[Footnote 1: Abstract of paper read before the Institution of
Civil Engineers, May 17, 1887.]
By Sir LOWTHIAN BELL, Bart., F.R.S.
The geology of the Middlesbrough salt region was first referred to,
and it was stated that the development of the salt industry in that
district was the result of accident. In 1859, Messrs. Bolckow &
Vaughan sank a deep well at Middlesbrough, in the hope of obtaining
water for steam and other purposes in connection with their iron works
in that town, although they had previously been informed of the
probably unsuitable character of the water if found. The bore hole was
put down to a depth of 1,200 feet, when a bed of salt rock was struck,
which proved to have a thickness of about 100 feet. At that time
one-eighth of the total salt production of Cheshire was being brought
to the Tyne for the chemical works on that river, hence the discovery
of salt instead of water was regarded by some as the reverse of a
disappointment. The mode of reaching the salt rock by an ordinary
shaft, however, failed, from the influx of water being too great, and
nothing more was heard of Middlesbrough salt until a dozen years
later, when Messrs. Bell Brothers, of Port Clarence, decided to try
the practicability of raising the salt by a method detailed in the
paper. A site was selected 1,314 yards distant from the well of
Messrs. Bolckow & Vaughan, and the Diamond Rock Boring Company was
intrusted with the work of putting down a hole in order to ascertain
whether the bed of salt extended under their land. This occupied
nearly two years, when the salt, 65 feet in thickness, was reached at
a depth of 1,127 feet. Other reasons induced the owners of the
Clarence iron works to continue the bore hole for 150 feet below the
bed of salt; a depth of 1,342 feet from the surface was then reached.
During the process of boring, considerable quantities of inflammable
gas were met with, which, on the application of flame, took fire at
the surface of the water in the bore hole. The origin of this gas, in
connection with the coal measures underlying the magnesian limestone,
will probably hereafter be investigated.
For raising the salt, recourse was had to the method of solution, the
principle being that a column of descending water should raise the
brine nearly as far as the differences of specific gravity between the
two liquids permitted--in the present case about 997 feet. In other
words, a column of fresh water of 1,200 feet brought the brine to
within 203 feet of the surface. For the practical application of this
system a hole of say 12 inches in diameter at the surface was
commenced, and a succession of wrought iron tubes put down as the
boring proceeded, the pipes being of gradually decreasing diameter,
until the bottom of the salt bed was reached. The portion of this
outer or retaining tube, where it passed through the bed of salt, was
pierced with two sets of apertures, the upper edge of the higher set
coinciding with the top of the seam, and the other set occupying the
lower portion of the tube. Within the tube so arranged, and secured at
its lower extremity by means of a cavity sunk in the limestone, a
second tube was lowered, having an outer diameter from two to four
inches less than the interior diameter of the first tube. The latter
served for pumping the brine. The pump used was of the ordinary bucket
and clack type, but, in addition, at the surface, there was a plunger,
which served to force the brine into an air vessel for the purposes of
distribution. The bucket and clack were placed some feet below the
point to which the brine was raised by the column of fresh water
descending in the annulus formed between the two tubes. In commencing
work, water was let down the annulus until the cavity formed in the
salt became sufficiently large to admit of a few hours' pumping of
concentrated brine. On the machinery being set in motion, the stronger
brine was first drawn, which, from its greater specific gravity,
occupied the lower portion of the cavity. As the brine was raised,
fresh water flowed down. The solvent power of the newly admitted water
was of course greater than that of water partially saturated, and
being also lighter it occupied the upper portion of the excavated
space. The combined effect was to give the cavity the form of an
inverted cone. The mode of extraction thus possessed the disadvantage
of removing the greatest quantity of the mineral where it was most
wanted for supporting the roof, and had given rise to occasional
accidents to the pipes underground. These were referred to in detail,
and the question was started as to possible legal complications
arising hereafter from new bore holes put down in close proximity to
the dividing line of different properties, the pumping of brine formed
under the conditions described presenting an altogether different
aspect from the pumping of water or natural brine.
The second part of the paper referred to the uses to which the brine
was applied, the chief one being the manufacture of common salt. For
this purpose the brine, as delivered from the wells, was run into a
large reservoir, where any earthy matter held in suspension was
allowed to settle. The clear solution was then run into pans sixty
feet long by twenty feet wide by two feet deep. Heat was applied at
one end by the combustion of small coal, beyond which longitudinal
walls, serving to support the pan and to distribute the heat,
conducted the products of combustion to the further extremity, where
they escaped into the chimney at a temperature of from 500° to 700°
Fahr. On the surface of the heated brine, kept at 196° Fahr., minute
cubical crystals speedily formed. On the upper surface of these, other
small cubes of salt arranged themselves in such a way that, in course
of time, a hollow inverted pyramid of crystallized salt was formed.
This ultimately sank to the bottom, where other small crystals united
with it, so that the shape became frequently completely cubical. Every
second day the salt was "fished" out and laid on drainers to permit
the adhering brine to run back into the pans. For the production of
table salt the boiling was carried on much more rapidly, and at a
higher temperature than for salt intended for soda manufacture. The
crystals were very minute, and adhered together by the solidification
of the brine, effected by exposure on heated flues. For fishery
purposes the crystals were preferred very coarse in size. These were
obtained by evaporating the brine more slowly and at a still lower
temperature than when salt for soda makers was required. At the
Clarence works experiments had been made in utilizing surplus gas from
the adjacent blast furnaces, instead of fuel, under the evaporating
pans, the furnaces supplying more gas than was needed for heating air
and raising steam for iron making. By means of this waste heat, from
200 to 300 tons of salt per week were now obtained.
The paper concluded with some particulars of the soda industry. The
well-known sulphuric acid process of Leblanc had stood its ground for
three-quarters of a century in spite of several disadvantages, and
various modes of utilizing the by-products having been from time to
time introduced, it had until recent years seemed too firmly
established to fear any rivals. About seven years ago, however, Mr.
Solvay, of Brussels, revived in a practical form the ammonia process,
patented forty years ago by Messrs. Hemming & Dyar, but using brine
instead of salt, and thus avoiding the cost of evaporation. This
process consisted of forcing into the brine currents of carbonic acid
and ammoniacal gases in such proportions as to generate bicarbonate of
ammonia, which, reacting on the salt of the brine, gave bicarbonate of
soda and chloride of ammonium. The bicarbonate was placed in a
reverberatory furnace, where the heat drove off the water and one
equivalent of carbonic acid, leaving the alkali as monocarbonate. Near
Middlesbrough, the only branch of industry established in connection
with its salt trade was the manufacture of soda by an ammonia process,
invented by Mr. Schloesing, of Paris. The works were carried on in
connection with the Clarence salt works. It was believed that the
total quantity of dry soda produced by the two ammonia processes,
Solvay's and Schloesing's, in this country was something under 100,000
tons per annum, but this make was considerably exceeded on the
Continent.
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