CAOUTCHOUC. SOURCES AND PROPERTIES. 231 



especially of the Artocarpece (Bread-fruit tribe), Apovynece 

 (Oleander tribe), and Euphorbiacece (Spurge tribe) which will be 

 hereafter more particularly described. To the first of these 

 orders, belongs the celebrated Palo de Vacca, or Cow-tree of 

 South America ; which yields a copious supply of a rich, bland, 

 and wholesome fluid, closely resembling milk. In the plants of 

 the second order, the milk is usually rendered bitter and poisonous, 

 by the admixture of other secretions : and in the third it is of a 

 very acrid character. In other orders of plants having milky 

 juices, however, caoutchouc forms but a very small proportion of 

 them ; such are the Papaveracecu (Poppy tribe) and Cichoracece 

 (Cichory tribe) ; and here it is replaced by opium, a substance 

 presently to be adverted to. The juices which contain caout- 

 chouc are obtained, by making incisions into the bark ; and the 

 fluid which runs from them soon thickens, on exposure to the air, 

 into a substance of a pure white colour, having neither taste or 

 smell. The dark colour which caoutchouc usually presents, is 

 received from the smoke of the fire over which it is dried. 



368. The use of Caoutchouc in the arts and manufactures 

 results from two distinct properties ; its high degree of elasticity ; 

 and its complete impenetrability to water. The modes in 

 which its elasticity is made useful are extremely numerous; 

 amongst others may be mentioned, the employment of it to form 

 elastic webs, which are partly woven with threads spun from it, 

 and which are introduced into braces, saddle-girths, and other 

 bands in which a steady and equable pressure is required. Its 

 impenetrability to fluid has long been known, and was applied 

 by the Indians of South America in the production of waterproof 

 boots ; these were made by spreading the juice, when flowing 

 fresh from the tree, over moulds of clay, which could be after- 

 wards broken away from their interior. Similar articles have 

 been made in this country, by keeping the juice in bottles from 

 which the air was excluded ; by which means it has been brought 

 over in a perfectly fluid state, without losing its power of hard- 

 ening when exposed to the atmosphere. 



369. But of late years, a much more effectual and ready 

 means has presented itself, of thus employing to great advantage 



