﻿of the common Surface of two Liquids, 461 



sealing-wax. The apparently pure mercury is then shaken for a 

 long time with distilled water, or (and this is a better process) 

 it is allowed to run again and again through a paper funnel with 

 a very narrow opening into a porcelain dish filled with hot 

 distilled water. The foreign liquids, acids, oils, &c. mixed with 

 the mercury dissolve in the water. The water is separated from 

 the mercury, as the sulphuric acid was, by means of a paper 

 funnel, in which a funnel made of blotting-paper, with a larger 

 opening, can be placed. In order to remove the last trace of 

 water, the mercury is finally passed through a funnel made 

 of writing-paper with a narrow opening into a warmed porcelain 

 dish*, and in the same manner into a dry flask, in which, after 

 the latter has been corked, it is allowed to cool. 



If the mercury thus purified be placed in a watch-glass which 

 has been washed with alcohol, dried with a clean cloth, and 

 warmed over a gas-jet, then water and an aqueous solution of 

 hyposulphite of soda will spread themselves out upon it. 



If the mercury be allowed to run through a funnel of writing- 

 paper with a narrow opening into a warmed clean flask and then 

 cooled in the well-corked flask, water will then spread on the 

 surface of the cold mercury. 



If the surface of the mercury be touched with a freshly drawn- 

 out glass thread 0*1 millim. or smaller in diameter, on the 

 surface of which there is a trace of olive-oil or oil of turpentine, 

 water will contract upon it into a lens-shaped drop; at the same 

 time the drop of water changes its position on the surface of the 

 mercury, being driven from the place on which the oil was put. 



The diameter of the drop of water diminishes as the quantity 

 of oil placed on the surface of the mercury is increased. The 

 superposed layer of oil spreads itself on the surface of the mer- 

 cury to a thin pellicle of uniform thickness, lessens, as was ex- 

 plained in § 13, the surface-tension of the mercury, and equation 

 (2) § 25 gives a real value of angle co 3 . The diameter of the drop 

 of water diminishes as the thickness of the layer of oil on the 

 surface of mercury increases. If the layer of oil spreads itself 

 out on one side of the drop of water and diminishes the surface- 

 tension of the mercury in that place, then the whole drop will 



* The porcelain dish shows in the place where the stream of mercury 

 fell a system of Newton's coloured rings of an irregular elliptical form. 

 The coloured layer, whose thickness decreases more slowly towards the 

 outside than towards the inside, exhibited in the thickest place, after from 

 10 to 15 pounds of mercury had run out, blue and violet of the first order 

 to yellowish green of the second order in reflected light ; it was difficultly 

 soluble in C1H, but easily so in N0 3 H 2 , and I am inclined to think it was 

 oxide of mercury. "Whether the electricity excited by the friction of mer- 

 cury and porcelain contributed to its formation, further experiments must 

 teach. 



