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.

Canvas coated or impregnated with such soluble cellulose gives us new flexible and durable fabrics that have other advantages over leather besides being cheaper and more abundant.  Without such material for curtains and cushions the automobile business would have been sorely hampered.  It promises to provide us with a book binding that will not crumble to powder in the course of twenty years.  Linen collars may be water-proofed and possibly Dame Fashion—­being a fickle lady—­may some day relent and let us wear such sanitary and economical neckwear.  For shoes, purses, belts and the like the cellulose varnish or veneer is usually colored and stamped to resemble the grain of any kind of leather desired, even snake or alligator.

If instead of dissolving the cellulose nitrate and spreading it on fabric we combine it with camphor we get celluloid, a plastic solid capable of innumerable applications.  But that is another story and must be reserved for the next chapter.

But before leaving the subject of cellulose proper I must refer back again to its chief source, wood.  We inherited from the Indians a well-wooded continent.  But the pioneer carried an ax on his shoulder and began using it immediately.  For three hundred years the trees have been cut down faster than they could grow, first to clear the land, next for fuel, then for lumber and lastly for paper.  Consequently we are within sight of a shortage of wood as we are