But compounded with other substances both yield excellent cements, in which a part of the properties distinguishing glue solution and paste is preserved. They both possess the property of decreasing the brittleness of many cements, but unfortunately the latter thereby lose their power of resisting the action of water; for starch as well as glue swells in water, and the latter, when moist, passes quickly into putrefaction and destroys the cement.
In a wider sense isinglass, compounds of glue and vinegar, of lime and glue, etc., must be classed with the glue cements, and ordinary flour and shoemakers’ paste with starch cements.
Lime Cements. Lime possesses the property of forming insoluble combinations with egg albumen or caseine, this being the reason why lime cements, of which there are a great number, are generally composed of burned lime and one or the other of the above substances. Lime compounded with a solution of water-glass forms also very solid and durable cements.
Although the cements and agglutinants mentioned in the foregoing are most frequently used, a compound of different cements is often employed, in consequence of which the composition of many cements is very complicated.
In the following we give a description of the preparation of the different kinds of cement, according to the manner of their employment.
[CHAPTER XIII.]
PREPARATION OF CEMENTS, PASTES, AND MUCILAGES.
OIL CEMENTS.
Oil cements, as already explained, must be considered as a variety of soaps insoluble in water, formed by the action of drying oils or varnish upon various basic combinations.
The most important of this class is the cement used for securing window-panes. Good glaziers’ putty is a product of extraordinary durability, and, besides for puttying glass and wood, can also be used for joining many other bodies.