thing is done in half a minute, and is moreover, done well, for the gelatine so treated, makes the very best and finest glue that can be had. This plan might be modified by dissolving a trace of chrome alum in the water used for moistening the gelatine, in which case, no doubt, the glue would become insoluble when set. But for general purposes there is no need for subsequent insolubility in glue.

Liquid Glue. (Polyt. Notizblatt. From Chem. and Drug., May, 1880.) A solution of sugar in three parts of water, smeared on paper, possesses neither adhesiveness nor varnishing property. If slaked lime, equal to a fourth part of the sugar used, is added to the solution, warmed to 150° to 170° F., and macerated with frequent shaking for several days, the resulting thick solution, when poured off clear, resembles gum mucilage in glazing and adhesive power. If 3 parts of bruised glue are added to 12 or 15 parts of this solution, it quickly dissolves on warming, and the solution remains fluid when cold, without losing its adhesiveness, as happens when heated with acids. Glue can be dissolved in various proportions in this sugar solution, and always with improved adhesiveness. It can be used for almost every purpose, except when it will come in contact with colours destroyed by alkalies.

The following may be used as a working formula:

Dissolve the sugar in the water, add the lime, and heat nearly to boiling, macerate for several days, pour off the clear liquid, and add it to the glue. Heat moderately until dissolved.

Glycerin Cement. T. Morawski. (Dingl. polyt. Journ., ccxxxv., 213.) Litharge, ground with glycerol, forms a cement which hardens rapidly. The author found, under various conditions, a glyceride of lead in the form of fine needle-shaped crystals of the formula CH, Pb Og; but much litharge usually remains uncombined. The combination takes place more rapidly on the water-bath. To prepare the compound quickly, a hot saturated solution of PbO in potash solution is mixed with glycerol, more Pb O added to saturation, and the solution quickly filtered; occasionally the compound crystallizes out immediately. Heated to 130°, the compound becomes coloured, and at 200-210° it slowly carbonizes. Decomposition soon begins on boiling with water, glycerol and lead oxide being separated. It is easily soluble in acetic acid with decomposi

tion, and potash-lye easily dissolves it, especially on warming It is acted on by nitric and sulphuric acids, although not very rapidly when the acids are concentrated.

The greatest tenacity of the cement is obtained with 50 grams of litharge to 5 c.c. of glycerol.

The author is investigating compounds of glycerol and other metallic oxides.

Cements. (From the Druggists' Circular.) Quite as much depends upon the manner in which a cement is used as upon the cement itself. The best cement that ever was compounded would prove entirely worthless if improperly applied. The following rules must be rigorously adhered to if success would be secured :

1. Bring the cement into intimate contact with the surfaces to be united. This is best done by heating the pieces to be joined in those cases where the cement is melted by heat, as in using resin, shellac, marine glue, etc. Where solutions are used, the cement must be well rubbed into the surfaces, either with a soft brush (as in the case of porcelain or glass), or by rubbing the two surfaces together (as in making a glue joint between two pieces of wood).

2. As little cement as possible should be allowed to remain between the united surfaces. To secure this the cement should be as liquid as possible (thoroughly melted if used with heat), and the surfaces should be pressed closely into contact (by screws, weights, wedges, or cords) until the cement has hardened.

3. Plenty of time should be allowed for the cement to dry or harden, and this is particularly the case in oil cements, such as copal varnish, boiled oil, whitelead, etc. When two surfaces, each half an inch across, are joined by means of a layer of white lead placed between them, six months may elapse before the cement in the middle of the joint has become hard. In such cases a few days or weeks are of no account; at the end of a month the joint will be weak, and easily separated, while at the end of two or three years it may be so firm that the material will part anywhere else than at the joint. Hence, where the article is to be used immediately, the only safe cements are those which are liquefied by heat, and which become hard when cold. A joint made with marine glue is firm an hour after it has been made. Next to cements that are liquefied by heat are those which consist of substances dissolved in water or alcohol. A glue joint sets firmly in twenty-four hours; a joint made with shellac varnish becomes dry in two or three days. Oil cements, which do not dry by evaporation, but harden by oxidation (boiled oil, white lead, red lead, etc.), are the slowest of all.

Aquarium Cement.-Litharge, fine, white, dry sand, and plaster of paris, each 1 gill; finely pulverized resin, gill. Mix thoroughly and make into a paste with boiled linseed oil to which drier has been added. Beat it well, and let it stand four or five hours before using it. After it has stood for fifteen hours, however, it loses its strength. Glass cemented into its frame with this cement is good for either salt or fresh water. It has been used at the Zoological Gardens, London, with great success. It might be useful for constructing tanks for other purposes, or for stopping leaks.

Casein Mucilage.-Take the curd of skim milk (carefully freed from cream or oil), wash it thoroughly and dissolve it to saturation in a cold concentrated solution of borax. This mucilage keeps well, and as regards adhesive power far surpasses the mucilage of gum arabic.

Wash it in cold water and
Place it warm on a levi-
It will join marble, stone,

Casein and Soluble Glass.—Casein dissolved in soluble silicate of soda or potassa, makes a very strong cement for glass or porcelain. Cheese Cement for Mending China, etc.-Take skim milk cheese, I cut it in slices and boil it in water. knead it in warm water several times. gating stone and knead it with quicklime. or earthenware so that the joining is scarcely to be discovered. Chinese Cement (Schio-liao). To three parts of fresh beaten blood are added four parts of slaked lime and a little alum; a thin, pasty mass is produced, which can be used immediately. Objects which are to be made specially water-proof are painted by the Chinese twice, or at the most three times. Dr. Scherzer saw in Pekin a wooden box which had travelled the tedious road vid Siberia to St. Petersburg and back, which was found to be perfectly sound and water-proof. Even baskets made of straw become, by the use of this cement, perfectly serviceable in the transportation of oil.

Pasteboard treated therewith receives the appearance and strength of wood. Most of the wooden public buildings of China are painted with schio-liao, which gives them an unpleasant reddish appearance, but adds to their durability. This cement was tried in the Austrian Department of Agriculture and by the "Vienna Association of Industry," and in both cases the statements of Dr. Scherzer were found to be strictly accurate.

Faraday's Cap Cement.-Electrical Cement.-Resin, 5 ounces; beeswax, 1 ounce; red ochre or venetian red, in powder, 1 ounce. Dry the earth thoroughly on a stove at a temperature above 212°. Melt the wax and resin together, and stir in the powder by degrees.

Stir until cold, lest the earthy matter settle to the bottom. Used for fastening brass work to glass tubes, flasks, etc.

Cement for Glass, Earthenware, etc.-Dilute white of egg with its bulk of water, and beat up thoroughly. Mix to the consistence of thin paste with powdered quicklime. Must be used immediately.

Glass Cement.-Take of pulverized glass, 10 parts; powdered fluorspar, 20 parts; soluble silicate of soda, 60 parts. Both glass and fluorspar must be in the finest possible condition, which is best done by shaking each, in fine powder, with water, allowing the coarser particles to deposit, and then to pour off the remainder, which holds the finest particles in suspension. The mixture must be made very rapidly by quick stirring, and when thoroughly mixed must be at once applied. This is said to yield an excellent

cement.

Gutta Percha Cement.-This highly recommended cement is made by melting together, in an iron pan, 2 parts of common pitch and 1 part gutta-percha, stirring them well together until thoroughly incorporated, and then pouring the liquid into cold water. When cold, it is black, solid, and elastic; but it softens with heat, and at 120° Fahr., is a thin fluid. It may be used as a soft paste or in the liquid state, and answers an excellent purpose in cementing metal, glass, porcelain, ivory, etc. It may be used instead of putty for glazing windows.

Iron Cement for Closing the Joints of Iron Pipes.-(1) Take of coarsely powdered iron borings, 5 pounds; powdered sal-ammoniac, 2 ounces; sulphur, 1 ounce; and water sufficient to moisten it. This composition hardens rapidly; but if time can be allowed, it sets more firmly without the sulphur. It must be used as soon as mixed, and rammed tightly into the joint.

(2) Take sal-ammoniac, 2 ounces; sublimed sulphur, 1 ounce; cast-iron filings or fine turnings, 1 pound. Mix in a mortar and keep the powder dry. When it is to be used, mix it with twenty times its weight of clean iron turnings or filings, and grind the whole in a mortar; then wet it with water until it becomes of convenient consistence, when it is to be applied to the joint. After a time it becomes as hard and strong as any part of the metal.

Kerosene Oil Lamps.-The cement commonly used for fastening the tops on kerosene lamps is plaster of paris, which is porous and quickly penetrated by the kerosene. Another cement, which has not this defect, is made with three parts of resin, one of caustic soda, and five of water. This composition is mixed with half its weight of plaster of paris. It sets firmly in about three-quarters of an hour.

It is said to be of great adhesive power, not permeable to kerosene, a low conductor of heat, and but superficially attacked by hot water. Cement for Uniting Leather and Metal.-Wash the metal with hot gelatine, steep the leather in an infusion of nut galls (hot), and bring the two together.

Cement for Leather Belting.-One who has tried everything says, that after an experience of fifteen years he has found nothing to equal the following:-Common glue and isinglass, equal parts, soaked for ten hours in just enough water to cover them. Bring gradually to a boiling heat, and add pure tannin until the whole becomes ropy or appears like the white of eggs. Buff off the surfaces to be joined, apply this cement warm, and clamp firmly.

Litharge and Glycerine Cement.-A cement made of very finely powdered oxide of lead (litharge) and concentrated glycerine unites wood to iron with remarkable efficiency. The composition is insoluble in most acids, is unaffected by the action of moderate heat, sets rapidly, and acquires an extraordinary hardness.

Cement for Attaching Metal to Glass.-Copal varnish, 15; drying oil, 5; turpentine, 3. Melt in a water-bath, and add 10 parts slaked lime.

Paris Cement for Mending Shells and other Specimens.-Gum arabic, 5; sugar candy, 2; whitelead, enough to colour.

Porcelain Cement.-Add plaster of paris to a strong solution of alum till the mixture is of the consistency of cream. It sets readily, and is said to unite glass, metal, porcelain, etc., quite firmly. It is probaby suited for cases in which large rather than small surfaces are to be united.

Soft Cement.-Melt yellow beeswax with its weight of turpentine, and colour with finely powdered venetian red. When cold it has the hardness of soap, but is easily softened and moulded with the fingers, and for sticking things together temporarily it is invaluable.

Soluble Glass Cements.-When finely pulverized chalk is stirred into a solution of soluble glass of 30° R. until the mixture is fine and plastic, a cement is obtained which will harden in between six and eight hours, possessing an extraordinary durability, and alike applicable for domestic and industrial purposes. If any of the following substances be employed besides chalk, differently coloured cements of the same general character are obtained :—1. Finely pulverized or levigated stibnite (grey antimony, or black sulphide of antimony) will produce a dark cement, which, after long burnishing with an agate, will present a metallic appearance. 2. Pulver