Here, then, is a chance for Necessity to exercise her maternal function. And she has responded nobly. A progeny of new substances have been brought forth and, what is most encouraging to see, they are no longer trying to worm their way into favor as surreptitious surrogates under the names of "leatheret," "leatherine," "leatheroid" and "leather-this-or-that" but come out boldly under names of their own coinage and declare themselves not an imitation, not even a substitute, but "better than leather." This policy has had the curious result of compelling the cowhide men to take full pages in the magazines to call attention to the forgotten virtues of good old-fashioned sole-leather! There are now upon the market synthetic shoes that a vegetarian could wear with a clear conscience. The soles are made of some rubber composition; the uppers of cellulose fabric (canvas) coated with a cellulose solution such as I have described. Each firm keeps its own process for such substance a dead secret, but without prying into these we can learn enough to satisfy our legitimate curiosity. The first of the artificial fabrics was the old-fashioned and still indispensable oil-cloth, that is canvas painted or printed with linseed oil carrying the desired pigments. Linseed oil belongs to the class of compounds that the chemist calls "unsaturated" and the psychologist would call "unsatisfied." They take up oxygen from the air and become solid, hence are called the "drying oils," although this does not mean that they lose water, for they have not any to lose. Later, ground cork was mixed with the linseed oil and then it went by its Latin name, "linoleum." The next step was to cut loose altogether from the natural oils and use for the varnish a solution of some of the cellulose esters, usually the nitrate (pyroxylin or guncotton), more rarely the acetate. As a solvent the ether-alcohol mixture forming collodion was, as we have seen, the first to be employed, but now various other solvents are in use, among them castor oil, methyl alcohol, acetone, and the acetates of amyl or ethyl. Some of these will be recognized as belonging to the fruit essences that we considered in Chapter V, and doubtless most of us have perceived an odor as of over-ripe pears, bananas or apples mysteriously emanating from a newly lacquered radiator. With powdered bronze, imitation gold, aluminum or something of the kind a metallic finish can be put on any surface.