INDIA-RUBBER 



Collection 



COMMERCIAL RUBBERS 



Albumen. 



Formaldehyde. 



Centri- 

 fugal Sepa- 

 rator. 



Dry-bark 

 Process. 



Chemical 

 Composi- 

 tion. 



Caoutchouc. 

 Kesin. 



Bmpyreumatic 

 Oil. 



Rubber. 



erroneous in that it is only the albumen which is coagulated by these 

 substances, and not the india-rubber itself. 



2. That the albumen contained in latex is very harmful in many 

 respects, and that it ought to be as far as possible eliminated from the milk 

 before attempting to agglutinate the rubber. 



3. The method he recommends for coagulation is briefly as follows : 

 First mix the latex with water, at least five times its volume. In cases 

 where the latex is thick, actual boiling water may be used with advantage. 

 In this state it can be easily strained to remove impurities. After this, 

 add formaldehyde in the proportion of 8 oz. to a petroleum barrel ; stir 

 well and let it stand for twenty-four hours, when the rubber will collect on 

 the top and can be lifted out in one mass. In order to remove any traces 

 of albumen that may be suspended, the rubber should next be cut into 

 strips and subjected to a thorough washing upon an ordinary rubbe 

 washing-machine. [Cf. Weber, Chem. India-Rubber, 1902.] 



But the use of formaldehyde does not seem to have been the success 

 that Weber anticipated, though his recommendation for cleanliness 

 and repeated washing has been universally accepted. BifEen (Annals of 

 Botany, 1898, xii., 165-71) suggested the use of a centrifugal separator* 

 The milk is mixed with 50 per cent, of water, and set revolving for a 

 time. It is then found that the rubber floats on the top in a thick mass 

 The albuminoids, etc., and all the adulterants are found below. It ha 

 next to be admitted that by many recent writers the value of centrifugal 

 force has been denied, and special machinery patented in which the merit 

 claimed is that they do not involve centrifugal action. 



Indian Planting and Gardening (March 29, 1900) published a letter 

 from Faber that gives particulars of a method of extracting caoutchouc 

 from dry bark, said to have been discovered by a French chemist, M. G. 

 Deiss. This process consists in keeping slices of bark and roots soaked 

 in dilute sulphuric acid while being heated. The woody portions become 

 decomposed and can then be washed out, thus leaving the rubber in a 

 pure state. For other methods of extracting india-rubber by solvents or 

 mechanical processes the reader should consult Gerber's article on that 

 subject. [Cf. Journ. Soc. Chem. Indust., 1902, 414-5 ; Kew Bull, 1898, 

 177-81 ; Mathieu, Agri. Bull. Straits and Fed. Mai. States, 1903, ii., 18-21 ; 

 1905, iv., 223-4. 



Composition of Rubber. India-rubber may be said to consist chemi- 

 cally of two substances an elastic material, on which its merit depends, 

 and a viscid resinous substance readily oxidisable, to which it owes its 

 depreciation. Hence the greater the.percentage of resin the less the value 

 of the sample. The property of the elastic substance also varies, and in a 

 marked degree, between that obtained from one genus of plants and that 

 of another, so that every gradation exists from the non -elastic hydrocarbon 

 known as gutta-percha (which see, pp. 625-8) to the finest gum elastic. 

 Caoutchouc yields by dry distillation a mixture of simpler hydrocarbons, 

 called oil of caoutchouc or caoutclwucin, which forms an excellent solvent for 

 caoutchouc and other resins. 



History. During the second voyage of Columbus it was noticed that the 

 inhabitants of Hispaniola (Hayti) played with balls made from the gum of a 

 tree. In 1770 Priestly recommended the use of that substance for the purpose 

 of erasing pencil markings, hence the name " rubber." The article was new to 

 Europe, and the proposed utilisation of it excited some interest. It was not, 

 however, '""until 1820 that the beginning of the modern industry can be traced. 



648 



