48 Proceedings of the Royal Physical Society. 



the liquid developed frictional electricity, the quantity aud 

 duration of which determined the time the clay was held in 

 suspension. Before proceeding, however, to consider this 

 question, I will mention two or three experiments interesting 

 in themselves. 



(1.) Sea Water. — I obtained from the end of Leith Pier, a 

 sample of water; its density was 1009, showing it was consider- 

 ably mixed with the Water of Leith. On shaking it up with 

 clay, in the usual manner, I found it just about the best 

 mixture that could be made to precipitate quickly. It cleared 

 in about two hours. This fact throws considerable light on the 

 silting up of harbours, etc., at the mouths of rivers. Through 

 the kindness of Mr Brown, I got a specimen of strong sea 

 water from Dunbar, and found that it took about twelve hours 

 to clear, but on mixing it with an equal bulk of rain water, it 

 cleared in six hours. I next tried the effect of lime carbonate 

 in place of clay, and found that both rain water and strong 

 sea water cleared in about the same time, viz., two to three 

 hours, and this too although I put four times the weight in, 

 to bring up the opacity of the liquid to the same point. 



(2.) In order to test the sensitiveness of the clay to any- 

 thing held in solution by the water, I took four glass bottles 

 (light green glass), and filled them with rain water. To one 

 I added a few pieces of lead, to another some copper filings, 

 and to a third a few pieces of zinc, while the fourth remained 

 with water only. In that state they remained for a week, 

 when clay was added to each, and shaken up as usual. The 

 result was 



"Water only took 96 hours to clear. 

 ,, with copper, 72 ,, ,, 



„ „ zinc, 72 „ 

 lead, 42 ,, 



It appeared to me that the water had acted on the glass in 

 the first case, and extracted a little soda. With the lead the 

 action was evident. With the copper and zinc the action was 

 doubtful ; but possibly there might have been a little oxide 

 dissolved by the water ; but this experiment shows the sen- 

 sitiveness of the reaction. 



It occurred to me that possibly there might be some con- 

 nection between these phenomena, and the solubility of the 



