2486b. Manifold Writing [1].

The demand for a rapid and simple method of multiplying letters, circulars, &c., has led in recent years to the invention of several ingenious processes. So few copies are obtainable by the ordinary reporters' system of sheets of tissue paper, or "flimsy," interleaved with sheets of prepared black paper, that various kinds of "graphs"

have been produced, by which upwards of a hundred, and in some cases many more, copies may be produced from one writing.

The "graph" process usually consists of transferring a writing made in an aniline dye on to a gelatine surface, from which, by the application of successive sheets of paper, subjected to a smoothing pressure by the hand, a number of copies may be obtained, in a manner very similar to the ordinary lithographic process. All those which may be cla.s.sed as "gelatine transfer" processes are, however, open to the objection that, after a certain number of copies, the colour grows very faint.

Some other methods of manifold writing, such es the Edison, the Trypograph, the Cyclostyle, &c. (by which 1,000 copies can be taken from one writing), do not possess this fault, being based on a principle of a fine stencil on prepared paper, and squeezing ink through the minute perforations on to a sheet of paper fixed underneath. The writing in these stencil systems, however, has a "dotty" and broken appearance, displeasing to many eyes--the Cyclostyle being, perhaps, least faulty in this respect. For those who would like to make a gelatine "graph," we append the following recipe:

Six parts by weight of pure glycerine, four parts by weight of water, two parts of barium sulphate, and one part of sugar. Mix them, and let them soak for twenty-four hours; then melt at a gentle heat, stir until thoroughly mixed, and pour the composition into a tray. Any chemist will supply an aniline dye for the ink.

[Footnote 1: Both these sections were numbered 2486 in the original text. txt Ed.]

[EVERY PEA HELPS TO FILL THE PECK.]

2487. Cements.

The term "cement" includes all those substances employed for the purpose of causing the adhesion of two or more bodies, whether originally separate, or divided by an accidental fracture. As the various substances that may require cementing differ very much in texture, &c., a number of cements possessed of very different properties are required, because a cement that answers admirably under one set of circ.u.mstances may be perfectly useless in others. The general principles upon which the success or failure of cementing usually depends are:

The different parts of a solid are held together by an attraction between their several particles, which is termed the attraction of cohesion. This attraction acts only when the particles are in the closest possible contact: even air must not be between them. If, after breaking any substance, we could bring the particles into as close a contact as before, and perfectly exclude the air, they would re-unite, and be as strongly connected as ever. But in general this is impossible: small particles of grit and dust get between them; the film of interposed air cannot be removed; and thus, however firmly we press the edges of a broken cup together, it remains cracked china still.

The cohesion between the particles of the cement is very much less than the adhesion of the cement to other bodies; and if torn apart, the connected joint gives way, not by the loosening of the adhesion, but by the layer of cement splitting down the centre. Hence the important rule that the _less_ cement in a joint the stronger it is.

To unite broken substances with a thick cement is disadvantageous, the object being to bring the surfaces as closely together as possible.

The general principles that ought always to be borne in mind having been mentioned, the manufacture and uses of some of the more useful cements may be described.

2488. Mouth Glue.

The very useful preparation sold under this t.i.tle is merely a thin cake of soluble glue, which, when moistened with the tongue, furnishes a ready means of uniting papers, &c. It is made by dissolving one pound of fine glue or gelatine in water, and adding half a pound of brown sugar, boiling the whole until it is sufficiently thick to become solid on cooling; it is then poured into moulds, or on a slab slightly greased, and cut into the required shape when cool. (_See_ LIQUID GLUE, No. 2491.)

[ECONOMY IS THE HOUSEHOLD MINT.]

2489. Paste.

Paste is usually made by rubbing up flour with cold water, and boiling; if a little alum is mixed before boiling it is much improved, being less clammy, working more freely in the brush, and thinner, a less quant.i.ty is required, and it is therefore stronger. If required in large quant.i.ty, as for papering rooms, it may be made by mixing one quartern of flour, one quarter pound of alum, and a little warm water; when mixed, the requisite quant.i.ty of boiling water should be poured on whilst the mixture is being stirred. Paste is only adapted to cementing paper; when used it should spread on one side of the paper, which should then be folded with the pasted side inwards, and allowed to remain a few minutes before being opened and used; this swells the paper, and permits its being mere smoothly and securely attached. If kept for a few days, paste becomes mouldy, and after a short time putrid; this inconveince may be obviated by the use of:

2490. Permanent Paste.

Permanent Paste, made by adding to each half-pint of flour paste without alum, fifteen grains of corrosive sublimate, previously rubbed to powder in a mortar, the whole to be well mixed; this, if prevented from drying, by being kept in a covered pot, remains good any length of time, and is therefore convenient; but unfortunately it is extremely poisonous, though its excessively nauseous taste would prevent its being swallowed accidentally. It possesses the great advantage of not being liable to the attacks of insects.

2491. Liquid Glue.

The liquid glue of the shops is made by dissolving shelac in water, by boiling it along with borax, which posesses the peculiar property of causing the solution of the resinous lac. This preparation is convenient from its cheapness and freedom from smell; but it gives way if exposed to long-continued damp, which that made with naphtha resists.

2492. Common Glue.

Of the use of _common glue_ very little need be said; it should always be prepared in a gluepot or double vessel, to prevent its being burned, which injures it very materially. The chief objection to the use of this contrivance is, that it renders it impossible to heat the glue in the inner vessel to the boiling point; this, however, can be obviated by employing in the outer vessel some liquid which boils at a higher temperature than pure water, such as a saturated solution of salt (made by adding one-third as much salt as water). This boils at 224 Fahr., 12 above the heat of boiling water, and enables the glue in the inner vessel to be heated to a much higher temperature than when pure water is employed. If a saturated solution of nitre is used, the temperature rises still higher.

2493. Diamond Cement.

Soak isingla.s.s in water till it is soft; then dissolve it in the smallest possible quant.i.ty of proof spirit, by the aid of a gentle heat; in two ounces of this mixture dissolve ten grains of ammoniac.u.m, and whilst still liquid add half a drachm of mastic, dissolved in three drachms of rectified spirit; stir well together, and put into small bottles for sale.

_Directions for Use_.--Liquefy the cement by plunging the bottle in hot water, and use it directly. The cement improves the oftener the bottle is thus warmed; it resists the action of water and moisture perfectly.

2494. Rice Flour Cement.

An excellent cement may be made from rice flour, which is at present used for that purpose in China and j.a.pan. It is only necessary to mix the rice flour intimately with cold water, and gently simmer it over a fire, when it readily forms a delicate and durable cement, not only answering all the purposes of common paste, but admirably adapted for joining together paper, cards, &c., in forming the various beautiful and tasteful ornaments which afford much employment and amus.e.m.e.nt to the ladies. When made of the consistence of plaster-clay, models, busts, bas-relievos, &c., may be formed of it; and the articles, when dry, are susceptible of high polish, and are very durable.

2495. Using Egg.

The white of an egg, well beaten with quicklime, and a small quant.i.ty of very old cheese, forms an excellent subst.i.tute for cement, when wanted in a hurry, either for broken china or old ornamental gla.s.sware.

2496. Cement for Broken China, Gla.s.s, &c.

This cement being nearly colourless, possesses advantages which liquid glue and other cements do not.--Dissolve half an ounce of gum acacia, in a winegla.s.s of boiling water; add plaster of Paris sufficient to form a thick paste, and apply it with a brush, to the parts required to be cemented together.

[AT NIGHT NATURE IS IN MOURNING FOR THE LOSS OF THE SUN.]

2497. Lime and Egg Cement.

Lime and Egg Cement is frequently made by moistening the edges to be united with white of egg, dusting on some lime from a piece of muslin, and bringing the edges into contact. A much better mode is to slake some freshly-burned lime with a small quant.i.ty of _boiling_ water; this occasions it to fall into a very fine dry powder, if excess of water has not been added. The white of egg used should be intimately and thoroughly mixed, by beating with an equal bulk of water, and the slaked lime added to the mixture, so as to form a thin paste, which should be used speedily, as it soon sets. This is a valuable cement, possessed of great strength, and capable of withstanding boiling water. Cements made with lime and blood, sc.r.a.ped cheese, or curd, may be regarded as inferior varieties of it.

2498. White Lead as Cement.

Cracked vessels of earthenware and gla.s.s may often be usefully, though not ornamentally, repaired by white lead spread on strips of calico, and secured with bands of twine.

2499. Marine Glue.

In point of strength, all ordinary cements yield the palm to Jeffery's Patent Marine Glue, a compound of India-rubber, sh.e.l.lac, and coal-tar naphtha. Small quant.i.ties can be purchased at most of the tool warehouses, at cheaper rates than it can be made. The colour of this glue, however, prevents its being much used.

2500. Coaguline.