THE metal gallium, which is the latest discovery among the recognized elements, was first seen by M. Lecoq de Boisbaudran in the autumn of the year 1875, and so named by him in honor of the land of its discovery, France. Like its four predecessors made known within the last 20 years, gallium was discovered by the pro,<;e!M of spectrum analysis, applied in this ins^rnce in a special manner contrived by the ingenuity of M. de Boisbaudran himself, long eminent as a spectroscopist. The spectrum of gallium is characterized by two marked violet lines , the less refrangible of them being especially brilliant. Hitherto the new metal has been recognized only in certain varieties of zinc blende, that of Pierre- fitte in the Pyrenees having furnished the chief portion of gallium hitherto obtained from any source whatever—nearly half a ton of this ore having been employed by M. de Boisbaudran to furnish the dozen grains or so of metal wherewith he has been able to establish the leading properties of the element. In its appearance gallium manifests a general resemblance to lead, but is not so blue-tinted or quite so soft, though it is readily malleable, flexible, and capable of being cut with a knife. Like lead again, and unlike zinc, gallium is not an easily volatile metal. Unlike lead, however, it acquires only a very slight tarnish on exposure to moist air, and undergoes scarcely any calcination at Ii red heat. The specific gravity of gallium is a little under 6, that of aluminum being 2'6, that of zinc 7'1, and that of lead 11 '4. A most remarkable property of gallium is its low melting point. It liquefies completely at 86° Fah. , or below the heat of the hand; and, still more curiously, when once melted at this temperature, it may be cooled down even to the freezing point of water without solidifying, and may be kept unchanged in the liquid state for months. Indeed, in the original communication of its discovery to the French Academy, it was described as a new liquid metal, similar to mercury; but on touching with a fragment of solid gallium a portion of the liquid metal in this state of so-called suffusion it at once solidifies. Unlike lead, again, gallium is a highly crystalline metal, its form being that of a square octahedron. In its chemical habitudes the rare element gallium shows the greatest analogy to the abundant element aluminum. In particular it forms a sort of alum not to be distinguished in its appearance from ordinary alum, but containing oxide of gallium instead of oxide of aluminum or alumina. • But the chief interest of gallium, from a scientific point of view, is connected with the history of its discovery. All previously known elements have been discovered, so to speak, accidentally, and their properties have been not in any way foreseen, but rather met with as subjects of surprise ; but the blende of Pierrefitte was deliberately taken up for” examination by M. Lecoq de Boisbaudran in the expectation of finding a new element. The existence of an element having the characteristic properties of gallium was, moreover, upon entirely different grounds, predicted very definitely by a Russian chemist. M. Mendele- jeff, in 1871, and in a more general way several years earlier by an English chemist, Mr. Newlands. This double prediction was based on a study of the relations of the known atomic numbers of the elements. These numbers have only lately been perceived to form a tolerably continuous seria- tion, which, again, is associated in a remarkable manner with the seriation in properties of the elements themselves. In the series of numbers, however, certain terms are here and there missing, and in particular a number was missing which should belong to an element having properties intermediate between those of aluminum and iridium. What these properties would be was predicted in most minute tail by M. Mendelejeff in 1871. He predicted, for example, that the specific gravity of the missing metal would prove to be about 5 '9. Operatinj^ on very small quantities, M. de Boisbaudran, in the first mstance, found the specific gravity of gallium to be 4'7; but on repeating his determination in 1876, with special precautions and on a somewhat larger though still very small scale, he found it to be exactly 5 '935, certainly a most remarkable fulfillment of the prediction with to it. In a recent number of La Nature, M. G. Tissandier gave the following account of the extraction of a quantity of gal- Hum by M. de Boisbaudran, accompanied by a description of some of its properties:—Without shrinking from the delicate and frequently troublesome operations necessary in treating a mass of blende weighing 4,300 kilogrammes, he has succeeded, in collaboration with M. E. Jungfieisch, in getting out 62 grammes of gallium. “If,” say these gentlemen, “we take account of inevitable losses and of a few grains of gal- Hum remaining in the various products of our operations, we may estimate the proportion of gallium in Bensberg blende at about one part in sixty thousand, or 16 milligrammes per kilogramme. The small proportion of matter to extract will sufficiently explain the large amount of time consumed in its extraction." The preliminary operations were carried out at the works at Javel belonging to M. Leon Thomas, a successful manufacturer as well as patron and student of science. The 4,300 kilogrammes of blende were concentrated in a mass weighing about 100 kilos., containing the whole of the gallium. From Javel this mass of concentrated stuff was transported to the laboratory of M. Lecoq de Boisbaudran at Cognac, : and, after further concentration, was purified and reduced to j a metallic condition at the Ecole de Pharmacie, at Paris. 1 After a long succession of attacks by acids and alternative I precipitations, the metals associated with gallium, such as I zinc, iron, cadmium, iridium, &c., were eliminated. The I gallium in the residue of the solutions from which the other metals had been separated was got in the metallic condition I by the action of the electric current. [ “The deposition of metallic gallium,” say Messrs. Lecoq de Boisbaudran and Jungfieisch, “is only carried out successfully under certain special conditions. The intensity of the electric current, for instance, should vary with the state of the solution. but the surface of the negative electrode should always be small, relatively to that of the positive elec- In one of our operations, by which we got 8 grammes I of gallium in twenty-four hours, forty Bunsen cells (18 centimeters high), ranged in eight parallel rows, each of five cells in tension, acted on a negative electrode,- the double, ; surface of which did not exceed 15 square centimeters, while | the positive electrode had a development of about 450 square centimeters. The metal on being thrown down cold frequently forms long threads of crystals' which take on the ; appearance of needles, fixed normally to the electrode by ; one of their extremities; some few have reached the length : of 3 centimeters. Above 30° the metal runs in drops, which coalesce at the foot of the electrode.' ' Crystals of gallium | were pre£nted on behalf of the operators to the Academy of Sciences by M. Berthelot, in its sitting of February 18th. These crystals, which have a distinct grayish-blue metallic luster, belong distinctly to the octahedric system, but their have not yet been measured, their faces being slightly .rounded. They are mounted on small glass stems, and kept . under a glass globe from the contact of the air. ; Crystallization was effected by introducing a platinum wire carrying a particle of solid gallium into the metal cooled to 10° or 15° C. below its melting point. After the lapse of : a very short period, varying from 3 to 10 seconds, octahe- ; dric crystals show themselves, very slightly modified at their summits by traces of their base. The crystals were shown in the accompanying drawings of the full natural size. If the crystals are not promptly withdrawn as soon as formed, the metal reacquires part of its lost heat, solidification slackens and the base enlarges. Gallium is a hard and ^lleable metal; it takes under the hammer the polish of the anvil, but rapidly grows harder and brittle, and is then liable to fly to pieces. In spite of its relatively considerable hardness, gallium leaves on paper ! strongly defined marks of a bluish-gray color. It retains its luster in the atmosphere of a laboratory constantly loaded with acid vapors, and undergoes no alteration in appearance in boiled water. In aerated water it tarnishes slightly. Gallium, which melts at 30°, may be kept superfused in a tube hermetically sealed. MM. Boisbaudran and Jungfieisch have prepared a certain quantity of it in this condition. It re- malns fluid like mercury, and when the tube • is inverted it creeps along the glass like melted wax. In a liquid condition, gallium has the brilliant whiteness of tin or silver. It would be of great value for the determination of tempera- i tures rising to 300° or 400° C., but its habit of clinging to the sides of the glass vessel in which it may be contained constitutes at present an impediment in the way of its being used for thermometric purposes. It is possible that some means may be found for correcting this tendency, and that the new metal may thus be made capable of receiving various applications in the domain of experimental science. i Gallium leaf has also been prepared by running the melted ' metal between heated glass surfaces. On cooling, especially if the cooling is carried out under water, the metal is easily ! detached from the glass. This specimen melts in the hand: . it retains its characteristic dull blue metallic reflection. A small bar has also been cast, the elasticity and malleability : of which are easily demonstrable. Crystallized gallium prepared cold by electrolysis of a po- tassic solution decrepitates on being thrown into hot water, and gives rise to bubbles of gas. “By electrolysis of a liquor heated up to 30° C.,” say the experimenters, “we have often obtained, especially toward the end of the operation, a puffy metallic mass swelling in warm water, and having the aspect of an ammonium amalgam. Kneaded in water at 40° C., this mass contracts and is finally resolved into ordinary fluid ' gallium. Some new compounds of gallium, comprising the chloride, bromide, and anhydric iodide, have been presented to the ' Academy. Chlorine attacks gallium in the cold state very ' actively, with an abundant disengagement of heat. The pro- i duct is faintly yellow; it would probably be perfectly colorless if pure. It is well crystallized, very fusible, easily becomes volatile, and imbibes the ordinary moisture of the . atmosphere. The action of bromine is less energetic than that of chlorine. To get the iodide it must be slightly heated.”
This article was originally published with the title "The New Metal Gallium"