692. _Sympathetic Ink._--With a clean pen write on paper with a solution of muriate of cobalt, so diluted with water, that the writing when dry will be invisible. On gently warming the paper, the writing will appear of a blue or greenish color, which will disappear again when cool. A solution of muriate of copper forms a yellow and sympathetic ink, and acetate of cobalt a rose or purple. If a landscape be drawn representing a winter scene, the paper being overlaid where the foliage should be with the green sympathetic ink, then, on gently warming the drawing, it will represent summer. Sky and water may be drawn with the blue, and standing corn with the yellow ink. 693. _Blue Ink._--Dissolve a small quantity of indigo in a little oil of vitriol, and add a sufficient quantity of water, in which gum-arabic has been dissolved. 694. _Yellow Ink._--Dissolve gamboge in a solution of gum-arabic. 695. _Scarlet Ink._--Dissolve vermilion in a solution of gum-arabic. 696. _Red Ink._--Boil one ounce of Brazil wood in half-a-pint of water for a quarter of an hour; add to the decoction three drachms of gum-arabic, and an ounce of alum. 697. _Green Ink._--Verdigris, two ounces; cream of tartar, one ounce; water, half a pint; boil till reduced to one half, and filter. 698. _Excellent Writing Ink._--Boil eight ounces of galls in coarse powder, and four ounces of logwood in thin chips, in twelve pints of rain water, for one hour: strain the liquor, and add four ounces of green copperas, three ounces of powdered gum-arabic, one ounce of blue vitriol, and one ounce of rock candy, powdered; stir the mixture until the whole be dissolved, then let it subside twenty-four hours; decant it very steadily, and put it into stone bottles for use. A clove kept in it will prevent it from becoming mouldy. 699. _Black Ink._--To make one gallon, take of pounded blue nutgalls one pound; copperas, six ounces; gum common, four ounces; soft water, one gallon. Dissolve the gum separately by the fire, and add, after it has boiled a quarter of an hour. Let the ink be boiled over a slow fire three-quarters of an hour. 700. _To make Ink._--To four ounces of bruised galls, allow two of copperas and two of gum-arabic; put the galls into a large bottle, with three pints of rain water; and, in three or four days, dissolve the gum in hot water, and add it with the copperas. Shake the bottle frequently for some days. A few cloves may be put into the bottle, to prevent the ink from moulding. 701. _Ink Powder._--Take five ounces of the cleanest nutgalls, bruise them, and sift the powder very fine; then add one ounce of white copperas, two ounces of Roman vitriol, gum-arabic, half an ounce; pound and sift them very fine. An ounce of this powder will make a pint of very black ink.