Electrification associated ivith Dust-Cloadi 



489 



are really derivatives of uric acid and should be called ureides; 

 salicin, tannin, vanillin, and guaiacum are probably gluco- 

 sides, and all give similar charges to each other but different 

 from those of the alkaloids. 



In Table IX. there is given a number of miscellaneous 

 substances which do not admit of convenient classification, 

 but those materials to which an acidic character is usually 

 attributed do in general give rise to positive electrification. 



Table IX. 



Substance. 



Charge. 



Substance. 



Charge. 



Calcium fluoride 



+ 

 -f 



' 4- 



4- 



4- 



4- 

 4- 



4- 



4- 



4- 

 4- 



Fine soil 



4- 

 4- 





Asbestos 



Precipitated silica 



Lycopodiuni 



Dextrose 



Methyl orange 





Dextrine 



Calcium acetate 







Potassium iodide 



4- 



Flour 



,, bromide 



,, permanganate.. 



,, bichromate 



,, hydrate 



,, ferrocyanide ... 



., bitartai'ate 



Urea 



-f 



Lead tartarate 





Tartar emetic 





Sodium aluminate 



+ 



4- 



,, salicylate 



,, bisulphite 





Amnion, bichromate 



+ 

 4- 



Conner cyanide 



Lead ehromate 





Pesorcin 





Pyro ff allol 



+ 



Carborundum 



Urea nitrate 



4- 



Tricalcic phosphate 



Monocalcic phosphate 



Sand 



Toluidine 





Nanbthylamine 





Diphenylamine 













In this table it may be noted that neutral potassium 

 ehromate acquires a negative charge, but the acid bichromate 

 acquires a positive. The same thing is seen with the neutral 

 tricalcic phosphate and the acid monocalcic phosphate. 

 Carborundum is a compound of two non-metallic elements, 

 and should be expected to give a positive charge. Emery- 

 powder is oxide of aluminium, and should behave as a basic 

 oxide and thus give a negative charge. The alcohol pyro- 

 gallol, commonly known as pyrogallic "acid," is not an 

 exception to the rule that acids should give positive charges. 

 It is rather remarkable that starch should give a positive 

 charge, and flour a negative one; urea is only very slightly 

 charged, but urea nitrate yields a strong charge. 



In all cases it is to be presumed that the air would acquire 

 a charge opposite to that upon the dust, and this was first 



