of Superheated Vapours* 



407 



In the second the question was, to realize a case in which a 

 variable <£ might be surely expected. I endeavoured to make 

 use of my earlier experience *, according to which, at not high 

 temperatures small quantities of aqueous vapour exhibit extra- 

 ordinary power of adhesion to glass and mercury. I put into a 

 tube a portion of dry mercury, and filled up one side with dry 

 air ; into the other side I then poured a quantity of somewhat 

 moist mercury : the rest of this side was likewise filled with air 

 and hermetically sealed. I now heated it strongly, in order to 

 expel the water from the mercury and so fill the air above it 

 with aqueous vapour. A sufficient quantity of vapour actually 

 entered the space which the air occupied, as the following series 

 of measurements show ; they contain the corresponding values 

 of t and H. 



Table III. 



t. 



II. 



t. 



H. 



t. 



H. 





millims. 



o 



millims. 



o 



millims. 



41-6 



-113-5 



183 



-104-8 



6i9 



-107-8 



51-7 



-115-4 



14 



-105-3 



84-7 



-107-3 



61-9 



-116-9 



21 



-104-5 



70-5 



-107-7 



71-5 



-116-4 



251 



-104 



70-7 



-107-8 



78-3 



-112-7 



301 



-103-2 



761 



-108-7 



83-7 



-111-3 



35 



-103-5 



76 



-109 



90 



-111-2 



40-3 



—104 



75 



-108-7 



93 



-111 



46-2 



-104-8 



80-5 



-109-5 



85 



-110-2 



32-7 



-103 







78-3 



-109-6 



50-4 



-105-5 







13-6 



-106-3 



60-1 



-106-9 







26-1 



-103-9 



70-5 



-108-4 







34-8 



-103-3 



80-4 



-109-9 







48-2 



-1051 



89-8 



-110-9 







58-1 



-108-7 



94-4 



-111 







48-2 



-1051 



83-6 



-109-8 







41 



-103-9 



73-6 



-108-4 







29-8 



-102-7 



641 



-107-1 







26-5 



-103-5 



54-9 

 54 



-105-4 

 -105-2 







This Table shows that as far as 90°, during the first heating 

 the air on the side of the moist mercury exerted a considerably 

 less pressure than afterwards, when the steam expelled by the 

 heating cooperated. 



In the numbers which were obtained after this high tempe- 

 rature had once been reached, such an agreement is recognized 

 in the repeated ascending and descending series, that greater 

 could not be expected if adhesion of the aqueous vapour took place. 



* Pogg. Ann. vol. exxxvii. p. 602. 



