquid are remixed; there is a complete
identity. Thus the affinity of the water for the alcohol modifies the
tension of the vapors which form or condense upon the free surface of
the mixture. The two phenomena are closely connected by the law of
equivalence.

It results from all the laws that we have cited that by properly
regulating the tensions of the vapors of a mixture of alcohol and water,
and the temperature of the liquid, we shall be able to obtain a liquid
of a desired richness by the condensation of these vapors.

III. It was likewise indispensable to make sure of one important fact:
When the temperature of a liquid like alcohol is considerably lowered,
can the distillation of a given weight of this substance be effected
with sufficient rapidity for industrial requirements? Repeated
experiments with a host of volatile liquids have demonstrated the
following laws:

If we introduce a volatile liquid into two spherical receivers connected
by a wide tube, and if these be kept at different temperatures after
driving out all the air from the apparatus, the liquid distills from the
warmer into the cooler receiver, and we ascertain that:

h. The weight of the liquid which distills in the unit of time increases
with the deviation of temperature between the two receivers.

i. The weight of the liquid which distills in the unit of time is
constant for a same deviation of temperature between the receivers,
whatever be, moreover, the absolute temperature of the receivers.

k. The weight of the liquid distilled in the unit of time is
proportional to the active surfaces of the receivers; that is to say,
to the surfaces which are the seat of passage of heat through their
thickness.

l. The least trace of a foreign gas in the vapors left in the apparatus
throws the preceding laws into confusion, and checks distillation to a
considerable degree, especially at low temperatures.

Thus, water distilling between 100 deg. and 60 deg. will pass over as
quickly as that which is distilling between 40 deg. and 0 deg.. Absolute
temperature is without influence, provided every trace of air or foreign
gas be got rid of.

The distillatory apparatus should be provided with an excellent
air-pump, capable of preventing all those entrances of air which are
inevitable in practice.

The following is the industrial application that we have endeavored to
make of these theoretical views: The rectification of alcohols is one
of the most complex of operations; it looks toward several results
simultaneously. Alcohol derived from the fermentation of grain, sugar,
and of all starchy matters in general, contains an innumerable host of
different products, which may be grouped under four principal heads:

1. Empyreumatic essential oils, characteristic of the source of the
alcohol, and having a powerful odor which infects the total mass of
the crude spirits. 2. A considerable quantity of water. 3. A certain
quantity of pure alcohol. 4. A variable proportion of volatile
substances, composed in great part of ethers, different alcohols, and
bodies as yet not well defined. These latter affect the quality of
the alcohol by an odor which is entirely different from that of the
essential oils.

The object of rectification is to bring out No. 3 all alone; that is
to say, to extract the alcohol in a pure state by ridding it of oils,
water, ether, and foreign alcohols.

The alcohol industry never realizes this operation in an absolutely
complete manner. All the rectifying apparatus in operation at the
present day are based on the use of high temperatures varying between
78.5 deg. and 100 deg.. The successive condensation and vaporization of the
vapors issuing from the spirits effect in the rectifying columns a
partial separation of these liquids, and there are received successively
as products of rectification:

1. Bad tasting alcohols, containing the majority of the ethers and
impure alcohols.

2. Fine alcohol.

3. Alcohols contaminated by notable proportions of empyreumatic oils.

Industry knows only one means of obtaining an excellent product, and
that is to diminish the quantity of fine alcohol which comes from a same
lot of spirits, and to make a large number of successive distillations.
Hence the large expenses attending rectification, which produce fine
alcohols necessarily at an elevated price. We may remark, in passing,
that the toxic action of commercial alcohols is in great part caused by
the presence of essential oils, amylic alcohol, and ethers, absolutely
pure alcohol, as compared with these, being relatively innocent.

Why is it that our present apparatus cannot produce good results in
rectifying alcohol? Because they are limited by the temperature at which
they must operate. Between 78 deg. and 100 deg. the tension of the vapors
of all the liquids mixed in the spirits is considerable for each of them;
they all pass over, then, in certain proportions during the operation of
rectification.

We have been led, by examining the theoretical question, to ascertain
that the proportion of alcohol which evaporates from a mixture is
maximum at low temperatures; consequently, we should seek to establish
some arrangement which can realize the following conditions: (1) Render
variable, at will, the temperature of the boiling liquid; and (2),
render variable the pressure of the vapors which act on the liquid.

Thus, to effect the rectification of alcohol it suffices to cause its
ebullition at very low temperatures, and to keep up the ebullition
without changing such temperatures when once obtained.

It is exactly these two conditions that we have fulfilled in the
apparatus that we have just installed in our factory in Rue Immeubles
Industriels, at Paris.

By their arrangement, which is shown in the opposite figure, they form
a mechanical system permitting of the rectification of alcohols at
temperatures as low as -40 deg. or even -50 deg.. They verify
experimentally, by their operation, the theoretical deductions which
precede. The boilers, A, which, in an industrial application, may be
more numerous, receive their supply of spirits from the country
distilleries in the vicinity of the factory. There may even be
introduced directly into them _vinasses_, or washes, that is to say,
liquids, such as are obtained by alcoholic fermentation.

Above the boiler rises a rectifying column composed of superposed plates
inclined one over the other, and surmounted by a tubular condenser,
which serves to effect the retrogression of the first condensation by
means of a current of water supplied by the reservoir placed above.

On leaving this condenser, the vapors which have escaped condensation
pass into the refrigerator, C, where they are totally condensed by a
current of water which goes to the reservoir above.

The first products obtained contain ethers and impure alcohols, which
are collected in the reservoir, E.

When the first products have been thus introduced into the reservoir,
and it is ascertained by tasting that good alcohol is passing over,
the liquid produced is directed into the second boiler, F. The sliding
valve, operated by a screw having a very fine pitch, establishes a
communication between the refrigerator, C, and the second boiler, F. The
office of this valve we shall learn further on. This first rectification
is performed in a vacuum, for a system of metallic pipes connects the
entire apparatus with an air-pump, O. The temperature at which the
liquids shall enter into ebullition in the boilers, A A, may, then, be
regulated in advance.

The operations will be carried on with a more or less complete vacuum,
according to the nature of the products to be rectified. The distiller
will have to be guided in this by practice alone.

The good tasted products are received in boiler No. 2, F, and there
the liquids are submitted to the action of an almost absolute vacuum.
As we have before said, their temperature falls immediately and
spontaneously. The vapors which issue from this liquid contain almost
solely pure alcohol. The other substances, which passed over in the
first distillation, no longer emit vapors at temperatures ranging
between -10 deg. and +5 deg.. Their temperature is shown by a
thermometer running into the boiler, F.

These vapors, purified by ebullition at a low temperature, rise into a
second rectifying column, G, which terminates in the refrigerator, H,
filled with liquid sulphurous anhydride. This refrigerator is like those
which we employ in our sulphurous anhydride frigorific apparatus. Under
the action of a special pump, M, this liquid produces and maintains a
constant temperature of -25 deg. to -30 deg. in the refrigerator. The
vapors of alcohol condense therein at this low temperature, and the cold
liquid alcohol flows into the lower part of the refrigerator.

By the action of a return cock, a portion of this liquid falls upon
the plates of the column, G, and descends, while the vapors are rising
therein. The other portion of the liquid obtained flows into the
reservoir, K, at the beginning of the operation, and into the reservoir,
L, during all the remainder of the rectification. The ice-making machine
keeps up of itself alone the two operations.

In fact, the exhaust of the steam engine which actuates the sulphurous
anhydride pump is directed into a worm which circulates through the
first boiler, A, and the refrigerator, H, of the frigorific machine
keeps up the second rectification, which was brought about below the
surrounding temperature, and which for this reason takes place without
necessitating any combustion of coal. It suffices to cause the current
of water which issues from the condenser of the frigorific machine to
pass into the worm of the boiler.

We have, then, two results, two like operations, both produced by
the working of a single machine. Moreover, these two operations are
performed _in vacuo_, and we know that under these conditions they are
effected at lower temperatures. Owing to this fact, likewise, the weight
of the water that must be evaporated diminishes just so much. Now, one
kilogramme of water requires 636 heat units to cause it to pass from the
liquid to the gaseous state, while one kilogramme of alcohol requires
only 230 heat units to vaporize it. Thus every decrease of temperature
in rectification has for an immediate corollary an important economy of
fuel, which is proved by the diminution of radiation, and by the less
quantity of water to be distilled.

Between the boilers, A, in which is maintained a temperature bordering
on +50 deg. to +60 deg., and the refrigerator, H, in which is easily
obtained a temperature of -30 deg. to -40 deg., there is at our disposal
a range of temperature of nearly 100 deg., an immense difference
compared with that which can be made use of in ordinary apparatus.
Thanks to this powerful factor, which is manageable at will, we can
take directly from the apparatus alcohols marking 98 and 99 degrees by
the centigrade alcoholmeter. Such results are unobtainable by the usual
methods.

We have likewise ascertained that at low temperatures the ebullition of
alcohol is as active as at near 100 deg..

For a same range of temperature between the boiler and the refrigerator,
the weight of alcohol which distills in an hour is constant. By the
operation of the valve, D, it becomes easy to allow all the liquid
condensed in the first refrigerator to pass into the second boiler;
and thus the second rectification, which is effected in a more perfect
vacuum, is supplied with exactness. The object of this valve, then, is
to allow the liquid to pass, and yet to cut off the pressure in such
a way as to have a double fall of temperature throughout the whole
apparatus; from 60 deg. to 20 deg. in the first operation, and from
0 deg. to -40 deg. in the second. We may add that the regulation of the
valve is extremely easy, because of the screw which actuates it.

To sum up the commercial advantages that our process procures, we may
say that it realizes the following _desiderata_: 1. With the cost of a
single distillation we have, at once, distillation and rectification,
or a single expense for two results. 2. With one operation at a low
temperature we obtain products which are almost impossible to get even
by an indefinite number of rectifications at a high temperature, the
temperature having an intrinsic value in the operation. 3. The alcohols
obtained are wholesome, and can be put on the market without danger. 4.
Their superior quality gives these alcohols an extra value difficult
to calculate, but which is very notable. 5. The whole operation being
performed in closed vessels, there is absolutely no waste. 6. For the
same reason there is scarcely any danger of fire. 7. The management of
the works and the service are performed by the pressure of the gases
entirely; there are only a few cocks to be turned to perform all the
interior maneuvers, empty and fill the vessels, etc. Hence economy in
_personnel_.

* * * * *

ELECTROLYTIC DETERMINATIONS AND SEPARATIONS.

[Footnote: NOTE.--Each of these determinations was accompanied by a
series of results in which the practical determinations obtained from
the method described were compared with the theoretical contents of the
solutions of the various elements. These, however, would take up too
much room for insertion in these columns.]

By ALEX. CLASSEN and M.A. VON REIS; translated by M. BENJAMIN, Ph.B.,
F.C.S.

Ever since the electrolytic method for the estimation of copper came
into general use, numerous chemists have endeavored to adapt this
peculiarly simple and elegant method to the determination of other
metals. According to the experiments which have been made up to the
present time, it has been found that the separation of copper is best
effected in a nitric acid solution, while that of nickel and cobalt
takes place most readily in an ammoniacal solution, and for the
precipitation of zinc and cadmium a potassium cyanide solution is the
best. The accuracy of the results depend chiefly upon the following of
certain fixed rules, such as, for instance, that the precipitation of
copper only takes place when there is a definite amount of nitric acid
in the solution; that of cobalt and nickel when a certain quantity of
ammonium hydrate and ammonium sulphate is present. The electrolytic
decomposition of the chlorides has not yet been successfully
accomplished, so that prior to the operation it is necessary to convert
them into sulphates. The experiments which have been made for the
purpose of investigating the application of the electric current in
quantitative analyses are very few, about the only exception being the
separation of copper from the metals which are not precipitated from a
nitric acid solution, or which are deposited as peroxides at the other
electrode. We shall endeavor to show in that which follows, that copper,
zinc, nickel, and cobalt, and even iron, manganese, cadmium, bismuth,
and tin, whether they be present as sulphates, chlorides, or nitrates,
may be precipitated and separated from each other by electrolytic
methods much more rapidly than by any previously known process.

DETERMINATION OF COBALT.

Neutral potassium oxalate is added in excess to the solution of a cobalt
salt, and the clear solution of cobalt potassium oxalate submitted to
electrolysis. The intense red color of this solution is soon changed
into a dark green; the latter diminishing in intensity as the metal is
deposited at the negative electrode. The electric current decomposes the
potassium oxalate into the carbonate, so that a precipitate of cobalt
carbonate is simultaneously formed with the separation of the metallic
cobalt. This precipitate may be dissolved by adding oxalic acid or
dilute sulphuric acid; the further action of the current will change the
solution to an alkaline reaction, upon which the treatment with acid is
repeated until all the cobalt has been separated out in its metallic
condition. The electrolytic separation of cobalt is much more easily
and rapidly effected when the potassium oxalate is substituted by the
corresponding ammonium salt, as the latter forms a soluble double
salt with the cobalt compounds. If the ammonium oxalate added is just
sufficient to form the double salt, a red cobalt oxalate (_which is only
slowly reduced by the current_) will separate out in addition to the
cobalt. In order to obviate this difficulty, the solution to which the
ammonium oxalate had been added in excess is heated, and then three
or four grammes more of solid ammonium oxalate are added. The _hot_
solution, when exposed to the action of the current, deposits the cobalt
as a closely adhering gray film. By the aid of two Bunsen's elements,
0.2 gramme cobalt can be separated in an hour's time. When the reduction
has been completed, and this is best determined by testing a small
sample (removed by a pipette) with ammonium sulphide, the positive
electrode[1] is removed from the solution, and the liquid poured off.
The dish is immediately rinsed several times with water, and the excess
of water removed at first with alcohol, and then with absolute ether.
The cobalt in the dish is dried in the air bath at 100 deg. C., and in the
course of a few minutes a constant weight is obtained.

[Footnote 1: A piece of platinum foil, 4.5 cm. in diameter, is used
for the positive electrode, and a deep platinum dish as the negative
electrode.--_Vide_ "Classen's Quantitative Analysis," 3d Edition, p.
46.]

DETERMINATION OF NICKEL.

This process is precisely identical with the previously described method
for cobalt. The ammonium oxalate is added in excess to the solution,
which is then heated, and four more grammes of the solid salt added. The
separation of the nickel is as rapid as that of the cobalt. The nickel
is precipitated as a gray, compact mass, tightly adhering to the
electrode.

DETERMINATION OF IRON.

For this estimation, solutions of the chloride as well as those of the
sulphate (ammonium, iron, alum) may be used in the manner previously
described. The electrolysis is best effected in the presence of a
sufficient quantity of ammonium oxalate; no separation of any iron
compound takes place. The iron is deposited in the form of a bright,
steel gray, firmly-adhering mass on the platinum dish. The iron may be
exposed to the air for several days without any noticeable oxidation
taking place.

DETERMINATION OF ZINC.

Zinc may be separated from a solution of the double salt fully as easily
and rapidly as the previously mentioned metals were. The reduced zinc
has a dark gray color, and adheres very firmly to the electrode. The
separated metal is dissolved by using dilute acids and heating. It is
only removed with difficulty, and generally leaves a dark coating on the
dish, which is separated by repeated ignitions and treatment with acid.

DETERMINATION OF MANGANESE.

It is already known that manganese may be separated as the peroxide from
its nitric acid solution. We find, however, that the precipitation is
only completely effected when the quantity present is small; the amount
of nitric acid must also be slight, and it is necessary to wash the dish
without interrupting the current. If the manganese is converted into
the soluble double salt, prepared by adding an excess of potassium, and
submitted to the electric current, the whole of the manganese will be
deposited at the positive electrode. When ammonium oxalate is used, the
complete precipitation does not take place. As the separated peroxide
does not adhere firmly to the electrode, it is necessary to filter it
and convert it, by ignition, into the trimangano-tetroxide (Mn_3O_4).

DETERMINATION OF BISMUTH.

This separation presents considerable difficulty, because the metal
is not precipitated as a compact mass on the platinum. The bismuth is
always obtained in the same form, no matter whether it is precipitated
from an acid solution, or from the double ammonium oxalate, or, finally,
from a solution to which potassium tartrate has been added. As large a
surface as possible must be used, and the dish piled to the rim; then,
if the quantity of bismuth is small, the washing with water, alcohol,
and ether may be effected without any loss of the element. If small
quantities of the metal separate from the dish, they must be collected
on a tared filter, and determined separately. In our experiments, an
excess of ammonium oxalate was added to a nitric acid solution of
bismuth. During the electrolytic decomposition, a separation of the
peroxide was observed at the positive electrode, which, however, slowly
disappeared. In order to prevent the reduced metal from oxidation, the
last traces of water are completely removed by repeated washings with
alcohol and anhydrous ether.

DETERMINATION OF LEAD.

The nitric solution of lead acts similarly to that of manganese. When
the amount of peroxide separated is so large that it does not adhere
firmly, and becomes mechanically precipitated on the negative electrode,
it becomes impossible to complete the estimation without loss from the
solution of the peroxide, and the results cannot be accepted.

If the double oxalate is submitted to electrolysis, the whole of the
lead is separated out in its metallic state, but it is so rapidly
oxidized by the air that it is very seldom that it can be dried without
decomposition even when the operation is conducted in a current of
illuminating gas. The electrolytic estimation of this element cannot be
recommended.

DETERMINATION OF COPPER.

The copper may be very easily and rapidly separated from the double
ammonium oxalate salt, provided a sufficient excess of ammonium oxalate
is present. Weak currents cannot be employed for the determination of
this element when it is present in large quantities, for under such
circumstances the metal does not adhere with sufficient firmness to the
electrode. We employed a current which corresponded to an evolution of
330 c.c. of gas per hour, and we were able to precipitate 0.15 gramme
metallic copper in about twenty-five minutes.

DETERMINATION OF CADMIUM.

When the cadmium ammonium oxalate is submitted to the action of the
electric current, the metal is thrown down in the form of a gray
coating, which does not adhere very firmly to the electrode, but,
however, sufficiently so as not to become separated on careful washing.

DETERMINATION OF TIN.

Tin may be easily estimated by electrolysis; it can be separated from
its hydrochloric acid solution, or from its double salt with ammonium
oxalate, as a beautiful silver gray coating on the platinum. When the
ammonium oxalate is substituted by the potassium salt, the operation
becomes more difficult, as a basic salt is formed at the opposite
pole, and is not easily reduced. If the tin is separated from an acid
solution, the current must not be interrupted while the washing takes
place, a precaution which it is not necessary to follow when the
ammonium oxalate is used. When the tin is dissolved from the platinum
dish, it acts like the zinc; that is to say, a black coating is left on
the electrode.

DETERMINATION OF ANTIMONY.

Antimony may be precipitated in its metallic state from a hydrochloric
acid solution, but it does not adhere very firmly to the electrode.
If potassium oxalate is added to a solution of the trichloride, the
antimony may be readily reduced, but the metal adheres still less firmly
to the electrode than it did in the first instance. An adherent coating
may be obtained by adding an alkaline tartrate, but in that case the
separation takes place too slowly. The precipitation of antimony may be
very readily effected from solutions of its sulpho salts.

To a liquid, which may contain free hydrochloric acid, hydrogen sulphide
is added, then neutralized with ammonium hydrate, and saturated with
ammonium sulphide in excess. The reduction may be accelerated by the
addition of some ammonium sulphate. The antimony separates out as a
fine, light gray precipitate on the electrode, and which adheres very
firmly, provided the precipitation has not been carried on too rapidly,
_i. e._, if the current employed for the reduction was not too strong.

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