It is added by Dr. Bancroft, that “when sulphate of iron is mixed with aquafortis, the latter undergoes a decomposition; the oxygen of the nitric acid combining with the iron, and raising it to a much higher degree of oxidation; the result of these operations is the production of a fluid which has the consistence and smooth appearance of oil, and which (though the name may not be quite unexceptionable) I will call a nitro-sulphate of iron. I have been induced to believe, from several trials, that a better prosubstantive black than any other within my knowledge may be formed, by taking a decoction, containing in each gallon the soluble matter of two pounds of the best galls, in sorts, and when cold, adding to it for each gallon twelve ounces of sulphate of iron, which had been previously mixed with half its weight of single aquafortis, (of which one wine pint should weigh about twenty ounces,) and, by the decomposition just described, converted to the nitro-sulphate of iron just mentioned. By thus employing twelve ounces of sulphate of iron, oxygenated by nitric acid, instead of six ounces of the latter, with six ounces of the green sulphate in its ordinary state, an improvement in the colour seems, by my experiments, to have been invariably produced, and without any corroding or hurtful action upon the fibres of the cotton.”
With these scientific receipts and suggestions it may be agreeable to close. Matters of this kind have not been before introduced, nor is it purposed to repeat them; and those who think they are out of place at present, may be asked to recollect whether any of themselves ever obtained knowledge of any kind that, at some period or other, did not come into use?
NATURALISTS’ CALENDAR.
Mean Temperature 40·72.
[68] Gentleman’s Magazine.
[69] Beckmann.
[70] Fosbroke’s Dict. of Antiquities. Beckmann.