±86 



Prof. W. A. Douglas Rudo-e on the 



A systematic investigation of the oxides of metals and 

 non-metals was made, the results being shown in Table IV. 

 Oxides may roughly be divided into " acidic" and " basic " 

 groups, the former being oxides of non-metals and the latter 

 those of metals, but of course the rule is not rigidly followed, 

 as many metals give acid oxides. We should thus expect to 

 find that some oxides should give positive clouds, and others 

 negative ones. 



Table IV. 



Oxide, 



Charge. 



Oxide. 



Charge. 



Aluminium ...... A1 2 3 



Antimony Sb 2 4 



+ 

 4- 

 + 



+ 

 4- 



Magnesium , MgO 



Mn0 o 

 Molybdenum M0O3 



„ HgO 



Nickel NiO 



Phosphoric . . . Y 2 5 



Tin Sn0 2 



Titanium TiO 



Tungsten W0 3 

 W 0, 



4- 

 4- 



4- 



f 

 + 



4- 



4- 

 4- 

 4- 

 + 

 + 



Sb o 0- 



Arsenic -As 2 3 



, As o 0- 



„ Ba0 2 



Cerium Ce 2 3 



CuO 



Chromium Cr 2 3 



, Fe o 0, 



uo 2 



Vanadium V,0- 



Lead PbO 



Pb0 2 



Pb 3 



Zinc ZnO° 



„ Zn0 2 





Manganous oxide MnO and chromic oxide might be 

 expected to give negative charges as they are decidedly 

 basic. Molybdenum, tungsten, and uranium form strongly 

 acid oxides. One oxide of antimony is basic and the other 

 acidic. The oxides of arsenic, phosphorus, and iodine are, 

 of course, very strongly acidic. From this table and the 

 preceding one another law may be deduced. 



Law III. Solid acids and acid-forming o.vides give positively 

 charged clouds, and basic oxides negatively charged 



ones. 



Assuming the truth of law III, it was of interest to 

 speculate as to what should be the nature of the charge 

 obtained on the cloud formed by raising a dust from a finely 

 powdered salt. Would the character of the base or the acid 



