Considerable interest has been aroused lately in scientific and
industrial circles by a report that separation of the oxygen and
nitrogen of the air was being effected on a large scale in London by a
process which promises to render the gases available for general
application in the arts. The cheap manufacture of the compounds of
nitrogen from the gas itself is still a dream of chemical enthusiasts;
and though the pure gas is now available, the methods of making its
compounds have yet to be devised. But the industrial processes which
already depend directly or indirectly on the chemical union of bodies
with atmospheric oxygen are innumerable.
In all these processes the action of the gas is impeded by the bulky
presence of its fellow constituent of air, nitrogen. We may say, for
instance, in homely phrase, that whenever a fire burns there are four
volumes of nitrogen tending to extinguish it for every volume of
oxygen supporting its combustion, and to the same degree the nitrogen
interferes with all other processes of atmospheric oxidation, of which
most metallurgical operations may be given as instances. If, then, it
has become possible to remove this diluent gas simply and cheaply in
order to give the oxygen free play in its various applications, we are
doubtless on the eve of a revolution among some of the most extensive
and familiar of the world's industries.
A series of chemical reactions has long been known by means of which
oxygen could be separated out of air in the laboratory, and at various
times processes based on these reactions have been patented for the
production of oxygen on a large scale. Until recently, however, none
of these methods gave sufficiently satisfactory results. The simplest
and perhaps the best of them was based on the fact first noticed by
Boussingault, that when baryta (BaO) is heated to low redness in a
current of air, it takes up oxygen and becomes barium dioxide
(BaO_{2}), and that this dioxide at a higher temperature is
reconverted into free oxygen and baryta, the latter being ready for
use again. For many years it was assumed, however, by chemists that
this ideally simple reaction was inapplicable on a commercial scale,
owing to the gradual loss of power to absorb oxygen which was always
found to take place in the baryta after a certain number of
operations. About eight years ago Messrs. A. & L. Brin, who had
studied chemistry under Boussingault, undertook experiments with the
view of determining why the baryta lost its power of absorbing oxygen.
They found that it was owing to molecular and physical changes caused
in it by impurities in the air used and by the high temperature
employed for decomposing the dioxide. They discovered that by heating
the dioxide in a partial vacuum the temperature necessary to drive off
its oxygen was much reduced. They also found that by supplying the air
to the baryta under a moderate pressure, its absorption of oxygen was
greatly assisted. Under these conditions, and by carefully purifying
the air before use, they found that it became possible to use the
baryta an indefinite number of times. Thus the process became
practically, as it was theoretically, continuous.
After securing patent protection for their process, Messrs. Brin
erected a small producer in Paris, and successfully worked it for
nearly three years without finding a renewal of the original charge of
baryta once necessary. This producer was exhibited at the Inventions
Exhibition in London, in 1885. Subsequently an English company was
formed, and in the autumn of last year Brin's Oxygen Company began
operations in Horseferry Road, Westminster, where a large and complete
demonstration plant was erected, and the work commenced of developing
the production and application of oxygen in the industrial world.
[Illustration: APPARATUS FOR MAKING OXYGEN.]
We give herewith details of the plant now working at Westminster. It
is exceedingly simple. On the left of the side elevation and plan are
shown the retorts, on the right is an arrangement of pumps for
alternately supplying air under pressure and exhausting the oxygen
from the retorts. As is shown in the plan, two sets of apparatus are
worked side by side at Westminster, the seventy-two retorts shown in
the drawings being divided into two systems of thirty-six. Each system
is fed by the two pumps on the corresponding side of the boiler. Each
set of retorts consists of six rows of six retorts each, one row above
the other. They are heated by a small Wilson's producer, so that the
attendant can easily regulate the supply of heat and obtain complete
control over the temperature of the retorts. The retorts, A, are made
of wrought iron and are about 10 ft long and 8 in. diameter.
Experience, however, goes to prove that there is a limit to the
diameter of the retorts beyond which the results become less
satisfactory. This limit is probably somewhat under 8 in. Each retort
is closely packed with baryta in lumps about the size of a walnut. The
baryta is a heavy grayish porous substance prepared by carefully
igniting the nitrate of barium; and of this each retort having the
above dimensions holds about 125 lb. The retorts so charged are closed
at each end by a gun metal lid riveted on so as to be air tight. From
the center of each lid a bent gun metal pipe, B, connects each retort
with the next of its series, so that air introduced into the end
retort of any row may pass through the whole series of six retorts.
Suppose now that the operations are to commence.
The retorts are first heated to a temperature of about 600° C. or
faint redness, then the air pumps, C C, are started. Air is drawn by
them through the purifier, D, where it is freed from carbon dioxide
and moisture by the layers of quicklime and caustic soda with which
the purifier is charged. The air is then forced along the pipe, E,
into the small air vessel, F, which acts as a sort of cushion to
prevent the baryta in the retorts being disturbed by the pulsation of
the pumps. From this vessel the air passes by the pipe, G, and is
distributed in the retorts as rapidly as possible at such a pressure
that the nitrogen which passes out unabsorbed at the outlet registers
about 15 lb. to the square inch. With the baryta so disposed in the
retorts as to present as large a superficies as possible to the action
of the air, it is found that in 1½ to 2 hours--during which time about
12,000 cub. ft of air have been passed through the retorts--the gas at
the outlet fails to extinguish a glowing chip, indicating that oxygen
is no longer being absorbed. The pumping now ceases, and the
temperature of the retorts is raised to about 800° C. The workman is
able to judge the temperature with sufficient accuracy by means of the
small inspection holes, H, fitted with panes of mica, through which
the color of the heat in the furnace can be distinguished. The pumps
are now reversed and the process of exhaustion begins. At Westminster
the pressure in the retorts is reduced to about 1½ in. of mercury. In
this partial vacuum the oxygen is given off rapidly, and if forced by
the pumps through another pipe and away into an ordinary gas holder,
where it is stored for use. With powerful pumps such as are used in
the plant under notice the whole of the oxygen can be drawn off in an
hour, and from one charge a yield of about 2,000 cub. ft. is obtained.
With a less perfect vacuum the time is longer--even as much as four
hours. The whole operation of charging and exhausting the retorts can
be completed in from three to four hours. As soon as the evolution of
oxygen is finished, the doors, K, and ventilators, L, may be opened
and the retorts cooled for recharging.
The cost of producing oxygen at Westminster, under specially expensive
conditions, is high--about 12s. per 1,000 cub. ft. When we consider,
however, that the cost should only embrace attendance, fuel, wear and
tear, and a little lime and soda for the purifiers, that the
consumption of fuel is small, the wear and tear light, and that the
raw material--air--is obtained for nothing, it ought to be possible to
produce the gas for a third or fourth of this amount in most of our
great manufacturing centers, where the price of fuel is but a third of
that demanded in London, and where provision could be made for
economizing the waste heat, which is entirely lost in the Westminster
installation. Moreover, in estimating this cost all the charges are
thrown on the oxygen; were there any means of utilizing the 4,000 cub.
ft. of nitrogen at present blown away as waste for every thousand
cubic feet of oxygen produced, the nitrogen would of course bear its
share of the cost.
The question of the application of the oxygen is one which must be
determined in its manifold bearings mainly by the experiments of
chemists and scientific men engaged in industrial work. Having
ascertained the method by which and the limit of cost within which it
is possible to use oxygen in their work, it can be seen whether by
Brin's process the gas can be obtained within that limit.
Mr. S.R. Ogden, the manager of the corporation gasworks at Blackburn,
has already made interesting experiments on the application of oxygen
in the manufacture of illuminating gas. In order to purify coal gas
from compounds of sulphur, it is passed through purifiers charged with
layers of oxide of iron. When the oxide of iron has absorbed as much
sulphur as it can combine with, it is described as "foul." It is then
discharged and spread out in the open air, when, under the influence
of the atmospheric oxygen, it is rapidly decomposed, the sulphur is
separated out in the free state, and oxide of iron is reformed ready
for use again in the purifiers. This process is called revivification,
and it is repeated until the accumulation of sulphur in the oxide is
so great (45 to 55 per cent.) that it can be profitably sold to the
vitriol maker. Hawkins discovered that by introducing about 3 per
cent. of air into the gas before passing it through the purifiers, the
oxygen of the air introduced set free the sulphur from the iron as
fast as it was absorbed. Thus the process of revivification could be
carried on in the purifiers themselves simultaneously with the
absorption of the sulphur impurities in the gas.
A great saving of labor was thus effected, and also an economy in the
use of the iron oxide, which in this way could be left in the
purifiers until charged with 75 per cent. of sulphur. Unfortunately it
was found that this introduction of air for the sake of its oxygen
meant also the introduction of much useless nitrogen, which materially
reduced the illuminating power of the gas. To restore this
illuminating power the gas had to be recarbureted, and this again
meant cost in labor and material. Now, Mr. Ogden has found by a series
of conclusive experiments made during a period of seventy-eight days
upon a quantity of about 4,000,000 cub. ft. of gas, that by
introducing 1 per cent. of oxygen into the gas instead of 3 per cent.
of air, not only is the revivification _in situ_ effected more
satisfactorily than with air, but at the same time the illuminating
power of the gas, so far from being decreased, is actually increased
by one candle unit.
[Illustration: THE PRODUCTION OF OXYGEN BY BRIN'S PROCESS.]
So satisfied is he with his results that he has recommended the
corporation to erect a plant for the production of oxygen at the
Blackburn gas works, by which he estimates that the saving to the town
on the year's make of gas will be something like £2,500. The practical
observations of Mr. Ogden are being followed up by a series of
exhaustive experiments by Mr. Valon, A.M. Inst. C.E., also a gas
engineer. The make of an entire works at Westgate is being treated by
him with oxygen. Mr. Valon has not yet published his report, as the
experiments are not quite complete; but we understand that his results
are even more satisfactory than those obtained at Blackburn.
In conclusion we may indicate a few other of the numerous possible
applications of cheap oxygen which might be realized in the near
future. The greatest illuminating effect from a given bulk of gas is
obtained by mixing it with the requisite proportion of oxygen, and
holding in the flame of the burning mixture a piece of some solid
infusible and non-volatile substance, such as lime. This becomes
heated to whiteness, and emits an intense light know as the Drummond
light, used already for special purposes of illumination. By supplying
oxygen in pipes laid by the side of the ordinary gas mains, it would
be possible to fix small Drummond lights in place of the gas burners
now used in houses; this would greatly reduce the consumption of gas
and increase the light obtained, or even render possible the
employment of cheap non-illuminating combustible gases other than coal
gas for the purpose.
Two obstacles at present lie in the way of this consummation--the cost
of the oxygen and the want of a convenient and completely refractory
material to take the place of the lime. Messrs. Brin believe they have
overcome the first obstacle, and are addressing themselves, we
believe, to the removal of the second. Again, the intense heat which
the combustion of carbon in cheap oxygen will place at the disposal of
the metallurgist cannot fail to play an important part in his
operations. There are many processes, too, of metal refining which
ought to be facilitated by the use of the gas. Then the production of
pure metallic oxides for the manufacture of paints, the bleaching of
oils and fats, the reduction of refractory ores of the precious metals
on a large scale, the conversion of iron into steel, and numberless
other processes familiar to the specialists whose walk is in the
byways of applied chemistry, should all profit by the employment of
this energetic agent. Doubtless, too, the investigation into methods
of producing the compounds of nitrogen so indispensable as plant
foods, and for which we are now dependent on the supplies of the
mineral world, may be stimulated by the fact that there is available
by Brin's process a cheap and inexhaustible supply of pure
nitrogen.--_Industries._
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