LECTURES. 205 



Displacement of one body by the solution of another. Rosin dis- 

 solved in alcohol. Water poured in. 



Alcohol dissolves some substances which water does not ; and the 

 converse. 



(74.) Adhesion of liquids to liquids. — Oil spreads on the surface of 

 water. First drop infilms the whole of a limited surface ; second 

 drop collects itself into the form of a lens. The film so thin as to 

 exhibit the colors of the soap bubble. Explanation of the spreading 

 of oil on water. 



Effect of oil in stilling surface waves. Dr. Franklin's magical cane. 



Surface motions — camphor, spirits of turpentine, &c., on water; 

 motion produced by alcohol, oil, &c., in light bodies. 



(75.) Adhesion of gases to solids. — Air to glass shown by pouring^ 

 mercury into glass tube — vapor of water to glass — clean surface of 

 platinum plunged into a vessel of oxygen and hydrogen ; same effect 

 with other metals slightly warmed. 



Rapid manufactory of vinegar ; object of dividing the metal. 



Adhesion of gases to liquids. — Air absorbed by Avater ; also by melted 

 metals. Shown by pouring the liquid metal into water. 



(76.) Adhesion of gases to gases. — Between the molecules of the 

 same gas continued repulsion exists ; but the molecules of different 

 gases probably slightly attract each other. Diffusion of gases the 

 same as if the one was a vaccuum to the other. [See Prteumatics.] 



Molecular repulsion. 



(77.) Examples. — Two glasses, one slightly convex the other flat, 

 placed on each other and pressed by a force of 1,000 pounds to the 

 square inch are still, at the distance from each other of the thickness 

 of the top of a soap bubble jufst before it bursts, or at least ^ - o tb of 

 an inch. Method of finding this. [Bobison.] 



Small drops of water rebound from a surface of water. Also alcohol 

 from a surface of the same liquid gently heated. 



Solids expand when the pressure of the air is withdrawn, this 

 shown by experiment. Liquids, compressed, spring back to the 

 original bulk when the pressure is removed. 



The particles of air repel eacli other, repulsion increases with dimi- 

 nution of distance. 



By a slight agitation of percussion powder it springs into a gaseous 

 state — the particles separate with immense velocity, and repel each 

 other with great force. 



The dew drop which rests on the surface of a leaf is not in mathe- 

 matical contact, but sustained by repulsion. 



Repulsion of solids when heated. Experiment with an instrument 

 called the Rocker. 



(78.) The molecular attractions and repulsions appear to predomi- 

 nate at different distances. All bodies attract each other at sensible 

 distances, but when brought nearly in contact they repel ; still nearer 

 attract and again repel. 



Experiments of Huygens and Robison on this point — two very 



