Caoutchouc or Indian Rubber. 295 



theory receives additional confirmation from 

 the following facts. 



EXPERIMENT 3. 



If a thong of Caoutchouc be stretched, in 

 water warmer than itself, it retains its elasticity- 

 unimpaired ; on the contrary, if the experiment 

 be made in water colder than itself, it loses 

 part of its retractile power, being unable to 

 recover its former figure ; but let the thong be 

 placed in hot water, while it remains extended 

 for want of spring, and the heat will imme- 

 diately make it contract briskly. The foregoing 

 circumstances may be considered as proving, 

 that the elasticity of Caoutchouc is not a con- 

 stitutional quality of the substance, but a con- 

 tingent eflfect, arising from the loss of equi- 

 librium between the portion of caloric, which 

 the resen happens to contain at any moment, 

 and its capacity to receive that fluid at the same 

 instant. Tlie object of the present letter is to 

 demonstrate, that the faculty of this body to 

 absorb the calorific principle, may be lessened, 

 by forcibly diminishing the magnitudes of its 

 pores; and this essential point of the theory 

 may be confirmed by experiment : for the spe- 

 cific gravity of a slip of Caoutchouc is increased, 

 by keeping it extended) while it is weighed in 

 water. JOHN GOUGIf. 



