TEST PAPERS.
On the otherwise barren rocks which fringe the shore of the Cape de Verd Islands, grows the archil—a famous seaweed or lichen, renowned among dyers. By a particular process of manufacture, this archil yields a beautiful blue pigment, known in the chemical laboratory by the name of litmus. Few colors are more fugitive than litmus. Being a fine violet-blue, it is changed to red by so minute a portion of any acid, that it becomes, when properly applied, a test of the presence of the latter substance. As it is so frequently desirable to know whether a fluid be acid or alkaline, one of the first practical lessons to a student in chemistry, is to prepare litmus test paper, thus: Put into a flask half an ounce of litmus, and three ounces of water; let them remain together in a warm place for a few hours, then filter the dark blue liquid from its impurities, divide the solution obtained into two parts, pour one portion into a saucer, and soak strips of white writing paper in it until it has acquired a distinct blue color. If not colored enough by once dipping and drying, repeat the operation. When dry, preserve these strips in a box, labeled "Blue litmus test papers." These serve to test any fluid, to ascertain if it has an acid reaction. It is instructive to learn how very small a portion of any acid in water will be indicated by the reddening of the litmus. With the second portion of the fluid, mix, cautiously, a few drops of lemon juice, until it is red; then color paper as before. When dry, this "red litmus test paper" serves to indicate the presence of alkalies, a class of bodies opposed to acids. Red litmus test paper, on being put into any fluid that is alkaline, such as lime-water, is immediately restored to its original blue color. Put the ashes of a cigar into water, the liquid, when "tested," will indicate the presence of an alkali. Test some stale milk. If your blue paper becomes red, the milk is sour; it is acid.
INFINITE DIVISIBILITY OF MATTER.
Dissolve a single grain of copper in about one dram of nitric acid, and dilute the solution with about one ounce of water, when it will be evident that a single drop of the mixture must contain an almost immeasurably small portion of copper. Yet, if the blade of a knife be dipped into it, it will become covered with a coat of copper; thus showing that the copper can be infinitely divided without any alteration in its properties.
AMUSEMENTS
IN
ELECTRICITY, GALVANISM AND MAGNETISM.
THE ORIGIN OF GALVANISM.