COMMON THINGS AIR. 



of heat. When the flask has been cooled, and its contents examined, 

 it will be found to contain eighty cubic inches of azote and a 

 quantity of water, whose weight is exactly equal to the combined 

 weights of twenty cubic inches of oxygen and forty cubic inches 

 of hydrogen. 



The inference from this experiment is, that, tinder the influence 

 of the electric spark, one of the constituents of the air has entered 

 into combination with the hydrogen, and that their compound is 

 water ; and since the air has lost twenty cubic inches, it follows 

 that this portion of it is a gas which has the property of combining 

 with twice its own measure of hydrogen, and thus forming water. 

 The gas which possesses this property is called oxygen. 



The experiment here described is attended with two results, 

 both of which have high importance. It proves first that 100 cubic 

 inches of common air consists of eighty cubic inches of azote, and 

 twenty of oxygen ; and, secondly, that twenty cubic inches of 

 oxygen mixed with forty of hydrogen will be converted into water 

 by passing through them the electric spark. 



It now remains to explain the chief properties of the two gases, 

 by the mixture of which, in the proportion of eighty to twenty, or 

 four to one, common air is formed. 



20. Azote, or nitrogen, which thus forms four-fifths of the air 

 we respire, is characterised by negative rather than positive 

 qualities. It has neither colour, taste, nor odour. A candle or 

 lamp is immediately extinguished when introduced into it. 'No 

 animal which requires respiration can live in it. 



Although this inability to support life by respiration is not pecu- 

 liar to this particular gas, it has nevertheless given to it the name 

 azote, from two Greek words signifying the negation of life. 



This gas is not inflammable. 



The destructive influence of this gas on animal life does not 

 arise from any poisonous or injurious quality in the gas itself, but 

 altogether from the absence of oxygen. 



This gas, when compressed by the same force, is very little 

 different in weight from common air. A hundred cubic inches 

 of it weigh 30^- grains, while 100 cubic inches of common air 

 weigh 31 grains. 



21. The other constituent of atmospheric air, called oxygen, is 

 characterised by many very remarkable properties. 



Like azote, this gas has neither colour, taste, nor odour. Bulk 

 for bulk, and under equal pressure, it is a little heavier than com- 

 mon air, 100 cubic inches weighing 34-j- grains. 



The properties which are most conspicuously characteristic of 

 this gas are those which relate to combustion and respiration. 



22. Combustion, or burning, is a phenomenon which consists of 

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