128 GENERAL PRINCIPLES 



respiration, which have the best tendency to promote health, 

 enjoyment, and cheapness of living ; and it sets him on his 

 guard against many unseen evils, to which those who are ig- 

 norant of its laws are continually exposed. In a word, from 

 a speculative science, chemistry, since the middle of the 

 eighteenth century, has become eminently and extensively a 

 practical one. From an obscure, humble, and uninteresting 

 place among the objects of study, it has risen to a high and 

 dignified station ; and instead of merely gratifying curio- 

 sity, or furnishing amusement, it promises a degree of utility, 

 of which no one can calculate the consequences or see the 

 end. 



Questions. — 1. What dors chemistry do for the husbandman? 

 2. For the manufacturer ? 3. For the mechanic arts ? 4. For the 

 physician ? 5. For the student of natural history ? C. For the public 

 economist? 7. For the philanthropist? 8. I or the domestic eco- 

 nomist ? 



LESSON 59. 

 General Principles of Chemistry. 



The object of chemistry is to ascertain the ingredients of 

 which bodies are composed, — to examine the compounds 

 formed by those ingredients, — and to investigate the nature 

 of the power which produces these combinations. The 

 science therefore naturally divides itself into three parts : a 

 description of the component parts of bodies, or o^ elementa- 

 ry or simple substances as they are called, — a description 

 of the compound bodies formed by the union of simple sub- 

 stances,— ^and an account of the nature of the power which 

 produces these combinations. This power is known in 

 chemistry by the name of ajfmity, or chemical attraction. 



By simple substances is not meant what the ancient phi- 

 losophers called elements of bodies, as fire, air, earth, and 

 water, nor particles of matter incapable of farther diminu- 

 tion or division. They signify merely bodies that have never 

 been decomposed, or formed by art. The simple substances 

 of which a body is composed are called the constituent parts 

 #f that body ; and, in decomposing it, we separate its co»- 



