212 Mr. R. Sabine on Motion* produced by 



Exp, 1. A rather rich amalgam of lead was filtered through 

 a paper funnel into a clean shallow dish, so as to produce as 

 bright a surface as the nature of the amalgam would allow. 

 Then a drop of very dilute nitric acid was carefully placed 

 upon it by means of a pipette. The acid-drop did not lie still 

 (as it would do upon a surface of pure mercury), but set itself 

 at once into a jerky motion. It gradually contracted its area 

 and then suddenly spread out again, then gradually contracted 

 again, and again suddenly spread, the pulsations being irre- 

 gular. That portion of the amalgam surface which was ex- 

 posed by the contraction of the drop was Aery bright and 

 smooth, and appeared to be free from floating particles of 

 foreign metal which roughened the surface at other points. 



In a repetition of the experiment with weaker acid, the drop 

 was observed to march bodily over the amalgam surface, going 

 from one side to the other, and sometimes returning. 



Dilute sulphuric, hydrochloric, oxalic, and acetic acids be- 

 haved similarly to nitric acid, but in somewhat different 

 degrees. 



Amalgams of tin, antimony, zinc, and copper behaved simi- 

 larly to lead amalgam, but also in different degrees. 



It was found that, in order to produce these motions, the 

 acid must be sufficiently diluted to avoid the perceptible for- 

 mation of gas. The extent to which the dilution might be 

 carried appeared to depend upon the richness and nature of 

 the amalgam. Weak motions were observed with the fol- 

 lowing : — 



Amalgam of 1 oz. water to 



Copper 1 drop nitric acid. 



Zinc 2 drops „ 



Antimony 6 ,, „ 



Tin 8 „ 



Lead 15 „ „ 



Exp. 2. Instead of the foregoing metals, which in very di- 

 lute nitric acid appear to be all positive to mercury, amalgams 

 of platinum, gold, and silver were next tried, these metals being 

 all negative to mercury. On placing the acid-drop on the 

 clean newly filtered surface, no motion whatever was observed. 

 When a trace of positive metal, however, was added, slight 

 motions were observed. 



Exp. 3. A dish containing lead amalgam having a drop of 

 dilute nitric acid on its surface was placed under a small glass 

 receiver. The motions of the acid-drop were observed to be 

 irregular, the edge darting out first in one direction and then 

 in another. The air in the receiver was changed by the steady 



