Preparation of Blue Ink.

Scientific American 25, 17.12.1864

Prussian blue dissolves in oxalic acid, giving a dark blue limpid liquid. This interesting discovery of MM. Stephen and Rasch, patented in England in 1837, is of great interest in tinctorial chemistry, as by its means Prussian blue may be very simply used in the form of a solution. To dissolve commercial Prussian blue in oxalic acid, first mix the blue with concentrated hydrochloric or sulphuric acid, then add an equal weight of water, leave to digest for forty-eight hours, then carefully extract all the acid by repeated washings. This process being minute and tedious, it is better to employ recently-precipitated Prussian blue, which does not need the previous treatment by a concentrated acid.

By the following process Vogel has always obtained a good solid blue ink with Prussian blue and oxalic acid:—

Dissolve in a matrass, in a large quantity of water, ten grammes of sulphate of protoxide of iron; boil, and then add sufficient nitric acid to sesquioxidise all the iron. Then add a solution of yellow prussiate of potash containing ten grammes of this salt, and leave the precipitate to deposit. After decanting the supernatant liquid, throw the deposit on a filter, wash with cold water, and leave it to drain until it can be easily raised from the filter with a knife; then, without further dryness, mix it in a porcelain mortar with two grammes of oxalic acid in crystals. Let the reaction continue for an hour, then gradually add 400 cubic centimetres of water. A dark blue solution is thus obtained, in which even after long standing no precipitate is to be found. This blue ink will not bear the least addition of black gall-nut ink; it is even advisable not to use a pen retaining a particle of this black ink.

- Moniteur Scientifique, vi, 666, 64.

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