114 EXPERIMENTAL GENERAL SCIENCE 



same thing occurs when a glass is partly filled with water. The 

 surface slopes upward wherever it is in contact with the glass. 

 If mercury instead of water is used, the surface curves down- 

 ward instead of upward. Experiments with various liquids 

 have shown that whenever a liquid wets or clings to the walls 

 of the vessel in which it is contained, the curvature is upward, 

 and when it does not wet the surface, the curvature is down- 

 ward. The phenomenon is best shown by means of small glass 

 tubes of different sizes. When several of these are stood in 

 the same dish of water, the liquid always rises highest in the 

 smallest tubes. In mercury, the surface is depressed, the 

 greatest depression occurring in the smallest tubes. The water 

 rises in the tubes because of a certain attraction between it and 

 the tubes, which is known as capillarity. Heat, which lessens 

 the attraction of molecules for one another, has a tendency to 

 reduce the effects of capillarity. The phenomena were first 

 studied in tubes with very fine hair-like openings, hence the 

 name from the Latin word capillus, meaning a hair. 



99. Absorption by Capillarity. A great deal of what we call 

 absorption is explained by capillarity. Wood takes up glue 

 or varnish, sponges soak up water, blotters take up ink in 

 fact, any substance with small openings in it will absorb 

 liquids when in contact with them. If one end of a towel is 

 left in a dish of water, the water will creep up in the capillary 

 spaces in the towel and soon leave the dish empty. Most 

 of the moisture used by plants moves through the soil by cap- 

 illarity. It is by this means that plants obtain moisture 

 at some distance from their roots. When the moisture in the 

 soil close to the roots has been taken up, more moves in by 

 capillarity. 



100. Deliquescence. Some crystalline substances have 

 such an affinity for moisture that they rapidly absorb it from 

 the air and are thus dissolved. A piece of sodium hydroxide 

 liquefies in a few minutes if exposed to the air and must be 



