March 31, 1916.

THE COLLIERY GUARDIAN.

603

Mr. Carr asked. Prof. Cobb’s opinion on the use of
fire cement for washing the' oven walls, the cement
usually containing about 20 per cent. ,of sodium silicate.

Prof. Cobb said that this was a point he covered in his
paper. There was a very great difficulty in any case of
that sort with the coefficient of expansion. To secure
adhesion of the cement was not very difficult, as, when
the cement was put on, the walls were new, but altera-
tions took place afterwards, and the action of the salt
on the material of the cement had to be considered—
chemically, because it might be chemically detrimental,
and physically, because it might so far alter the
coefficient of expansion of the iapplied cement that this
would no longer adhere to the wall. It seemed to him
it was entirely a question of practical experiment. A
wash sometimes \ gave a complete glaze which was
adherent, and sometimes it gave a complete glaze which
was not adherent and might not remain adherent very
long. What he had attempted to indicate was that so
many considerations came into play that it was a very
difficult thing indeed to get a cement that could be
expected to answer that purpose. He did not say that
it was impossible, but it seemed to him entirely a
question of trial; giving an ex cathedra verdict on <a
subject of that sort would be somewhat futile.

Mr. Cooper said it seemed to him that they had to
look at the effect of salty coal on refractory materials
from two points of view—the purely scientific point of
view, for getting-at the cause; and the practical point
of view, for dealing with it. He had rather expected
that Prof. Cobb would have dealt more particularly
with the latter—from the purely practical point of view
of overcoming the difficulty. There had been a great
deal of correspondence in the technical papers as to
whether a silica brick or an alumina brick was the better
adapted for dealing with coal of a salty nature. Per-
sonally, he was absolutely convinced that the silica
brick had it, although he knew there were members
present who were equally convinced that the silica
brick was absolutely rotten for the purpose. He had to
deal with one of the most notorious salty coals in the
country, and used silica bricks, and he believed he
would get some very useful experience from them. He
was also in the unhappy situation Mr. Riley had
spoken of with regard to water. He had samples taken
during the past week, and found 28 grammes per litre
of soluble salt—almost running out of the bunkers in
crystals—so that he had a very good opportunity of
seeing how the silica would stand it. There was another
point which had puzzled him very considerably, but
Prof. Cobb had cleared it up—that was with regard to
the temperature factor in the action of the salt on fire-
clay material. The temperature to which the brick was
exposed played a very important part in the action of
the salt on the brick. Some experiments were con-
ducted a year or two since in Birmingham showing con-
clusively that bricks with a high silica content with-
stood the action much better than did lower silica
bricks; but there was another factor which perhaps was
. not brought into full account, and that was the ques-
tion of temperature. If he had understood Prof. Cobb
rightly, when one got above a certain temperature, the
action of the salt would be very considerably minimised.
Silica bricks were almost invariably associated with
high temperature carbonisation. Therefore, it might
be a mere coincidence that silica bricks stood better.
In his own experience they did, but it might be due to
the fact of silica bricks being worked at a high tempera-
ture. In Birmingham they usually had a temperature
of about 1,200 degs. to obtain gas of the highest pos-
sible quality. The physical structure of the bricks was
also an important point, a brick of close texture being-
able to resist the action of the salt better. He had
conducted a number of experiments, which also sug-
gested the possibility that iron had something to do
with the action, whilst it had also been suggested that
neither sodium or iron was responsible, but chlorine.
He would like Prof. Cobb’s opinion if the action was
equally extensive with other sodium compounds.
Suppose sodium carbon, were substituted, would the
same results be obtained as noth sodium chloride ?

Prof. Cobb feared he must have been misunderstood
if he gave an impression that the higher temperature
minimised in any sense the action of the sodium
chloride. The point was that, supposing one had a
fireclay surface of high temperature, and the sodium
chloride attacked it at that'temperature, there would
be a glaze formed which was very nearly impervious,
with the result that there would be very little disinte-
grating- effect. Even if a coke oven were worked at
a high temperature, it had to pass through the lower
temperature first, and in the region of the lower tem-
perature the action of the sodium chloride could occur
as he had described, viz., the penetration of the com-
pounds of sodium and alumina-silica, which then fused
as the temperature of the oven rose. Physical and
chemical change took place at the lower temperature,
but the particular physical change which resulted from
fusion did not take place until the higher temperature
was reached. If one had a high = temperature on the
face of the coke oven, and simply introduced the salt,
he would get a salt glazing, on the interior of the oven,
which would not be of anything like the. same nature
as the. penetration of the brickwork at a lower
temperature, followed by its fusion afterwards. As to
whether the use of a glazed, brick, would be. of any
advantage in resisting salt action, if one were dealing
with glazed brick, one would .be up against the diffi-
culty, of the coefficient of expansion. Any ordinary
glaze applied to the face of the bricks placed in a coke
oven would be cracked off before it had been , in use
very long.

Mr. Finn thought Prof. Cobb’s explanation as to the
difference between the actual attack of salt on fireclay
in a heated condition could be brought home by a com-
parison of the condition of the arches and that of the
walls. They would know that though the arches were
covered with a genuine salt glaze due to the volatilisa-
tion of the coal and the formation of real salt glaze on
the arch, it was a quite different phenomenon to the
disintegration of the coke oven wall itself. He quite-
understood that there was a little misconception on the
part of some members as to Prof. Cobb’s meaning. What
was meant, he took it, Was that at the lower tempera-
ture the salt formed a silicate or sodium-alumina
silicate on the surface of the brick, not of the same
nature as fusion would glaze it. . As the silicate
penetrated the brick it came nearer to the actual source
of heat, and therefore attained a higher temperature,
finally reaching a point at which incipient fusion com-
menced, and the brick began to disintegrate, as could
be seen in any brick that had been in use for some time.

Prof. Cobb, in answer to a question raised by Mr.
Cooper, said there was a great difference in the amount
of the volatilisation which took place with various com-
pounds of soda, but sodium chloride was probably the
worst of any of the ordinary compounds. He did not
think that the ■ same amount of sodium carbon present
in the coal would be quite so destructive.

Mr. Myers asked if the formation of ammonium

• chloride which took place after the splitting up or
volatilisation of the sodium chloride, had any bearing
on the disintegration of the refractory material.

Prof. Cobb said he could not answel that question
satisfactorily. The presence of ammonium chloride he
had always taken as indicative of the presence of sodium
chloride in the coal, so that the formation of the sodium
chloride is accompanied by the presence of ammonium
chloride, but he should certainly trace no connection
between the ammonium chloride itself and disintegra-
tion.

Mr. Myers said he only asked the question because if
ammonium chloride was heated in contact with
refractory materials, the refractory materials underwent
a tremendous amount of disintegration.

Prof. Cobb replied that under certain conditions one
might get dissociation of the ammonium chloride, but
it. was not a point to which he had paid any special
^consideration.

Mr. Green wondered whether the production of
hydrochloric acid inside the oven with coals high in
salt had any effect on the refractory material. Would
any dissociation not have its effect on the metallic
oxides in the brick, and consequently produce disinte-
gration?

Prof. Cobb thought this quite conceivable. It was
substantially the same question as was raised by Mr.
Myers, who, he believed, was assuming that the action
was not one of ammonium chloride itself, but hydro-
chloric acid.

Mr. Fleming said that Prof. Cobb’s close study of the
subject seemed to have entirely cleared up the causes
of the corrosion of bricks by salty coals. With regard
to the T s. d. of the matter, it appeared to him that
the limit they could fix for salt, in coal, without con-
sidering it necessary to adopt special qualities of fire-
bricks, should be 0-3 per cent. With regard to the
remedv Prof. Cobb proposed, the ideal seemed to be to
get a firebrick with a coarsely crystalline silica base, and
vet with a fine and coherent surface: and between the
large grain silica base and the fine grain surface, there
should be no wide difference in the expansion
coefficients. He questioned whether it would not be
advisable in the case of coal containing a high percentage
of salt, say, over 0-3, to glaze the surface of the coarse-,
grain silica brick by means of a very high temperature
flame—oxyhydrogen or acetylene—-to make a fine coat-
ing on the surface of the brick and fuse the silica. It
appeared to him that in that way they might overcome
the difficulty due to any differences of expansion between
the surface of the brick and the inner portions of the
same. Of course, it would cost more to treat bricks in
that wav. But if the coal were very salty, it might
be possible, by this means, to get longer life with the
ovens, and thus make the first cost a negligible factor.

Prof. Cobb thought that idea quite satisfactory, except
from the point of view of the brick maker. The process of
bringing the brick to the glazing point without breaking
the brick involved practical difficulties of an exceedingly
grave character. It would mean that, for the time
being, there would be such great local differences of
temperature that it would be an extraordinary material
that would stand the strain.

Mr. Green said he would like to have Prof. Cobb’s idea
on a suggestion drawn from American steel practice.
There had been references in the technical. Press to a
steel-faced brick which was in use in open-hearth steel
works in America. Before adopting it they had had
excessive trouble with the lining of their furnaces, but
now they had in use furnaces, consisting of these bricks,
which had lasted two years. Could not these be (adapted
to coke oven purposes? Another point on which he was
not clear was the varying effects of salty coals; he had
known of some with a high percentage of salt having less

effect on the walls of the ovens than coal with a lower
percentage. In one case where coal with 0’1 -per cent,
of salt was in use, they had had to reline the ovens in
two years.

Prof. Cobb said he would like to have the reference
to the experiment made with steel-faced, bricks, which
was quite new to him. As to the curious anomaly
mentioned in regard to the effects of.high.and low per-
centage salty coals, such experiences formed' one of the
difficulties in dealing with the subject.

Mr. Green thought the (association might render the
industry a great service by collecting data as to the
chemical analysis of bricks, observations as to their
appearance, method of working, etc.

The President said it only remained for him to
endeavour to express the members’ great appreciation of
Prof. Cobb’s most interesting and valuable paper. Prof.
Cobb had evidently been at considerable pains to develop
the subject for them, and the least that they could do
would be to tender him their very warm thanks.

Mr. B. W. Haig, in seconding, said that Prof. Cobb
seemed the ideal combination of practical man end
university professor, and if there were more of that
combination there would be less complaint concerning
the impracticability of the university professor and the
ignorance of the ordinary man in regard to the scientific
aspect of his industry. Prof. Cobb seemed equally at
home with both sides of the question, and he had listened
to him with very great profit, and what he had told
them would prove of the greatest utility in their work.

Prof. Cobb, in responding, said it had been not so
much his aim to put before the association a complete
remedy for the troubles which occurred in the coke
oven and other industries on account of the salt content
of coal, as to give what was in his mind an explanation
to how that trouble really came about, because it was
essential to understand the nature of a disease before
one could work systematically for a complete cure.

WILTON’S SULPHATE OF AMMONIA
PLANT.

In this plant (fig. 1), which is placed on the market
by the Chemical Engineering Company and Wilton’s
Patent Furnace Company, of Hendon, the' gas liquor
first passes through multitubular heaters, and is raised
to boiling point by the waste heat from the saturator.
It then enters the top of the liquor still, and slowly
flows by a series of weirs in a downward, direction
through the chambers to the automatic exit. Steam is
admitted at the bottom of the still, and bubbles through
the liquor in each chamber, travelling in a reverse direc-
tion to the liquor, and carrying with it the. ammonia
and combined gases, H2S and CO2, which pass away
from the top to the saturator. To complete the removal
of the fixed salts, lime is added in a continuous stream
in the middle chamber of the still, in conjunction with
the auxiliary lime chamber, which .acts as a reservoir,
and retains the sludge. The lime is slacked with spent
liquor from the still, and forced at boiling temperature
at the required rate by automatic pumps or injectors.

In the saturator the ammonia is distributed by per-
forated pipes and bubbles in the acid bath, which is
continuously fed with acid in proportion to the ammonia.
The chemical reaction produces a boiling heat, and
crystals of sulphate of ammonia are deposited at the
bottom, whence they are either pumped by means of a
steam discharger, or Removed by a copper ladle to the
draining table.

When the production of sulphate amounts to or
exceeds two tons per day, a centrifugal drying machine
is used, the- sulphate gravitating from the drainer to
the machine, where the mother liquor is separated, and
flows back to the saturator, the dry sulphate of ammonia
being dropped through the centre valve on to an
elevator conveyor. In smaller works where centrifugal
machines are not employed, the sulphate, after being
allowed to drain, is shovelled into the lead-lined stores,
and the mother liquor returned to the saturator.

The waste gases from the saturator, after cooling, are
purified with oxide of iron, and the H2S is recovered
as sulphur.

Where the condensed or devil liquor is of,any appre-
ciable quantity, it is allowed to gravitate to sealed
receivers, and is pumped with the gas liquor through the
liquor still, and thus rendered inodorous.

The liquor still has been designed to overcome the
necessity for completely dismantling the whole still in
order to remove the lime deposits. All working parts
are easily accessible for cleaning purposes, it only being
necessary toA’emove the doors covering the bubbling
hood openings to take out the hoods and obtain access
to the inside of the sections. The overflows are also
provided with doors for the same purpose. The
bubbling hoods are of steel, to make them as light as
possible to handle, and practically unbreakable.

A cast iron pot fitted to the still acts as safety valve,
and also serves as an indicator for the working level.
In place of the ordinary seal pot, an automatic spent
liquor valve is provided, which is operated on the float
principle, and releases the waste liquor without any loss
of steam, and further prevents the flooding or blowing
empty of the still. The auxiliary lime chamber into
which the milk of lime' is fed, is arranged in such a
manner that after the liquor has passed through the
upper part of the still it enters the lime chamber, where
the fixed ammonia is released, the liquor subsequently
returning to the still to flow through the lower portion