BaC2 + 2H2O = C2H2 + Ba(OH)2
Maquenne proposes the barium carbide as a source of acetylene. He obtained this compound by heating carbonate of barium, magnesium powder, and retort carbon in a Perreau furnace (BaCO3 + 3Mg + C = 3MgO + BaC2). One hundred grams of BaC2 evolve 5,200 to 5,400 c.c. of acetylene, mixed with about 2–3 p.c. of hydrogen.
The relation of acetylene, C2H2, to these metallic carbides is evident from the fact that these metals (Ca, Sr, Ba) replace 2 atoms of hydrogen, and therefore C2Ba corresponds to C2H2, so that they may be regarded as metallic derivatives of acetylene. Moissan (1893) obtained similar carbides directly from the oxides by subjecting them to the action of the voltaic arc, in the presence of carbon, for instance, BaO + 3C = CO + C2Ba, although at a furnace heat carbon has no action on the oxides CaO, BaO, SrO. Concerning Al4C5, see Chapter XVII. Note 38.
[13] When subjected to pressure, charcoal loses heat, hence the densest form stands to the less dense as a solid to a liquid, or as a compound to an element. From this the conclusion may be drawn that the molecules of graphite are more complex than those of charcoal, and those of the diamond still more so. The specific heat shows the same variation, and as we shall see further on, the increased complexity of a molecule leads to a diminution of the specific heat. At ordinary temperatures the specific heat of charcoal is 0·24, graphite 0·20, the diamond 0·147. For retort carbon Le Chatelier (1893) found that the product of the sp. heat and atomic weight varies, between 0° and 250°, according to the formula: = 1·92 + 0·0077t, and between 250° and 1000°, = 3·54 + 0·00246t (see Chapter XIV. Note [4]).
[14] There are places where anthracite gradually changes into graphite as the strata sink. I myself had the opportunity of observing this gradual transformation in the valley of Aosta.
[15] Pencils are made of graphite worked up into a homogeneous mass by disintegrating, powdering, and cleansing it from earthy impurities; the best kinds are made of completely homogeneous graphite sawn up into the requisite sticks. Graphite is found in many places. In Russia the so-called Aliberoffsky graphite is particularly renowned; it is found in the Altai mountains near the Chinese frontier; in many places in Finland and likewise on the banks of the Little Tungouska, Sidoroff also found a considerable quantity of graphite. When mixed with clay, graphite is used for making crucibles and pots for melting metals.
Graphite, like most forms of charcoal, still contains a certain quantity of hydrogen, oxygen, and ash, so that in its natural state it does not contain more than 98 p.c. of carbon.
In practice, graphite is purified simply by washing it when in a finely-ground state, by which means the bulk of the earthy matter may be separated. The following process, proposed by Brodie, consists in mixing the powdered graphite with 1⁄14 part of its weight of potassium chlorate. The mixture is then heated with twice its weight of strong sulphuric acid until no more odoriferous gases are emitted; on cooling, the mixture is thrown into water and washed; the graphite is then dried and heated to a red heat; after this it shrinks considerably in volume and forms a very fine powder, which is then washed. By acting on graphite several times with a mixture of potassium chlorate and nitric acid heated up to 60°, Brodie transformed it into a yellow insoluble acid substance which he called graphitic acid, C11H4O5. The diamond remains unchanged when subjected to this treatment, whilst amorphous charcoal is completely oxidised. Availing himself of this possibility of distinguishing graphite from the diamond or amorphous charcoal, Berthelot showed that when compounds of carbon and hydrogen are decomposed by heat, amorphous charcoal is mainly formed, whilst when compounds of carbon with chlorine, sulphur, and boron are decomposed, graphite is principally deposited.
[15 bis] Diamonds are found in a particular dense rock, known by the name of itacolumite, and are dug out of the débris produced by the destruction of the itacolumite by water. When the débris is washed the diamonds remain behind; they are principally found in Brazil, in the provinces of Rio and Bahia, and at the Cape of Good Hope. The débris gives the black or amorphous diamond, carbonado, and the ordinary colourless or yellow translucent diamond. As the diamond possesses a very marked cleavage, the first operation consists in splitting it, and then roughly and finely polishing it with diamond powder. It is very remarkable that Professors P. A. Latchinoff and Eroféeff found (1887) diamond powder in a meteoric stone which fell in the Government of Penza, in the district of Krasnoslobodsk, near the settlement of Novo Urei (Sept. 10, 1886). Up to that time charcoal and graphite (a special variety, cliftonite) had been found in meteorites and the diamond only conjectured to occur therein. The Novo Urei meteorite was composed of siliceous matter and metallic iron (with nickel) like many other meteorites.
[16] Diamonds are sometimes found in the shape of small balls, and in that case it is impossible to cut them because directly the surface is ground or broken they fall into minute pieces. Sometimes minute diamond crystals form a dense mass like sugar, and this is generally reduced to diamond powder and used for grinding. Some known varieties of the diamond are almost opaque and of a black colour. Such diamonds are as hard as the ordinary ones, and are used for polishing diamonds and other precious stones, and also for rock boring and tunnelling.