The American Cyclopædia (1879)/Borax
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|Edition of 1879. Written by C. A. Joy. See also Borax on Wikipedia, and the disclaimer.|
BORAX (Arabic, bûrak), a salt first mentioned by Geber in the 10th century; its chemical nature was discovered by Geoffroy in 1732. It is largely prepared from the natural product boric acid, and is itself found native in various parts of the world. The anhydrous borax, or borate of sodium, has the formula Na2B4O7, and is composed in 100 parts of boric anhydride (B2O3) 69.05, soda (NaO) 30.95. It is found native in some Alpine lakes, in the snowy mountains of India, China, and Persia, in Ceylon, and especially in the lake of Teshu-Lumbu in Great Thibet. This lake is distant 15 days' journey from a town of the same name, and it formerly furnished large quantities of borax. Is also occurs in still greater quantities near Potosí in Bolivia; in Pyramid lake, Washoe co., Nevada, and near Columbus, Esmeralda co., in the same state; also in Borax lake, California. The supply at the last named places seems to be inexhaustible. Formerly a large quantity of the borax formed by the spontaneous evaporation through the sun's heat of the waters of borax lakes, was imported into Europe under the name of tincal, tincana, swaga, or pounxa. It appears in small hexagonal crystals more or less flattened out, either colorless or having a yellowish or greenish tinge, with an earthy crust. It has a greasy feel, and smells like soap. The crude borax was first refined in Venice, where for a long time the process was kept a secret. Afterward it was also refined in Holland. At Lake Clear in California, 250 m. N. of San Francisco, where 4,000 lbs. of borax per day is produced, the muck which contains it is obtained by dredging, dried in the sun, and the borax dissolved out and crystallized. — The purification of tincal may be accomplished in various ways. The oldest method was to place it on a wire sieve or bolter and wash it with a lye containing 5 per cent. of soda so long as the liquor ran through colored. This removed all fatty substances that might adhere to it, forming a very soluble soap. After allowing the borax to drain, it is dissolved in boiling water, 12 per cent. of crystallized carbonate of soda added, and the solution filtered. It is then evaporated to the specific gravity of 18° to 20° B., and allowed to crystallize in wooden vessels well lined with lead. In order to obtain single, well formed crystals, and to prevent a crust forming, the liquor must cool very slowly. Another process consists in pouring over the tincal a small quantity of cold water, and gradually adding, while stirring, 1 per cent. of caustic lime. Some time after boiling water is added and the liquor strained. The greasy substances that contaminated the tincal remain behind as an insoluble lime soap. Two per cent. chloride of calcium is added, and it is again strained and allowed to crystallize. Clouet reduces the tincal to a fine powder, mixes with 10 per cent. of nitrate of sodium, and calcines the mixture in an iron pan over a gentle fire, thus burning out all the fatty matter. The calcined mass is then dissolved in water, the solution separated from the carbon left behind, evaporated, and the crude borax crystallized out. Its varying crystalline form depending on the amount of water it contains, borax is divided into (1) the common or prismatic (natural or artificial), and (2) the octahedral, containing but half as much water of crystallization. Prismatic borax (Na2B4O7 + 10H2O) consists in 100 parts of boric acid 36.6, soda 16.2, water of crystallization 47.2. Octahedral borax (Na2B4O7 + 5H2O) contains boric acid and soda 69.36, water of crystallization 30.64. — Prismatic borax is made as follows: About 26 cwt. of sal soda is dissolved in 400 gallons of water, placed in a large tightly closed vat lined with lead. The solution is caused to boil by a jet of steam entering it. About 24 cwt. of crude boric acid is introduced, in portions of 9 or 10 lbs. at a time, through a tube dipping under the surface of the liquor. A discharge pipe conducts off the carbonic acid, together with some carbonate of ammonia formed at the same time, the ammonia being retained by passing it through dilute sulphuric acid. The solution is brought to a density of 21° to 22° B. by the addition of either crude borax or water as may be required. The solution is allowed to settle and drawn off into the crystallizing vessels, also lined with lead, and left two or three days, the crystals placed on an inclined plane to drain, and then recrystallized, the mother liquor being used to dissolve a fresh quantity of soda. After using this mother liquor three or four times, it contains sufficient Glauber's salt for it to crystallize out, when cooled below 33° C., at which point it is most soluble. The crude borax is purified by recrystallization, 5 per cent. of carbonate of sodium being added to the solution. To obtain large crystals the crystallizing vessels are surrounded by some non-conductor, usually wool, and thickly covered. In the English factories borax is made by fusing the crude boric acid with one half its weight of calcined soda on the hearth of a muffle furnace, under continual stirring. The ammonia, existing in crude boric acid as sulphate, goes off in the form of carbonate, and is condensed in a suitable chamber. The fused mass is dissolved in hot water, clarified by allowing it to settle, and cooled slowly in an iron vessel. In France its manufacture has been united with that of fuming sulphuric acid; the boric acid and calcined Glauber's salt being distilled together, and borax obtained from the residue left in the retort. — Very recently borax has been obtained from the native borate of lime and soda (tiza or boronatrocalcite), which is found in Tarapaca in Peru, and on the W. coast of Africa. The mineral is ground and triturated, then covered with two thirds its own weight of commercial hydrochloric acid, and to this double its volume of water added, and digested at a boiling heat until entirely decomposed, the heat being increased toward the close and water added to preserve the original volume. It is allowed to settle, and decanted while hot. On cooling, nearly all the boric acid crystallizes out, leaving the chloride of sodium and chloride of calcium, together with a slight excess of hydrochloric acid, in the mother liquor. The boric acid thus obtained is allowed to drain, pressed or squeezed out, washed in cold water, and again dried, when it is so pure that on adding soda a pure borax is obtained on the first crystallization. In England the boronatrocalcite is fluxed with soda, but the process offers many difficulties. The use of stassfurtite to make borax has also been successfully tried in Germany. Prismatic borax forms almost colorless, transparent crystals, of a specific gravity 1.75, soluble in 12 parts cold water or 2 parts of boiling water; the solution is slightly alkaline. Exposed to the air, the crystals effloresce only on the surface; on being warmed they decrepitate, and swell up into a spongy mass known as calcined borax; at a red heat they fuse to a transparent glass (borax glass), which takes up water and loses its transparency very slowly. Octahedral borax (Na2B4O7 + 5H2O) is prepared as follows: A boiling solution of prismatic borax is made of a specific gravity of 1.26=30° B., and allowed to cool slowly and regularly. The octahedral crystals begin to form at 79° C., and continue to do so down to 56°, below which temperature the mother liquor produces only prismatic crystals, and hence must be removed. Buran obtained them from a solution of a specific gravity of 32° B., ten days being allowed for 10 cwt. to cool. The tincal from India and half-refined borax from China are sometimes octahedral. It differs from the ordinary borax in crystalline form, has a specific gravity of 1.81, is hard enough to scratch a prismatic crystal, and when exposed to moist air becomes opaque, takes up water, and goes back into the prismatic form. — The uses of borax are numerous. It has the property at a high temperature of dissolving metallic oxides, and forming transparent glasses, the color depending on the metal used; thus cobalt oxide gives a blue glass, chromium oxide a green glass, and so on. On this property depends its use not only in analytical chemistry, where it serves to determine certain metals before the blowpipe, but also in soldering. Borax is largely used in making strass, enamels, and some kinds of glass, and in vitreous pigments for glass and porcelain; in glazing earthenware; as a flux to reduce certain metals from their ores; and in South America, under the name of quemason, the crude substance is actually used in smelting copper. With shellac (in the proportions 1 to 5) it forms a varnish soluble in water, used in stiffening felt hats. With caseine it makes an adhesive substance that may be used instead of gum arabic. Borax is used instead of soap for washing the gum out of silk, instead of sal soda in the laundry, to cleanse the hair, and as a cosmetic. In printing and dyeing establishments it has been proposed to use it to fix the mineral mordants. Aqueous borax has been proposed as an agent for tho preservation of wood. In medicine it is employed for many diseases connected with the bladder and the uterus, and also as a wash for cutaneous eruptions, canker in the mouth, and ringworm. It has the property of making cream of tartar, when boiled together with it, very soluble in water, and this soluble cream of tartar is often found a convenient preparation when large doses of this medicine are required. It is also used to expel cockroaches from closets and pantries, these insects seeming to have an antipathy for it.