[41 bis] Beilstein and Blaese (1889), after preparing many salts of antimonic acid, came to the conclusion that it is monobasic, but all the salts still contain water, so that their general type is mostly: MSbO33H2O, for example, M = Li, Hg (salts of the suboxide), ½ Pb, &c. The type of the ortho-salts, M2SbO4, is quite unknown, although it is reproduced in the thio-compounds, for instance, Schlippe's salt, Na2SbS4, but this salt also contains water of crystallisation, 9H2O (Chapter XX., Note [29]).
[42] Among the other compounds of antimony, antimoniuretted hydrogen, SbH3, resembles arseniuretted hydrogen in its mode of formation and properties (it splits up at 150°, Brunn 1890; when liquified, it boils at -65° and solidifies at -92°), whilst the halogen compounds differ in many respects from those of arsenic. When chlorine is passed over an excess of antimony powder, it forms antimony trichloride, SbCl3, but if the chlorine be in excess it forms the pentachloride, SbCl5. The trichloride is a crystalline substance which melts at 72° and distils at 230°, whilst the pentachloride is a yellow liquid, which splits up into chlorine and the trichloride when heated; at 140° it begins to give off chlorine abundantly, carrying away the vapour of the trichloride with it; and at 200° the decomposition is complete, and pure antimonious chloride only passes over. This property of antimony pentachloride has caused it to be applied in many cases for the transference of chlorine; all the more that when it has given up its chlorine, it leaves the trichloride, which is able to absorb a fresh amount of chlorine; and therefore many substances which are unable to react directly with gaseous chlorine do so with antimony pentachloride, and in the presence of a small quantity of it chlorine will act on them, just as oxygen is able, in the presence of nitrogen oxides, to oxidise substances which could not be oxidised by means of free oxygen. Thus carbon bisulphide is not acted on by chlorine at low temperatures—this reaction requires a high temperature—but in the presence of antimony pentachloride its conversion into carbon tetrachloride takes place at low temperatures. Antimony tri- and pentachloride, having the character of chloranhydrides, fume in air, attract moisture, and are decomposed by water, forming antimonious and antimonic acids. But in the first action of water the trichloride does not evolve all its chlorine as hydrochloric acid, which is intelligible in view of the fact that antimonious anhydride is also a base, and is therefore able to react with acids; indeed antimony sulphide dissolved in an excess of hydrochloric acid (hydrogen sulphide is evolved) gives an aqueous solution of antimony trichloride, which, when carefully distilled, even gives the anhydrous compound. Antimony trichloride is only decomposed by an excess of water, and then not completely, for with a large quantity of water it forms powder of algaroth—i.e. antimony oxychloride. The first action of water consists in the formation of oxychloride, SbOCl—that is, a salt corresponding to oxide of antimony as a base. If antimony oxide or antimony chloride be dissolved in an excess of hydrochloric acid, and the solution diluted with a considerable amount of water, then this same powder of algaroth is precipitated. The composition varies with the relative amount of water; namely, between the limits SbOCl and Sb4O5Cl2. The latter compound is, as it were, a basic salt of the former, because its composition = 2(SbOCl)Sb2O3.
With bromine and iodine, antimony forms compounds similar to those with chlorine. Antimonious bromide, SbBr3, crystallises in colourless prisms, melts at 94°, and boils at 270°; antimonious iodide, SbI3, forms red crystals of sp. gr. 5·0; antimony trifluoride, SbF3 separates from a solution of antimonious oxide in hydrofluoric acid, and SbF5 is formed by a similar treatment of antimonic acid. The latter gives easily-soluble double salts with the fluorides of the metals of the alkalis.
De Haën (1887) obtained very stable double soluble salts, SbF3,KCl (100 parts of water dissolve 57 parts of salt), SbF3,K2SO4, &c., which he proposed to make use of in the arts as very easily crystallisable and soluble salts of antimony.
Engel, by passing hydrochloric acid gas into a saturated solution of antimonious chloride at 0°, obtained a compound HCl,2SbCl3,2H2O, and with the pentachloride a compound SbCl5,5HCl,10H2O. Bismuth trichloride, BiCl3, gives a similar compound.
Saunders (1892) obtained 5RbCl,3SbCl3 and RbCl,SbCl3. Ditte and Metzner (1892) showed that Sb and Bi dissolve in hydrochloric acid only owing to the participation of the oxygen of the air or of that dissolved in the acid.
[43] Metallic bismuth is very easily obtained when the compounds of the oxide are reduced by powerful reducing agents, but when less powerful reducing agents—for example, stannous oxide—are taken, bismuth suboxide is formed as a black crystalline powder. It is a compound of the type BiX2, its composition being BiO; it is decomposed by acids into the metal and oxide, which passes into solution.
[44] The type BiX5 is represented by the pentoxide, Bi2O5, its metahydrate, Bi2O5,H2O, or BiHO3, known as bismuthic acid, and the pyrohydrate, Bi2H4O7. Bismuth pentoxide is obtained by the prolonged passage of chlorine through a boiling solution of potassium hydroxide (sp. gr. 1·38), containing bismuth oxide in suspension; the precipitate is washed with water, with boiling nitric acid (but not for long, as otherwise the bismuthic acid is decomposed), then again with water, and finally the resultant bright red powder of the hydrate BiHO3 is dried at 125°. The prolonged action of nitric acid on bismuthic anhydride, Bi2O5, results in the formation of the compound Bi2O4,H2O, which decomposes in moist air, forming Bi2O3. The density of bismuthic anhydride is 5·10, of the tetroxide, Bi2O4, 3·60, and of bismuthic acid, BiHO3, 5·75. Pyrobismuthic acid, Bi2H4O7, forms a brown powder, which loses a portion of its water at 150°, and decomposes on further heating, with the evolution of oxygen and water. It is obtained by the action of potassium cyanide on a solution of bismuth nitrate. The meta-salts of bismuthic acid are known, for example KBiO3. They generally occur, however, in combinations with metabismuthic acid itself. Thus André (1891) took a solution of the double salt of BiBr3 and KBr, treated it with bromine after adding ammonia, and obtained a red-brown precipitate, which after being washed (for several weeks) had the composition KBiO3,HBiO3 When washed with dilute nitric acid this salt gave bismuthic acid.
[44 bis] Hérard (1889) obtained a peculiar variety of bismuth by heating pure crystalline bismuth to a bright red heat in a stream of nitrogen. A greenish vapour was deposited in the cooler portions of the apparatus in the form of a grey powder, which under the microscope had the appearance of minute globules. An atmosphere of nitrogen is necessary for this transformation, other gases such as hydrogen and carbonic oxide do not favour the transition. The resultant amorphous bismuth fuses at 410° (the crystalline variety at 269°), sp. gr. 9·483. (Does it not contain a nitride?)
[45] Basic bismuth carbonate is employed for whitening the skin (veloutine, &c.)