186 M. F. C. Heurici on the Action of Solid Bodies 



was increased, aud the film could only be removed from the sur- 

 face by a tolerably strong pressure. 



The same effect was produced in the case of all kinds of metal. 

 A clean silver teaspoon had its hollow held over the flame, after 

 which this inner surface had no particular appearance, and be- 

 came wetted with water much in the same way as the simply 

 rubbed surfaces; nevertheless it cost me trouble to get rid of the 

 frictional impediment in wiping out the hollow. 



At the extremity of a strip of milk-white glass which had been 

 held in the small flame, there could be seen, with the assistance 

 of a lens, minute specks which could only be removed by very 

 strong pressure. 



We must also refer to the deposit of carbon on the bottom of 

 flasks &c. heated by a spirit-flame. 



Hence I must confidently conclude that, by the action of a 

 spirit-flame, glass and other solids become covered with a scarcely 

 recognizable (carbon?) film, which is itself sufficient to prevent 

 the separation of gas-bubbles from aerated water, probably by 

 absorption. The dust-particles which cover all .bodies exposed 

 to the air are most readily removed by rubbing with a clean 

 duster, or rinsing with clean water. Surfaces which after pre- 

 vious cleaning are long exposed to the air and then so treated, 

 act in fact like freshly cleaned ones. A glass rod so treated, a 

 silver wire which had stood twenty-four hours and upwards in 

 water, were covered abundantly with bubbles when put into 

 aerated supersaturated water. The most convincing proof is the 

 action of a pure quicksilver surface. In a small glass cylinder 

 5 centims. in height and If in width, a drop of pure mercury was 

 poured sufficient to cover the bottom, and carbonic-acid water 

 was carefully agitated with it. The mercury was immediately 

 covered with rapidly swelling bubbles, which ascended and others 

 formed in their place. As by the shaking of the glass the bub- 

 bles escaped from the mercury, this was immediately covered 

 with new ones; and this result, notwithstanding the small quan- 

 tity 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 — thus showing that mercury, 

 separating numerous bubbles, possesses a surpassing activity. 

 Pure mercury forms indeed the most perfect surface that can be 

 used ; and it is completely wetted by water. 



The choice of solids for these researches is somewhat limited. 

 Thus pure metallic surfaces cannot be compared with oxidized 

 ones, since the mechanical condition of the surface has the most 

 powerful influence on the results, and is often entirely different 

 in the two cases. If a clean polished brass wire be compared 

 with one that has been well rubbed with sand paper, the latter 



