LATVS OF CHEMICAL COMBINATION. NOTATION. 41 



( A ^ ( A^ m - 1 f The given "\ C Number of ^ 



A ) -k-T^V * 5 M f I ^ -a 3 number of f ... } grammes off 

 As -< weight of > is to 4 weight of s so is < CTamraes of ( to ^ potassium T 

 (hydrogen) (potassium,) ( g h ydJeu ) ( required. ) 



1 : 39.1 :: 100 : the answer ; 



whence - - =3910 grammes of potassium. Such calculations are 



very useful as a discipline for students, impressing on their minds the four 

 great laws of chemical combination, particularly the law of definite pro- 

 portions. Examples may be multiplied at the discretion of the teacher, 

 employing from time to time the equations given in different parts of the 

 book. The questions of percentage composition and of volume relations 

 can not be entered upon in an elementary work. 



QUESTIONS. 



27. How do elementary bodies unite ? Illustrate by taking iron and sul- 

 phur. What is the first great law governing chemical combinations? 28. 

 Explain the nature of symbols ? How are they used ? What do they sig- 

 nify ? Write five atoms of nitrogen. How are molecules expressed ? 29. 

 What is a formula of a body ? What is the formula for common salt ? 

 What of sulphuric acid ? Explain the small figure in the latter formula. 

 What is the use of the period ? AVhat of the plus sign ? How are several 

 molecules of one substance written ? Do molecules ever contain several 

 atoms ? 30. What else do the symbols stand for ? Explain the law of 

 molecular weights. (The teacher should place examples on the black- 

 board.) 31. Give the law of multiple proportions. Illustrate with iron and 

 sulphur. What is the law of reciprocal proportions ? Explain by referring 

 to a Table of Atomic Weights. 32. Recapitulate the four laws. 33. Give 

 in your own language the use of chemical equations. Write the action of 

 water on potassium. Explain this equation. 34. How do the elements 

 combine as regards volumes ? 35. What three points are expressed by 

 equations ? 36. What is stoichiometry ? Calculate how many pounds of 

 caustic potash can be made from 100 pounds of potassium. How many 

 grammes of potassium are required to make 100 grammes of hydrogen ? 

 Explain the calculation. 



