Phenomena of some Substances and Mixtures. 



177 



certain number of safety-tubes dipping in mercury. I found 

 that the amount of spring in the apparatus was quite sufficient, 

 and that special glass springs were superfluous. 



7. For the observations properly speaking, I used Ducretet's 

 apparatus. The temperatures of air-manometer and gas-tube 

 were kept constant with the running water of the supply. A 

 constant water-pressure was obtained by means of an overflow 

 arrangement, and the current before passing round the gas- 

 tube was heated by a long coil in warm water. A sufficiently 

 constant temperature was obtained in this manner. 



Table I. 

 Ethane from Sodium Acetate (April 1897). 



, 



Pb- 



Pe- 



«*■ 



v e- 



5*55 



26-90 



27'42 



231-2 



33 



14-5 



3291 



33-52 



177-1 



35-6 



15-0 



3323 



3377 



176-1 



35-5 



2305 



39-74 



40-27 



130-9 



39-0 



30-2 



46-35 



4672 



94-5 



46 2 



32-2 



48 



64 ( 



) 61 



•5 



8. Table I. gives the results obtained : p b and v b are the 

 pressures and volumes when the condensation begins, p e and 

 v e when the whole substance is liquefied; p is expressed in 

 parts of an atmosphere, the v's in this and in all the other 

 tables are expressed in an arbitrary unit, but reduced to the 

 some initial volume at 0° and 1 atmosphere. C indicates the 

 critical point. The experimental determination of the p/s 

 gives no difficulty if the stirring-rod is continually used. 

 For pb this is not always the case, because stirring is not so 

 effective when the volume is much larger. In cases of doubt 

 p b and v b were therefore determined graphically as the 

 points of intersection in the p-v diagram of the two parts of 

 the isothermal, the part where the substance (mixture) is 

 homogeneous and the part where there are two phases. 

 Another advantage in drawing the latter part of the isother mal 

 is that from its shape and the direction of its curvature 

 some idea may often be obtained as to the nature of the 

 admixture *. 



* Compare a paper on ethane in the Proc. R. S. of Edinburgh, 1897. 

 1 thought it unnecessary to publish the p-v diagrams as they offer no 

 special interest. 



