CHAPTER IX 



MAKING OF FORMULAE AND EQUATIONS 



THE formula (p. 78) is a condensed statement of the composi- 

 tion of a substance. Before we can make (i.e., calculate) the for- 

 mula for a substance, we must (1) measure the proportions by weight 

 of the constituent elements. Then, we must (2) express these propor- 

 tions in multiples of the known atomic weights of the elements. 



Analysis and Synthesis. In the case of water H 2 O we 

 saw (p. 58) how the weights of hydrogen and of oxygen required 

 to give a measured amount of water were determined. The 

 composition of the water was found out by putting the substance 

 together out of the elements. This method is called synthesis 

 (Greek, putting together). 



In the case of mercuric oxide we can take a weighed amount 

 of the oxide, decompose it, and weigh the mercury formed. The 

 difference is the weight of the oxygen. This process, of decom- 

 posing a substance to learn its composition, is called analysis, the 

 Greek word for decomposition. 



One or other sometimes both of these plans can be used 

 with every compound. 



Some of the results of such experiments have been given in the 

 earlier chapters. For example : 



Tin (100) + Oxygen (26.9) - Tin oxide (p. 9). 



Lead (100) + Oxygen (7.72) - Lead oxide (p. 10). 



Iron (100) + Oxygen (43) -> Ferric oxide (p. 10). 



Zinc (2.04) + Sulphur (1) > Zinc sulphide. 



Mercuric oxide (108) - Mercury (100) + Oxygen (8) (pp. 15, 19). 



