38 BACTERIOLOGICAL AND ENZYME CHEMISTRY 



volumes of all gases under the same conditions of temperature 

 and pressure contain the same number of molecules. Avogadro's 

 conception of molecules served to explain certain discrepancies 

 met with when comparing the weights of equal volumes of 

 different gases : thus, e.g., if the weights of equal volumes 

 of hydrogen and oxygen and of steam be compared — always, of 

 course, under the same conditions of temperatui'e and pressure 

 — it will be found that the ratio of the weights is as follows, 

 viz., H = 1, = 16, and steam = 9. 



It was further found that two volumes of hydrogen com- 

 bined with one volume of oxygen to form two volumes of 

 steam. Now it is evident that each of the two volumes 

 of steam contains an equal proportion of oxygen, inasmuch 

 as their weights and physical properties are identical. By 

 introducing the conception of molecules, Avogadro enabled 

 a clear conception to be formed of the action taking place. 

 He assumed that the molecule of oxygen contained at least 

 two atoms, one of which combined with hydrogen to form 

 a molecule of steam. We may represent the union of two 

 volumes of hydrogen with one volume of oxygen to form two 

 volumes of steam in the following manner : — 



+ 



o„ 



H,0 H,0 



32 



18 18 



Taking hydrogen as unit, bhe weights of the molecules 

 will be represented by the figures below the squares, and we 

 thus see how it is that if a volume of hydrogen is taken as 

 weighing 1, the same volume of oxygen will weigh 16, and 

 the same volume of steam 9. Assimiing the molecule of 

 hydrogen to contain two atoms, the molecular weight of all 

 other substances will be represented by the weight of their 

 vapour when compared under identical conditions with an 

 equal volume of hydrogen whose weight is taken as two. 



