CONCLUSIONS 



43 



mercury were found to combine to form water, carbonic acid 

 gas, and red oxide of mercury. In the second part of these 

 studies an inquiry will be made into the proportions in which 

 other elements combine. 



It has been observed that when hydrogen and oxygen 

 combine they do so iii definite proportions, a liquid — water — 

 is formed, the properties of which are entirely and permanently 

 different from the component gases, and heat is produced. 

 These three characteristics of chemical combination show that 

 water is a chemical compound. Air consists of oxygen, 

 nitrogen, carbonic acid gas, and water vapour in variable 

 proportions. If these gases be mixed together no heat is 

 produced, but the mixture has the same properties as air. Air 

 has therefore none of the characteristics of a chemical 

 compound, and is merely a mixture. 



For identifying chemical substances, both physical and 

 chemical methods are available. Thus, the co-efficient of 

 solubility of gypsum, the boiling point and freezing point of 

 water, and the relative density of hydrogen gas are " physical 

 constants " which are available for identifying these three sub- 

 stances. By chemical methods red oxide of mercury could be 

 distinguished from red lead, as they behave differently on 

 heating, and nitrogen from carbonic acid gas, as they differ in 

 their action upon lime water and litmus. 



QUESTIONS AND PROBLEMS FOR REVISION AND 

 EXAMINATION. 



The problems marked with an asterisk (*) are intended for practical 

 examination. 



Weights and Measures. 



1. Express 2195.817 grams in kilograms, hectograms, etc. 



2. Express l hectogram, 6 grams, 4 centigrams, and 9 milligrams in 



grams. 



3. Calculate the number of milligrams in a kilogram. 



