After the rubber is dry, and has been tested by the chemist, it goes to the grinding mills where it is refined on warm rolls and made ready for the compounding or mixing. It is impossible to make out of rubber alone, shoes or other products that will withstand extreme changes in temperature; certain amounts of sulphur, litharge and other ingredients are necessary in combination with the pure rubber to give a satisfactory material. The gum from the grinding mills is taken to the mixing mills, where, between the large rolls, the various materials are compounded into a homogeneous mass. The compounded rubber goes from the mixing mills to refining mills, to be prepared for the calenders. [Illustration: _Courtesy of the United States Rubber Co._] Automobile, motorcycle and bicycle tires, belting, footwear and many other rubber articles must have a base or backbone of cotton fabric, and in order that the fabric may unite firmly with the rubber it must be “frictioned” or forced full of rubber. This is done by drawing it between enormous iron rollers, rubber being applied on its surface as it passes through. The pressure is so great that every opening between the fibers of cotton, every space between threads is forced full of rubber. [Illustration: THE MILL ROOM _Courtesy of the B. F. Goodrich Co._] The fabric is then ready to go with the milled rubber to the various departments of the factory to be incorporated into rubber goods. The calender is also used to press rubber into sheets of uniform thickness. How are Rubber Shoes Made? In making footwear, the linings and such parts as can be piled up layer on layer are cut by dies, usually on the large beam-cutting machines, commonly seen in leather shoe factories. The uppers are cut by hand from the engraved sheets, while metal patterns are used on the plain stock. The soles are cut by specially designed machines. The sheets of rubber from which the uppers and soles are cut are at this stage of the work plastic and very sticky. It is necessary on this account to cut the various pieces one by one and keep them separate, by placing them between the leaves of a large cloth book. In an ordinary rubber shoe there are from twelve to fifteen pieces, while in a common boot there are over twenty-five pieces. [Illustration: MAKING RUBBER BULBS _Courtesy of the B. F. Goodrich Co._] The various pieces are next delivered to the making department, where they are fitted together on the “lasts” or “trees” in such a way that all the joints and seams are covered and the lines of the shoe kept exactly. Considerable skill is required to do this, as all the joints and seams must be rolled down smooth and firm to ensure a solid boot or shoe. The goods are all inspected before they are loaded on the iron cars to go to the varnishing department, where they receive the gloss which makes them look like patent leather. [Illustration: MAKING STRAIGHTLINE RUBBERS] [Illustration: IN THE TRUCK TIRE STOCK ROOM]