Mr Durham on the Suspeoision of Clay in Water. 49 



salts, etc. used, so I made several experiments for the purpose 

 of testing this idea. Taking quantities of the salts propor- 

 tional to their solubilities to see if they cleared in equal times, 

 and equal quantities of salt, to see if they cleared in times 

 bearing any relation to their solubilities; but I could not 

 trace any relation whatever between the two phenomena. 

 As an example, I may mention Barium Nitrate, and Potas- 

 sium Sulphate, which, at the temperature of the experiment, 

 are equally soluble. With equal quantities of the salts 



Barium Nitrate cleared in 2 hours 45 minutes. 

 Potassium Sulj)liate, ,, 16 ,, ,, 



I now turned to my original idea of electricity. I cannot 

 say that I have been successful, as yet, in proving this to be 

 the true cause of the phenomena ; but will state my experi- 

 ments on the subject so far as they have gone. Through the 

 kindness of Professor Tait, I have been enabled to make some 

 experiments in his laboratory (in conjunction with his assist- 

 ant, Mr Scott Lang), on the electric conductivity of saline 

 solutions of various strength. 



We used distilled water, which I find much more sensitive 

 than rain water to the action of salts in precipitating the 

 clay. We have as yet only made a few experiments on 

 common salt, and find that the electric resistance (which of 

 course is inversely as the conductivity) diminishes in a very 

 rapid manner with each addition of small quantity of salt. 

 Thus, suppose with the hundredth part of a grain of salt, the 

 resistance is about 30,000 B A Units ; with the fiftieth part 

 the resistance will be, say 20,000 B A Units. I am not at 

 present giving strictly accurate results, but only general. 

 This rapid diminution of resistance agrees very well with my 

 experiments of the rapid diminution of the time of clearing 

 with addition of salt. The turning point, however, that is 

 the point when the liquid began to take longer to clear, is 

 very soon reached, although the resistance is still diminish- 

 ing. This may be accounted for by the increase of specific 

 gravity. 



I got from Professor Tait the results of some former ex- 

 periments by two of his students on the electric resistance of 

 Zinc Sulphate, Copper Sulphate, and Potassium Sulphate. 



