A crystalline form was obtained by Debray as olive-green prisms by igniting a mixture of sodium tungstate and carbonate in a current of hydrochloric acid gas, and by Nordenskjold by heating hydrated tungstic acid with borax.
Of an olive-green above, deeply tinted in some parts with black and in others lightened by yellow, and beneath of a yellowish-white again marked with black, the male of this species has at least a becoming if not a brilliant garb, and possesses a song that is not unmelodious, though the resemblance of some of its notes to the running-down of a piece of clockwork is more remarkable than pleasing.
It is more hygroscopic than the tetrachloride; and when treated with much water the bulk is at once decomposed into the blue oxide and hydrochloric acid, but an olive-green solution is also produced.
Brown or even blood-red stripes have been observed in the North Atlantic when swarms of the copepod Calanus finmarchicus were present; the brown alga Trichodesmium erythraeum, as its name suggests, can change the blue of the tropical seas to red; swarms of diatoms may produce olive-green patches in the ocean, while some other forms of minute life have at times been observed to give the colour of milk to large stretches of the ocean surface.
Copper quadrantoxide, Cu 4 0, is an olive-green powder formed by mixing well-cooled solutions of copper sulphate and alkaline stannous chloride.