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is greater than that of natural silk, and in the dye-bath it takes 

 up colouring matter freely. One defect it has and that is a 

 considerable loss of strength when wetted, which, however, is 

 recovered on drying. The fibres are said to be strengthened by 

 immersion in a solution of formaldehyde, which is supposed to 

 condense the cellulose molecule. 



Celluloid, formerly called xylonite, is another useful product of 

 which the basis is cellulose. A nitrocellulose, made usually from 

 tissue paper, is mixed with camphor dissolved in some solvent 

 such as alcohol. After the evaporation of the solvent the mass 

 remains plastic when warm, but solidifies on cooling and can be 

 turned on a lathe. The process was invented by Daniell Spill, of 

 Hackney, some forty years ago. 



CHAPTER XXV 



RUBBER 



THE substance long known as india-rubber is familiar enough, 

 but down to a period about forty years ago the demand for it 

 was comparatively moderate. Its use for waterproofing was 

 known long before that time, and the great increase in the 

 commercial application of rubber dates from the introduction 

 of the rubber tyre as applied to bicycles and later to motor 

 vehicles of all kinds. This increase in consumption has naturally 

 led not only to the cultivation of the plants from which rubber 

 is obtained, but to extensive chemical investigations into its 

 properties and constitution which have culminated in the artificial 

 production of what is always referred to as " synthetic rubber." 

 Synthetic rubber has not become as yet a commercial article. 



Rubber is produced by the coagulation of the latex or milky 

 juice secreted by many plants. Those which yield commercial 

 rubber flourish only in tropical or sub-tropical regions and belong 

 to several natural orders. Of these the most important is Hevea 

 brasiliensis (N.O. Euphorbiacece), which yields Para rubber, of 

 which the amount constitutes about two-thirds of the total 

 rubber of commerce. Other plants of the same order are the 

 Manihot and Sapium, which furnish a portion of the wild rubbers 

 of Brazil. 



Rubber is also obtained from different species of Funtumia 

 and Landolphia (N.O. Apocynacece) growing in Africa. 



Ficus elastica (N.O. Urticacece) is a native of India and the 



