t20 CHEMISTRY FOR AGRICULTURAL STUDENTS 



40. Two oxides of copper are known having the formulas CugO and 



CuO. How would they be distinguished by name ? An oxide 

 of hydrogen is known having the formula HgOg ; it yields oxygen 

 on heating. How would it be distinguished by name from water ? 



41. What happens when quicklime is slaked with water? What 



evidence is there of a compound being formed ? What are com- 

 pounds with water termed ? 



42. Describe the method of determining the composition of slaked lime. 



Describe the construction of the dessicator, and its use. It was 

 found that slaked lime contains 24.3 per cent, of combined water. 

 Express its composition by a formula. 



43. Are the hydrates of metallic oxides usually decomposed by heat ? 



What hydrates resist decomposition, even at a red heat ? 



44. When compounds combine, do they, like elements, combine in 



definite proportions ? What relation does the proportion in which 

 they unite bear to the combining weight of the elements of which 

 they are composed ? Give examples. 



45. What is meant by the term *' metallic hydroxide " ? Ferilc 



hydroxide contains 52.34 per cent, of iron, 44.86 per cent, of 

 oxygen, and 2.80 per cent, of hydrogen. Express its composition 

 by a formula. 



46. Of the two substances one is an oxide and one a hydroxide. Identify 



the hydroxide. (Slaked lime and dried magnesia. ) 

 *47. Determine (i) the free water, (2) the combined water, in the metallic 

 hydroxide. (Calcium hydroxide, undried.) 



The Non-metatxic Elements : Sulphur. 



48. How are non-metallic elements distinguished from metallic elements ? 



For what reasons is oxygen classed as a non-metal ? 



49. Describe the several changes that occur when sulphur is heated from 



the solid, through the liquid, to the gaseous state. What occurs 

 when very hot molten sulphur is suddenly cooled, and how is the 

 modification formed distinguished from ordinary sulphur ? What 

 do you understand by " allotropy "? 

 55. Describe what happens when sulphur and iron filings are heated 

 together. State your reasons for believing that chemical combina- 

 tion occurs. If the product were a mere mixture, what would 

 be its behaviour to a magnet and to a solvent such as bisulphide 

 of carbon ? What formula expresses the composition of the 

 product ? 



