Singular Property of Caoutchouc. 341 



Art. XXVI. — Singular Property of Caoutchouc, illustrating 

 the value of Latent Heat in giving Elasticity to solid bodies^ 

 and the distinct functions in this respect of latent and free or 

 sensible heat; by Charles G. Page, M.D., Prof. Chem. Na- 

 tional Medical College, Washington, D. C. 



The fact is familiar that if a strip of India rubber is forcibly 

 stretched, it becomes quite hot from the development of latent 

 heat, owing to the compression which the particles undergo in 

 one direction, by distention in another ; and on suffering the strip 

 to relapse, the heat thus developed is absorbed or becomes latent, 

 and the strip appears with its original degree of sensible heat. 

 While thus much has been known nearly as long as the article 

 caoutchouc has been in common use, yet I believe no special ob- 

 servations have been made upon this point, and the following inter- 

 esting fact, first noticed by me about ten years ago, has excited 

 no particular attention. If when the strip of rubber is in the 

 stretched condition, it be quickly cooled, which can be readily 

 done by wetting it, and evaporating the moisture by vibrating or 

 loving it rapidly in the air, it will be found to have lost its elas- 

 ticity, and may be left for an indefinite time without regaining 

 its elastic property. It resembles a piece of frozen rubber in 

 some respects, although not quite so rigid. A piece of this sub- 

 stance, which has become stiff and inelastic by exposure to a 

 a great degree of cold soon regains its elasticity by immersion in 

 a n atmosphere of 70° Fahr., or even much below this. But the 

 rubber deprived of its latent heat by compression, I have kept in 

 ^ atmosphere of 80°, for several weeks, without its returning to 

 "normal condition. If the heat be raised much above 

 80 °, or if it be placed in contact with a good conductor at 

 80 °, it gradually recovers its latent heat, and in a few 

 minutes is restored to its original dimensions. A curious 

 sensation is experienced if it be inclosed in the hand, 

 "ke the creeping of an insect. If successive portions 

 of the inelastic strip be pinched between the thumb 

 a nd finger, it contracts powerfully in these parts, leav- 

 m g the others unaffected, and presenting the appear- 

 ance— as in the figure— of a string of knots or beads, 

 ^hich may be preserved in this state for any length 

 of time, if not handled, and kept at a moderate tempera- 

 tore. Upon examination by a sensitive thermometer, the 



As 



may 



temperature 

 ards the amount of heat contained, the portions c 

 differ considerably, and in respect to latent heat, a 



portions continues abrupt and 



The junction 



