Removal of Ink from Hectograph.—It is recommended in SÜdd. Ap. Ztg. to pour crude hydrochloric acid upon the hectograph, rub with a wad of cotton, then wash off by holding under cold running water and drying with a cloth. The hectograph may be used again immediately.

To Clean Wall Paper.—Four ounces of pumice stone in fine powder are thoroughly mixed with 1 quart of flour and the mass is kneaded with water enough to form a thick dough. This dough is formed into rolls about 2 inches in diameter and 6 or 8 inches long; each one is sewed up in a piece of cotton cloth and then boiled in water for from 40 to 50 minutes—long enough to render the dough firm. After cooling and allowing the rolls to stand for several hours, the outer portion is peeled off and they are then ready for use, the paper being rubbed with them as in the bread process.—Druggist's Circular.

Insulating Compound.—Prof. Fessenden recommends for armature work a compound made by boiling pure linseed oil at about 200 degrees with ½ per cent. of borate of manganese, the boiling being continued for several hours, or until the oil begins to thicken. An advantage of this borated oil is that it always retains a slight stickiness, and so gives a good joint when wrapped around wires, etc. Many substances so used are not sticky and let moisture in through the joints. Where a smooth surface is required, it is readily obtained by dusting on a little talc. It can also be given a coat of japan on the outside.—American Electrician.

How to Clean Diatoms.—As a general rule, we may say that every specimen of diatomaceous earth or rock needs a special treatment. The following, however, may serve as a basic treatment, from which such departure may be taken in each case as the nature of the specimen would indicate: Boil the material in hydrochloric acid, in a test tube, from two to five minutes. Let settle, pour off the hydrochloric acid, substitute nitric acid in its place, and boil again for two or three minutes. Pour into a beaker of water, stir a moment with a glass rod and let settle. After the material has fallen to the bottom, decant the liquid, and fill with fresh water. Repeat the operation until the water no longer shows an acid reaction. A portion of the deposit may now be examined, and if not clean, boil the deposit with tincture of soap and water in equal parts, decant, wash, first with water, then with stronger ammonia water, and finally, with distilled water. This usually leaves the frustules bright and sharp.—National Druggist.

Red Indelible Ink.—It is said that by proceeding according to the following formula, an intense purple red color may be produced on fabrics, which is indelible in the customary sense of the word.

Moisten the place to be written upon with No. 1 and rub a warm iron over it until dry; then write with No. 2, and, when dry, moisten with No. 3. An intense and beautiful purple-red color is produced in this way. The following simpler and less expensive method of obtaining an indelible red mark on linen has been proposed by Wegler: Dilute egg albumen with an equal weight of water, rapidly stir with a glass rod until it foams, and then filter through linen. Mix the filtrate with a sufficient quantity of finely levigated vermilion until a rather thick liquid is obtained. Write with a quill, or gold pen, and then touch the reverse side of the fabric with a hot iron, coagulating the albumen. It is claimed that marks so made are affected by neither soaps, acids nor alkalies. This ink, or rather paint, is said to keep moderately well in securely stoppered bottles, but we should not rely on it as a "stock" article. A white paint for marking dark colored articles might be made by substituting zinc white for the red pigment in the foregoing formula.—Druggist's Circular.

Brown or Black Discoloration of Silvered Mirrors.—Generally these spots are due to faulty manipulation, too great dilution of the silver solution, or touching the plates with the fingers after they have been cleaned. Sometimes, however, they are due to chemical defects in the glass itself. In these cases, as a general thing, the discolorations occur only after several days—a faultless mirror having been made at first, and the browning subsequently developing slowly. The writer was a student in the laboratory of Baron Liebig during the time that distinguished chemist was carrying out the series of experiments which resulted in devising a method of making silver mirrors commercially. One of the greatest troubles with which he had to contend was this browning—the cause for which was never fully cleared up by him. Some years ago, the writer, having in his possession two mirrors made by Liebig, and which had gradually become brown throughout, undertook an examination of the deposit (which had been thoroughly protected from extraneous influences by a strong film of varnish), and was surprised to find that it consisted of a layer of silver sulphide. Without going into detail, the source of the change was later found to lie within the glass itself. In making glass to be used for mirrors, a considerable portion of sodium sulphate is used, and in annealing, this is partly reduced to sodium sulphide, which effloresces on the surface of the glass. This efflorescence is, of course, removed on cleaning the glass before silvering; but it is found that, in many instances, on exposure of the mirror to the light for some time, a further efflorescence occurs, and it is this which produces the discoloration in cases such as we have cited. It has been suggested that the tendency to subsequent efflorescence may be corrected by boiling the plates, intended for silvering, for a couple of minutes, in a 10 per cent. solution of sodium carbonate or bicarbonate. We have no experience with the process, however.—National Druggist.