Ultramarine Red?





In Gmelin's Handbook of Chemistry it is remarked that "Hydrogen gas

passed over ignited ultramarine, colours it light red, from formation of

liver of sulphur, hydrosulphuric acid gas and water being evolved at the

same time." On most carefully making the experiment with a sample of

native blue (the variety referred to) we did not succeed in effecting

this change: no alteration to red or even to purple took place, the only

result being that the colour was entirely spoilt, having assumed a

leaden slate-gray hue. At our request, the trial was kindly repeated by

well-known chemists, who took every precaution to ensure success.

Several specimens of ultramarine were acted upon, but in no case was a

red or anything like a red obtained, the products ranging from a

slate-gray to a drab-grey. Sufficient hydrosulphuric acid gas was

evolved to blacken paper moistened with acetate of lead, a fact which

proved that the blue had lost some of its sulphur. Seeing that not only

no red was produced, but that no tendency to red was imparted, is it

possible the change described by Gmelin occurred under exceptional

circumstances? All conversant with chemical matters will admit that

results are obtained occasionally which cannot be repeated, owing it may

be to some slight difference in the materials employed, or some slight

variation of the process. Perhaps a link, considered of no importance

at the time and overlooked, has been lost, and thus the whole chain of

proceeding becomes useless. It is, therefore, within the bounds of

probability that the red ultramarine of the great German chemist was

furnished either by a peculiar specimen of blue, or by a modified form

of the method he gives. We have noticed the subject at some length

because if a red ultramarine, brilliant and durable, could be obtained,

the colour might prove of value. A permanent artificial compound

corresponding to French blue would certainly be an acquisition.





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