in chemistry, an imperfect metallic substance, that falls to the bottom of the crucible, in the melting of ores or impure metallic substances.

REGULUS of Antimony. See Chemistry, p. 158, 211, 258, 449.

REGULUS of Arsenic. This is a white arsenic, to which the properties of a semi-metal have been given, by combining it properly with a sufficient quantity of phlogiston.

Regulus of arsenic may be made by several methods. The process anciently used for this purpose consisted in mixing four parts of arsenic with two parts of black flux, one part of borax, and one part of filings of iron or copper, and quickly fusing the mixture in a crucible. When the operation is finished, a regulus of arsenic will be found at the bottom of the crucible, of a white livid colour, and considerably solid. The iron Regulus and copper employed in this process are not intended, as in the operation for the martial regulus of antimony, to precipitate the arsenic, and to separate it from sulphur or any other substance; for the white arsenic is pure, and nothing is to be taken from it; but, on the contrary, the inflammable principle is to be added to reduce it to a regulus. The true use of these metals in the present operation is to unite with the regulus of arsenic, to give it more body, and to prevent its entire distillation in vapours. Hence the addition of iron, while it procures these advantages, has the inconvenience of altering the purity of the regulus: for the metallic substance obtained is a regulus of arsenic alloyed with iron. It may, however, be purified from the iron by sublimation in a close vessel; by which operation the regulus arsenical part, which is very volatile, is sublimed to the top of the vessel, and is separated from the iron, which being of a fixed nature, remains at the bottom. We are not, however, very certain, that in this kind of rectification the regulus of arsenic does not carry along with it a certain quantity of iron; for in general a volatile sublimate rises along with it, in sublimation, a part of any fixed matter with which it happened to be united.

Mr Brandt proposes another method, which we believe is preferable to that described. He directs that white arsenic should be mixed with soap. Instead of the soap, olive-oil may be used, which has been found to succeed well. The mixture is to be put into a retort or glass matras, and to be distilled or sublimed with fire at first very moderate, and only sufficient to raise the oil. As the oils, which are not volatile, cannot be distilled but by a heat sufficient to burn and decompose them, the oil therefore which is mixed with the arsenic undergoes these alterations, and after having penetrated the arsenic thoroughly is reduced to a coal. When no more oily vapours rise, we may then know that the oil is reduced to coal. Then the fire must be increased, and the metallised arsenic will be soon sublimed to the upper part of the vessel, in the inside of which it will form a metallic crust. When no more sublimes, the vessel is to be broken, and the adhering crust of regulus of arsenic is to be separated. The regulus obtained by this first operation is not generally perfect, or not entirely so, as a part of it is always overcharged with fuliginous matter, and another part has not enough of phlogiston; which latter part adheres to the inner surface of the crust, and forms grey or brown crystals. This sublimate must then be mixed with a less quantity of oil, and sublimed a second time like the first; and even, to obtain as good regulus as may be made, a third sublimation in a close vessel, and without oil, is necessary. During this operation, the oil which rises is more fetid than any other empyreumatic oil, and is almost inapplicable. This smell certainly proceeds from the arsenic, the smell of which is exceedingly strong and disagreeable when heated.

Regulus of arsenic made by the method we have described, and which we consider as the only one which is pure, has all the properties of a semi-metal. It has metallic gravity, opacity, and lustre. Its colour is white and livid, it tarnishes in the air, is very brittle, but much more volatile than any other semi-metal. It easily loses its inflammable principle, when sublimed in vessels into which the air has access; the sublimate having the appearance of grey flowers, which by repeated sublimations become entirely white, and similar to white crystalline arsenic.

When regulus of arsenic is heated quickly and strongly in open air, as under a muffle, it burns with a white or bluish flame, and dissipates in a thick fume, which has a very fetid smell, like that of garlic.

Regulus of arsenic may be combined with acids and most metals. As white arsenic also can unite with these substances, we refer to that article. We shall only observe here, that, according to Mr Brandt, in the Swedish Memoirs, the regulus of arsenic cannot be united with mercury. Although the phenomena exhibited by white arsenic and regulus of arsenic in solutions and alloys are probably the same, yet an accurate comparison of these would deserve notice, especially if the regulus employed were well made; for some difference must proceed from the greater or less quantity of phlogiston with which it is united. See Chemistry, n° 467.

Regulus of Cobalt, is a semi-metal lately discovered, and not yet perfectly well known. It receives its name from cobalt, because it can only be extracted from the mineral properly so called.

The process by which this semi-metal is obtained, is similar to those generally used for the extraction of metals from their ores. The cobalt must be thoroughly torrefied to deprive it of all the sulphur and arsenic it contains; and the unmetallic earthy and stony matters must be separated by washing. The cobalt thus prepared is then to be mixed with double or triple its quantity of black flux, and a little decrepitated sea-salt; and must be fused either in a forge or in a hot furnace, for this ore is very difficult of fusion.

When the fusion has been well made, we find, upon breaking the crucible, after it has cooled, a metallic regulus covered with a scoria of a deep blue colour. The regulus is of a white metallic colour. The surface of its fracture is close and small-grained. The semi-metal is hard, but brittle. When the fusion has been well made, its surface appears to be carved with many convex threads, which cross each other diversely. As almost all cobalts contain also bismuth, and even as much as of the regulus itself, this bismuth is reduced by the same operation, and precipitated in the same manner, as the regulus of cobalt; for although these two metals are frequently mixed in the same mineral, that is, in cobalt, they are incapable of uniting together, and are always found distinct and separate from one another when they are melted together. At the bottom of the crucible there we find both regulus of cobalt and bismuth. The latter, having a greater specific gravity, is found under the former. They may be separated from each other by the blow of a hammer. Bismuth may be easily distinguished from the regulus of cobalt, not only from its situation in the crucible, but also by the large shining facets which appear in its fracture, and which are very different from the close ash-coloured grain of regulus of cobalt.

This semi-metal is more difficult of fusion than any other; is less easily calcinable, and much less volatile. Its calx is grey, and more or less brown; and when fused with vitrifiable matters, it changes into a beautiful blue glass called smalt. This calx then is one of those... which preserve always a part of their inflammable principle. It is soluble in acids, as the regulus is. This regulus is soluble in vitriolic, marine, nitrous acids, and in aqua regia, to all which it communicates colours.

The solution in vitriolic acid is reddish; the solution in marine acid is of a fine bluish-green when hot, and its colour is almost totally effaced when cold, but is easily recoverable by heating it, without being obliged to uncork the bottle containing it. This solution of the calx of regulus of cobalt is the basis of the sympathetic ink; for without marine acid this ink cannot be made.

All the solutions of regulus of cobalt may be precipitated by alkalies; and these precipitates are blue, which colour they retain when vitrified with the strongest fire.

Not only sympathetic ink, but also regulus of cobalt, may be made from the zaffre commonly sold, which is nothing else than the calx of regulus of cobalt mixed with more or less pulverized flints. For this purpose we must separate as well as we can the powder of flints from it, by washing, as Mr Beaumé does, and then reduce it with black flux and sea-salt.

Regulus of cobalt seems incapable of uniting with sulphur: but it easily unites with liver of sulphur; and the union it forms is so intimate, that Mr Beaumé could not separate these two substances, otherwise than by precipitation with an acid.

Many curious and interesting remarks are still to be discovered concerning this singular semi-metal, and we may hope to receive further information from the endeavours of chemists who have undertaken the examination of it. Mr Beaumé particularly has made considerable experiments on this subject, part of which he communicates to the public in his Course of Chemistry. All the new remarks in this article are from him. See Chemistry, n° 159, 212, 213, 259.