ON SUPERHEATED STEAM. 203 



expands only in a uniform degree with its incre- 

 ments of heat. Supposing this vulcanizer to be 

 one cubic foot (which it is not), three cubic inches 

 of water would be evaporated at 45 lbs. pressure ; 

 and if one degree only of heat more be applied, 

 it becomes superheated steam. A much larger 

 weight is put on the valve than the required 

 pressure, to prevent the chance of escape, as much 

 as possible, of odour or steam. A pressure of 120 

 lbs. to the inch, will set free small quantities of 

 steam at 50 lbs., by merely the vibrations on the 

 lever, caused by a person walking across the floor, 

 if it be boarded, or by opening or shutting the 

 door quickly ; and if the steam leaks, it becomes 

 a dry chamber, and the quality of the work is 

 injured. The only care required is, to keep it 

 steam-tight, and this is done with very little atten- 

 tion at first; and surely so simple an apparatus, 

 if it be a good one, deserves that little attention. 



Many curious and original questions have been 

 asked, which scarcely require to be answered ; 

 such as, Do the mineral teeth dissolve with the heat 

 and pressure used ? But one question has been 

 asked which I will take the opportunity of answer- 

 ing; that is, with respect to the formation of 

 hydrogen. Now, if hydrogen did form, it would 

 combine with the sulphur, and would not be as 

 elastic as steam. Steam will not decompose with 

 red-hot ii'on, and I doubt if it would with white- 

 hot iron, if no air or other body were present ; 



