166 COUNT RUMFORD. 



resting on a horizontal surface, and restrained solely by 

 the resistance of a pellicle exerting a given force on its 

 surface. This pellicle he considers to be due to the 

 adhesion of the particles of liquids to each other, and he 

 makes various ingenious calculations to determine the 

 size of a particle of heavy matter of gold, for instance 

 which would rest suspended in water because of its 

 inability to force asunder the particles of the liquid. 

 The diameter of a sphere of gold which would behave 

 in this way he found to be ^sVor of an inch. 



Even among scientific men, probably few are aware 

 that Eumford experimented on the diffusion of liquids; 

 a field of investigation in which Graham afterwards 

 rendered himself so eminent. Into a glass cylinder, If 

 inch in diameter and 8 inches high, he poured a layer of 

 saturated aqueous solution of muriate of soda 3 inches 

 thick; over this he carefully poured a layer of distilled 

 water of the same thickness; he then let a drop of the 

 oil of cloves fall into the vessel. This oil, being heavier 

 than the pure water and lighter than the solution, 

 rested as a sphere at the common boundary of the two 

 liquids. A layer of olive oil four lines in thickness was 

 then poured over the water, in order to shut off the air. 

 The object of the experiment was to ascertain whether 

 one liquid remained permanently superposed upon the 

 other without any mixing. If this proved to be the 

 case, the position of the drop of oil would remain con- 

 stant; but if the heavy mineral solution rose into 

 the water overhead, the drop of oil, which Rumford 

 called his " little sentinel," would warn him of the 

 event by rising in the liquid. After twenty-four hours 

 he entered the cellar in which the experiment was 

 made, and found that the little ball of oil had risen 

 three lines. For six days it continued to rise at the 

 rate of about three lines a day. He afterwards experi- 



