SCIENCE OF COMMON THINGS. 



Adhesion. Examples of cohesion^ | 



bodies. Cohesion acts only between particles of pat- 

 ter of the same kind, and at distances which are not 

 measurable, or, as they are termed, insensible distaaices. 



63 What is adhesion ? 



Adhesion is attraction between particles of matter 

 of different kinds acting at immeasurably small dis- 

 tances only, and uniting the dissimilar particles into 

 one mass. 



63 Why is mortar used to fasten bricks together f 



Because the adhesive attraction between the particles 

 of the brick and the particles of mortar is so strong, 

 that they unite to form one solid mass. j 



64 Why is a bar of iron stronger than a bar of wood of the same size ? 



Because the cohesion existing between the particles 

 of iron is greater than that existing between the par- 

 ticles of wood. 



65 Why are the particks of a liquid more easily separated than those 

 of a solid ? 



Because the cohesive attraction which binds together 

 the particles of a liquid is much less strong than that 

 which binds together the particles of a solid. 



66 Why will a small needle, carefully laid upon the surface of water, 

 float f 



Because its weight is not sufficient to overcome the 

 cohesion of the particles of water constituting the sur- 

 face ; consequently, it cannot pass through them and 

 sink. 



6*7 If you drop water and laudanum from the same vessel why wiU 

 sixty drops of the water fill the same measure as one hundred drops of 

 laudanum ? 



The cohesion between the particles of the two liquids 

 is different, being greatest in the water. Consequently, 

 the number of particles which will adhere together to 

 constitute a drop of water is greater than in the drop 

 of laudanum. 



68 Why is the prescription of medicine by drops an unsafe method f 



Because not only do drops of fluid from the same 

 vessel, and often of the same fluid from different ves- 



