According to the use to which rubber is to be put, it has to be mixed with certain other materials, to make a material that is neither too heavy nor too light, too hard nor too soft, too tough nor too elastic, to fulfil its purpose. And according to the price at which the goods are to be sold, certain other materials must be mixed with the rubber. It is with regard to the proportions in which such mixings are made that the manufacturers have secrets of their own which they specially want to guard. The compounding materials consist of such things as zinc oxide, white lead, and magnesia. Always to the “dough,” “mixing,” or “batch,” as the compound is called, some sulphur is added to bring about vulcanization. A colouring ingredient is also put into some of the dough, according to the taste and fancy of customers for whom goods are going to be made. The dough is worked smooth, and is then put into moulds shaped like the required articles, or built up into shape and form. The goods are generally vulcanized by steam heat. Much skill, together with great care and patience, goes to the making of all rubber goods; and when such goods have to be canvas backed, or to be made of a material that is bodily a mixture of thread and rubber, the process of manufacture calls for particularly good workmanship. Printed in Great Britain by Messrs. Billing and Sons, Ltd., Guildford [Illustration: _R. B. Lodge, Enfield_ SAMPLING BOLIVIAN RUBBER AT BULL WHARF, LONDON. _Page 86_] Transcribers’ Notes: Punctuation, hyphenation, and spelling were made consistent when a predominant preference was found in this book; otherwise they were not changed. Simple typographical errors were corrected; occasional unbalanced quotation marks retained. List of Illustrations: The page number for Illustration 16 was hand-written as “76”, which is the page it faces in the book; and “On the cover” was crossed out. A different edition of this book included neither this illustration nor the cover. End of the Project Gutenberg EBook of Rubber, by Edith A. Browne