Many attempts have been made to pioduce an ink which cannot be removed by chemical means, and the most satisfactory ink has been found to be a solution of Chinese (or so-called Indian) ink in acidulated or alkaline water. Hydrochloric acid is used for the acid solution, and caustic soda for the alkaline water. With steel pens only the alkaline may be used. Indian ink is a preparation of carbon in a very fine state of division, and is not affected by any chemical. Another indelible ink is made thus: Saturate boiling water with borax, and add as much brown lie gum as it will dissolve, and then add lampblack. This ink dries with a gloss. An indelible aniline ink may be made by rubbing 60 gr. of aniline black with 60 drops of strong hydrochloric acid and 1 oz. of alcohol. Dilute this blue liquid with 3oz. of water in which 3/4 oz. of gum has been dissolved. Or mix lampblack with a solution of 5 parts (by weight) of lac and 1 part of borax in sufficient water. Impulse Indian ink (by analysis) contains much animal glue, therefore if a small quantity of bichromate of potash be added to it, after being exposed for one hour to sunlight it should prove indelible. Another, mix together 3 oz. of pulverised verdigris, 6oz. of sal-ammoniac, 2oz. of lampblack, and 35 oz. of water.

Shake well before using. Hausmann's indelible ink is said to be made by mixing 1 part of Trinidad asphaltum with 4 parts oil of turpentine and sufficient colouring matter - plumbago for black and vermilion for red. This is said to be the recipe for Close's indestructible ink: Mix 25 gr. of powdered cobalt with 200 gr. of oil of lavender; for blue-black ink colour with 3gr. of lampblack, and for a red ink with sufficient vermilion. To make Gaffard'sindelible ink, mix together 1 part of lampblack, 12 parts of potash water glass of the consistency of syrup, 1 part of aqua ammonia, and 3S parts of distilled water. For indelible marking ink, take 1/2oz. of any pigment used in making ticket inks and 1 dr. of salts of steel; mix with linseed oil to the proper consistency. Use with pen or metal stamp (not rubber). Indelible ink for glass or metal is made by boiling under cover borax 1 oz., shellac 2oz., and water 18 oz. (fluid). Colour with lampblack and levigated indigo, and in two hours drain off and bottle. In certain safety papers, which have been invented, the object has been to introduce into the paper a chemical which should yield a black compound in contact with the ink. By Bellande's patented process, calomel, or a salt of iron, copper, or lead is combined with the paper.

Calomel is preferable. If combined with the pulp, 25 per cent, by weight of calomel is added; if fixed to the surface of the paper by gums or gelatines only 4 per cent, of calomel is necessary. The ink used is 1 part of prussiate of potash and 1 part of hyposulphite of soda in 23 parts of thin gum solution.