SECT. II.] 



PROPERTIES OF STEAM. 



URE'S EXPERIMENTS ON THE FORCE OF STEAM. 



If a nice agreement with a particular set of observations had been attempted, 

 the formula could have easily been arranged to represent these better ; but by so 

 doing it appears to me that the elastic forces would have increased in a higher 

 ratio than we are warranted in expecting from other experiments, and the later 

 inquiries of Mr. Dalton justify the numbers being higher at or about 150 than 

 Dr. Ure's. 



99. Mr. Southern's experiments on high pressure steam were made with a 

 digester, with a thermometer fitted to a metallic tube, so that the stem of the ther- 

 mometer might be immersed as far as it contained mercury. Also, instead of 

 measuring the force of the steam by a loaded valve, a nicely bored cylinder was 

 used, with a piston fitting it so as to have very little friction, to the rod of which a 

 lever was applied, constructed to work on edges like those of a scale beam ; and 

 that no error might arise from this construction, a column of mercury was substi- 

 tuted, and the correspondence was within TOT of an inch. 



The observations at each of the points of temperature and pressure were con- 

 tinued some minutes, the temperature being alternately raised and lowered, so 

 as to make the pressure in excess and defect ; and a mean temperature was taken 

 for the result. This method seems to me entitled to great confidence, and hence 

 I have made the results the principal data for my formula. (See art. 86.) 



The experiments below 212 were conducted nearly as Dr. Robison's, and those 

 below 62 were made by Mr. W. Creighton. These low pressure experiments do 

 not seem to be of equal value with the four high pressure ones. 



