This semi-metal has not yet been applied to any use.
Of Arsenic.
What is commonly called arsenic is the calx of a semi-metal called the regulus of arsenic. It is a white and brittle substance, expelled from the ores of several metals by heat. It is then refined by a second sublimation, and melted into the masses in which it is commonly sold. This calx is soluble in about eighty times its weight of cold water, or in fifteen times its weight of boiling water. It acts in many respects like an acid, as it decomposes nitre by distillation, when the nitrous acid flies off, and the arsenical salt of Macquer remains behind.
When the calx of arsenic is distilled with sulphur, the vitriolic acid flies off, and a substance of a yellow colour, called orpiment, is produced. This appears to consist of sulphur and the regulus of arsenic; part of the sulphur receiving pure air from the calx, to which it communicates phlogiston; and thus the sulphur becomes converted into vitriolic acid, while the arsenical calx is reduced, and combines with the rest of the sulphur.
The combination of sulphur and arsenic, by melting them together, is of a red colour, known by the name of realgal, or realgar. It is less volatile than orpiment.
The solution of fixed alkali dissolves the calx of arsenic, and by means of heat a brown tenacious mass is produced, and having also a disagreeable smell, it is called liver of arsenic.
The regulus of arsenic is of a yellow colour, subject to tarnish or grow black, by exposure to the air, very brittle, and of a laminated texture. In close vessels it wholly sublimes, but burns with a small flame in pure air.
Vitriolic acid has little action upon this semi-metal, except when hot; but the nitrous acid acts readily upon it, and likewise dissolves the calx, as does boiling marine acid, though it affects it very little when cold.
Most of the metals unite with the regulus of arsenic.
Dephlogisticated marine acid converts the calx of arsenic into arsenical acid by giving it pure air.