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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 is fit for use.

Another, finer.—Take resin, one ouuce; pitch, two ounces; add red ochre, finely powdered, until you perceive it strong enough. Sometimes a small quantity of tallow is used, according to the heat of the weather, more being necessary in winter than in summer.

Either of these cements is of excellent use for 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 hold while you tạrn it ; when you want it off again, strike it on the top with your tool, and it will drop off immediately.

A strong Cement for Electrical Purposes.

Melt one pound of resin in a pot or pan, over a slow fire; add to it as much plaster of Paris, in fine powder, as will make it hard enough, then add a spoonful of linseed-oil, stirring it all the while, and try if it be hard and tough enough for

your purpose; if it is not sufficiently hard, add more plaster of Paris; and if not tough enough, a little more linseed-oil.

This is a very good cement for fixing the necks of globes or cylinders of electrical machines, or any thing else that requires to be strongly fixed.

Another, softer. - Take resin, one pound; beeswax, one ounce; add to it as much red-ochre'as

2 will make it of sufficient stiffness ; pour it into water, and make it into rolls. This cement is useful for cementing hoops on glasses, or any other mounting of electrical apparatus.

A Cement for Glass-Grinders.

Take pitch, and boil it; add to it sifted-wood ashes, and keep stirring it all the while, until you have it of a proper temper : the addition of a little tallow may be added, as you find necessary.

Another, for small work. To four ounces of resin add one-fourth of an ounce of bees-wax, and four ounces of whiting, made previously red hot and melt them together. The whiting should be put in while hot, that it may not have time to imbibe moisture from the atmosphere.

Shell-lac is a very strong cement for holding metals, glass, or precious stones, while cutting, turning, or grinding them. The metal, &c. should be warmed, to melt it. For fastening ruby cylinders in watches, and similar delicate purposes, shelllac is excellent.

To solder or cement broken Glass.

Broken glass may be soldered or cemented in such a manner as to be as strong as ever, by interposing between the parts, glass ground up like a pigment, but of easier fusion than the pieces to be joined, and then exposing them to such a heat as will fuse the cementing ingredient, and make the pieces agglutinate without being themselves fused.

A glass for the purpose of cementing broken pieces of flint glass, may be made by fusing some of the same kind of glass previously reduced to

a

powder, along with a little red-lead and borax, or with the borax only.

Cement for Derbyshire Spar and other Stones.

A cement for this purpose may be made with about seven or eight parts of resin and one of beeswax, melted together with a small quantity of plaster of Paris. If it is wished to make the cement fill up the place of any small chips that may have been lost, the quantity of plaster must be increased a little. When the ingredients are well mixed, and the whole is nearly cold, the mass should be well kneaded together. The pieces of spar that are to be joined must be heated until they will melt the cement, and then pressed together, some of the cement being previously interposed.

Melted sulphur applied to fragments of stones previously heated by placing them before a fire, to at least the melting point of sulphur, and then joined with the sulphur between, makes a pretty firm and durable joining.

Little deficiencies in the stone, as chips out of corners, &c. may also be filled up with melted sulphur, in which some of the powder of the stone has been melted.

A Cement that will stand against boiling Water, and

even bear a considerable Pressure of Steam.

In joining the flanches of iron cylinders, and other parts of hydraulic and steam engines, great inconvenience is often experienced from the want of a durable cement.

Boiled linseed-oil, litharge, red and white lead, mixed together to a proper consistence, and applied on each side of a piece of flannel previously shaped to fit the joint, and then interposed between the pieces before they are brought home (as the workmen term it) to their place by the screws or other fastenings employed, make a close and durable joint.

The quantities of the ingredients may be varied without inconvenience, only taking care not to make the mass too thin with oil. It is difficult in many cases instantly to make a good fitting of large pieces of iron work, which renders it necessary sometimes to join and separate the pieces repeatedly, before a proper adjustment is obtained. When this is expected, the white-lead ought to predominate in the mixture, as it dries much slower than the red. A workman, knowing this fact, can be at little loss in exercising his own discretion in regulating the quantities. It is safest to err on the side of the white-lead, as the durability of the cement is no way injured thereby, only a longer time is required for it to dry and harden.

When the fittings will not admit easily of so thick a substance as flannel being interposed, linen may be substituted, or even paper or thin pasteboard.

This cement answers well also for joining broken stones, however large.

Cisterns built of square stones, put together with this cement, will never leak or want any repairs. In this case the stones need not be entirely bedded in it: an inch, or even less, of the edges that are to lie next the water, need only be so treated; the rest of the joint may be filled with good lime.

Another Cement that will stand the Action of Boiling

Water and Steam.

This cement, which is preferable even to the former for steam-engines, is prepared as follows.

Take two ounces of sal ammoniac, one ounce of flowers of sulphur, and sixteen ounces of cast iron filings or borings. Mix all well together by rubbing them in a mortar, and keep the powder dry.

When the cement is wanted for use, take one part of the above powder and twenty parts of clean iron borings or filings, and blend them intimately by grinding them in a mortar. Wet the compound with water, and when brought to a convenient consistence, apply it to the joints with a wooden or blunt iron spatula.

By a play of affinities, which those who are at all acquainted with chemistry will be at no loss to comprehend, a degree of action and re-action takes place among the ingredients, and between them and the iron surfaces, which at last causes the whole to unite as one mass. In fact, after a time, the mixture and the surfaces of the flanches become a species of pyrites, holding a very large proportion of iron, all the parts of which cohere strongly together.

Blood Cement.

A cement often used by copper-smiths to lay over the rivets and edges of the sheets of copper in large boilers, to serve as an additional security to the joinings, and to secure cocks, &c. from leaking, is made by mixing pounded quick-lime

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