23 SCIENTIFIC AGRICULTURE. 



TENACITY. 



By tenacity, we understand the degree of force or cohesion 

 with which the particles of a body are held together, in other 

 words tenacity means toughness. Some substances, as some 

 of the metals, are extremely tenacious, while others want this 

 quality almost totally. The tenacity of the metals varies great- 

 ly, cast steel being the most tenacious of them all, while lead 

 is the least so. The tenacity of the woods varies as does also 

 that of soils : clay soil is tenacious, while sand soil is destitute 

 of this property. 



CHEMICAL ATTRACTION, OR AFFINITY. 



This is a peculiar power in bodies, which disposes them to 

 unite with other bodies and form compounds. It is the power 

 by which chemical phenomena are produced: it is different 

 from cohesion and all other forces in nature: it acts with 

 various degrees of energy in different elementary bodies, 

 showing a preference for some, and refusing to act on others 

 at all. Chemical affinity is influenced by many other agents, 

 as heat, electricity, gravity, cohesion, moisture, elasticity and 

 light. An affinity originally weak, may by some of these 

 agencies be made strong, while an affinity originally strong 

 may be rendered weak or, destroyed altogether. 



When common salt is thrown in water, it unites with it, 

 (dissolves,) by means of a weak affinity or chemical attraction, 

 but if oil be thrown into water, it does not unite with it, 

 because it has no affinity for it Some substances unite in all 

 proportions, as, for example, vinegar and water; while others 

 unite only in definite and fixed proportions, as sulphuric acid 

 and lime, &c. When two substances of opposite natures are 

 brought together, as, vinegar and pearlash, they readily unite, 

 by means of simple affinity, and form a third substance dif- 

 ferent from either of the other two. If now a third substance 

 be added, which has a stronger affinity for one of these two 

 than they have for each other, the two first separate, or are 



