150 PHYSIOLOGY FOR NURSES 



PROPERTIES OF LIQUIDS 



If a small tube is inserted into a glass of water it 

 will be seen that the water in the tube rises to a higher 

 level than that in the glass. This is due to cohesion 

 between the particles of water and adhesion between 

 the water and the tube, the adhesion being, in this case, 

 the stronger. If the experiment is repeated, but mer- 

 cury substituted for water, the column in the tube will 

 be lower than the level of the mercury in the glass. 

 Here the cohesion of the particles of mercury is stronger 

 than the adhesion of the mercury to the tube. 



Diffusion is another property of liquids by which two 

 liquids of different specific gravity will mix without shak- 

 ing even though the lighter be placed at the top. This 

 does not apply to liquids not soluble in each other. If the 

 two liquids are separated by a thin membrane they will 

 still mix, a process called dialysis. Some fluids will not 

 mix in this way. Those which diffuse through a mem- 

 brane are called crystalloid, and those which will not dif- 

 fuse are called colloid. 



Solution. When matter, solid, liquid or gaseous, is 

 permanently mixed with liquid, forming a uniform body 

 which does not separate on standing, the one is said to 

 be dissolved in the other, or a solution has been formed. 

 The most familiar example is the solution of sugar in 

 coffee, or other drink, to sweeten it. "When it is de- 

 sired to separate a solid from a liquid in which it has 

 been dissolved, the liquid is passed through some porous 

 material to which the solid adheres, leaving the liquid 

 behind. This process is called filtration. Many solids 

 in solution can not be extracted by this process, but 

 some can be with much saving of time and labor. 



