Potassium in 1809, Ludwig Wilhelm Gilbert proposed the name "Kalium" for Davy's "potassium". In 1814, the Swedish chemist Berzelius advocated the name "kalium" for potassium, with the chemical symbol "K". The English and French speaking countries adopted Davy and Gay-Lussac/Thénard's name Potassium, while the Germanic countries adopted Gilbert/Klaproth's name Kalium. The "Gold Book" of the International Union of Physical and Applied Chemistry has designated the official chemical symbol as K. Potassium is the second least dense metal after lithium. It is a soft solid with a low melting point, and can be easily cut with a knife. Freshly cut potassium is
Potassium alum a liquid known as "dousa" (), and used as an undercoat for paper sizing. Alum is an ingredient in some recipes for homemade modeling compounds intended for use by children. These are often called "play clay" or "play dough" for their similarity to "Play-Doh". Potassium alum was formerly used as a hardener for photographic emulsions (films and papers), usually as part of the fixer. It has now been replaced in that use by other chemicals. Potassium alum may be a weak irritant to the skin. Potassium alum Potassium alum, potash alum, or potassium aluminium sulfate is a chemical compound: the