490 Mr. R. Sabine on the Motions produced 



Viewed in this light, the water-drop maybe said to perform 

 two distinct functions : — (1) that of determining the area of 

 mercury the visible molecules of which are to be changed 

 from metal to suboxide, and vice versa ; (2) that of showing to 

 what extent the covered mercury surface is expanded or con- 

 tracted in consequence. 



And if this view is correct, it follows that, by knowing the 

 relative atomic volumes of mercury and its suboxide, we could 

 predict approximately to what extent any given water-drop on 

 a common surface of mercury would be contracted by the re- 

 ducing current. 



The atomic weight of mercury is 200, whilst its specific gra- 

 vity is 13*595 ; therefore its atomic volume is 



200 1*7. 



13-595 



The atomic weight of suboxide of mercury is 416. Its specific 

 gravity is not so well ascertained. Different authorities assign 

 it different values: — Gerstenhofer * gives 12*07 ; Her apath 

 found it 10*69, and Karsten 8*95 f. I assume that Hera- 

 path's value is the most trustworthy, viz. 10" 69, which is 

 nearly a mean of the other two. The atomic volume of sub- 

 oxide of mercury would therefore be 



416 " 38*9. 



10-69 



Now if the diameter of the water-drop when first placed 

 upon the mercury is d, and it contracts to d! under the action 

 of the reducing current, it is evident that we should find 



38-9 



d 3 / 



% = x/ """ =1-098; 

 d 1 X 2x14-7 



that is to say, we should be prepared to find the water-drop 

 about 10 per cent, larger in diameter Avhen first placed upon 

 the mercury than when the latter is put under the reducing 

 action of the battery. 



The following series of measurements with different drops 

 of distilled water was made before and after deoxidation of 

 the mercury. 



* H'ulfsbuch fur den Gewerb. Chemiker (1851), p. 4-5. 



t Watts's < Dictionary of Chemistry ' (1875), vol. iii. p. 907. 



