Boracic acid forms two salts with soda; the borate, properly so called, and borax. It is supposed to be our borax, that Pliny mentions under the name _crysocolla_, so called by the ancients. Others, however, assert, that their crysocolla was nothing more than the rust of copper, triturated with urine. The impure borax in the East Indies, is called _tincal_. When borax is melted, and exposed for some time to heat, it loses its water, and is changed into what is known by the name of _calcined borax_. The easiest process for obtaining boracic acid is to make a concentrated solution of borax in hot water, and add by degrees, sulphuric acid, which will unite with the soda; and, as the fluid cools, the boracic acid will separate in shining laminated crystals. No more acid should be added than is sufficient to make the solution slightly sour. The crystals are to be washed with cold water, and drained upon brown paper. One of the principal characters of boracic acid is, that it is very soluble in alcohol, to the flame of which it communicates a green colour. Paper dipped in this solution, burns in the same manner. In consequence of this property of imparting a green colour to flame, I made some experiments with it, for the purpose of preparing _green fire_; and found, that, by employing it in the proportion of one-eighth, the flame was always green, provided that the flame of the combustible used, was not tinged of any other colour. Nitre, charcoal, and boracic acid will give a green; also nitre, lamp oil, and boracic acid; nitre, alcohol, and boracic acid, along with charcoal; and chlorate of potassa, charcoal, and boracic acid, with or without the addition of alcohol. But, although boracic acid communicates a lively green, its expense will prevent its use in that way, especially as many other preparations, as those of copper, will have the same effect, and are more economical on account of their price. See the _Coloured Flame of Alcohol, and Coloured Fire_. Oils, when assisted by heat, will dissolve boracic acid. In naphtha, it is very soluble. With oils, it yields fluid and solid products, which give a green colour to the flame of alcohol. It is not a combustible acid, but only imparts colour to the flame of combustible bodies. Boron will unite with fluorine, the radical of fluoric acid. When one part of vitrified boracic acid, two of fluate of lime or fluor spar, and twelve of sulphuric acid are distilled, an acid gas will be obtained, called fluo-boric gas. For the properties of boron, consult Thenard's _Traité de Chimie_. PART II. INSTRUMENTS, TOOLS, AND UTENSILS. CHAPTER I. OF THE LABORATORY.