Copper is obtained from its ores by three principal methods, which may be denominated - (r) the pyro-metallurgical or dry method, (2) the hydro-metallurgical or wet method, and (3) the electro-metallurgical method.
The subject of pyro-electricity, or the power possessed by some minerals of becoming electrified when merely heated, and of exhibiting positive and negative electricity, now began to attract notice.
He also made many experiments with the tourmaline when cut into thin slices, and reduced to the finest powder, in which state each particle preserved its pyro-electricity; and he showed that scolezite and mesolite, even when deprived of their water of crystallization and reduced to powder, retain their property of becoming electrical by heat.
For Sir David Brewster's work on pyro-electricity, see Trans.
The pyro-electric characters of quartz are closely connected with its peculiar type of symmetry and especially with the three uniterminal dyad axes.
Of the salts of these acids, those of the orthoand pyro-acids are the least stable, the orthovanadates being obtained on fusion of vanadium pentoxide with an alkaline carbonate.
Of these salts several series are known, namely the ortho-arsenites, which are derivatives of the acid H3AsO3, the metaarsenites, derivatives of HAsO2, and the pyro-arsenites, derivatives of H4As2O5.
C. P. Brard (1788-1838) discovered that pyro-electricity was a property of axinite; and it was afterwards detected in other minerals.
In the other pyro-electric crystals above mentioned, Hatly detected the same deviation from the rules of symmetry in their secondary crystals which occurs in tourmaline.
In repeating and extending the experiments of Haiiy much later, Sir David Brewster discovered that various artificial salts were pyro-electric, and he mentions the tartrates of potash and soda and tartaric acid as exhibiting this property in a very strong degree.