Journal of the Society of Arts 267, 1.1.1857
Sir, - As Mr. Underwood, in his paper on the "History and Chemistry of Writing Ink, &c.," read before the Society on the 16th December, did not mention that we are indebted to M. Runge for the intervention of a writing ink made with chromate of potash and decoction of logwood, which combination appears to be the nolvety in the ink introduced to the notice of teh meeting, I trust that in supplying the omission, I shall not be trespassing on the pages of your Journal; and I send you for insertion M. Runge's receipt, copied from the Chemical Gazette for 1849, page 108.
"A most excellent ink for steel pens is obtained by exhausting ten parts of logwood with a sufficient quantity of boiling water to obtain 80 parts of liquid. To [] thousand parts of this decoction is now gradually added one part of yellow chromate of potash, when the liquid turns dirst reddish-brown and finally blueish.black. No gum or any other addition is requisite; on the contrary, they are injurious. This liquid is an actual solution, which may be filtered. No deposit is formed in it, and the writing is not removed by immersing the paper in water. Digler's Polyt. Journal, c. ix, page 227."
I am, &c., B WINSTONE.
----
Sir, - In the report of the discussion which took place after the reading of Mr. Underwood's paper, the reporter has misunderstood the purport of what I stated.
The observations I made applied to the ferro-prussia, and not to the indigo blue, as he represents. It is very unfortunate that these two colours, so different in their chemical constituents, should always get confounded in the public mind, as is evidenced by the observations of Mr. Pearsall, reported in your Journal, who says that, having found that blue ink was obliterated from the accidental spilling of water over a sheet written upon with it, it had determined him against using it in future. It is in this way that prejudices are created and perpetuated, for if Mr. Pearsall had ascertained what sort of blue ink he had been using, he would have found that it was indigo, and not prussian blue, as he imagined. The one indigo, in the form long used for ruling and private marking, being a very soluble composition, and the other prussian blue, being one of the most fixed and durable colours, the writing from which bears soaking in water, in chlorine, and acids for a number of years, without parting with any of its colouring matters.
Having tested the surability of the solution of prussian blue, by using it on wood tickets for distinguishing the variations of plants and flowers in gardens, as well as soaking it in solutions of chlorine and acids, I feel desirous to prevent, as far as I can, the perpetuation of prejudices which have no foundation beyond the mistake that is made by confounding the blue colour from indigo with that from prussian blue, and making the latter responsible for all the failings of the former colour.
I drew a sketch of the comparative permanence of the blue ink (prussian blue I mean) and that from the galls and iron, which your reporter has missed in his report. The following is the purport of what I said: - The inherent tendency of iron to pass from the state of a protoxide to that of per-oxide, is the main cause of the destruction of colour in the black ink. The iron in the ink, under the influence of moisture, absorbs oxygen, and gradually destroys the vegetable matter with which it is combined, leaving the writing a sort of iron mould upon the paper, in which state it is seen in old records and in writings that have been exposed to damp. The reverse of this takes place with blue ink made with the ferro-prussiate. The tendency of the iron to absorb oxygen increases the intensity and durability of the blue colour; thus the cause that leads to destruction in the one case, gives increased colour and permanence in the other.
I am, &c.,
Henry Stephens.
Ei kommentteja :
Lähetä kommentti