332 



Prof. Gr. Quincke on the Edge-angle and 



Table II. 





Edge-angle. 



Water on 

 Clean surface. Greasy surface. 



Olive-oil on 

 clean surface. 



Topaz 



min. 



0(0/ 



7 37 1 58 

 4 15 2 24 

 3 2 

 2 8 1 22 

 1 16 

 55 

 



i 



80 



18 1 



8 4 



12 39 



7 58 



O 1 



14 11 

 47 3 



34 38 

 17 29 

 10 35 

 24 24 



Calc-spar 



Black glass 



Selenite 



Mica 



Quartz 



Slate j 



i 



A gold-leaf electroscope was immediately discharged on 

 contact with the clean surfaces of topaz, calc-spar, glass, mica, 

 and quartz, but not discharged, or only very slowly, on con- 

 tact with the greasy surfaces of the same substances. Plates 

 of selenite with either clean or greasy surfaces discharged the 

 gold-leaf electroscope. 



6. Metals are still more difficult to obtain with a clean sur- 

 face than glass or the substances named in the preceding 

 parapraphs. 



Noble metals, as platinum and gold, in thin strips of 10 

 millims. breadth, are ignited in the non-luminous Bunsen's 

 flame, and allowed to cool in a clean watch-glass between clean 

 glass plates. 



For silver I employed a film of silver deposited upon clean 

 plate-glass by Martin's process*, which was rinsed with water 

 as hot as possible and dried in the warm air-current over the 

 Bunsen-flame. 



Other metals were scraped with a clean knife, and the flat 

 drops brought as quickly as possible onto the clean surfaces so 

 prepared. 



After waiting a longer or shorter time T after the prepara- 

 tion of the clean surface before depositing the flat drops of 

 fluid, different values are always found for the edge-angle. 

 In the case of water and aqueous saline solutions the difference 

 is specially astonishing ; it is less in the case of olive-oil. 



Pure alcohol and petroleum spread over a clean surface upon 

 the whole of the metalsi nvestigated by me, and gave the edge- 

 angle 0°. 



* Pogg. Ami. cxxix. p. 55 (18('6). 



