Improvements in the Production of Blocks of Salt.
Year: 1895

page_text: Date of Application, 8th Apr.,- 1895-Accepted, 1st June, 1895
Improvements in the Production of Blocks of Salt.
I, ALFRED LE CHATELIER of 20, Rue Saint Georges, Paris, in the Republic
of France, Engineer, do hereby declare the nature of my invention and in what
manner the same is to be performed to be particularly described and ascertained
in and by the following statement :-
It has for some time been proposed to agglomerate salt by compression but the
process has not hitherto been of practical use owing to very heavy pressure having
been requisite to render a block of salt sufficiently hard.
This invention has for its object to obtain the agglomeration of salt in blocks
by means of relatively small pressures by making use of a newly discovered
phenomenon which is due to the effect of compression on the solubility of the salt
when in contact with a liquid which is not compressed. If two grains of salt be
placed in a saturated solution and forcibly pressed against each other they dissolve
at the points where they meet and are compressed and yield a super saturated
solution which will then allow the salt dissolved in excess to crystallize at the part
of compression and over the grains or fragments of salt so as to gradually fill up
the spaces between them and unite them together.
If instead of two grains of. salt a large quantity be taken under the conditions
aforesaid and enclosed in a mould and then compressed with a piston which allows
the liquid and enclosed air to escape so that the said liquid be not compressed the
same phenomenon is observed and all the grains will gradually unite together so as
to form a compact block.
After a time the empty spaces will have ceased to exist and a block of salt is
obtained of the same density as a single crystal of salt.
By this means the required result can be obtained with the employment of but
small pressures not sufficient to crush the grains or crystals, whereas agglomeration
by compression alone, as hitherto attempted necessitates pressures which are so
heavy as to crush all the grains or crystals and mould their fragments against each
other.
The agglomeration by progressive crystallization as aforesaid depends on the
quantity of salt which is temporarily dissolved and it is consequently more complete
(1) as the time is longer (2) as the number of points of contact in the mass to be
agglomerated are greater that is to say as the size of the crystals or grains is
smaller and (3) as the pressure is greater.
Blocks of salt obtained by this process present a great solidity or density some
time before the disappearance of the spaces.
In order to obtain blocks which can be moulded and then transported without
any special precaution a density should be reached between 1.5 and 1.8 which will
vary according to the uniformity and the size of the grains or crystals.
In order to obtain a given compactness or solidity the length of time for the
operation the pressure employed and the size of the salt crystals may be varied and
differently combined: for example good results are obtained with a salt which bas
been ground very fine and employing a pressure of 100 kilogrammes for the
square centimetre the time of compression being about 5 minutes. With salt with
crystals of the ordinary size and supposing the same duration of time is to be taken
for compression, the pressure must be raised to 30 kilogrammes, or if it is desired
to keep the pressure at 100 kilogrammes then the time of compression must extend
to half an hour or thereabouts.

page_text: I do not limit myself to these details however as even by reducing the pressures
by one half a fairly satisfactory agglomeration can be obtained but great care will
then be necessary in the removal of the blocks of salt from the moulds and in their
transport. Whereas by the employment of the pressures aforesaid an agglomeration
of the salt is obtained sufficiently strong for all practical purposes.
The amount of water employed does not affect the hardening of the block to be
obtained. It suffices even if the surface of the grains be slightly moistened the
water then uniting by capillary attraction around the points of contact of the
grains of salt, there is always sufficient at the points where the crystallization should
take place. It is well however in order to avoid deterioration of the mould and to
allow the use of iron without tainting the salt that the water be in sufficiently
small quantity to enable it to remain in the spaces of the salt and not to ooze or
leak against the sides of the mould for example the ordinary fine salt a proportion
of 5 per rent, and for extra fine salt of 10 per cent. of water gives good results.
Fine natural salt may be employed or the dry or wet salt may be ground in mills,
cylinders, grinders, and other suitable grinding apparatus.
The compression may be effected by any suitable apparatus such as a hydraulic
press, a brick or like press or an Everard's pressing machine, moderating the
movement so as to give the required length of time of pressing.
The blocks of salt may be dried by the action of heat or a current of air.
Having now particularly described and ascertained the nature of this inven-
tion, and in what manner the same is to be performed I declare that what 1.
claim is :-
The agglomeration of salt into blocks sufficiently strong for transport in the
manner and under the conditions hereinbefore set forth.
Dated this 8th day of April 1895.
JOHNSONS & WILLCOX,
47, Lincoln's Inn Fields, London, W.C., Agents.