Читать книгу A Manual of Mending and Repairing; With Diagrams - Charles Godfrey Leland - Страница 4

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“There are full many admirable and practical recipes (Hausmitteln), which are often known only in certain families.”—Die Natürliche Magie. By Johann C. Wiegleb, 1782.

The art of mending or of repairing may be broadly stated as being effected, firstly, by mechanical processes, such as those employed by carpenters in nailing and joining, in embroidery with the needle, and in metal-work with clumps, or soldering; and, secondly, by chemical means. The latter consist of cements and adhesives, which are, however, effectively the same thing. This glue, or gum, is an adhesive or sticker; that is, a simple substance which causes two objects to adhere. The same, when combined with powder of chalk or glass, would be a Cement. This latter term is again applied somewhat generally and loosely by many, not only to all adhesives, but also more correctly to all soft substances which harden, such as Portland cement, mortar, and putty, and which are often used by themselves to form objects, such as “bricks” and castings; but these latter, having also the quality of acting as adhesives or stickers, are naturally regarded as being the same.

As will be speedily observed in the great number of recipes for mending which will be given in this book, there are many which occur frequently in different combinations; therefore it will be advisable and indispensable for those who wish to master mending as an art to indicate these as a basis.

As Sigmund Lehner has observed in his valuable work on Die Kitte- und Klebemittel, there have been such vast numbers of recipes published of late years for adhesives in various technological works, that the combination of the usual materials depends almost on the judgment of the experimenter, and every practical operator will soon learn to make inventions of his own. These materials, according to Stohmann, may be classified as follows:—

I.	Those in which Oil is the basis.
II.	Resin or pitch.
III.	Caoutchouc (indiarubber) or gutta-percha.
IV.	Gum or starch.
V.	Lime and chalk.

Lehner extends the list as follows into adhesives, or cements:—

I.	For glass and porcelain in every form.
II.	For metals not exposed to changes of temperature.
III.	For stoves and furnaces, or objects exposed to heat.
IV.	For chemical apparatus and objects exposed to corrosive liquids.
V.	Luting or cements, to protect glass or porcelain vessels from the action of fire.
VI.	Cements for microscopic preparations, for filling teeth and similar work.
VII.	Those for special objects, such as are made of tortoise-shell, meerschaum (ivory), &c.

Oils are divided into those (such as olive) which never become hard, and the linseed, which in time dries into a substance like gum. The latter combined with a great variety of mineral substances, such as plumbago, calcined lime, magnesia, chalk, red oxide of iron, soapstone, or with varnishes, forms insoluble “soaps,” which, as cements, resist water. They require a long time to set or become hard.

Resins and Gums include a great number of substances, such as resin or hard pitch, which is distilled from pine-trees; shellac, mastic, elemi, copal, kauri gum, amber, gum arabic, dextrine made from flour, the gum of the peach and cherry, and of many other trees. To these may be added frankincense and tragacanth, which is less an adhesive than a stiffener and dresser. Gums are generally rather brittle; this is remedied by combination with oily substances, volatile oils, or caoutchouc. With these gums Lehner includes asphaltum. The defect of such adhesives is, as he also remarks, that they will not resist high temperatures. This, however, will apply to most objects.

Varnish.—This belongs properly to the gums, but is technically regarded as a separate material. It is gum in solution in turpentine or spirits. For details vide Die Fabrikation der Copal- Terpentinöl und Spiritus-Lacke, by L. E. Andés; Leipzig, price 5 m. 40 pf.

Caoutchouc and Gutta-Percha are gums which when hard are still elastic, and resist the action of water. I have read that a perfect imitation or substitute for them has been made of turpentine, but have not seen it, though I have met with glue made with oil and turpentine, which very much resembled them in elasticity or flexibility. Reduced to a liquid form with ether, benzine, &c., these gums can be kept in a liquid state for a long time, and then hardened in any form by exposure to the air. They enter into a very great variety of cements, such as are meant to be tough or waterproof. Indiarubber is, on the whole, the best, and gutta-percha the cheapest, for cements.

Glue.—This is made, by boiling, from horns and bones; it is essentially the same as gelatine. It is the most generally known of all adhesives, and may be modified by certain admixtures to suit almost any substance. It has the peculiarity that it must always be boiled in a balneum mariæ, or in a kettle in hot water in another kettle. Its strength is vastly increased by admixture with nitric acid or strong vinegar. On the subject of glue in all its relations, the reader may consult Die Leim- und Gelatine-Fabrikation, or “The Manufacture of Glue and Gelatine,” by F. Dawidowsky; Vienna, price 3s.

Flour-Paste and Starch-Paste.—These mixtures, though generally used for weak work, such as to make papers adhere, can be very much strengthened by admixture with glue and gums. Combined with certain substances, such as paper, mineral powders, and alum, they, when submitted to pressure, become intensely hard, and resist not only water but heat, when not excessive. Also combined with varnishes they are decided resistants. Lehner speaks of them as if they were perishable in any condition.

Sturgeon’s Bladder.—With this the bladders of several kinds of fish are classed. Cut in small pieces and dissolved in spirits it makes a very strong adhesive, which is mixed with many others.

Lime is the most extensively used cement in the world. Combined with water it forms mortar. It is united with many substances, such as caseine or cheese, the white of eggs, and silicate of soda, to make powerful minor cements. On the subject of lime the practical technologist should consult Kalk und Luftmortel, by Dr. Herrmann Zwick; Vienna, A. Hartleben, price 3s., in which all details of the subject are given in full.

Eggs.—The yolk, and more particularly the white, of eggs is sometimes used as an adhesive, and it enters into many very excellent cements. For details as to the chemistry and technology of this material consult Die Fabrikationen von Albumin- und Eierkonserven (A Full Account of the Characteristics of all Egg Substances, the Fabrication of Egg, and Blood Albumen, &c.), by Karl Ruprecht; Vienna, A. Hartleben, price 2s. 3d.

Neutral Substances, or Binding Materials.—Almost any substance not easily soluble in water, and many which are, from common dust or earth, or clay, sand, chalk, powdered egg-shells, sawdust, shell-powder, &c., when combined with certain adhesives, form cements. This is sometimes due to chemical combination, but more frequently to mechanical union. In the latter case the adhesive clinging to every separate grain has the more points of adhesion, just as a man by clinging with both hands to two posts is harder to remove than if he held by one.

Caseine or Cheese.—This in several forms, but chiefly of curd in combination with several substances, but mostly with lime or borax, forms a very valuable cement. It is also combined with strong lye and silicate of soda. It must not, however, be too much depended on as a resistant to water or heat.

Blood, generally of oxen or cows, combined with lime, alum, and coal ashes, forms a solid and durable cement.

Glycerine forms the basis, with plumbago, &c., of several cements. Like oil, it renders glue flexible and partly waterproof. For chemical details on this subject, vide Das Glycerin, by J. W. Koppe, Leipzig.

Gypsum is combined with many substances to form cements, some of them of great and peculiar value.

Iron pulverised is the basis of a great number of very durable and strongly resistant cements.

Alum may be included among the bases, as it is very important in several compositions, forming a powerful chemical aid. It is excellent as aiding resistance to both moisture and heat. For an exhaustive work on alum consult Die Fabrikation des Alauns, &c., by Frederic Junemann, which should be carefully studied by all who work in cements.

There is a very great number of “indifferent” or minor aids to these, such as sugar, milk, honey, spirits of wine, water, ochre, galbanum, tannin, ammonia, feldspar, plumbago, sulphur, vinegar, salt, zinc (white), umber, bismuth, tin, cadmium, clay, ashes, &c., which are essential in certain combinations.

Dextrine, the gum of flour or starch, or Leiokom, much resembles gum-arabic, but is more brittle. Its adhesiveness depends somewhat on the manner in which it is dissolved. “It is,” says Lehner, “prepared by heating starch which has been moistened with nitric acid; also by warming paste with very much diluted sulphuric acid.”

Wax, including that of bees as well as paraffine, is used in repairs, and forms a part of several cements. On this subject consult Das Wachs, or “Wax and its Technical Applications,” by Ludwig Sedna; Leipzig, 2s. 6d.

Silicate of Soda, or Liquid Glass.—This is generally sold in the form of a very dense liquid. It is prepared by mixing quartz or flint sand with soda, or more rarely with potash. “It is,” says Lehner, “a glass which is distinguished from other glasses by being easily soluble in water. It is believed to be a very modern invention; but I have seen Venetian glasses of the fifteenth century which appeared to be painted with it, or something very similar; and I have found decided indications of a knowledge of it in two writers of the sixteenth century, Wolfgang Hildebrand and Van Helmont. According to Wagner, there are three kinds of liquid glass. By itself liquid glass can only be used for mending glass; but when combined with other substances, such as cement, calcined lime, or clay, or glass, in powder, it forms a body as hard as stone, or a double silicate, which is strongly resistant to chemical influences.” It occupies the first position as an adhesive for glass, nor is it surpassed as a cement in solid form. On this subject vide Wasserglas und Infusorienerde, &c., by Hermann Krätzer; Vienna, 3s.

Natural Cement, or Hydraulic Lime.—This is familiarly known to all readers as Portland cement, but it is found of different qualities in many countries, and is also made artificially. Certain mineral substances have the quality when powdered and combined with water of setting hard as stone; hence the name hydraulic. I have seen at Budapest articles of Portland cement made in Hungary which equalled in appearance fine black slate or marble, and, while much less brittle, were indeed in every respect more durable and resistant to exposure. These artificial cements can be largely incorporated with indifferent substances, such as sand; they, however, require intense baking, and may in consequence be regarded as a kind of fictile ware.

Portland cement is very thoroughly treated in Hydraulischer Kalk und Portland Cement (in all their relations), by Dr. H. Zwick.

Tragacanth, though called a gum, is properly nothing of the kind, not being a true adhesive. It is the product of the Astragalus verus, a tree found in Asia. It swells out in water, and softens, but without dissolving. It is more of a glaze than a paste; hence it is used extensively by confectioners, bookbinders, or to stiffen laces. It enters, however, into the composition of several cements.

Bread may be classed as a material by itself, as it derives certain peculiar virtues from the yeast which causes its fermentation. With certain combinations it becomes wax-like, or hard, and may be used to advantage in many repairs as well as for modelling. It has the great advantage of being easily worked and always at hand.

Celluloid is treated of in this work under the head of Artificial Ivory. It is made from gun-cotton and camphor. For full information on this subject consult Das Celluloid, or “Celluloid, its Raw Materials, Manufacture, Peculiarities, and Technical Applications, &c.,” by Dr. Fr. Böckmann, Vienna and Leipzig.

Potatoes, peeled and mashed, and kept for thirty-six hours in a mixture of eight parts of sulphuric acid to a hundred of water, and then dried and pressed, form a white, hard substance very much like ivory, or, as one may say, like white boxwood. Lehner expresses his doubt as to whether artificial meerschaum pipes were ever made of this substance, but I have seen them, and can testify that they looked like meerschaum, and certainly were much harder than bruyere, or briar-wood. Whether they will “colour” I cannot say.

The principle by which potatoes, paper, and many other substances can be hardened like parchment or horn is curious. Potatoes consist of about seventy per cent. water and twenty-five per cent. of starch, the remainder being salts and cellulose, which forms cells surrounded by the grains of starch. “When such a substance is for some time brought into contact with diluted sulphuric acid, that which results is simply a contraction of the cells” (i.e., a hardening), “or a kind of parchmenting.” Thus soft paper is converted into parchment.

It is evident that chemistry is as yet in its infancy as regards the conversion of cellulose by acid into hard substances. Since cotton, paper, and potatoes all produce by this process different substances, it is probable that hundreds of organic, or at least vegetable, substances will all yield new forms.

There is a marked difference between paste made of starch or flour, each having its peculiar merits. The former is principally prepared from potatoes. To prepare the cement we mix it with a very little water, stirring it very thoroughly till it assumes a bluish appearance. A little more hot water is then added, and the mass left till an opal-like tinge indicates that it has formed. To this then add hot water ad libitum. As it is almost colourless in very thin coats, it is largely used to glaze and give body or weight to, and often to simply falsify, woven fabrics, which by its aid seem heavier. To increase this weight white lead and other substances are used.

To make the best flour-paste, flour should be kneaded in a bag under water till all the starch is washed away. What remains is a substance closely allied to caseine, or the white of egg. Combined with lime it forms a hard cement. A very slight admixture of carbolic acid (also oil of cloves) will keep paste from souring or decay. This acid has the property of destroying the growth of the minute vegetation which constitutes fermentation, just as other strong scents or perfumes are supposed to disinfect rooms, &c.

A very great number of other ingredients, such as the oxides of lead or zinc, manganese, baryta, sulphur, sal ammoniac, flint-sand, clay, salt, ochre, varnish, galbanum, or frankincense, enter into certain recipes, but those already given may be regarded as constituting by far the principal portion of all cements in ordinary use.