160 On the apparent Repulsion 



tore ^^•c decide iii regard to the effect oi ammonia, let us 

 pay attenlion to the tollowing remarkable observations, 



Thiow small bits of gold or silver leaf on the surface of 

 oil contained in a goblet, and then bring near to it a drop 

 of ammonia, a commotion will be observed in the surface 

 of the oil, and in the small bits of metallic leaf which float 

 on it : if the drop of ammonia be applied lo the surface of 

 the oil, the small bodies will fly still more, and the fluid 

 will be seen to spread itself over the surface of the oil in the 

 most visible manner, while it produces in it an agitation. 



If this operation be performed on water, that is to say, if 

 after throwing on the surface of water containedln a similar 

 vessel very light bodies, such for example as bits of metallic 

 leaf or ra/pings of cork, a drop of anunonia be brought 

 near or applied, no movement will take place. The same 

 thing w-ill happen if spirit of wine, or any other fluid^ not 

 oily,~ be used in the place of water; but if instead of these 

 supernatant bodies there be on the water a drop or two of 

 oil, the latter will experience a commotion. On the drop 

 of ammonia being brought near, in a perpendicular direc- 

 tion, to the oil which floats on the water, if the oil be en- 

 tirely in the form of a drop, it causes it to dilate, and if it 

 be spread over the surface of the water, it divides and is 

 dispersed. If an orange skin be squeezed over the surface 

 of the water, and if a drop of ammonia be then applied, a 

 slisrht atiitation will be manifested in all the oily points with 

 which the surface of the water is interspersed. 



It appears then from these experiments, that ammonia 

 renders sensible to the sight the emanations on oil, not by 

 n>echanical impulse, but by a physical action, because it 

 doc;< not manifest itself on other fluids. 



It is bcvond all doubt that the shock or expansive force 

 of ammoniacal emanations ought to act without distinction 

 on all bodies, and connnunicate to them all the same im- 

 pulse when they can easily move; and a drop of anunonia 

 1>rou!iht near to the surface of spirit of wine ought to pro- 

 diu-ein it a coUnnotion equal to that which it communi- 

 cates to the oil, because it is equally light, and may be also 

 liirhler than oil. I have found also that ammonia applied 

 to the smoke of a candle, which bends itself on the least 

 breath of air, docs not make it move in the least. The eflcct 

 iif the ammonia on the oil cannot therefore be ascribed to a 

 nil ehanical action. 



But the following is a proof which admits of no reply : — 

 U raspings of cork be thrown upon water, and if a drop of 



ammonia 



