BORAX, in chemistry, is a name given to a species of white salt much used by various artists. Its use in soldering me tals appears to have been known to Agri cola. Borax is found mixed with other substances in Thibet. It seems to exist in some lands adjacent to lakes, from which it is extracted by water, and de posited in those lakes ; whence, in sum mer, when the water is shallow, it is ex tracted, and carried off in large lumps. Sometimes the water in these lakes is ad mitted into reservoirs, at the bottom of which, when the water is exhaled by the summer's heat, this salt is found. Hence it is carried to the East Indies, where it is in some measure purified and crystal lized; in this state it comes to Europe, and is called tineal. In other parts of Thibet, it seems; by accounts received from China, they dig it out of the ground at the depth of about two yards, where they find it in smaller crystalline masses.
Borax, or sub-borate of soda. This salt, the only one of the borates which has been accurately examined, is supposed to have been known to the ancients, and to be the substance denominated chrysocol la by Pliny. At any rate, it is mentioned by Geber as early as the ninth century, under the name of borax. Its composi tion was first pointed out by Geoffroy, in 1732, and Baron, in 1748. Bergman de monstrated that it has an excess of base, and is therefore in the state of a sub-bo rate.
Borax, purified, may be obtained crys tallized in hexangular prisms, of which two sides are much broader than the re mainder, and terminated by triangulai pyramids ; it is of a white colour : its spe cific gravity is 1.740: it converts vegeta ble blues to green : its taste is styptic and alkaline ; it is soluble in twenty times its weight of water, of the temperature of 60°, and six times its weight of boiling water : when exposed to the air it efflo resces slowly and slightly : when heated, it swells, loses about four-tenths of its weight, becomes ropy, and then assumes the form of a light, porous, and very fria ble mass, known by the name of calcined borax ; in a strong heat it melts into a transparent glass, still soluble in water. When two pieces of borax are struck to gether in the dark, a flash of light is emit ted. This salt, according to Bergman, is
composed of Acid . . . 39 Soda . . . 17 Water . . . 44 100 Though borax has been in common use for nearly three centuries, it was only in 1702 that Homberg, by distilling a mix ture of borax and green vitriol, discover ed the boracic acid. He called it narco tic or sedative salt, from a notion of his that it possessed the properties indicated by these names. Geoffroy afterwards dis covered, that borax contained soda ; and, at last, Baron proved, by a number of ex periments, that borax is composed of bo racic acid and soda ; that it may be re produced by combining these two sub stances ; and that therefore the boracic acid is not formed during the decompo sition of borax, as former chemists had imagined, but is a peculiar substance, which pre-existed in that salt. This acid, for purposes of experiment, is obtained from the purified borax of commerce, by one of the following processes : 1. To a solution of borax in boiling water, add half its weight of sulphuric acid, previ ously diluted with an equal quantity of water. Evaporate the solution a little ; and on cooling, shining, scaly crystals will appear, which consist of boracic acid. Let them be well washed with distilled water, and dried on filtering paper. 2. Let any quantity of borax be put into a retort, with half its weight of sulphuric acid, and half its weight of water. Bo racic acid may be obtained by distillation, and may be purified by washing in water, as before. Boracic acid has the fol lowing qualities : 1. It has a solid form, is destitute of smell, and nearly so of taste : 2. It fuses, when heated, and loses its water of crystallization. If the heat be increased suddenly, before it has lost its water of crystallization, it sublimes ; but, otherwise, it melts into a glass, which is permanent in the strongest fire : 3. It is soluble in twelve parts of cold water, and in three or four of boiling water : 4. This solution reddens vegetable blue co lours, and effervesces with alkaline car bonates: 5. It is soluble in alcohol, and the solution burns with a beautiful green flame : 6. It combines with alkalies and earths ; but the only important combina tion which it forms is with soda.