Leave oil of turpentine for a long time in contact with a mixture of nitric acid and alcohol. Crystals of terpine form. By boiling an aqueous solution of ter-pine with a small quantity of sulphuric or other acid, terpinol is formed, and may be separated by distillation. It has the odour of hyacinths.
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 vapours likely to affect it; and afterwards kept in bottles, jars, or cases. Dr. Faraday recommends unsized paper, but Mr. Parnele and other good authorities direct good letter paper to be used. * Dr. Fresenius recommends unsized paper.
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 greyish colour; 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 colour.]
From the petals of violet dahlias, as cabbage paper.
This is merely paper stained with the juice of the berries. Its blue colour is changed to red by acids, and to green by alkalies.
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 colour may be extracted from the litmus by hot water, but the liquid will require to be concentrated by evaporation. [Acids change the colour to red, but it does not become green with alkalies.]
As the last, adding to the strained infusion a few drops of nitric acid, or of pure acetic acid. Dr. Faraday recommends holding blue litmus paper over a large jar, into which a few drops of hydrochloric acid have been introduced, till sufficiently reddened.
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 colour.
Dip paper in a solution of sulphate of of manganese. [It becomes black in an ozonized atmosphere.]