The author even regrets the removal from the paintbox of rich greens based on arsenic and flame-red vermilion formed from powdered mercuric sulphide.
Mercury II) or mercuric compounds predominate.
The metal was isolated (1808) by Sir Humphry Davy, who electrolyzed a mixture of the moist hydroxide or chloride with mercuric oxide, using a mercury cathode, and then evaporated the mercury from the resultant amalgam.
The silvery, rather soft, lightweight metal itself was first isolated (1808) by Sir Humphry Davy after distilling mercury from an amalgam formed by electrolyzing a mixture of lime and mercuric oxide.
The red lacquer (tihong), so well known and justly appreciated, was coloured with cinnabar (red mercuric sulfide).
The latter can be detected by the so-called Marsh test, in which arsine is thermally decomposed, forming a black arsenic mirror inside a narrow tube, or by the Gutzeit method, in which a test paper impregnated with mercuric chloride darkens when exposed to arsine because of the formation of free mercury.
Priestley's lasting reputation in science is founded upon the discovery he made on August 1, 1774, when he obtained a colourless gas by heating red mercuric oxide.
The recognition of its potential toxicity (because of disassociation into mercury and mercuric chloride), together with the development of superior and safer cathartics, led to a decline in its use in internal medicine.
Ferrous 1,10-phenanthroline, an oxidation-reduction indicator, changes from red to pale blue when the oxidation potential of the solution is increased from 1.04 to 1.08 volts; and diphenylcarbazone, an indicator for mercuric ion, changes from yellow to violet when the mercuric ion concentration is increased from 0.000001 to 0.00001 mole per litre.
It can also be converted to phosphine with boiling sodium hydroxide solution or with zinc and sulfuric acid; the phosphine is identified by means of test paper containing either silver nitrate or mercuric chloride, both of which are reduced to the free metal by phosphine, thereby darkening the paper.
