deposited on the cooling of the solution. To purify the acid, it is first washed with cold water, in which it is but sparingly soluble, and then dissolved in boiling water, and made to crystallize afresh. The boracic acid thus obtained is sufficiently pure for most of the purposes to which it is applied, but it retains a trace of sulphuric acid, probably in a state of chemical combination. This small quantity of sulphuric acid may be separated, if necessary, by fusing the boracic acid in a platinum crucible at a red heat.

Boracic acid is inodorous, and has a weak taste scarcely at all acid. In aqueous solution it is one of the feeblest of acids; instead of changing the colour of blue litmus to that clear red produced by the strong acids, it imparts a wine-red tint similar to what is communicated by carbonic acid, and its combinations with the alkalies retain alkaline characters, though they contain an excess of boracic acid. But at a red heat this acid seems to possess a very powerful affinity for bases; it then displaces the greater number of those acids which are more volatile than itself, from their saline combinations, an effect referable to the great fixedness of boracic acid when in the anhydrous condition. When unmixed with any volatile substances, boracic acid is perfectly fixed at a bright red or even white heat; but it is remarkable, that in the presence of the vapour of water or of alcohol this acid is certainly capable of volatilizing to a considerable extent, and may be condensed in small sparkling crystals. In the original process for the preparation of this acid, instead of crystallizing it from a solution of borax mixed with oil of vitriol, such a mixture was distilled in a retort, in the neck

of which the acid was collected in small crystals. The acid prepared by this and similar processes was long ago employed in medicine under the names of Homberg's sedative salt, Sal volatile narcoticum, Flores boracis, Sal album alchymistarum, &c. Neumann seems to have been the first who prepared boracic acid without distillation.

Anhydrous boracic acid melts under a red heat into a colourless and transparent glass, which is still soluble in water. The specific gravity of the vitrified acid is 1.83, and of the crystallized acid 1·48. The crystallized acid requires 25.66 times its weight of water at 60° for its solution, but only 2.97 times at 212° (Berzelius). Boracic acid is soluble in alcohol, and the solution when set on fire burns with a fine green flame; a property which affords an excellent test for the presence of this acid. The alcoholic solution of boracic acid communicates a brown colour to yellow turmeric paper, like an alkali, and the colour becomes deeper as the alcohol evaporates.

The constitution of boracic acid was first ascertained by Sir H. Davy in the year 1807. By exposing it to the action of a powerful galvanic battery he obtained a small quantity of a greenish-brown powder, which burned vividly when heated in atmospheric air or oxygen gas, and then returned to the state of boracic acid. Boracic acid is hence viewed as a combination of oxygen with the above substance, which is regarded as an element, and called boron. MM. Gay-Lussac and Thenard prepared boron by heating boracic acid with potassium, when the latter sepa

rates oxygen from the former, and sets the boron at liberty. The easiest method of preparing this substance is to decompose by means of potassium the salt called borofluoride of potassium, which is a combination of fluoride of potassium with fluoride of boron. When that substance is heated with potassium, the fluoride of boron is decomposed, with production of fluoride of potassium and consequent liberation of boron.

Boron is a tasteless and inodorous substance, insoluble in water, alcohol, ether, and oils. It It may be heated in vacuo, or in gases which do not combine with it, without undergoing any change, except a slight deepening of colour and increase of density. It is devoid of the metallic lustre, and is a nonconductor of electricity. At common temperatures it undergoes no change by exposure to atmospheric air or oxygen; but if heated to 600° Fahr., it burns with brilliant scintillations, and forms boracic acid, which is the only known combination of boron and oxygen. The generally received equivalent number of boron is 11. Its symbol is B.

When boron passes into the state of boracic acid, it unites with a quantity of oxygen equal to 68.6 per cent. of the product, which is considered to contain three equivalents of oxygen and one of boron, thus (B+0,); in which case, the equivalent of anhydrous boracic acid is 35, or one equivalent of boron = 11 +three equivalents of oxygen = 24. The boracic acid deposited in crystals from an aqueous solution is a hydrate containing 43.5 per cent., or three equivalents of water.

Boracic acid is found in nature not only in combination with soda, and to a small extent with some earthy bases, but likewise in a free state, constituting in that form a very abundant, interesting, and highly important volcanic product. It is found in the Lipari Islands, but most abundantly in the hot springs of a small district in Tuscany, the boracic lagoons of which have now become the common European source of borax. These lagoons or lakes may be ranked among the wonders of the age, and are unique in Europe, if not in the world. They are situated on the sides of hills, and are supplied with water by the condensation in them of volcanic vapours or soffioni, highly charged with free boracic acid, together with borate and sulphate of ammonia, and several other saline matters. The soil surrounding these beds of hot water is covered with a saline efflorescence, consisting chiefly of boracic acid, but likewise containing, in smaller proportion, ammoniacal salts, borate and sulphate of alumina, and persulphate of iron.

presence

The of boracic acid in these vapours was first announced by Hoefer in the year 1776, and the manufacture of borax from this source was suggested about the same time by Mascagni. It was not attempted, however, till several years afterwards. Some experiments performed by Professor Gazzeri, in 1807, tended to shew that the quantity of boracic acid contained in the lagoons was too small to render them an advantageous source of borax; and this was afterwards fully proved to be the case, when the water, as found in the lagoons, was evaporated by heat obtained artificially in the ordinary manner. A

succession of adventurers had in this way produced a considerable quantity of boracic acid, but the cost of fuel for the evaporation was so great as to leave but little profit; so that the lagoons, now a source of wealth, "more valuable, perhaps, and certainly less capricious, than any mine of silver that Mexico or Peru possesses, were formerly considered all but worthless. Important improvements were, however, gradually introduced; one of the earliest of which was the subjecting the same quantity of water to successive impregnations of vapour, so as to increase the proportion of boracic acid. This improvement was made by Signor Ciaschi, who perished miserably in 1816, from having fallen into a lagoon of his own excavation. In the following year the lagoons came into the possession of their present spirited proprietor, the Count de Pomerance (better known as M. Larderelle), who conceived the happy idea of abandoning the use of wood-fuel in the evaporation of the waters, and applying the heat of the superabundant vapour itself. This is the grand improvement which has given the boracic lagoons of Tuscany their present importance.

Without the assistance of fuel, machines, or chemical materials, a produce of seven hundred and fifty thousand kilogrammes (a little more than one million six hundred and fifty thousand pounds) of boracic acid is obtained yearly with an evaporation of more than eighty millions of kilogrammes of water; and all this is effected merely by giving a proper direction to the vapours of the soffioni themselves. For the following account of the lagoons I am

* Dr. Bowring.