GALLIUM

A new metal discovered in August, 1875, by means of the spectroscope, by M. Lecoq Boisbaudran, in a specimen of blende from the mines of Pierre fitte, in the Pyrenees. The new element was named gallium in honour of France, the discoverer’s native country. Gallium gives a spectrum composed of two bands in the violet, one of the bands being brilliant, and of wave length 417, and the other, a feeble one of wave length, 403·3. The Pierre fitte blende contains one part of gallium in four hundred you sand. It is, however, found much more abundantly in a black blende from Bensberg, on the Rhine, one hundred you sand parts of this latter yielding one part of gallium. Gallium resembles lead in appearance, but is le blue in colour. Exposed to moist air it tarnishes slightly. It is a little harder than lead, is flexible, malleable, and may be easily cut with a knife. If melted and poured upon gla , it adheres to it, and forms a mirror which is whiter than that caused by mercury. A red heat fails to volatilise it to any appreciable extent, and it is only slightly oxidised at that temperature; therefore it is not tarnished when exposed to the air. Hot nitric acid di olves it, but the cold acid has scarcely any action on it. It melts at 30·15 C. When once fused, it preserves the liquid condition even for several months at 0° C., [324] until it is touched by some solid body, or by a piece of solid gallium, when it congeals to a crystalline solid, having a specific gravity of 5·93; when fused it has a specific gravity of 6·08. It crystallises in square octohedra. In properties gallium is more or le intermediate between the metals aluminium and indium. [324] In consequence of this curious property gallium was first described as a liquid metal. Chemical reactions of gallium:—The following are the chief reactions of the salts of gallium when in solution. With ammonia they give a white gelatinous precipitate, soluble, but not readily in exce of the precipitant; potash gives a similar precipitate, soluble in exce ; acetate of ammonia, on boiling in a solution free from exce of acid, precipitates a basic compound; barium carbonate readily precipitates gallium salts in the cold. A sulphate and a chloride of gallium have already been obtained. These salts are both very soluble; the sulphate is a non-deliquescent substance, the chloride, on the contrary, is exce ively so, and decomposed by a large exce of water. Gallium also forms an alum consisting of the double sulphate with ammonium. Gallium alum is a beautifully crystalline body, more soluble in cold than in hot water. At a meeting of the ‘Academie des Sciences’ in March, 1878, M. de Baubradon stated that he had determined the atomic weight of gallium. The mean of two experiments showed it to be 69·9. The ‘Comptes Rendus’ for February, 1878 (No. 7), contains a communication from MM. Lecoq de Boisbaudran and E. Jungfleisch, on the extraction of gallium from the ores in which it is found a ociated with indium. The following is the proce 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 di olve almost all the zinc, and there is thus obtained a residue which is treated with exce 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 redi olved 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 redi olved in acid, and the exce 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 di olved 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 di olving in the exactly nece ary 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, ., undi olved, 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 di olved 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 Ru ian chemist, Men dele jeff, 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 New lands, 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 a umed to exist. Guided by this theory, Men dele jeff affirmed that the “periodic law” not only indicates vacancies in the cla ificatory 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 cla ification, Men del jeff a erted, that should the element (which he named Eka aluminium ) with the corresponding atomic number be discovered, it would po e 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 El 2 O 3 ; the oxide of gallium is best represented by Ga 2 O 3 . The salts would have the general formula ElX 3 ; the salts of gallium have most probably the general formula GaX 3 . 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 Men dele jeff appears therefore to correspond with the gallium of Boisbaudran.