260 CHEMICAL DISCOVERY AND INVENTION 



economically on a large scale. By the application of these modern 

 agents some metals, calcium for example, are now obtained on 

 a fairly large scale which a few years ago would have been found 

 only in the form of small specimens, the product of a trouble- 

 some laboratory operation. 



Space will not allow of the description of many of the pro- 

 cesses which are now applied to the production of metals for 

 industrial or practical purposes, but a few of the more important 

 may be briefly mentioned. 



SODIUM 



In September, 1807, Humphry Davy began those experiments 

 on the action of an electric current on caustic potash and caustic 

 soda which resulted in the isolation of the two strange metals, 

 potassium and sodium. On the 19th November he gave his 

 second Bakerian Lecture to the Royal Society in which he an- 

 nounced his discovery. Very shortly after this Gay Lussac and 

 Thenard succeeded in obtaining potassium by heating caustic 

 potash to redness in contact with iron turnings. These metals 

 were afterwards made by distilling at a red heat a mixture of 

 the carbonate with charcoal, and by this process these metals 

 were made for upwards of fifty years. A modification of these 

 methods was then introduced by Castner. about 1887, but this 

 has long been superseded by a process, also invented by Castner, 

 which is identical with that of the discoverer but adapted to 

 operations on a large scale. Electric current is now obtainable 

 at moderate expense, and sodium is made in large quantity by 

 the electrolysis of caustic soda fused and kept at a temperature 

 about 20 C. above its melting point. Sodium is at the present 

 time of much greater importance than potassium, as it is used 

 in considerable quantities in the manufacture of various chemical 

 compounds, among them indigo, several of the synthetic drugs, 

 and the cyanides. These metals are not familiar to the public 

 and cannot be handled safely by the inexperienced. Both 

 potassium and sodium are silvery white, almost as soft as cheese, 

 and melt easily. They cannot be exposed unprotected to air, 

 as they absorb oxygen and instantly become covered with a 

 coating of oxide. Thrown into water they decompose it explo- 

 sively with evolution of hydrogen gas and formation of a solution 

 of the caustic alkali. 



A few years ago sodium was consumed in rather large quantity 



