FREE BOOKS

Author's List




PREV.   NEXT  
|<   68   69   70   71   72   73   74   75   76   77   78   79   80   81   82   83   84   85   86   87   88   89   90   91   92  
93   94   95   96   97   98   99   100   101   102   103   104   105   106   107   108   109   110   111   112   113   114   115   116   117   >>   >|  
rcentages of oxygen and nitrogen that the question has arisen, whether these two elements are not combined in the air, forming a definite chemical compound. That the two are not combined but are simply mixed together can be shown in a number of ways, among which are the following. 1. When air dissolves in water it has been found that the ratio of oxygen to nitrogen in the dissolved air is no longer 21: 78, but more nearly 35: 65. If it were a chemical compound, the ratio of oxygen to nitrogen would not be changed by solution in water. 2. A chemical compound in the form of a liquid has a definite boiling point. Water, for example, boils at 100 deg.. Moreover the steam which is thus formed has the same composition as the water. The boiling point of liquid air, on the other hand, gradually rises as the liquid boils, the nitrogen escaping first followed by the oxygen. If the two were combined, they would pass off together in the ratio in which they are found in the air. ~Why the air has a constant composition.~ If air is a mixture and changes are constantly taking place which tend to modify its composition, how, then, do we account for the constancy of composition which the analyses reveal? This is explained by several facts. (1) The changes which are caused by the processes of combustion and respiration, on the one hand, and the action of plants, on the other, tend to equalize each other. (2) The winds keep the air in constant motion and so prevent local changes. (3) The volume of the air is so vast and the changes which occur are so small compared with the total amount of air that they cannot be readily detected. (4) Finally it must be noted that only air collected in the open fields shows this constancy in composition. The air in a poorly ventilated room occupied by a number of people rapidly changes in composition. ~The properties of the air.~ Inasmuch as air is composed principally of a mixture of oxygen and nitrogen, which elements have already been discussed, its properties may be inferred largely from those of the two gases. One liter weighs 1.2923 g. It is thus 14.38 times as heavy as hydrogen. At the sea level it exerts an average pressure sufficient to sustain a column of mercury 760 mm. in height. This is taken as the standard pressure in determining the volumes of gases as well as the boiling points of liquids. Water may be made to boil at any temperature between 0 deg. and considerably above 100 deg. b
PREV.   NEXT  
|<   68   69   70   71   72   73   74   75   76   77   78   79   80   81   82   83   84   85   86   87   88   89   90   91   92  
93   94   95   96   97   98   99   100   101   102   103   104   105   106   107   108   109   110   111   112   113   114   115   116   117   >>   >|  



Top keywords:

composition

 

nitrogen

 

oxygen

 
liquid
 

boiling

 

compound

 

chemical

 

combined

 
constancy
 

mixture


constant

 
definite
 

properties

 
pressure
 

elements

 

number

 

Inasmuch

 
largely
 

inferred

 

principally


discussed

 
composed
 

rapidly

 

Finally

 

detected

 

amount

 
readily
 

collected

 
ventilated
 

occupied


people

 

poorly

 

fields

 

mercury

 
column
 
average
 
sufficient
 

sustain

 

height

 

points


volumes

 

determining

 
liquids
 

standard

 

exerts

 

considerably

 
weighs
 

temperature

 

hydrogen

 

changed