IMPROVEMENTS IN THE MANUFACTURE OR TREATMENT OF POTASH IN ORDER TO OBTAIN USEFUL PRODUCTS THEREFROM
Year: 1879

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PROVISIONAL SPECIFICATION left by Gilbert Jean-Baptiste Lacombe at the
Office of the Commissioners of Patents on the 13th September 1879.
GILBERT JEAN-BAPTISTE LACOMBE, of Lille, in the Republic of France, Engineer
and Analytical Chemist. "IMPROVEMENTS IN THE MANUFACTURE OR TREATMENT
OF POTASH IN ORDER TO OBTAIN USEFUL PRODUCTS THEREFROM."
When heating a mixture composed of the proper proportions of sulphate of
potash, chalk, and coal, according to what is known as the Leblanc process, the
following substances are formed, viz., caustic potash, corbonate of potash, and a
compound containing calcium and sulphur in an insoluble state.
The alkalis are easily isolated by a washing followed by concentration and
calcination.
I have recently discovered that if some substances containing iron and nitrogen
are introduced into the reverberatory furnace in which the melting of the above
materials takes place, they combine, and some cyanide of potassium which during
the washing in tepid water is changed into prussiate of potash. The price of this
latter substance being high, it is advantageous to produce a large quantity of it to
be extracted for commercial purposes. With this object I proceed in the following
manner-
I take 275 parts of sulphate of potash, 200 parts of chalk, and 100 parts of
pulverised pit-coal; these I mix and introduce together into a furnace with 6 parts
of oxide of iron produced by the roasting of pyrites or other suitable means, and 10
parts of horn or wool waste, old leather or other suitable substance containing
azote. It is not even necessary to add the latter materials, if the pit-coal employed
contains from one to one and a half per cent. of azote as is the case with certain
descriptions of coal.
The materials are not long before melting and undergoing the above mentioned
reactions. When these are over I permit the liquid to flow into iron tanks of
prismatic shape, and to cool. I then break the blocks into pieces of the size of
one's fist, or thereabouts, and this I treat by stirring them up several times in water
at about 104° Fahrenheit (40° centigrade).
On the following day I decant the clear liquid and submit it to a current of
carbonic acid in order to transform the caustic potash into a carbonate, and I
evaporate the same; a black residuum is soon produced which should be carefully
gathered as it contains in an anhydrous state the prussiate formed under the
conditions above stated. The said residuum is treated with water which dissolves

page_text: the prussiate of potash as well as small quantities of sulphate of potash and chloride
of potassium, and at the same time some insoluble sulphide of iron is deposited, I
again dissolve, and on a further concentration there will be found a deposit
containing up to 40 per cent. of prussiate of potash, or cyanoferride of potassium.
It suffices to refine the latter or to treat it by chemical processes in order to extract
the product in the form required for the market.
Firstly. Refining the crude prussiate of potash, I pour on the raw prussiate the
quantity of cold water sufficient to dissolve the pure salt it contains, and the
proportion of which has been previously determined by a chemical analysis. I heat
and saturate the carbonate with some sulphuric acid mixed with water. After a
few hours I decant, evaporate, and cause the substance to crystalise, observing the
usual precautions.
Secondly. Chemical process. I treat the deposit containing say 40 per cent. of
prussiate with water so that the salts may be completely dissolved, saturate as has
been above explained, with sulphuric acid, and I precipitate by means of some
sulphate of protoxide of iron; I thus obtain a compound of a bluish white color
that may be sold, as it is for manufacturing prussian blue, or regenerating pure
prussiate.
The foregoing reactions are also produced if in the concentration of the water
employed in washing wool or the water residuum left from the distillation of beet
root, molasses, some ferruginous substances are added, it is only necessary to heat
at the end until the substances are melted and to run the liquid into sheet iron
tanks in order to prevent the burning action of air during the cooling..
The rest of the operation is carried on as above,