Persulphomolybdates
:
ON THE PRIMARY, RED.
The metallic compounds formed by the combination of persulphomolybdic
acid with a base are pulverulent, in many cases of a red colour, and for
the most part insoluble in water. With barium, the acid furnishes a
yellowish-red powder, insoluble in, but made denser by water, which
imparts to it a cinnabar colour. With calcium it is said to yield a
scarlet, sparingly soluble in water. With chromium, uranium, lead,
platinum
and copper, it gives a dark red; that from the last metal
turning brown when collected on a filter. It likewise produces reds with
zinc, cadmium, iron, mercury, and tin; of which the last is slightly
soluble in water.
Molybdenum being a rare metal, and persulphomolybdate of potash, the
salt used in the foregoing reactions, difficult to prepare, it is
unlikely that the colours named will rank among the pigments of this
generation. Nevertheless, as we have observed before, such fancy
products should not be altogether ignored, it being quite as well to
have some knowledge of our resources, even though those resources be not
at present available. All the rare metals afford coloured compounds:
tantalum, niobium, pelopium, vanadium, tellurium, titanium, yttrium,
lanthanum, didymium, glucinum, cerium, thorinum, zirconium, palladium,
rhodium, iridium, ruthenium, osmium, indium, thallium, &c.; and it is
just possible that some of these may one day scrape acquaintance with
the palette.