VI. MISCELLANEOUS. 177 



686. Apparatus for determining the Tension of the Vapours 



of different liquids at the boiling point. Prof. W. F. Barrett. 



This is a useful and strong form of the usual apparatus. The liquids 

 whose tensions are to be measured are inserted in the barometer tubes, 

 and either steam or the vapour of some liquid having a lower boiling point, 

 such as alcohol, is sent through the larger tubes. 



670. Parabolic Diagram of the relation between tension 

 and volume of the saturated steam. 



H. Hadicke, Demmin, Pomerania. 



The area of this parabolic tension diagram shows that it is justifiable to 

 replace the area of Mariotte's oder Pambour-Navier's tension-lines of the 

 saturated steam by a parabola. This method gives for the ratio of the mean 

 pressure (p ~) on one side of the piston to the absolute pressure at the 

 commencement (p), and the cut off (e) the elementary formula : Po^p ^ 

 0- ) 2 (4 ;>+!), or 



4p+l 



(See " Practical Tables and Rules for Steam Engines," by H. Haedicke 

 Kiel, 1871.) 



687a. Independent Bed Plate for Pneumatic Machines. 



Geneva Association for the Construction of Scientific In- 

 struments. 



This plate is made entirely of cast-iron, as well as its stand, so as not to 

 become damaged in experiments where mercury is employed. 



4C075. 



