By the fusion of potassium bichromate with boric acid, and extraction of the melt with water, a residue is left which possesses a fine green colour, and is used as a pigment under the name of Guignet's green.
The boron contained in solution in the salt lakes has very probably been supplied by hot springs and solfataras of volcanic origin, such as those which at the present day charge the waters of the lagoons in Tuscany with boric acid.
O, which, in turn, when boiled with a solution of boric acid, gives PbB407.4H20.
A high silica-content tends towards both hardness and chemical stability, and this can be further increased by the addition of small proportions of boric acid; in larger quantities, however, the latter constituent produces the opposite effect.
It combines directly with ammonia to form the compound SiF 4 2NH,, and is absorbed by dry boric acid and by many metallic oxides.
Kiihne (D.R.P. 147,871) described a process in which external heating is not necessary, a mixture of aluminium turnings, sulphur and boric acid being ignited by a hot iron rod, the resulting aluminium sulphide, formed as a by-product, being decomposed by water.
The specific effect of boric acid in this respect was correctly ascertained by Stokes and Harcourt, but they mistook the effect of titanic acid.
Raschig (Be y ., 1908, 4 1, p. 4 1 94) as a highly explosive colourless gas on acidifying a mixture of sodium azide and hypochlorite with acetic or boric acid.
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.
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.