The position with regard to the future supply of alkali is very interesting. The competition between the Leblanc and the Solvay processes for supremacy in the market is very keen. At the same time, both processes are in some degree of danger of being supplanted by the newer electrical methods, which will be mentioned in the last chapter.
The following table shows very clearly the rapid progress made by the Solvay process in ten years. The quantities are given in tonnes (1 tonne = 0·9842 ton).
| 1884. | 1894. | |||
|---|---|---|---|---|
| Leblanc soda. | Solvay soda. | Leblanc soda. | Solvay soda. | |
| Great Britain | 380,000 | 52,000 | 340,000 | 181,000 |
| Germany | 56,500 | 44,000 | 40,000 | 210,000 |
| France | 70,000 | 57,000 | 20,000 | 150,000 |
| United States | — | 1,100 | 20,000 | 80,000 |
| Austria-Hungary | 39,000 | 1,000 | 20,000 | 75,000 |
| Russia | — | — | 10,000 | 50,000 |
| Belgium | — | 8,000 | 6,000 | 30,000 |
| 545,500 | 163,100 | 456,000 | 776,000 | |
Mild Potash. Potassium carbonate (mild potash) was formerly obtained from wood ashes. The clear aqueous extract was evaporated to dryness in iron pots, and the substance was on this account called potashes; later, potash. A whiter product was obtained by calcining the residue, and this was distinguished as pearl-ash. Chemically pure potassium carbonate was formerly obtained by igniting cream of tartar (potassium hydrogen tartrate) with an equal weight of nitre. It is for this reason that potassium carbonate is sometimes called “salt of tartar.”
About the middle of last century, natural deposits of potassium chloride were discovered in Germany. The beds of rock salt near Stassfurt are covered over with a layer of other salts, and for many years these were removed and cast aside as “waste salts” (abraumsalze). When at a later date they were examined more carefully, they were found to contain valuable potassium compounds, notably the chloride. After that discovery, mild potash was made by the Leblanc process., and Germany controlled the world’s markets for all potassium compounds.
At the outbreak of war, the German supplies of potassium compounds ceased as far as the allied nations were concerned, and an older method of making potassium chloride from orthoclase or potash-felspar was revived. This involves the heating of the powdered mineral to a high temperature after mixing it with calcium chloride, lime, and a little fluorspar. The potassium chloride is then extracted from the fused mass with water. This method has been worked with great success in America, and it is claimed that potassium chloride can be made in that country at a cost which is lower than that formerly paid for the imported article.
Mild potash and soda are so very similar in chemical properties that in most cases it is immaterial which compound is used. In all cases in which there is this choice, soda is employed, both because it is cheaper and because it is more economical, for 106 parts of soda ash are equivalent to 138 parts of potash. There are, however, some occasions when soda cannot be substituted, notably for the manufacture of hard glass and soft soap, and for the preparation of caustic potash, potassium dichromate, and other potassium salts.
Potassium Bicarbonate. This resembles the corresponding sodium salt in nearly every respect. It is, however, much more readily soluble in water, so much so, that it is not possible to obtain this substance by the Solvay method. It is made from potassium carbonate by saturating a strong aqueous solution of that substance with carbon dioxide.
CHAPTER IX
CAUSTIC ALKALIS
The Alkali Metals. The discovery of current electricity in 1790 furnished the chemist with a very powerful agency for bringing about the decomposition of compounds. Hydrogen and oxygen were soon obtained by passing an electric current through acidulated water; and in 1807, Sir Humphry Davy, who is perhaps better remembered for his invention of the miners’ lamp, isolated the metals sodium and potassium by subjecting caustic soda and caustic potash respectively to the action of the current.