196 ON SUPERHEATED STEAM. 



Apart from the safety of using sub-saturated 

 steam, is the avoidance of the deposits which 

 result from water, and the consequent less injury 

 to the material of the vessels. 



When steam only is used, and at too high an 

 expansion for the strength of the vessel, it is not 

 so liable as saturated steam is to burst it, but 

 bends or tears the metal only, and the moment of 

 escape lessens the force behind. I have had 

 slight-made malleable vessels bend and twist out 

 to all kinds of shapes and tear open, but never 

 burst. I have seen steam passed through red- 

 hot pipes for years, but never knew of explosions 

 therefrom. 



We will now in a few words enter upon the 

 chemical formation of rubber and its change by 

 being hardened with heat. Faraday and Brande 

 have both written and experimented upon the 

 subject, the result of which may be told in two or 

 three words; viz., that india-rubber is a carbo- 

 hydrogen — Cgo, Hjo; but Ure, who has also 

 written upon the subject, states that it contains a 

 small amount of oxygen, less than 1 per cent. I 

 incline to the latter as the correct formula. If I 

 may be permitted to express a theory upon the 

 subject, not founded upon actual analysis, but 

 founded upon the observation of appearances in 

 my experiments, which are analogous to changes 

 and appearances in other carbo-hydrogens of 

 which I have a correct knowledge, I am decidedly 



