308 



Mr. H. A. 



M c Tao-gart on the 



The tetravalent salt neutralizes the positive charge at a 

 much smaller concentration than the trivalent. 



The monovalent positive ion H, and negative ion OH in 

 HOI and KOH respectively were tried in water made electri- 

 cally neutral by adding a very small quantity of A1(N0 3 ) 3 . 

 When HC1 was added to this solution the bubble became 

 positively charged. When KOH was added it gave the 

 bubble a negative charge. 



In ordinary distilled water bubbles of hydrogen and 

 oxygen have practically the same velocity. There is probably 

 a difference which, however, cannot be detected with certain ty 

 under the conditions of the experiment. This difference 

 might show itself more definitely in a solution almost electri- 

 cally neutral. The following readings with air, hydrogen, 

 and oxygen were taken to see if a difference could be 

 observed : — 



A1 2 (S0 4 ) 3 . 



Air. 



0. 



n. 



10" 9 .2 







_ 



_ 



10 _9 .3 







— 



+ 



— Q 



10 .5 



+ 



- 



+ 



10~ 8 



+ 







+ 



10" 7 



+ 



+ 



+ 



It appears that the hydrogen changes sign at a smaller 

 concentration than the oxygen, so that in this case, at least, 

 the surface electrification is not independent of the gas. 



The following unexpected effect was observed when water 

 was used which had been boiled to free it from air. The 

 water was made almost but not quite electrically neutral by 

 adding Th(N0 3 ) 4 , and a bubble, placed in this solution, was 

 observed under the microscope. In this partially air-free 

 solution, the bubble was gradually absorbed by the liquid 

 and finally disappeared, but its electric charge during this 

 process did not remain the same. At first it was negatively 

 charged. As it diminished in size the negative charge 

 gradually disappeared until the bubble was neutral. As it 

 continued to diminish in size it began to acquire a positive 

 charge whicn slowly increased till the bubble became too 

 small to examine. This effect will be referred to again. 



