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.