ELASTIC GUM. ^9 



/elastic properties, thus affording an analogy to the influence of heat 

 in promoting the ductility of metals. 



The chief uses to which caoutchouc is applied in this country 

 are, 1st, The rubbing out of black-lead marks, by which it is uni- 

 versally known, and from which its name of Indian rubber is de- 

 rived. 2d, The formation, by means of turpentine or linseed oil, 

 of a varnish for air. balloons. 3dly, It supplies the surgeon with 

 flexible syringes, catheters, and bougies; and the chemist with 

 flexible tubes to gassometers and other apparatus. And, lastly, 

 Mr. Howison has shewn that cloth of all kinds may be made impe- 

 netrable to water by impregnating it with the fresh juice; and that 

 boots, gloves, &c. made of cloth thus prepared, wnichmay be join- 

 ed without sewing, by only moistening the edges with the juice, are 

 more durable and retain their shape better than those made of pure 

 caoutchouc. If more of this juice couM be obtained, there is no 

 doubt that it might be applied to a great variety of valuable and im- 

 portant purposes. 



There are, however, various other plants, from which the elas- 

 tic gum may be obtained in smaller quantities. Dr. Barton men- 

 tions several in America ; and Mr. Woodcock, of Islington, has 

 found it in some of the esclipias genus, aspecially a vincetoxicum, 

 and a fruticosa*. 



[Editor. 



* There is a curious mineral sul>6tance called mineral caoutchouc found in 

 the spar mine, near Castleton in Derbyshire, and which bears in many of its 

 properties a resemblance to the vegetable caoutchouc described above. It 

 was thought, says F. St. Fond, an astonishing circumstance, that a substance 

 which distils from exotic trees, which grow in fh** torrid zone, should be found 

 between strata of argillaceous schist in the bosom of the mountains in the 

 northern part of England. The depth at which this mineral has been found 

 is not less than four hundred and fifty feet below the upper stratum. There 

 appear to be two species of it, the elastic or compressible, and the solid or 

 brittle ; and several varieties of each. See Maw's Mineralogy of Derbyshire ; 

 and the memoir of Faujas-Saint-Fond, in Phil. Mag. vol. xv, 225. 



