342 Singular Property of Caoutchouc. 



seen in the figure, showing that there is no tendency to distri- 

 bution or equilibrium of latent heat between the two portions. 

 When the inelastic strip is inclosed in the hand, a slight degree 

 of coolness is felt from the rapid absorption of heat. 



I have been led to revive these interesting facts, in consequence 

 of a recent observation of the difference, in this respect, between 

 the native and the artificial rubber. The artificial rubber is at 

 present prepared in two ways; first, by solution in turpentine 

 and subsequent drying, and chiefly now without the aid of any 

 solvents, by merely grinding the native rubber to a pasty mass, 

 and reducing it to thin sheets between a succession of heated 

 . rollers.* In both of these preparations, the peculiarity of the na- 

 tive rubber, above noticed, is hardly perceptible. It is somewhat 

 remarkable that the interesting substance, gutta percha, appears 

 very much like the India rubber when rendered inelastic as above, 

 or by exposure to cold. This valuable modification of caout- 



hyd 



Macla 



Arts 



aday, gives carbon 87-2, and hydrogen 12*8. The gutta percha 

 yields by destructive distillation similar products to caoutchouc. 

 Like caoutchouc it is soluble in coal naphtha, in caoutchoucine, 

 and in ether, and insoluble in water and alcohol. " Its most 

 remarkable and distinctive peculiarity, as stated by Dr. Macla- 

 gan in his communication to the Scottish Society of ' '" ^" 

 effect of heat upon it. When placed in water at 111 , - 

 is produced upon it, except that it receives the impression of the 

 nail more readily ; but when the temperature is raised to 145° or 

 upwards, it gradually becomes so soft and pliant, as to be capa- 

 ble of being moulded into any form, or of being rolled out into 

 long pieces or flat plates. When in the soft state, it possesses all 

 the elasticity of common India rubber, but it does not retain this 

 property long. It soon begins again to grow hard, and in a short 

 time, varying according to the temperature and the size oi the 

 piece operated upon, regains its original hardness and rigidity. 

 May not this be a case of isomerism, in which the different 

 arrangement of atoms determines these physical distinctions- 

 The specific heat of gutta percha, I presume, has not yet been 

 determined, but it would be interesting to compare the two sud- 

 stances in this respect. 



August 31st, 1847. 



During the operation of rolling, great quantities of electricity are develope 



d 



