212 CAPILLAEITY. 



the tube, and bent into the form shown in fig. 150 ; the fine narrow 

 tube, however, must not be bent in the flame, but above it, otherwise 

 it will form a sharp bend. The mercury is poured into the wider 

 end of the tube by means of a small paper funnel. 



The glass plates should be cut by a glazier out of a very flat piece ; 

 they should be from 4 to 6 cm long and 3 or 4 cm wide. They a 

 clamped between two pieces of cork of a suitable form, shown i 

 fig. 151 B, and placed in a very shallow saucer or upon a flat piec 

 of glass, which may also serve for the experiment with the tubes 

 (fig. 149) ; it is then only necessary to place a few drops of alcohol 

 upon the plate, with a pipette or a glass rod. 



The ascent of liquids in bodies which possess fii 

 pores or cavities is also caused by capillarity ; it is froi 

 this cause that water rises in wood, sponge, 

 blotting-paper, or oil in the wick of a lamp. Bodi( 

 float on the surface of a liquid because, as we have seen, 

 the upward pressure of the liquid is greater than theii 

 weight. It follows that if a body can be placed upoi 

 the bottom of a vessel in such a manner that there 

 no liquid between it and the vessel, no upward pressure 

 can be exerted upon it, and the body will not rise t< 

 the surface. Thus a flat cork, having one side vei 

 evenly cut or filed, and placed with that side upoi 

 the bottom of a small vessel or saucer, will not rise if 

 mercury be poured over it, provided that the cork b< 

 prevented from sliding while the mercury is poure< 

 into the vessel by a slight pressure of the finger ; if th( 

 finger is removed, it will even require a certain amount 

 of force to lift the cork from the bottom in consequence 

 of the downward pressure of the liquid. This experi- 

 ment will not succeed with water, because the action of 

 capillarity forces some water between the cork and the 

 bottom of the vessel, even if their contact is very close ; 

 but if care be taken to prevent the liquid from moisten- 



