The Leblanc process, too, has its advantages. In the next chapter we shall see that it is adaptable for the production of caustic as well as mild alkali. The chlorine which is recovered in the Leblanc process is a very valuable by-product. In the Solvay process, chlorine is lost, for hitherto no practicable method has been found for its recovery from calcium chloride. 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 _Solvay _Leblanc _Solvay soda._ soda._ soda._ 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.