Page:The American Cyclopædia (1879) Volume III.djvu/95

BORAX . 89 carbonate of soda added, and the solution fil- tered. It is then evaporated to the specific gravity of 18 to 20 B., and allowed to crystal- lize 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 crystal- lize. Clouet reduces the tincal to a fine pow- der, mixes with 10 per cent, of nitrate of sodi- um, 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 car- bon left behind, evaporated, and the crude bo- rax 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 (NajBjOr + lOHjO) consists in 100 parts of boric acid 36-6, soda 16'2, water of crystallization 47'2. Oc- tahedral borax (NaaB^ + oIIsO) contains bo- ric acid and soda 69-36, water of crystalliza- tion 30-64. Prismatic borax is made as fol- lows : About 26 cwt. of sal soda is dissolved in 400 gallons of water, placed in a large tightly closed vat lined with lead. The solu- tion is caused to boil by a jet of steam enter- ing it. About 24 cwt. of crude boric acid is introduced, in portions of 9 or 10 Ibs. at a time, through a tube dipping under the surface of the liquor. A discharge pipe con- ducts off the carbonic acid, together with some carbonate of ammonia formed at the same time, the ammonia being retained by pass- ing it through dilute sulphuric acid. The so- lution 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 recrys- tallization, 5 per cent, of carbonate of sodium being added to the solution. To obtain large crystals the crystallizing vessels are surround- ed by some non-conductor, usually wool, and thickly covered. In the English factories bo- rax 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 car- bonate, and is condensed in a suitable cham- ber. The fused mass is dissolved in hot water, clarified by allowing it to settle, and cooled slowly in an iron vessel. In France its manu- facture 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 Tara- paca in Peru, and on the W. coast of Africa. The mineral is ground and triturated, then cov- ered with two thirds its own weight of com- mercial 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 borona- trocalcite 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 ef- floresce 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 trans- parency very slowly. Octahedral borax (Nai B^T + SHjO) is prepared as follows: A boil- ing 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 tempera- ture 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 crys- tal, and when exposed to moist air becomes opaque, takes up water, and goes back into the prismatic form. The uses of borax are numer- ous. It has the property at a high tempera- ture of dissolving metallic oxides, and forming transparent glasses, the color depending on the