NITEOGEN AND ITS OXIDES. 61 



ygen of interest ? 49. Describe a more convenient way of obtaining oxy- 

 gen from the same material. 50. How do gases and vapors differ ? What 

 is a permanent gas? 51. How is oxygen prepared from manganese di- 

 oxide? 52. How from potassium chlorate? 53. Explain the process. 

 Why is there danger of explosion ? How is explosion avoided ? Write 

 and explain the equation. 54. Name two other methods of making oxy- 

 gen. Who invented a commercial process ? 55. What are the properties 

 of oxygen ? 5G. What is said of oxygen as a supporter of combustion ? 

 57. What of burning charcoal in it ? What becomes of the oxygen in this 

 case ? 58. What forms when phosphorus burns in oxygen ? 59. How may 

 steel be burned in oxygen ? What is striking fire ? CO. Why is oxygen 

 essential to life ? 61. What are oxides? Mention an unstable oxide. 62. 

 What is said of metals uniting with oxygen in different ratios ? What is 

 a peroxide? What a suboxide? What a sesquioxide? 63. How may 

 ozone be prepared ? 64. How does ozone act on potassium-iodide-starch 

 paper ? 65. What are the properties of ozone ? What is said of its nat- 

 ure? 



CHAPTER VL 



NITROGEN AND ITS OXIDES. 



66. Abundance of Nitrogen and its Combinations. Nitro- 

 gen gas forms about four fifths of the atmosphere. It is one 

 of the elements in all animal substances, constituting about 

 one fifth of the flesh of animals when dried that is, when 

 freed from the water that is in it. It enters also into the 

 composition of many of the vegetable substances that are 

 designed for food for animals. It forms some important 

 substances by uniting with oxygen and other elements, as 

 nitric acid, ammonia, etc. It does not enter into any thing 

 like the number of combinations that oxygen does. For 

 example, while oxygen makes with the metals a multitude 

 of substances called oxides, there are very few compounds 

 of the metals with nitrogen. 



66 . How Nitrogen can be Obtained. Nitrogen gas can 



