Cinnabar. According to Pliny, this is an Indian name given to a mixture of the blood of the dragon and elephant, and to other substances which produce a similar color. It was afterward applied to the common ore of mercury, the sulphuret, on account of its blood-red color. The ancient Romans were probably acquainted with this ore of mercury, for the mines of Almaden, near Cordova in Spain, which still produce it, are known to have been worked nearly 3,000 years ago; and both Pliny and Yitruvius refer to the ore of mercury in amalgamating gold. The name is also given to an artificial preparation, identical in composition with the ore. Cinnabar consists of 1 atom of mercury, the chemical equivalent of which is 200, and 1 atom of sulphur, 32; or per cent., 86.2 of mercury and 13.8 of sulphur. It forms beds and veins in the upper secondary and older stratified rocks, and is also met with in granite and porphyry. The strata near the veins often contain the ore disseminated through them. It crystallizes in rhombohedral forms, possesses an adamantine lustre, and a brilliant red color, passing from cochineal to ruby red.
Its hardness is from 2 to 2'5; its specific gravity is 8.998. It sublimes at a red heat, and without decomposition if protected from the air; and when mixed with iron or lime in retorts, the sulphur is retained and the mercury volatilized. When finely ground, it becomes of a very lively red, and in this condition is known as vermilion. The most important mines of native cinnabar are those of Almaden, already referred to, of New Almaden in California, of Idria in Austria, and of Huanca Velica in Peru.
In Hungary, Bohemia, Bavaria, China, Japan, and Brazil, the ore is also worked. - Artificial cinnabar, from which the greater part of the vermilion used in the arts is prepared, is made by subliming an intimate mixture of 5 or 6 parts of mercury and 1 of sulphur. The mercury is introduced and stirred into melted sulphur. When the mixture becomes thick, combination suddenly takes place, attended with violent crackling and movement of the mass, and evolution of light and heat. The blackish red product is pounded to powder and mixed with a little sulphur. A glass flask half filled with it, and loosely closed with a charcoal stopper, is partially buried in a sand bath, and kept at a red heat for some hours. The excess of sulphur passes out of the flask, and the cinnabar sublimes and condenses in its upper part, leaving the fixed impurities in the bottom. It is then broken up and ground with pure water as finely as possible, and finally dried. The finer the powder is made, the more beautiful is the color. In Idria the process is somewhat different, mercury being thoroughly intermixed with powdered sulphur by placing them together in casks, which are made to revolve. In a few hours a brown powder is produced, which is heated and sublimed in cast-iron vessels.
The Chinese have still another process; and their cinnabar is said to incline to a carmine color, while all the European has a yellow tinge. These processes are all in the dry way; but the substance is also prepared in the wet way by the action of the alkaline hydrosulphites upon the black sulphuret of mercury, which is obtained by passing sulphuretted hydrogen through a solution of some mercurial salt. The finest artificial product is obtained by Brunner's process. Mercury, 100 parts, is triturated with 38 parts of sulphur, till the whole is converted into AEthiops mineral (a black compound of the two substances). This is placed in a solution consisting of hydrate of potash in 6 parts of water, and kept at a temperature varying little from 45° C, with constant stirring at first. As the water evaporates it is replaced. The reddening usually begins in about 8 hours. The heat must not then rise above 45° C. When the color is the brightest it is allowed to cool slowly. It is then washed and freed from the metallic mercury. From 109 to 110 parts of cinnabar to 100 of mercury is the product. Vermilion is adulterated with brick dust, oxide of iron, red lead, and dragon's blood.
The last is detected by its empyreumatic odor on applying heat; the others by their remaining behind when the pigment is ignited.