The other method consists in the introduction into the paper during its manufacture of some substance or mixture of substances which
shall strike a characteristic colour when chemical agents are applied to the ink.
One of the earliest attempts of this kind was that of Stephenson, who introduced ferrocyanide of potassium into the pulp. When any acid was applied to the writing, Prussian blue was formed with the aid of the iron of the ink. In another process iodide of potassium and starch were introduced into the paper, the application of chlorine then producing a blue stain (iodide of starch), while in a third (Robson’s) the pulp was stained with the ingredients of common writing ink.
None of these methods gave, however, any very efficient protection against fraud, for in each case it was tolerably easy to restore the paper to its original condition. But another process which followed upon the others has proved more successful, and, when properly applied, gives a paper which is practically secure. This process was patented by Barclay, and consists in the introduction into the pulp of ferrocyanide of manganese. When any acid is applied to the writing on this paper the blue stain of Prussian blue appears. This can, it is true, be removed by alkalies, but in that case the manganese is precipitated as the brown peroxide, an effect also produced by bleaching powder. This brown stain can be removed by sulphurous acid, but in that case Prussian blue appears simultaneously, so that the forger has merely a choice between a brown and a blue stain.
When such paper is printed with a delicate design in some fugitive ink (common writing ink would be best), the greatest attainable safety is obtained.
Ferrocyanide of manganese is easily formed by adding to the pulp pure crystallised chloride of manganese, and rather more than an equal weight of ferrocyanide of potassium, both in solution. (Heaton.)
Paper, Ra′′zor. Smooth unsized paper, one of the surfaces of which, whilst in a slightly damp state, has been rubbed over with a mixture of calcined peroxide of iron and emery, both in impalpable powder. It is cut up into pieces (about 5 × 3 inches), and sold in packets. Used to wipe the razor on, which thus does not require stropping.
Paper, Razor-strop. From emery and quartz (both in impalpable powder), and paper pulp (estimated in the dry state), equal parts, made into sheets of the thickness of drawing paper, by the ordinary process. For use, a piece is pasted on the strop and moistened with a little oil.
Paper, Re′sin. Syn. Poor-man’s plaster; Charta resinosa, L. Prep. 1. Beeswax, 1 oz.; tar and resin, of each, 3 oz.; melted together and spread on paper.
2. (Ph. Bor.) Paper thinly spread over with black pitch. Calefacient, stimulant, and counter-irritant; in rheumatism, chest affections,