Persulphomolybdates





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.





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