The paper I have to lay before you describes the last product of the
brain of one of your past presidents--Alexander Angus Croll--in
connection with our industry. It may not be so well known to some of
the younger as it is to many of the older members of the Institute
that the fertile brain of Mr. Croll has done much for the improvement
and the extension of the gas industry. I consider that he has been the
most successful pioneer both in the cheapening and the purification of
gas--two elements without which our industry would progress but slowly
if at all; and the success which has crowned his efforts, to our
advantage, has reflected itself favorably on himself, showing by his
financial success that he has also been a good man of business. All
these are conditions which enhance the value of this paper. In the
present instance, I claim no other credit than that of being the
mouthpiece of Mr. Croll, whose assistant I was for ten of the busiest
and most important years of his eventful life; and having (with my son
Bruce) taken part in the experiments, I have been asked to describe
the process to the Institute.
The manufacture of sulphate of ammonia, as hitherto conducted, has
consisted either in bringing together sulphuric acid and ammoniacal
liquor or in distilling the liquor by external heat, or by the
introduction of steam, and bringing it into contact with the acid in
the form of gases and vapor of water. In either case a large volume of
noxious gases is given off, the chief of which, being sulphureted
hydrogen, has to be fixed by another method, in order to comply with
acts of Parliament for the prevention of nuisances.
By the processes hitherto used, we sometimes get only 1¼ tons of salts
to every ton of acid used; while in the more perfect forms of
apparatus, we may get 1-1/3 tons of salts. By Mr. Croll's process,
however, we get an increased yield of salts on the acid used, as
follows: The experiments were made with sulphuric acid of the specific
gravity of 1838, or nearly concentrated oil of vitriol; and the
quantity used was 8 ounces in each experiment. The ammoniacal liquor
was of uniform strength throughout all the experiments, being kept in
a corked jar; and the solution of sulphate of ammonia was passed
through filter paper before being crystallized. Thus we obtained a
white salt. In each experiment the solution of sulphate was divided
into four equal parts by weight, and one part filtered and
crystallized to dryness over a spirit lamp; the weight in each
experiment being as nearly as possible the same, or 3¼ oz. of salt to
2 oz. of acid--being in the proportion of 26 oz. of sulphate to 1 lb.
of acid, or 32½ cwt. of salts to 20 cwt. of acid.
The results surprised me; and being uniform over a number of
experiments, pleased me. Still, I preserved the character of a critic
and said: "I should like to treat 8 oz. of acid in the ordinary
way--saturating it with ammoniacal liquor, and then crystallizing it."
"Oh!" Mr. Croll said, "we know what that will produce." I replied:
"Yes; but I would like to do it with the precise acid and liquor we
have been using, so that we may have the experiment on all fours with
yours, barring your process." These experiments were made at his
country residence. I was staying there for the night. So next morning
I got down before him, went at my experiment, saturated 8 oz. of acid
(and a nice smell I made) out in the grounds, treated it afterward by
division into four parts, filtered and crystallized it, all as before,
with the result that I obtained 2¾ oz., as against his 3½ oz.--or in
the proportion of 27½ cwt. of salt to the ton of acid, as against his
32½ cwt.
I now thought of business. "What is the royalty to be?" I said, as we
sat at breakfast. This we settled as we Scotch say "in a crack," or as
an Englishman would say "in a jiffy." Mr. Croll decided to have the
apparatus put up on a manufacturing scale here in Glasgow; and I
determined to erect similar apparatus at one of my gas works.
I dare say that it will be uppermost in your minds, Whence comes the
increased yield of salts? Well, I will state one fact, and leave you
to ruminate on it, namely, by Mr. Croll's process we did not seem to
produce any sulphureted hydrogen. The experiments were conducted in a
room with ordinary doors and windows, but without a chimney; and we
were not troubled with any offensive smell--a state of things that
could not possibly have existed had we been experimenting with any
other apparatus hitherto employed in the manufacture of sulphate of
ammonia. The apparatus, which will presently be described, only
substitutes, for the present mode of distillation, a new one, which
forms the subject of Mr. Croll's patent. All other parts of present
apparatus can remain as they now exist.
Mr Croll has also introduced another mode of producing sulphate of
ammonia, which dispenses with all the apparatus hitherto in use after
the distillatory portion, and produces the salt in a state fit for the
farmer, ready to be put on the land. This process consists in sending
the products of distillation through a vessel filled with wood sawdust
saturated with sulphuric acid. The ammonia becomes fixed and
crystallized in the sawdust, and is ready for use. There are many
works, both at home and abroad, to which the conveyance of sulphuric
acid is both difficult and expensive, on account of the cost of
carriage and the breakage which occurs; and thus in many such works
the ammonia is not utilized. This saturated sawdust process will, I
think, remove the difficulty; for I find that dry sawdust absorbs
double its own weight of sulphuric acid, and this could be conveyed in
the most ordinary casks in a damp state, and save all waste and
annoyance from breakage of bottles. In this state it could be used by
the farmer, or the sulphate of ammonia could be washed out,
crystallized, and exported in the state of salt.
In the remainder of this paper I have been assisted by my son Bruce,
who also assisted in the experiments that I have described. He has
since been engaged on the trials on a manufacturing scale; and I ask
you to permit him to read the concluding portion of the paper, in
which he will describe the process, and what he has done.
The process referred to in the foregoing portion of the paper is a
method employed for heating the liquor, whereby a chemical action is
brought into play, with the results already mentioned. This method
consists in passing the products of combustion of a furnace from a
clear fire in a hot state through a still containing the ammoniacal
liquor. The hot gases from the furnace impart their heat to the
liquor, causing the volatilization of the condensed gases, and at the
same time act chemically upon the liquor and evolved gases, so that
ammonia and sulphuric acid are resulting products, in the compound
state of sulphate of ammonia. The formation of the ammonia produced in
the process is probably due to the decomposition of nitrogenous bodies
contained in solution in the liquor--the sulphocyanide, for instance;
the nitrogen being given off in the form of ammonia. Of the sulphuric
acid produced, we look upon the sulphureted hydrogen as the source,
also any sulphites existing in the liquor, which in their volatile
state take up the atom of oxygen necessary for their conversion into
sulphate.
[Illustration]
The apparatus used in working the process consists of a tower still,
containing a number of superposed trays about 3 or 4 inches apart,
with a lipped hole through the bottom of each at the side. The trays
are so placed in the tower that the holes are at alternate sides. The
liquor passes into the top of the still, and zigzags down through the
series of trays, as in an ordinary Coffey still. The bottom tray
differs from the rest; being much deeper, and having holes through it
connecting it with the furnace, which is set immediately below it. The
products of combustion of the fuel are caused to pass from the furnace
up through the holes in the trays in the still, and, together with the
gases evolved from the liquor, are directed into the saturator, where
the sulphate of ammonia is obtained either in solution or in the
crystalline state.
Where the process is at present being worked, an exhauster is used to
draw the furnace gases through the still; but it might be advantageous
to use a blower.
A small plant has been put in action at the gas works in Kilkenny and
another on a larger scale, and differing somewhat in detail, here in
Glasgow at the Alum and Ammonia Company's works, where the liquor from
the Tradeston Gas Works is converted. The trials on a working scale
have only been made at both places within the past ten days; and, so
far, nothing has appeared against the principle, though in certain of
the details of construction some alterations are being made to improve
it. The extra yield of salt from a given quantity of acid obtained in
the experiments has been proved in practice, as also the absorption of
the sulphureted hydrogen.
The other day, while ammoniacal liquor of about 9 oz. strength was
being run at the rate of 70 gallons per hour through the still, 5 feet
in diameter and 10 feet high, containing seventeen trays, no smell of
sulphureted hydrogen was perceptible from the waste gases from the
saturator, although on applying lead paper a slight trace of this
impurity was noticeable, and it may be stated that the gases were
being delivered at the ground level, where there was no difficulty in
testing them.
In the Glasgow apparatus we have found it advisable to enlarge the
pipe leading the gases into the saturator, as the volume of these is
much greater than would be the case in the ordinary method of working.
Further experience will probably indicate the desirability of
increasing the height of the still, which, being only 10 feet, is not
more than half the height that Coffey stills are ordinarily made.
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