These are intended for use in cheques, vouchers, and other valuable documents, the object being to prevent tampering with the writing, and expose any such attempt if made. The following recipes have been published: - (1) An ink that cannot be erased, even with acids, is obtained by the following: To good gall ink, add a strong so1 ition of fine soluble Prussian blue in distilled water. This addition makes the ink, which was pre-viously proof against alkalies, equally, proof against acids, and forms a. writing fluid which cannot be erased without destruction of the paper. The ink writes greenish blue, but afterwards turns black. (Pharmacist.) (2) Mathieu Plessy, who has long manufactured a peculiar ink much used in France, has taken out a patent for the application of organic matter and a chemical substance which, when united. in, the ink,, can be converted into carbon by the. application of heat not sufficient to destroy the paper, parchment, or other substance on which it is used. The inventor claims to use any organic matter soluble in water or any other vehicle, such as cane sugar, caramel, glucose, or any of the vegetable substances which; give glucose by reaction, such as sugar of milk.

To accelerate the carbonisation, with heat, of the above substances, acid or neutral salts with alkaline earthy bases, or metallic oxides which do not affect the paper or parchment, or other similar substances, are employed. The heat of a hot-air stove at. a temperature between 230° and 237° F. (110° to 114° C), a plate of heated metal, or a hot iron, may be employed for the carbonisation, according to circumstances. (3) A very little quantity of aniline black triturated with a mixture of alcohol and hydrochloric acid, and the liquid obtained diluted with about twice its weight of water containing a trace of gum-arabic, gives an ink which proves indestructible alike with respect to strong mineral acids and towards concentrated lyes. (Bayer. Ind.- und Gew. Blatt.) (4) Dissolve 25 gr. of gum copal powder in 200 gr. of lavender oil by the aid of a gentle heat; then add 2 1/2 gr. of lampblack and 1/2 gr. of powdered indigo. To be applied to paper with a quill pen. (5) Eisner prepares an ink which resists the action of bleaching agents, thus: - Take equal parts of copperas and vermilion, powder thoroughly, sift, and grind the finest portions with linseed-oil; finally squeeze through linen.

A thick paste is thus obtained, which can be used either for writing or printing on calico or wool. (Les Mondes.) (6) Bdttger prepares an ink that does not corrode steel-pens by triturating 3.65 gr. of aniline black with 22 gr. of alcohol, and 4 drops of hydrochloric acid; a porcelain mortar is employed, and the paste thus produced is mixed with 1.82 gr. of gum-arabic previously dissolved in 85 gr. of hot water. If this ink be added to an alcoholic solution of shellac (21 gr. of lac to 85 of alcohol), a black product results, suitable for colouring leather and wood. (Dingler's Polytech. Jl.) (7) If the ink is to be used for writing or drawing, and there is no danger of the letters, etc., being rubbed off mechanically, printing-ink or Indian ink may be used. (8) Printing-ink sinks into woven fabrics to a considerable depth, and will last a long time. It is probably one of the cheapest marking-inks to be used with stencils. (9) In many cases Indian ink answers as well, and in some cases, as for engrossing valuable documents, it is the only safe ink, since nothing but the destruction of the document itself will be able to obliterate it.

It is made by triturating 100 gr. of best Indian ink (Chinese) with very dilute hydrochloric acid (about 22 parts of absolute hydrochloric acid in 1000 parts), or with a solution of acetate of manganese in diluted acetic acid. (10) Another fine indelible ink, which resists all ordinary reagents, is made by means of vanadium. Vanadium and its salts are rather expensive still, although their price has fallen during the last few years to about one-tenth of what it was formerly. (11) An indelible aniline ink may be made thus: 100 gr. of hydrochlorate of aniline and 60 gr. of chlorate of sodium are dissolved in 3 1/2 oz. of water, and 1/2 gr. of vanadate of ammonium added to the liquid, when it will soon become dark-coloured, and deposit an abundant precipitate of aniline black. This may be dried, made into a paste with powdered acacia, water, and glycerine, and used with a stencil. (12) 1 part of pyro-galiic acid is triturated with 3 parts of powdered acacia, 3 parts of vanadate of ammonium, and a sufficient quantity of cold distilled water, in a porcelain capsule, until a uniform mixture is made. This forms a fine ink, flowing black from the pen.

This may also be made into a stencil ink by using less water and adding a little glycerine. (13) A composition prepared by mixing well triturated carbon with an alkaline silicate (potash or soda), the following proportions answering well: - lampblack, 1 part; syrupy silicate solution, 12; ammonia liquor, 1; distilled water, 38. (14) (a) 1 lb. extract of logwood, 1 gal. water; (6) 4 oz. sulphate of protoxide of iron, 4 oz. water; (c) 1/4 oz. potassium sulphide, 2 oz. water. After dissolving the logwood by boiling, add (c) to (6), until the iron assumes a black colour; then add this compound to (a), and boil a few minutes; add 1/2 oz. potassium cyanide, which fixes the colour; for ink, add gum and alcohol (15) Take 1 1/2 part by measure of a cold saturated aqueous solution of cupric chloride, saturated at 59° F. (15° C); 20 parte by measure of a cold saturated aqueous solution of chloride of aniline; 20 parts by measure of water; 50 parts by measure of an aqueous solution of gum-arabic (1 part by weight of gum-arabic to 2 of water) at 59° F. (15° C.); 2 parts by measure of glycerine; and some finely-powdered potassium chlorate.

In mixing the ingredients, it is preferable to add the solution of chloride of aniline to that of cupric chloride first, and the other ingredients in the order named; then, when the whole has been well shaken, to add powdered potassium chlorate in sufficient quantity to saturate, at 59° F. (15° C), the compound solution so formed. After writing, the ink is at first slate-coloured, but on warming gently it becomes black. All the solutions are to be made at 59° F. (15° C), that is, practically, the average temperature.

H. and W. S. Richmond, of New York, supply indelible cancelling inks, well adapted for marking postage and other stamps; they can, by suitable dilution, be used for legal, commercial, and other writings, in which permanency of the ink is of importance. The inks consist of the following ingredients, namely: - Eosine, aniline black, aniline blue, cu-pric chloride, sodium chlorate, ammonium chloride (sal-ammoniac), glycerine, lampblack, water, and oil. These sab-stances are taken in the following proportions: - Eosine, 1 part; aniline black, 4; aniline blue, 2; cupric chloride, 1; ammonium chloride, 3; sodium chlorate, 2; and of the remaining ingredients a sufficient quantity to bring the ink to the proper consistency for the use for which it is intended. The ingredients are thoroughly incorporated by grinding or stirring, when the composition is ready for use. The ink described is absolutely indelible. Stamps cancelled therewith are effectually destroyed,- and the fraudulent alteration of matter written therewith is impossible. The rationale of the operation of the ink is as follows: - Besides having as an ingredient aniline black, it embodies also the substances necessary to produce that colour - to wit, an aniline, an oxidizing agent, and a cupric salt.

The reaction of these substances is, however, retarded by the oil, which also forms a part of the ink. As a consequence, the aniline black, which is a product of the reaction of the ingredients of the ink, is partly formed within the body of the stamp paper. In preparing the composition for ordinary writing-ink, the oil and lampblack are preferably omitted, a small portion of gum-arabic being added in their stead, the latter subserving the same end as the oil. To prevent moulding, a small proportion of some antiseptic agent, such as salicylic acid, may also be added. The novelty consists essentially in such a compound as contains the ingredients for forming aniline black, and for retarding the reaction sufficiently to defer its completion until after the ink shall have been applied to the paper or surface upon which it is to be used.