India-rubber is vulcanized to reduce its elasticity and give it more firmness than is natural to the crude material.
India-rubber, vulcanized, is not so perfectly a repellent of water, as before being vulcanized.
India-rubber is not a perfect repellent of water, but is more or less absorbent, according to quality.
Gutta-percha has an exceedingly fine grain, and its oily property makes it a perfect repellent of liquids, oils, acids, and all oleaginous substances, so that when united to tanned leather, the oil in the leather will not affect the adhesive properties of the gutta-percha. Whereas oil in leather will decompose any India-rubber cement that may be applied to it.
Pure gutta-percha is without smell or disagreeable odor, and whenever it is found to produce any but a perfectly sweet odor, it arises from its impurities, and may be regarded as a test of its quality.
India-rubber when vulcanized has an odor about it very disagreeable. It will decompose, become sticky like tar, and much of it becomes entirely useless. It is vulcanized to reduce its elasticity and give it more firmness than is natural to the crude material, and when exposed to friction, even after vulcanization, it rolls up a dirty, sticky mass.
The foregoing analysis is so simple and clear, that the attentive reader will at once comprehend the natural as well as chemical differences existing in gutta-percha and India-rubber, being not only chemically, but mechanically and commercially different.
BOOK II.
CHAPTER I.
PREPARATION OF STOCK.
In the preparation of the leather for outer soles, after it has been stripped up in the common form, remove all the loose flesh by skiving or splitting, or any other process. The stock should be thoroughly dry. Then raise a thick and even fibre on the flesh side, (remembering always, that the adhesive quality is in proportion to the thickness of the fibre) with a common card or rasp, or other convenient tool. The cement should be applied hot, with a coarse paint brush, as evenly as possible, then expose the leather to dry air a day or two, in order to allow the solvent to evaporate. If the first coat is too thin, apply a second in the same manner, until the leather is well coated. Then the leather should be again exposed, as before, until completely dry. It may then be wet in water, in the usual form, until properly tempered or prepared. The leather is then in a condition to be rolled, or hammered. If hammered it should be first cut up into soles. If rolled it may be placed in a cutting machine, and cut up in the usual form. Sole leather is cut to the best advantage by hands with the proper patterns, or “dies.” After the soles are properly rounded to the desired pattern, for all thin edged work the cement should be featheredged, from the edge of the sole at a proper distance, in order to secure a good finish. This process prevents the cement from adhering or sticking to the upper, when the sole is pressed on.