To prepare litmus-paper, rub good litmus with a little hot water in a mortar, and pour the mixture into an evaporating basin; add water until the proportion is 1/2 pint water to 1 oz. litmus; cover up so as to keep warm for an hour, after which the liquid must be filtered, and fresh hot water poured on the residue. This is boiled, covered up as before, and allowed to stand. The operation is repeated a second time, and if much colour comes, a third time. The first solution is kept separate from the second and third, which may be mixed together. The first will not require evaporation, but the others may be so far reduced in quantity that when a piece of blotting- or filtering-paper is dipped into them and dried, they will impart to it a blue colour of sufficient intensity for use. The paper is then dipped in the solution. The paper - blotting will suit very well - should always be unsized, of good colour, and moderate thickness, say 15 to 20 lb. demy, and cut into pieces of a convenient size for dipping. Particular care should be taken to use paper as free as possible from earthy matter, and especially from carbonate of lime. Sized papers produce a finer tint on the surface, but are not so delicate as a test.
Pour the litmus solution into a plate, and draw the slips of paper through it in such a manner that the fluid will come into contact with both sides; allow it to drip, then hang them across two thread lines to dry. The tint ought to be a distinct blue, and may be tested as to its delicacy by touching the paper with a very dilute acid, observing whether the red colour produced is vivid or not. It should, when dry, be tied up into bundles, and preserved from the air and light. A wide-necked glass-stoppered bottle is best suited for the purpose. Put in the test-papers, and paste round the sides of the bottle a piece of dark paper to exclude the light, as both air and light tend to destroy the colour and efficacy of the test-paper.
This is prepared in a manner similar to litmus-paper. A hot infusion of finely-crushed turmeric is made by boiling 1 oz. turmeric in 12 oz. water for 1/2 hour; strain through a fine cloth or silk bag, and leave the fluid to settle for a few minutes. The liquid should he of such strength that paper dipped into it and then dried will have a fine yellow colour. The paper should be of the same quality in erery respect as for litmus-paper. No particular care is necessary in drying, as with litmus-paper; but both papers should be prepared where acid and alkaline fumes cannot come into contact with them, as they injure the colour of both.