Force and Osmotic Pressure. 

 Concentration-cells without migration. 

 Moser's observations. 



389 



E.M.F. in 



Daniells. 



ZnSO 4 +800II 2 O. 

 ZnSO 4 +100H 2 O. 



002 



gm.-equiv./litre. log C 



1U00C. =-4>. 



0146 

 1-126 



4-1644 

 30515 



E.M.F. in 



volts X 10-4 



24.", 



Goodwin's observations. 



gm.-equiv./litre. j c . 



1000 c. 10 ° u 



0-2 to 0-02 

 01 to 001 

 0-02 to 0002 



4-301 to 5-301 

 4-000 to 5-000 

 5301 to 6-301 



E.M.F' 



427 

 440 



y With FbS0 4 as 

 : depolarisator. 



(vii.) New Experiments. 



To test the accuracy of the relation between electromotive 

 force and osmotic pressure as given in the foregoing theo- 

 retical treatment, and to provide data for calculating the 

 osmotic pressure, it is clearly necessary to make more syste- 

 matic and complete experiments than has so far been 

 done. In endeavouring to fill up this deficiency, I chose in 

 the first place the salts of zinc, because zinc electrodes are 

 well known to give results of a satisfactory degree of 

 constancy. The measurements so far made have been on the 

 chloride and sulphate of zinc : the former possesses the 

 advantage of an exceptionally great solubility, allowing of 

 investigations in the regions of concentration which are 

 especially interesting from the point of view of this paper. 

 The sulphate is, however, preferable in the matter of purity, 

 and neutrality; whilst as the course of the molecular con- 

 ductivity curve is considerably different for the two salts, a 

 comparison of results will give some indications as to the 

 properties common to salts in general. 



Materials. — For electrodes, zinc rod (obtained from John- 

 son and Matthey) was cleaned with emery-cloth, and amal- 

 gamated : or when liquid electrodes were to be used, some of 

 the same zinc was dissolved by gentle heating in about 100 

 times its weight of mercury. The zinc rods on standing for 

 davs in a zinc solution sometimes became coated with a 



