The following is the process given by the authors:—The blende of Bendsberg is pulverised and then roasted in a Perret furnace, by which treatment the greater part of the indium is volatilised. The residue is treated with sulphuric acid in quantity sufficient to dissolve almost all the zinc, and there is thus obtained a residue which is treated with excess of sulphuric acid.
The persalts of iron present are then reduced by means of metallic zinc, and the filtrate fractionally precipitated with carbonate of sodium; the precipitates are redissolved in sulphuric acid, and the reduction with zinc and the fractional precipitation repeated, the latter operation being in both cases watched by the spectroscope.
The precipitate containing the gallium concentrated in a small bulk, is redissolved in acid, and the excess of the latter reagent removed by evaporation, after which it is boiled with much water. The filtrate separated from the sediment containing titanic acid, which form is treated with sulphuretted hydrogen, then mixed with acetate of ammonium and again treated with sulphuretted hydrogen, which throws down the galliferous sulphide of zinc free from alumina. Again the precipitate is dissolved in sulphuric acid, and the solution fractionally precipitated with carbonate of sodium, which operation, guided as it is by spectral examination, entirely removes the zinc. By once more dissolving in the exactly necessary amount of sulphuric acid, and treating with sulphuretted hydrogen, cadmium, lead, indium and zinc are removed, and the filtrate is then largely diluted with water and boiled. The bulky sub-salt of gallium which separates at this temperature is treated with potash, which leaves iron, indium, &c., undissolved, and the alkaline liquor when treated with sulphuretted hydrogen, and subsequently with sulphuric acid to slight acidity, yields a deposit consisting mainly of sulphide of indium.
The slightly acid liquid is then boiled with much water, and the deposit of sub-salt of gallium thus obtained is dissolved in potash, and the solution subjected to electrolysis, by which means a metallic deposit of gallium is obtained.
It is interesting to note how accurately many of the chemical physical properties to gallium had, previously to its discovery, been predicted by the Russian chemist, Mendelejeff, by reasoning on the so-called “periodic law,” which he thus defines:—“The properties of the simple bodies, as also the properties and constitution of their combinations, are periodic functions of the atomic weights of the elements.”
In 1864 an English chemist named Mr Newlands, observing certain relations existing between the atomic weights of many of the elements, was the first to arrange them in such a manner or serial form as to suggest that when certain gaps were observed in the atomic weights of a series, new elements might be assumed to exist. Guided by this theory, Mendelejeff affirmed that the “periodic law” not only indicates vacancies in the classificatory scheme of the known elements, but enables us to predict the properties of elements as yet undiscovered, and of their compounds.
Thus, of one of the vacancies observable in the table of the elements arranged according to his classification, Mendeljeff asserted, that should the element (which he named Eka aluminium) with the corresponding atomic number be discovered, it would possess the following characteristics:—It would most probably, like indium and thallium, be discovered by the aid of spectrum analysis. Gallium, as we have seen, was found by this means. The formula of its oxide would be El2O3; the oxide of gallium is best represented by Ga2O3.
The salts would have the general formula ElX3; the salts of gallium have most probably the general formula GaX3. It will form an alum isomorphous with common alum, this we have seen gallium does. Its salts would be precipitable by barium carbonate; the gallium salts are thrown down by this reagent. It would not oxidise in the air; gallium does not tarnish upon exposure to the air. It would decompose water at a red heat; gallium readily does this at high temperatures. Its specific gravity (and this is very remarkable) would be about 5·9; gallium has a specific gravity of 5·93. Its atomic weight would be about 68; that of gallium is 69·9.
The hypothetical Eka aluminium of Mendelejeff appears therefore to correspond with the gallium of Boisbaudran.
GALLS. Syn. Gall-nuts, Nut-galls; Galla (B. P.); Gallæ (Ph. E.). “Excrescences on Quercus infectoria caused by the puncture and deposited ova of Diplolepis Gallæ tinctoriæ.” The best galls are blueish-black, heavy, and not yet perforated; intensely astringent. They are imported from Aleppo, and are known in commerce as black or blue galls (GALLÆ NIGRÆ, G. CŒRULÆ). The next quality is termed, from their colour, green galls (GALLÆ VIRIDES). Both are gathered before the insect has escaped, and are styptic and powerfully astringent. White galls (GALLÆ ALBÆ) are lighter, less astringent, and inferior.