between some Kinds of Fluids , 161 



ammonia be then brought near, no movement is produced ; 

 if a few more raspings of cork be rubbed with the fingers 

 dipped in oil, and then thrown on the surface of the water, in 

 another glass, on approaching another drop of ammonia, all 

 these small parts will move in a wonderful manner. If the 

 farina of wheat be thrown into another glass of water, the 

 approach of a drop of ammonia will not cause these small 

 moleculae to move ; but if the farina of almonds, which is 

 oily, be thrown mto the water, it will cause them to move,^ 

 and precipitate them in an instant to the bottom. The same 

 experiment repeated a thousand ways, will always confirm 

 my conclusion, that is to say, that the action of ammonia 

 is rendered sensible only on oils, and on all oily matters, 

 or matters imbibed with oil. 



I think then I ha\e proved that the repulsion exercised 

 by ammonia over oil is not the effect of the force of its va- 

 pours or emanations ; and I am of opinion that it ought to 

 be ascribed to the attmction of surface possessed by the 

 ammonia in the state of fluid, as well as of vapour, with 

 oil itself, together with a chemical attraction which results 

 from the changes which the oil undergoes when exposed 

 to the effluvia of ammonia. This phcenomenon, in my 

 opinion, may be explained like that of a drop of spirit of 

 wine exposed in the middle of a stratum of, water, that is 

 to sav, that the repulsive force which ammonia seems to 

 exercise over oil, arises from the expansion of the ammonia, 

 or from its vapours on oil by means of the attraction of 

 surface. 



If a drop of ammonia, indeed, be thrown on the bottom 

 of a vessel, and if a very little oil be poured around it in 

 such a manner as to surround the drop of ammonia, if the 

 oil be extended with (he finger, and annnonia be applied, 

 the oil will be seen to recede ; but when it touches it, the 

 drop of ammonia will then break its limits, extend itself 

 over the oil, and disperse with surprising velocity. 



The antients would have ascribed it to an antipatljy be- 

 tween the ammonia and the oil ; but these chimerical ideas 

 have been banished by the light of experimental philosophy. 

 It does not appear tliat now the repulsions between the dif- 

 ferent fluids can be maintained, since I have established the 

 laws oi' the attraction of' ^urj'uce, which I have observed*. 



* See my Memoir on the Attraction of Surface, lo:. cit. 

 Vol. 21. No. 82. March 1805. L XXVI. A 



