PRINCIPLES OF COMBUSTION. 



137 



I would here observe on the importance of keeping in mind 

 this double relation of weight and volume, and the atomic consti- 

 tution of these gases, as it will prevent much of that confusion 

 which too often embarrasses those who are not familiar with 

 the subject of gaseous combinations. 



Let us now, in the same analytical manner, examine an atom 

 of atmospheric air, the other ingredient in combustion. 



Atmospheric air is composed of two atoms of nitrogen and one 

 atom of oxygen : and here again we find a great disproportion 

 between the relative volumes of these constituents ; one atom of 

 nitrogen being double the volume of an atom of oxygen, while 

 their relative weights are as 14 to 8 : the gross volume of the 

 nitrogen, in air, being thus four times that of the 'oxygen; and 

 in weight^ as 28 to 8, as shown in the annexed figure. 



Atmospheric Air, (or thus,) Atmospheric Air. 



Here we are relieved from the complexity arising out of any 

 difference in volume between these constituents, when united and 

 when separate. In the coal gas we found the constituents con- 

 densed into two fifths of their gross bulk when separate : this, 

 we see, is not the case with air ; an atom of which is the same, 

 both as to bulk and weight, as the sum of its constituents. 



relation between volumes and half volumes. As, however, I shall have to 

 do with masses of these gases, I have adopted circular figures, the rela- 

 tion between the sizes of the volumes of the different gases being the 

 same. 



