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.