Note 11 — Chapter XIII · POTASSIUM, RUBIDIUM, CÆSIUM, AND LITHIUM. SPECTRUM ANALYSIS
George Kamensky translation
Caustic potash is not only formed by the action of lime on dilute solutions of potassium carbonate (as sodium hydroxide is prepared from sodium carbonate), but by igniting potassium nitrate with finely-divided copper (see Note 15), and also by mixing solutions of potassium sulphate (or even of alum, KAlS2O8) and barium hydroxide, BaH2O2. It is sometimes purified by dissolving it in alcohol (the impurities, for example, potassium sulphate and carbonate, are not dissolved) and then evaporating the alcohol.
The specific gravity of potassium hydroxide is 2·04, but that of its solutions (see Chapter XII., Note 18) at 15° S = 9,992 + 90·4p + 0·28p2 (here p2 is +, and for sodium hydroxide it is -). Strong solutions, when cooled, yield a crystallo-hydrate, KHO,4H2O, which dissolves in water, producing cold (like 2NaHO,7H2O), whilst potassium hydroxide in solution develops a considerable amount of heat.