238 CATECHISM OF 



44 and Table II. How much water is contained in 8() lbs. of 

 plaster ? 44. If this be heated to redness, what takes place ? 44. 

 Could- you now look into Table II., and learn precisely how an}'' 

 of these salts are constituted ? 



Will you give some account of chloric acid ? 45. Of sulphuric 

 acid? 46. Of phosphoric acid ? 47. Of carbonic acid ? 48. How 

 is carbonic acid constituted ? 48 and Table I. What is its form ? 

 48. What its weight ? 48. When first formed, what takes place ? 

 48. What takes place soon ? 48. What portion of the air on an 

 average is carbonic acid ? 48. 



Of what do plants consist largely ? 48. Whence do they ob- 

 tain this ? 48. How do they receive it? 48. What of the vege- 

 tation of the globe ? 48. 



When vegetable matter is burnt, what becomes of its carbon ? 

 48. When it is eaten ? 48. When it decays ? 48. 



Lime-stone is carbonate of lime ; what proportion of it is car- 

 bonic acid ? 48. What proportion oT this is carbon ? Table I. 



The shells of fish and coral rock are also carbonate of lime; 

 when shells, coral and lime-stone, are burnt into quick-lime, what 

 becomes of the carbonic acid ? 48. . 



What is said of volcanoes ? 48. Of some springs ? 48. Of fis- 

 sures in the earth ? 48. 



What is said of the exhaustion and re-supply of carbonic acid 

 in the air ? 48. 



Is carbonic acid poisonous to breathe ? 48. How much of it 

 is there in pure air ? 48. How much in air from the lungs? 48. 



Why should school-rooms and churches be often ventilated ? 

 48. 



What is silicic acid ? 49. By what other name is it more com- 

 monly called? 49. How is it composed? 49. In what two 

 states does it exist in soils ? 49. What part does silica perform 

 in tht growth of crops? 49. What is said of oats grown on peat, 

 in which there is little or no silica ? 49. How much of it do we 

 generally find in soils? 49. 



Of what is nitric acid composed ? 50. What is said of its 

 salts? 50. Of old plastering ? 50. Of Chinese gardeners ? 50. 



What is muriatic acid composed of? 51. What was it for- 

 merly called? 51. » 



What is the composition of water ? 52. Give an account of 

 its decomposition and its recomposition ? 52. 



Where does the protoxide of iron often exist abundantly ? 53. 

 Is it hurtful to plants ? 53. How may the farmer know whether 

 his land is troubled with it ? 53. What is the cure ? 53. How 

 do you account for that variegated film that sometimes appears 

 on water? 53. May lime be used in such cases? 53. If ashes 

 are applied, why should the ground be first drained ? 53. 



How is the sesquioxide of iron composed ? 54. How does it 

 differ from the protoxide ? 54. What are those scales by the 



