30 CHEMISTEY. 



QUESTIONS. 



19. What is the use of theories ? 20. What is said of the divisibility of 

 matter ? What are molecules ? Give the reason for their not touching 

 each other in masses. State what is given as the probable size of mole- 

 cules ? Are molecules motionless? 21. What are the advantages of this 

 theory ? Why do bodies expand by heat ? 22. Of what are molecules 

 made up ? Show the difference between Chemistry and Physics ? 23. De- 

 scribe the illustration of this difference in the example given. What is 

 sulphide of iron ? 24. Explain the nature of elements with reference to 

 the atomic theory. 25. What other properties are ascribed to atoms ? Is 

 any thing lost or destroyed when burned up ? 26. What is the most im- 

 portant attribute of atoms ? Are these absolute weights ? What is the 

 standard now adopted ? 



CHAPTER III. 



LAWS OF CHEMICAL COMBINATION. NOTATION. 



27. Law of Definite Proportions. Chemists have made 

 innumerable experiments and analyses by which it is proved 

 that elementary bodies unite in definite proportions by 

 weight. Thus, if you take 32 pounds of sulphur and heat 

 it with iron filings to make sulphide of iron, as in the experi- 

 ment noticed in 23, you will require just 56 pounds of iron, 

 no more and no less. If you should take 32 pounds of sul- 

 phur and GO pounds of iron, you will have four pounds of 

 iron left over, i. e., uncombined ; or if you take 50 pounds of 

 sulphur and 56 of iron, you will have 18 pounds of sulphur 

 too much. While, therefore, there may be great indefinite- 

 ness in mere mixtures, there is none in the formation of 

 compounds. Every compound always has exactly the same 

 composition. No matter under what circumstances the 

 compounds are produced, this exactness is preserved. The 

 carbonic anhydride formed by combustion, by respiration, 



