Volume 2

The principles of chemistry / by D. Mendeleeff ; translated from the Russian (5th ed.) by George Kamensky ; edited by A.J. Greenaway.

  • Mendeleyev, Dmitry Ivanovich, 1834-1907.
Date:
1891
Catalogue details

Licence: Public Domain Mark

Credit: The principles of chemistry / by D. Mendeleeff ; translated from the Russian (5th ed.) by George Kamensky ; edited by A.J. Greenaway. Source: Wellcome Collection.

    77/518 (page 63)
    Free boron was obtained (1S09) by Davy, Gay-Lussac, and Thenard when they obtained the metals of the alkalis, because boric anhydride when fused with sodium gives up its oxygen to the sodium, and free boron is liberated as an amorphous powder like charcoal.10 It is of a brown colour, and when dry does not alter in the air at the ordinary temperature ; but it burns when ignited, and in so doing combines not only with the oxygen of the air, but also with the nitrogen. However, the combustion is never complete, because the boric anhydride formed on the surface covers the remaining mass of the boron, and so pre- serves it from the action of the oxygen. Acids, even sulphuric and phosphoric, easily oxidise amorphous boron, especially when heated, converting it into boric acid. Alkalis have the same action on it, only in this case hydrogen is evolved. Boron decomposes steam at a red heat, also with evolution of hydrogen. Amorphous boron also easily and directly combines with the metals, and with sulphur, chlorine, and nitrogen at a red heat. Amorphous boron, like charcoal, dissolves in certain molten metals. The property of fused aluminium of dissolving boron in considerable quantity is very striking ; on cooling such a solution the boron, par- tially combined with the aluminium, separates out in a crystalline form, and its properties are then exceedingly remarkable. The crystalline boron maybe obtained by heating (to 1300°) the pulverulent boron with aluminium in a well-closed crucible, the access of air being prevented as far as possible. After cooling, crystals are observed on the surface of the aluminium, and may easily be separated by dissol ving the aluminium in hydrochloric acid, which does not act on the crystals. The sp. gr. of the crystals is 2’68 ; they are partially transparent, but are mostly coloured dark brown ; they contain about 4 p.c. of carbon and up to 7 p.c. of aluminium, so that they cannot be counted as pure boron. Nevertheless, the properties of this crystalline substance, which wicks, which are made of cotton twist, contain an ash which is infusible by itself but which fuses when mixed with boric acid. 10 Amorphous boron is prepared by mixing 100 parts of powdered boric anhydride with 50 parts of sodium in small lumps; this mixture is thrown into a powerfully-heated cast-iron crucible, covered with a layer of ignited salt, and the crucible covered. Reaction proceeds rapidly; the mass is stirred with an iron rod, and poured directly into water containing hydrochloric acid. The action is naturally accompanied by the forma- tion of sodium borate, which is dissolved, together with the salt, by the water, whilst the boron settles at the bottom of the vessel as an insoluble powder. It is washed in water and dried at the ordinary temperature. Magnesium, and even charcoal and phosphorus’ are also able to reduce boron from its oxide. Boron, in the form of an amorphous powder’ very easily passes through filter-paper, remains suspended in water, and colours it brown, so that it is considered soluble in water. Sulphur precipitated from solutions shows the same (colloidal) property.