Cement for Electrical Apparatus. One pound of bees'-wax added to five pounds of resin, one pound of red ochre, and two table-spoonfuls of plaster of Paris, all mixed together, make an excellent composition; but a cheaper one, for cementing voltaic plates into wooden troughs, is made with six pounds of resin, one pound of red ochre, half a pound of plaster of Paris, and a quarter of a pint of linseed oil. The ochre and plaster of Paris should be well dried, and added to the other ingredients in a melted state.

Universal Cement, particularly adapted for joining glass, porcelain, and metallic surfaces, is thus prepared. To an ounce of mastic add as much highly rectified spirits of wine as will dissolve it. Soak an ounce of isinglass in water until quite soft, then dissolve it in pure rum or brandy, until it forms a strong glue, to which add about a quarter of an ounce of gum ammoniac, well rubbed and mixed. Put the two mixtures together in an earthen vessel, over a gentle heat; when well united, the mixture may be put into a phial, and kept well stopped. When wanted for use, the bottle must be set in warm water, the china or glass articles must be also warmed, and the cement applied. It will be proper that the broken surfaces, when carefully fitted, shall be kept in close contact for twelve hours at least, until the cement is fully set; after which, the fracture will be found as secure as any part of the vessel, and scarcely perceptible.

Cement for Chemical Glasses. Mix equal quantities of wheat flour, finely powdered Venice glass, pulverized chalk, with half the quantity of fine brick-dust, and a little scraped lint, into some whites of eggs. This mixture must then be spread upon a linen cloth, and applied to the crack of the glasses; it should be dried before they are put to the fire.

Cement for Stone Paper or Artificial Slates. Linseed oil rendered drying, intimately mixed with white-lead and chalk: this should be used in a nearly fluid state, as by doing so it will insinuate itself amongst the joints and interstices, and cover the heads of the nails perfectly.

Water Cements, or Roman Cements, harden under water, and consolidate almost immediately on being mixed. The ancient Romans, in making their water cements, employed a peculiar earth obtained at the town of Puteoli. This they called Pulvis Puteolanis: it is the same that is now called Puzzolana. There is a substance called tarras, terras or trass, mostly employed by the Dutch in their great aquatic structures. It is very durable in water, but inferior to the other kinds in the air. In an analysis of Parker's Roman cement, by Monsieur Berthier, he finds that its constituents differ so little from the constituents of chalk and common clay, that he proposes the manufacturing of a similar cement by the mere mixture of them in certain proportions. One part of clay, and two and a half parts of chalk, sets almost instantly, and may therefore be regarded as Roman cement. If clay and oxide of iron be mixed with oil, according to Mr. Gad, of Stockholm, they will form a cement that will harden under water.

It has been discovered that manganese is a valuable ingredient in water cements: four parts of grey clay are mixed with six of the black oxide of manganese, and ninety of good limestone, reduced to fine powder; then the whole is calcined to expel the carbonic acid.

When this mixture has been well calcined and cooled, it is to be worked into the consistence of a soft paste, with sixty parts of washed sand. If a lump of this cement be thrown into water, it will harden directly.

Turners' Cement. Melt together resin one pound, pitch four ounces; and while boiling-hot, add brick dust, until, by dropping a little upon a stone, you perceive it hard enough; then pour it into water, and immediately make it up in rolls, and it will be fit for use. A finer cement is made of pitch two ounces, resin one ounce, and red ochre finely powdered. A small quantity of tallow is used sometimes, according to the heat of the weather, more being necessary in winter than summer. Either of these cements are of great use to turners. By applying it to the side of a chuck, and making it warm before the fire, you may fasten any thin piece of wood, which will adhere while it is turned; when it is wanted off again, it need only be struck on the top with a tool, and it will immediately fall off.

Rice Cement. This useful and elegant cement, which is beautifully white, and dries almost transparent, is made by mixing rice flour intimately with cold water, and then gently boiling it. Papers pasted together with this cement will sooner separate in their own substance than at the joining. It is, therefore, an excellent cement in the preparation of curious paper articles, as tea-trays, ladies' dressing and work boxes, and other articles which require layers of paper to be cemented together. In every respect it is preferable to common paste made with wheat flour. It answers well for pasting into books the copies of writing taken off by copying machines on unsized silver paper. With this composition, made with a small quantity of water, that it may have a consistence similar to plastic clay, models, busts, statues, basso-relievos, and the like, may be formed. When dry the articles made of it are susceptible of a high polish; they are also very durable. The Japanese make quadrille fish of this substance, which so nearly resemble those made of mother-of-pearl, that the officers of our East Indiamen are often imposed upon.

Petrolic Cement. To prepare this cement, take the unsalted curd of skimmed milk, after pressing the whey out of it, and break it into lumps; distribute these lumps upon linen sheets laid upon the floor of an airy room to dry; and frequently, from time to time, as the curd acquires greater consistency, stir and break it into smaller masses, either with the hands, or with the assistance of a flat board, and a bar or rubber of wood, until at length it becomes dry enough to grind in a steel coffee-mill to a powder about as fine as the best gunpowder, when it must be gently dried over a stove, and kept dry for use. 100 lbs. of curd from the cheese-press will only afford about 30 lbs. of the dry curd. To 90 parts of this dried curd, 10 parts of caustic quick lime, made of blue marble, finely rubbed to powder and searced, and 1 part of camphor, must be added, and well mixed, by rubbing the whole together with a pallet-knife upon a stone slab; and the whole must be then inclosed in bottles, holding about an ounce each, and well corked immediately afterwards, in order to prevent the access of air to the composition.

In this state the cement will remain good a long time; and when wanted for use, a little of it must be poured out upon any flat earthen plate, etc, and, by the aid of a pallet or case-knife, be instantly mixed with a proper quantity of water, to render it of a fit consistency for the purpose to which it is to be applied. The bottle must be again carefully closed, after taking out the quantity of cement required, as, otherwise, the lime would lose its causticity, upon which its solvent action, or the caseous part of the cement, entirely depends.

The manufacture of that important and valuable cement, glue, is described in its initial order in this work.