Very Slight Solubility In Water Would Be A Fatal Objection; And





although they would be liable to suffer from a foul atmosphere, we are

inclined to think the effects would not be so lasting as in the

chromates of lead. Like lead sulphide, the sulphide of thallium ranges

from brown to brownish-black, or grey-black; and, like it too, is

subject to oxidation and consequent conversion into colourless sulphate.

It is, however, much more readily oxidized than sulphate of lead; and

hence the thallium chromates would doubtless soon regain their former

hue on exposure to a strong light.



Mr. Crookes, who discovered this new metal in 1861, believes that the

deep orange shade observable in some specimens of sulphide of cadmium is

due to the presence of thallium. He has frequently found it, he says, in

the dark-coloured varieties, and considers the variations of colour in

cadmium sulphide to be owing to traces of thallium. That thallium

affects the colour is most probable, but it is not necessarily the cause

of the orange hue. The tint of cadmium sulphide is a mere matter of

manufacture, seeing that from the same sample of metal there can be

obtained lemon-yellow, pale yellow, deep yellow, orange-yellow, and

orange-red. With deference to the opinion of a chemist so distinguished,

we hold that thallium rather impairs the beauty of cadmium sulphide than

imparts to it an orange shade, the thallium being likewise in the form

of sulphide, and therefore more or less black. On chromate of cadmium,

made with bichromate of potash, thallium would naturally confer an

orange hue.





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