The presence of boric acid or its salts has been noted in sea-water, whilst it is also said to exist in plants and especially in almost all fruits (A.
Artificial soffioni are sometimes prepared by boring through the rock until the fissures are reached, and the water so obtained is occasionally sufficiently impregnated with boric acid to be evaporated directly.
The specific effect of boric acid in this respect was correctly ascertained by Stokes and Harcourt, but they mistook the effect of titanic acid.
The chief source of boric acid for commercial purposes is the Maremma of Tuscany, an extensive and desolate tract of country over which jets of vapour and heated gases (soffioni) and springs of boiling water spurt out from chasms and fissures.
Boron can be estimated by precipitation as potassium fluoborate, which is insoluble in a mixture of potassium acetate and alcohol, For this purpose only boric acid or its potassium salt must be present; and to ensure this, the borate can be distilled with sulphuric acid and methyl alcohol and the volatile ester absorbed in potash.
It combines directly with ammonia to form the compound SiF 4 2NH,, and is absorbed by dry boric acid and by many metallic oxides.
The residue is then heated in a current of superheated steam, in which the boric acid volatilizes and distils over.
The supply of borax is, however, mainly derived from the boric acid of Tuscany, which is fused in a reverberatory furnace with half its weight of sodium carbonate, and the mass after cooling is extracted with warm water.
After fusion the mass solidifies to a transparent vitreous solid which dissolves readily in water to form boric acid (q.v.); it is exceedingly hygroscopic and even on standing in moist air becomes opaque through absorption of water and formation of boric acid.
It forms slightly coloured small crystals possessing a strong disagreeable smell, and is rapidly decomposed by water with the formation of boric acid and sulphuretted hydrogen.