monia from ferric chloride, and diluting it to 500 cubic centimeters. Exposure to the sunlight under a drawing for a quarter of an hour will afford an impression, which may be fixed by washing it in water.-14 C, CCXVIII., 62.

FRENCH METHOD IN ENGRAVING ON WOOD.

A French method in engraving on wood consists in first covering the block with a layer of gelatin (0.39 gramme to 31 grammes of water) by means of a soft brush. When this coating is dry it is covered, in the dark, with a solution prepared of (1) red prussiate of potash, 7.80 grammes; water, 62.20 grammes; (2) ammonio-citrate of iron, 9.10 grammes in 62.20 grammes of water. These solutions are mixed and filtered, and the mixture is kept in the dark. After the layer is dry it is exposed under a negative from ten to twelve minutes, and washed with a soft sponge, when a blue image appears. If thus prepared the coating does not shell off under the graver.-5 A, 1875, 98.

RETOUCHING VARNISH FOR NEGATIVES.

It is claimed that a film of the following varnish on negatives, as suggested by Monckhoven, can be retouched with a brush or lead-pencil three or four times as rapidly as one of gum: Add common shellac, in scales, to a saturated aqueous solution of carbonate of ammonia. After twenty-four hours pour off the clear liquid, add about an equal quantity of water, and bring the mixture slowly to boiling, while continually stirring it with a glass rod. A brown shellac solution is thus obtained, and there should be about one hundred parts of water to eight of shellac, and no odor of ammonia. The negative, after being washed, should be flowed with distilled water and allowed to drain, and should then be coated by flowing the varnish over it twice in succession. After drying, the coating is brilliant and hard, and insoluble in water. If many prints are desired, the retouched negative should be varnished as usual.-18 C, VI., 461.

PHOTOGRAPHIC POWER OF ARTIFICIAL LIGHT.

Comparative tests of the photographic effect of light from different artificial sources have been made by Riche and Bardy. Plates were sensitized with bromide of silver, and ex

posed for sixty seconds at a distance of nineteen inches from the light, while screened from its action by ten unequal layers of waxed paper, the first four inches long, covering the whole plate, and each successive layer being one tenth shorter, the last being four tenths of an inch long. The effects were compared by noticing, after development, the number of layers of paper through which the light had acted. Thus it was found that the oxyhydric light penetrated but one layer; the Drummond light, three; that of zinc burned in oxygen, four; of the magnesium light, five; of a jet of nitric oxide passed through a flask containing bisulphide of carbon, six; of a jet of nitric oxide in a vessel of burning bisulphide of carbon, six and seven; of a jet of oxygen in a vessel of bisulphide of carbon, seven; of a jet of oxygen in a vessel of burning sulphur, eight. The introduction of oxygen into a jet of burning sulphur, as it produced the greatest effect upon the bromide of silver, seems to merit further tests as to its practical value.-19 C, VIII., 127.

FIRE-PROOF PAPER AND INK FOR VALUABLE DOCUMENTS, ETC.

The fire-proof writing-paper prepared, according to an English patent, of one part vegetable fibre, two parts asbestus, one tenth of a part borax, and two tenths of a part alum, can also be made of a heavier quality, suitable for binding books and preserving manuscripts, etc. The fire-proof ink may be used for printing as well as writing. It is composed of twenty-two drams finely powdered graphite, twelve grains copal varnish, two drams sulphate of iron, and eight drams tincture of gall-nuts and indigo carmine; all well mixed, and boiled in water. Any mineral pigment may be substituted for the graphite to form a colored ink.-9 C, XIII., 152.

IMITATION OF JACOBSEN'S COPYING-INK PENCILS.

Imitations of Jacobsen's substitute for ink, in the form of copying-ink pencils, have made their appearance. They consist essentially of the same ingredients as the original, namely, graphite and aniline color, but are consolidated simply by means of tragacanth or other mucilage, instead of by the pe culiar process by which the compact, homogeneous mass of the original is formed. The imitation is, therefore, readily distinguished, since it is very porous and brittle, is never

pointed, and is generally carelessly finished. The pencils also absorb moisture from the air, and soon become soft and smeary.-6 C, 1875, 38.

PREPARATION OF COPYING-INK PENCILS.

According to Viedt, these pencils, or substitutes for ink, can be prepared by making a thick paste of elutriated graphite, finely powdered kaolin, and a very concentrated solution of violet-blue aniline, soluble in water (or of any other aniline color soluble in water), and pressing it, by means of a small press, into sticks about four inches long and 0.1 to 0.15 of an inch thick. When dry they are fit for immediate use. The proper proportions of the ingredients can easily be ascertained by trial; and perhaps gum arabic can be substituted for clay as a cement.-13 C, July 1, 849.

MARKING-INK UNAFFECTED BY CHLORINE.

An ink for marking linen, etc., which is proof against chlorine, may be prepared, according to Dr. Waltl, by dissolving eight ounces of extract of logwood in water, and adding half an ounce of yellow chromate of potash and a quarter of an ounce of chromate of copper, and evaporating the mass until it begins to thicken, and finally adding half an ounce of varnish.-26 C, XI., 14.

INERASIBLE BLACK INK.

A so-called inerasible ink is prepared by Gaffard, of Paris, of one part by weight of lampblack, twelve of potash waterglass, of the consistency of sirup, one of ammonia water, and thirty-eight of distilled water.-6 C, XI., 8.

COHAUSEN'S PERIGRAPH.

Tracing the profiles of architectural objects, by obtaining the co-ordinates of different points, rests so much upon the delicacy of touch and sight of the individual that the results are not accurate. A very simple instrument, devised by Cohausen and named a perigraph, eliminates this personal source of error by rendering the operation a purely mechanical one. It consists essentially of a lever, moving and sliding in such a way on a pivot, on a board covered with drawing-paper, that, when the board is held by the left hand from a ladder,

near to the object to be traced, and the one end of the lever is moved by the right hand so that the other end continually touches the object, a pencil fixed in the lever will trace a diminished profile of the object on paper. This can afterward be enlarged to the full size by means of the same instrument.-14 C, CCXVI., 204.

A PRINTER'S INK READILY REMOVABLE FROM WASTE PAPER. The following process for the preparation of a printer's ink that can be far more readily removed from waste paper than ordinary printer's ink has been patented by Kirscher & Ebner. Iron is dissolved in some acid-sulphuric, hydrochloric, acetic, etc., will answer-and half of the solution is oxidized with nitric acid and added to the other half, and the oxide precipitated from the mixture by means of soda or potash. The precipitate is thoroughly washed and treated with equal parts of solutions of tannic and gallic acids, and the bluish-black or pure black pigment formed is thoroughly washed and dried and mixed with linseed-oil varnish, and can then be immediately used for printing from type, copper, wood, steel, or stone. Waste paper printed with it can be bleached by digesting it for twenty-four hours in a lukewarm bath of pure water and ten per cent. of caustic potash or soda, and then grinding it well in the rag-engine, and throwing the pulp upon cloth and allowing it to drain. It is then to be washed with pure water containing ten per cent. of hydrochloric, acetic, or oxalic acid, or of binoxalate of potassa, and allowed to digest for twenty-four hours, and may then be worked up into paper, or it can be dried, and used as a substitute in the manufacture of finer paper.-5 C, XXXIX., 1875, 312.

FOR TAKING TRACINGS.

The following process has lately been suggested: One part by volume of castor-oil should be dissolved in two or three volumes of alcohol, and this solution applied to the paper with a brush. The spirit soon evaporates, leaving the paper transparent and ready for use. A tracing in pencil may then readily be made, and when finished the paper is immersed in alcohol, which dissolves out the oil, restoring the sheet to its original condition. The drawing may afterward be completed in Indian ink or in colors.

COPYING APPARATUS OF BAUER & CO.

A copying apparatus, manufactured by Bauer & Co., of Vienna, consists of a metallic tablet framed in wood, and covered with a paste containing aniline violet, or red. By tracing with a pencil or style on paper laid upon this, enough of the material will be taken up by it to yield copies on moistened paper, by laying the latter on it and patting it with the hand. The results, however, are very limited in quantity and quality, since the paper is not strong enough to yield even fifty copies.-6 C, January 20, 1876, 28.

PAPIER-MACHÉ ORNAMENTS, ETC.

Some English papier-maché articles are remarkable not only for their form and general appearance, but also for their durability. They are manufactured by first pressing a sheet of very porous but strong paper, manufactured expressly for the purpose, upon the metal greased with tallow. This is then coated with good flour paste and a second sheet is laid on, and pressed and rubbed until it takes the form of the model and adheres firmly. The whole is then placed in a drying-chamber at about 104°, and then the operations of laying on and drying are repeated until the desired thickness is produced-twenty to forty sheets being frequently required for the purpose. The form is then removed, all the sides are carefully adjusted, and the article is then hardened by first. immersing it in linseed-oil and purified wood-tar, and coating six to eight times with varnish, allowing it to dry thoroughly after each coat. It is finally ground down with pumice-stone, and ornamented with bronze, gold, or mother-ofpearl. Cheaper articles are manufactured from a species of paper pulp with certain proportions of white-lead, rosin, linseed-oil, and sugar of lead, carefully kneaded and rolled by the aid of steam. This is then pressed into moulds and dried. The most ordinary articles are made of pulp and earth colors, with the addition of some hardening cement.-5 C, L., 400.

PRESERVATION OF PLASTER CASTS.

Mr. John Bell communicates to the Society of Arts the statement that the thorough saturation of plaster in melted