280 Mr. C. Tomlinson on the Action of Solid Bodies 



adhesion is perfect. If dirty, the surface of liquid in contact 

 with it will be as free, or almost so, as the upper surface. We 

 hope to give a more definite idea of the word " dirty " presently. 



If further proof were wanting that Dr. Henricihas fallen into 

 error in consequence of an inadequate conception of the term 

 " chemically clean," it is to be found in his experiments and 

 remarks on the action of mercury in liberating gas from solution. 

 "When what he terms " pure " mercury was put into soda-water, 

 it " was immediately covered with rapidly swelling bubbles, which 

 ascended, while others formed in their place. Or when by sha- 

 king the glass the bubbles escaped from the mercury, new ones 

 immediately covered it; and this result, notwithstanding the small 

 quantity of gas in solution, could be repeated many times with 

 scarcely any diminution. Even in but slightly impregnated 

 water, in which other surfaces did not act, mercury, by separating 

 numerous bubbles, displayed its surpassing activity. Pure mer- 

 cury forms indeed the most perfect surface that can be used in 

 these experiments, since it is perfectly wetted by water." 



Dr. Henrici does not state by what means he obtains pure 

 mercury ; but it is well known to all who have much to do with 

 this metal that it becomes very readily tarnished or dirty, and 

 that it is troublesome to clean. Indeed from the time of Pre- 

 vost to that of Quincke it was alw r ays an anomaly in the pheno- 

 mena of surface-tension, that water, in which / = 7*3 5 would not 

 spread out into a film upon mercury, in which t = 4>7. But the 

 fact is that in trying this important experiment no one had de- 

 voted sufficient attention to the obtaining of chemically clean 

 mercury until Quincke* fulfilled this necessary condition, and 

 thus removed this anomaly from science. So also in testing 

 the liberating action of mercury on the carbonic acid of soda- 

 water, the results are sure to be erroneous unless special means 

 be adopted for obtaining a pure and clean metal. I had some 

 mercury by me that had been cleaned a few years ago ; it was 

 bright, convex, and tailless, and when last purified fragments of 

 phosphorus would move over its surface with great freedom. 

 Such was not the . case now ; the phosphorus was motionless on 

 the surface. A portion of the metal was therefore put into a 

 clean stoppered phial and shaken up with acid nitrate of mer- 

 cury, and a day or two afterwards with the strongest oil of vitriol, 

 and lastly well rinsed with clean water. The bottle was then 

 filled up with soda-water, and the metal, as was to be expected, 

 so far from displaying the singular activity referred to by Dr. 



* Poggendorff's Annalen, January 1870. A translation of this paper 

 appeared in the Philosophical Magazine for April, May, and June 1871. 

 Quincke's method of obtaining pure mercury is given at p. 460. 



