Distilled water only should be used in these preparations. In preparing the papers the liquid should be placed in an earthenware plate or dish, and the paper carefully immersed in it so as to be uniformly wetted then dried out of the reach of acid, ammoniacal, or other vapors likely to affect it; and afterwards kept in bottles, jars, or cases.
Dip paper in a strong decoction of Brazil wood and dry it. [It is rendered purple or violet by alkalies; generally yellow by acids.
Make a strong infusion of red cabbage leaves, strain it, and evaporate it by a gentle heat till considerably reduced. Then dip the paper in it and dry it in the air. [This paper is of a grayish color; alkalies change it to green, acids to red. It is a very delicate test; if rendered slightly green by an alkali, carbonic acid will restore the color.
From the petals of violet-dahlias, as cabbage paper.
This is merely paper stained with the juice of the berries. Its blue color is changed to red by acids, and to green by alkalies.
Immerse paper in sulphate of indigo, wash it with water rendered slightly alkaline, then with pure water, and dry it in the air.
_Iodide of Potassium and Starch Paper._
Mix starch paste with solution of iodide of potassium, and moisten bibulous paper with it. [It becomes blue when exposed to ozone. Chlorine has the same effect.
Paper dipped in a solution of acetate of lead. [When moistened it detects sulphuretted hydrogen, which renders it black.
_Blue Litmus Paper._
Bruise 1 oz. of litmus in a mortar, and add boiling water; triturate together, put them in a flask and add boiling water to make up to half a pint; when cool strain it, and dip paper in it. More color may be extracted from the litmus by hot water, but the liquid will require to be concentrated by evaporation. [Acids change the color to red, but it does not become green with alkalies.
_Red Litmus Paper._
As the last, adding to the strained infusion few drops of nitric acid, or of pure acetic acid.
Make a strong infusion of the petals of the red rose, and dip unsized paper in it. [Dipped in an alkaline solution so weak as not to affect turmeric paper, it assumes a bright green color.
Dip paper in a solution of sulphate of manganese. [It becomes black in an ozonized atmosphere.
Dip paper in a strong infusion of rhubarb, and dry it. [Alkalies render it brown. It is not, like turmeric paper, affected by boracic acid.
This is merely paper imbued with starch paste. Cotton cord is sometimes used instead of paper. [As a test for iodine, which turns it blue.
Boil 1 oz. of coarsely powdered turmeric-root in 1/2 a pint of water for 1/2 an hour, and strain; dip paper in the liquid and dry it. [It is rendered brown by alkalies, and also by boracic acid and borates.]
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