This chamber is provided with water lutes, through which the tar
condensed in it is from time to time removed. From this chamber the
gases, which are now cooled down to about 100° C., and are loaded with
a large amount of water vapor, are passed through a scrubber filled
with perforated bricks, in which the ammonia contained in the gases is
absorbed by sulphuric acid. In this scrubber a fairly concentrated
solution of sulphate of ammonia containing 36 to 38 per cent. is used,
to which a small quantity of sulphuric acid is added, so that the
liquid leaving the scrubber contains only 2.5 per cent. of free acid.
This is necessary, as a liquid containing more acid would act upon the
tarry matter and produce a very dark-colored solution. The liquid
running from the scrubber is passed through a separator in which the
solution of sulphate of ammonia separates from the tar. The greater
portion of the clear liquid is, after adding a fresh quantity of acid
to it, pumped back through the scrubber. A certain portion of it is,
after treatment with a small quantity of heavy tar oils, which take
the tarry matter dissolved in it out, evaporated in conical lead-lined
pans furnished with lead steam coils, and which are kept constantly
filled by the addition of fresh liquor until the whole mass is thick.
This is then run out on a strainer and yields, after draining and
washing with a little water, a sulphate of ammonia of very fair
quality, which finds a ready sale. The mother liquor, which contains
all the free acid, is pumped back to the scrubber.
The gas on entering this scrubber contains only 0.13 volume per cent.
of ammonia, and on leaving the scrubber it contains not more than
one-tenth of this quantity. Its temperature has been reduced to
80° C., and is fully saturated with moisture, so that practically no
condensation of water takes place in the scrubber. The gas is next
passed through a second scrubber filled with perforated wood blocks.
In this it meets with a current of cold water which condenses the
steam, the water being thereby heated to about 78° C. In this scrubber
the gas is cooled down to about 40°-50° C., and passes from it to the
gas main leading to the various places where it is to be consumed. The
hot water obtained in this second scrubber is passed through a vessel
suitably constructed for separating the tar which is mixed with it,
and is then pumped through a third scrubber, through which, in an
opposite direction to the hot water, cold air is passed. This is
forced by means of a Roots blower through the scrubber into the
producer.
The air gets heated to about 76° C. and saturated with moisture at
that temperature by its contact with the hot water, and the water
leaves this third scrubber cold enough to be pumped back through the
second scrubber. The same quantity of water is thus constantly used
for condensing the water vapor in one scrubber and giving it up to the
air in the other. In this way we recover and return to the producer
fully two-thirds of the steam which has been originally introduced, so
that we have to add to the air, which has thus been loaded with
moisture, an additional quantity of steam equal to only one-third of
the total quantity required before it enters the producer. This
additional quantity of steam, which amounts to 0.6 ton of steam for
every ton of fuel burnt, we obtain as exhaust steam from the engines
driving the blowers and pumps required for working the plant.
The gas producers which I prefer to use are of rectangular shape, so
that a number of them can be put into a row. They are six feet wide
and 12 feet long inside. The air is introduced and the ashes removed
at the two small sides of the producer which taper toward the middle
and are closed at the bottom by a water lute of sufficient depth for
the pressure under which the air is forced in, equal to about 4 inches
of water. The ashes are taken out from underneath the water, the
producers having no grate or fire bars at all. The air enters just
above the level of the water through a pipe connected with the blower.
These small sides of the producer rest upon cast iron plates lined to
a certain height with brickwork, and this brickwork is carried by
horizontal cast iron plates above the air entrance. In this way a
chamber is formed of triangular shape, one side of which is closed by
the ashes, and thus the air is distributed over the whole width of the
producer.
The gas is taken out in the middle of the top of the producer by an
iron pipe, and fuel charged in by hoppers on both sides of this pipe.
Between the pipe and the hoppers two hanging arches are put into the
producers a certain distance down, and the fuel is kept above the
bottom level of these hanging arches. This compels the products of
distillation, produced when fresh fuel is charged in, to pass through
the incandescent fuel between the two hanging arches, whereby the
tarry products are to a considerable extent converted into permanent
gas, and the coal dust arising from the charging is kept back in the
producer.
The details of construction of this plant will be easily understood by
reference to the diagrams before you.
The fuel we use is a common kind of slack, and contains, on an
average, 33.5 per cent. of volatile matter, including water, and 11.5
per cent. of ashes, leaving 55 per cent. of non-volatile carbon.
The cinders which we take out of the producer contain, on an average,
33 per cent. of carbon. Of this we recover about one-half by riddling
or picking, which we return to the producer. The amount of unburnt
carbon lost in the cinders is thus not more than 3 per cent. to 4 per
cent. on the weight of fuel used.
The gas we obtain contains, in a dry state, on an average, 15 per
cent. of carbonic acid, 10 per cent. of carbonic oxide, 23 per cent.
of hydrogen, 3 per cent. of hydrocarbons, and 49 per cent. of
nitrogen.
The caloric value of this gas is very nearly equal to 73 per cent. of
the caloric value of the fuel used, but in using this gas for heating
purposes, such as raising steam or making salt, we utilize the heat it
can give very much better than in burning fuel, as we can completely
burn it with almost the theoretical quantity of air, so that the
products of combustion resulting do not contain more than 1 to 2 per
cent. of free oxygen. Consequently the heat escaping into the chimney
is very much less than when fuel is burnt direct, and we arrive at
evaporating, by means of the gas, 85 per cent. of the water that we
would evaporate by burning the fuel direct, in ordinary fireplaces.
We have, however, to use a certain quantity of steam in the producers
and in evaporating the sulphate of ammonia liquors, which has to be
deducted from the steam that can be raised by the gas in order to get
at the quantity of available steam therefrom obtainable. The former
amounts, as already stated, to 0.6 ton, the latter to 0.1 ton of steam
per ton of fuel burnt, making a total of 0.7 ton. The gas obtained
from one ton of fuel evaporates 5.8 tons of water in good steam
boilers, working at a rate of evaporation of 50 to 55 tons per 24
hours under 90 lb. pressure. Deducting from this the 0.7 ton necessary
for working the plant leaves an available amount of steam raised by
the gas from one ton of fuel of 5.1 tons, equal to 75 per cent. of the
steam that we can obtain from the same fuel by hand firing.
In addition to the gas, we obtain about 3 per cent. of tar from the
fuel. This tar is very thick, and of little commercial value. It
contains only 4 per cent. of oils volatile below 200° C., and 38 per
cent. of oils of a higher boiling point, consisting mostly of creosote
oils very similar to those obtained from blast furnaces; and only
small quantities of anthracene and paraffin wax.
I have made no attempts to utilize this tar except as fuel. It
evaporates nearly twice as much water as its weight of coal, and we
have thus to add its evaporative efficiency to that of the gas given
above, leading to a total of about 80 per cent. of the evaporative
efficiency of the fuel used in the producers. The loss involved in
gasifying the fuel to recover the ammonia therefrom amounts thus to 20
per cent. of the fuel used. This means that, where we have now to burn
100 tons of fuel, we shall have to burn 125 tons in the producers in
order to obtain ammonia equal to about half the nitrogen contained
therein. Our actual yield of ammonia on a large scale amounting on an
average to 32 kilos., equal to 70.6 lb. per ton of fuel, 125 tons of
fuel will turn out 4 tons of sulphate of ammonia. We thus consume 6.25
tons of fuel for every ton of sulphate obtained, or nearly the same
quantity as is used in producing a ton of caustic soda by the Le Blanc
process--a product not more than half the value of ammonium sulphate.
At present prices in Northwich this fuel represents a value of 35s. If
we add to this the extra cost of labor over and above the cost of
burning fuel in ordinary fireplaces, the cost of sulphuric acid, bags,
etc., we come to a total of 4l. 10s. to 5l. per ton of sulphate of
ammonia, which at the present selling price of this article, say 12l.
per ton, leaves, after a liberal allowance for wear and tear of plant,
an ample margin of profit. With a rise in the price of fuel, this
margin, however, rapidly decreases, and the working of the process
will, of course, be much more expensive on a small scale, as will also
be the cost of the plant, which under all circumstances is very
considerable. The great advantages incidental to this process over and
above the profit arising from the manufacture of sulphate of ammonia,
viz., the absolute impossibility of producing smoke and the great
regularity of the heating resulting from the use of gas, are,
therefore, as far as I can see for the present, only available for
large consumers of cheap fuel.
We have tried many experiments to produce hydrochloric acid in the
producers, with the hope of thereby increasing the yield of ammonia,
as it is well known that ammonium chloride vapor, although it consists
of a mixture of ammonia gas and hydrochloric acid gas, is not at all
dissociated at temperatures at which the dissociation of ammonia alone
has already taken place to a considerable extent.
I had also hoped that I might in this way produce the acid necessary
to combine with the ammonia at very small cost. For this purpose we
moistened the fuel used with concentrated brine, and also with the
waste liquors from the ammonia soda manufacture, consisting mainly of
chloride of calcium; and we also introduced with the fuel balls made
by mixing very concentrated chloride of calcium solution with clay,
which allowed us to produce a larger quantity of hydrochloric acid in
the producer than by the other methods.
We did in this way succeed in producing hydrochloric acid sometimes
less and sometimes more than was necessary to combine with the
ammonia, but we did not succeed in producing with regularity the exact
amount of acid necessary to neutralize the ammonia. When the ammonia
was in excess, we had therefore to use sulphuric acid as before to
absorb this excess, and we were never certain that sometimes the
hydrochloric acid might not be in excess, which would have
necessitated to construct the whole plant so that it could have
resisted the action of weak hydrochloric acid--a difficulty which I
have not ventured to attack. The yield of ammonia was not in any case
increased by the presence of the hydrochloric acid. This explains
itself if we consider that there is only a very small amount of
ammonia and hydrochloric acid diffused through a very large volume of
other gases, so that the very peculiar protective action which the
hydrochloric acid does exercise in retarding the dissociation of
ammonia in ammonium chloride vapor, where an atom of ammonia is always
in contact with an atom of hydrochloric acid, will be diminished
almost to zero in such a dilute gas where the atoms of hydrochloric
acid and ammonia will only rarely come into immediate contact with
each other.
When we burnt coke by a mixture of air and steam in presence of a
large excess of hydrochloric acid, the yield of ammonia certainly was
thereby considerably increased, but such a large excess cannot be used
on an industrial scale. I have therefore for the present to rest
satisfied with obtaining only half the nitrogen contained in the fuel
in the form of ammonia.
The enormous consumption of fuel in this country--amounting to no less
than 150 million tons per annum--would at this rate yield as much as
five million tons of sulphate of ammonia a year, so that if only
one-tenth of this fuel would be treated by the process, England alone
could supply the whole of the nitrogenous compounds, sulphate of
ammonia, and nitrate of soda at present consumed by the Old World. As
the process is especially profitable for large consumers of fuel
situated in districts where fuel is cheap, it seems to me particularly
suitable to be adopted in this country. It promises to give England
the privilege of supplying the Old World with this all-important
fertilizer, and while yielding a fair profit to the invested capital
and finding employment for a considerable number of men, to make us,
last not least, independent of the New World for our supply of so
indispensable a commodity.
Before leaving my subject, I will, if you will allow me, give you in a
few words a description of two other inventions which have been the
outcome of this research. While looking one day at the beautiful,
almost colorless, flame of the producer gas burning under one of our
boilers, it occurred to me that a gas so rich in hydrogen might be
turned to better use, and that it might be possible to convert it
direct into electricity by means of a gas battery.
You all know that Lord Justice Grove showed, now fifty years ago, that
two strips of platinum partly immersed in dilute sulphuric acid, one
of which is in contact with hydrogen and the other with oxygen,
produce electricity. I will not detain you with the many and varied
forms of gas batteries which Dr. Carl Langer (to whom I intrusted this
investigation) has made and tried during the last four years, in order
to arrive at the construction of a gas battery which would give a
practical result, but I will call your attention to the battery before
me on the table, which is the last result of our extended labors in
this direction, and which we hope will mark a great step in advance in
the economic production of electricity.
The distinguishing feature of this battery is that the electrolyte is
not employed as a mobile liquid, but in a quasi-solid form, and it is,
therefore, named dry gas battery. It consists of a number of elements,
which are formed of a porous diaphragm of a non-conducting material
(in this instance plaster of Paris), which is impregnated with dilute
sulphuric acid. Both sides of this diaphragm are covered with very
fine platinum leaf perforated with very numerous small holes, and over
this a thin film of platinum black. Both these coatings are in contact
with frameworks of lead and antimony, insulated one from the other,
which conduct the electricity to the poles of the battery.
A number of these elements are placed side by side, with
non-conducting frames intervening, so as to form chambers through
which the hydrogen gas is passed along one side of the element and air
along the other.
This peculiar construction allows us to get a very large amount of
duty from a very small amount of platinum. One of the batteries before
you, consisting of seven elements, with a total effective surface of
half a square meter, contains 2½ grammes of platinum leaf and 7
grammes of platinum black, a total of 9½ grammes of platinum, and
produces a current of 2 amperes and 5 volts, or 10 watts, when the
outer resistance is properly adjusted. This current is equal to nearly
50 per cent. of the total energy obtainable from the hydrogen absorbed
in the battery.
In order to maintain a constant current, we have from time to time
(say once an hour) to interchange the gases, so as to counteract the
disturbing influence produced by the transport of the sulphuric acid
gas from one side of the diaphragm to the other. This operation can
easily be performed automatically by a commutator worked by a clock.
The water produced in the battery by the oxidation of the hydrogen is
carried off by the inert gas mixed with the hydrogen, and by the air,
of which we use a certain excess for this purpose. This is important,
as if the platinum black becomes wet, it loses its absorbing power for
the gases almost completely and stops the work of the battery. To
avoid this was in fact the great difficulty in designing a powerful
gas battery, and all previous constructions which employed the
electrolyte as a mobile liquid failed in consequence.
The results obtained by our battery are practically the same whether
pure oxygen and hydrogen or air and gases containing 25 per cent. of
hydrogen are used; but we found that the latter gases must be
practically free from carbonic oxide and hydrocarbons, which both
interfere very much with the absorbing power of the platinum black.
We had thus to find a cheap method of eliminating these two gases from
the producer gas, and converting them at the same time into their
equivalent of hydrogen. The processes hitherto known for this purpose,
viz., passing a mixture of such gases with steam over lime (which I
mentioned some time ago) or over oxide of iron or manganese, require
high temperatures, which render them expensive, and the latter do not
effect the reaction to a sufficient extent for our purpose.
We have succeeded in attaining our object at a temperature below that
at which the gases leave my producers, viz., at 350° C. to 450° C., by
passing the producer gases, still containing a considerable excess of
steam, over metallic nickel or cobalt. These metals have the
extraordinary property of decomposing almost completely, even at the
low temperature named, carbonic oxide into carbon and carbonic acid
and hydrocarbons into carbon and hydrogen.
In order to carry the process out with small quantities of nickel and
cobalt, we impregnate pumice stone or similar material with a salt of
nickel or cobalt, and reduce this by means of hydrogen or producer
gas. These pieces of pumice stone are filled into a retort or chamber
and the hot gases passed through them. As the reaction produces heat,
it is not necessary to heat the chambers or retorts from the outside
when the necessary temperature has once been attained. This process
has not yet been carried out on a large scale, but the laboratory
experiments have been so satisfactory that we have no doubt as to its
complete success. It will enable us to obtain gases containing 36 per
cent. to 40 per cent. of hydrogen and practically free from carbonic
oxide and hydrocarbons from producer gas at a very small cost, and
thus to make the latter suitable for the production of electricity by
our gas battery. We obtain, as stated before, 50 per cent. of the
energy in the hydrogen absorbed in the battery in the form of
electricity, while, if the same gas was consumed under steam boilers
to make steam, which, as I have shown before, could in this way be
raised cheaper than by burning fuel direct, and if this steam was
turned into motive power by first-rate steam engines, and the motive
power converted into electricity by a dynamo, the yield of electricity
would in the most favorable case not exceed 8 per cent. of the energy
in the gas. I hope that this kind of battery will one day enable us to
perform chemical operations by electricity on the largest scale, and
to press this potent power into the service of the chemical
industries.
The statement is frequently made that "Necessity is the mother of
invention." If this has been the case in the past, I think it is no
longer so in our days, since science has made us acquainted with the
correlation of forces, teaching us what amount of energy we utilize
and how much we waste in our various methods for attaining certain
objects, and indicating to us where and in what direction and how far
improvement is possible; and since the increase in our knowledge of
the properties of matter enables us to form an opinion beforehand as
to the substances we have available for obtaining a desired result.
We can now foresee, in most cases, in what direction progress in
technology will move, and in consequence the inventor is now
frequently in advance of the wants of his time. He may even create new
wants, to my mind a distinct step in the development of human culture.
It can then no longer be stated that "Necessity is the mother of
invention;" but I think it may truly be said that the steady,
methodical investigation of natural phenomena is the father of
industrial progress.
Sir Lowthian Bell, Bart., F.R.S., in moving a vote of thanks, said
that the meeting had had the privilege of listening to a description
of results obtained by a man of exceptional intelligence and learning,
supplemented by that devotion of mind which qualified him to pursue
his work with great energy and perseverance. The importance of the
president's address could not possibly be overrated. At various
periods different substances had been put forward as indications of
the civilization of the people. He remembered hearing from Dr. Ure
that he considered the consumption of sulphuric acid to be the most
accurate measure of the civilization of the people.
In course of time sulphuric acid gave way to soap, the consumption of
which was probably still regarded as the great exponent of
civilization by such of his fellow citizens as had thereby made their
name. From what he had heard that morning, however, he should be
inclined to make soap yield to ammonia, as sulphuric acid had in its
time succumbed to soap. For not only was ammonia of great importance
to us as a manufacturing nation, but it almost appeared to be a
condition of our existence. England had a large population
concentrated on an area so small as to make it almost a matter of
apprehension whether the surface could maintain the people upon it.
We were now importing almost as much food as we consumed, and were
thus more and more dependent on the foreigner. Under certain
conditions this would become a very serious matter, and thus any one
who showed how to produce plenty of ammonia at a cheap rate was a
benefactor to his country. Mr. Mond's process seemed to come nearer to
success than any which had preceded it, and it needed no words from
him to induce the meeting to accord a hearty vote of thanks to the
president for his admirable paper.
Mr. J. C. Stevenson, M.P., in seconding the motion, said that no paper
could be more interesting and valuable to the society than that
delivered by the president. It opened out a future for the advancement
of chemical industry which almost overcame one by the greatness of its
possibilities. Mr. Mond had performed an invaluable service by
investigating the various methods proposed for the manufacture of
ammonia, and clearing the decks of those processes supposed by their
inventors to be valuable, but proved by him to be delusive. It gave
him hearty pleasure therefore to second the vote of thanks proposed by
Sir Lowthian Bell.
The vote having been put and carried by acclamation, after a brief
reply from the president:
The secretary read the report of the scrutators, which showed that 158
ballot papers had been sent in, 154 voting for the proposed list
intact, and four substituting other names. The gentlemen nominated in
the list issued by the Council were therefore declared elected.
* * * * *
In his brief report for the year ending May 1, 1889, the director of
the Pasteur Institute, Paris, announces the treatment of 1,673
subjects, of whom 6 were seized with rabies during and 4 within a
fortnight after the process. But 3 only succumbed after the treatment
had been completely carried out, making 1 death in 554, or, including
all cases, 1 in 128.
* * * * *