CAOUTCHOUC. !K)3 



gliinia madagascariensis, the last highly poisonous, but none of 

 them has been fully investigated. 



Caoutchouc, or Indian rubber is the dried milky juice of 

 several trees which grow in South America and the East Indies. 

 The fresh juice was found by Mr. Faraday to contain in 100 

 parts, 31.7 of caoutchouc, 1.9 of vegetable albumen, a trace of 

 wax, 7-13 of an azotised substance, bitter, soluble of a brown 

 colour in water and alcohol, and precipitable by nitrate of lead, 

 2.9 of a substance soluble in water, but insoluble in alcohol, and 

 56.37 parts of water containing in solution a small quantity of 

 a free acid, which precipitated nitrate of lead and coloured per- 

 salts of iron green without precipitating them. These subs- 

 tances are dried and included in common caoutchouc, of which 

 the density is 0.9335. Pure caoutchouc carefully prepared 

 from the milk is of density 0.925, transparent and colourless, 

 or of a light yellowish tint in mass. It contains no oxygen, but 

 in 100 parts 87-5 carbon and 12.5 hydrogen, which are nearly 

 in the proportion of C 8 H 7 (Faraday). 



Caoutchouc is remarkable for its extraordinary elasticity, and 

 its application to remove marks^ of black lead pencil from paper. 

 It is soluble in pure ether ; a small bag of caoutchouc left 

 in common ether for twenty four hours is softened, and 

 may then be greatly expanded by gradually inflating it, so 

 as to become light enough to ascend in the air when filled 

 with hydrogen gas (Mitchell). Caoutchouc when cut into 

 small pieces and well dried at 230, is dissolved by rectified 

 petroleum, and by the rectified oils from tar ; solutions which 

 are extensively used as caoutchouc varnish. Caoutchouc also 

 dissolves in the volatile and fat oils, but loses its elasticity in the 

 latter. Oil of turpentine is often used in the preparation of 

 caoutchouc varnish ; to dissolve the caoutchouc, it is said, after 

 it is softened and expanded by the naphtha. To render 

 cloth air and waterproof, Mr. C. Macintosh first applied several 

 coats of this varnish to one side of cotton or woollen cloth, and 

 then bringing the varnished surfaces of two pieces together, 

 passed the double cloth between heavy rollers, by which the 

 two pieces are made to adhere, and the intersticial spaces are 

 completely filled up. The sheet caoutchouc used by chemists 

 is obtained by sawing off a thin slice from a solid block of the 

 material. In forming short connecting tubes of it, the sheet 

 should be folded round the glass tube it is to fit, and the 



