QUESTIONS AND PROBLEMS 129 



"165. Identify the solids. (Powdered charcoal, black oxide of manganese, 

 and black oxide of copper. ) 



The Oxides of Carbon. 



166. Describe the method of preparation of carbonic acid gas. Explain 



why carbonates are decomposed by hydrochloric acid. When 

 chalk or marble are used, why should hydrochloric, and not 

 sulphuric, acid be employed ? 



167. To what substances does carbonic acid gas act as a supporter of 



combustion? State whether potassium and sodium would burn 

 in the gas if magnesium is able to do so. Represent the reaction 

 that would occur by an equation. 



168. Describe the reaction that occurs when carbonic acid gas is passed 



over heated charcoal. Explain the occurrence of a blue flame 

 over a coke fire. What is the danger in the use of slow combus- 

 tion stoves ? What are " producer gas " and " water gas " ? 



169. What are the properties of carbon monoxide? How is it distin- 



guished in (i) properties and (2) percentage composition from 

 carbon dioxide ? 



1 70. Describe the use of carbon as a reducing agent of metallic oxides. 



State how the reduction may be carried out on a small scale, and 

 name some of the metals which are produced by this means on a 

 large scale. In the case of the metallurgy of magnesium from 

 magnesium chloride, what reducing agent is employed ; and in the 

 case of mercury, why is no reducing agent necessary ? 



*I7I. Distinguish the three gaseous compounds of carbon from each other. 

 (Marsh gas, carbon monoxide, and carbon dioxide.) 



*I72. Identify the three gases. (Oxygen, hydrogen, nitrogen, ammonia 

 [nitrous oxide, nitric oxide, nitrogen peroxide], sulphur dioxide, 

 sulphuretted hydrogen, chlorine, hydrochloric acid gas, marsh 

 gas, carbon monoxide, carbonic acid gas, or air.) 



*I73. The oxide is believed to be either ferric oxide or an oxide of lead, 

 To distinguish, reduce with carbonate of sodium on charcoal by 

 means of a blow-pipe. Lead will give soft metallic globules, 

 iron a black magnetic powder. 



The Carbonates. 



174. In what proportion is lime combined with carbonic acid gas in 

 chalk ? Calculate what weight of quicklime is obtained from 100 

 tons of chalk, and what weight of dry slaked lime will it yield ? 



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