Critical Phenomena of some Substances and Mixtures. 175 



Ethane from Ethyl Iodide. 



3. In order to ascertain the probable reason of this diver- 

 gence I prepared some ethane from ethyl iodide, the method 

 used by Haenlen, and investigated its properties. The 

 results have been communicated to the Royal Society of 

 Edinburgh. I will therefore simply state my conclusions 

 here so far as they bear upon the point in question. 



Ethane from ethyl iodide contains a variable quantity which 

 may go up to several per cent, of an admixture of higher 

 critical temperature and higher density than ethane, probably 

 butane. This impurity raises both the critical temperature 

 and pressure, and lowers its vapour-pressures. Pure ethane 

 is difficult if not impossible to obtain by this method. 



This result accounts for Haenlen's critical values being 

 higher than mine (and probably also for Olszewski's figures), 

 and it shows at the same time the greater purity of my ethane. 

 Even this was not absolutely pure, as shown by some change 

 of the vapour-pressure with volume. But whatever the ad- 

 mixture may be that this was due to, it was probably too 

 small to affect the critical temperature by more than a few 

 tenths of a degree and the critical pressure by more than some 

 tenths of an atmosphere. 



Ethane from Sodium Acetate. 



4. In order to confirm my results, and at the same time to 

 obtain some more pure ethane for further experiments, I 

 repeated the preparation of ethane from sodium acetate. The 

 anode, consisting of two pieces of platinum foil (joint surface 

 150 cm. 2 ), was placed inside a good-sized porous pot, care being- 

 taken to obtain a high current-density *. A current of about 

 15 amperes was used. Special precaution was required to 

 prevent the indiarubber stopper which closed the porous pot 

 from being burnt by the heat developed. A glass tube, 

 passing through the stopper, was bent into a U-shape outside 

 and contained some mercury. The contact with the platinum 

 foil w T as made by platinum wires soldered to the foil. 



The gas was washed in sodium hydrate, fuming sulphuric 

 acid, and potash, and collected in a gasometer which was 

 filled with a solution of potash. This gasometer consisted of 

 two carboys, closed with indiarubber stoppers and connected 

 by a wide glass tube. The yield of ethane was very high, 

 very little oxygen being formed. The oxygen was moreover 

 absorbed by introducing a piece of phosphorus into the gaso- 

 meter- 



* Murray, Journal Chem. Soc. Ixi. pp. 10-36. 



