374 NINETEENTH CENTURY. pt. ill. 



compared to the nitrogen than the one before it ; and this 

 volume ahvays weighs i6 grammes^ while each volume of 

 nitrogen weighs 14 grammes. 



Oxygen behaves in this way in all compounds, only 

 joining itself to other elements in weights of 16 or multiples 

 of 16. Thus, if you he^t mercury as Lavoisier did, so that 

 it takes up oxygen out of the air, 200 parts by weight of 

 mercury will combine with 16 of oxygen and no more. If 

 you heat carbon with oxygen, 1 2 parts by weight of carbon 

 will take up 16 of oxygen to make carbonic oxide, or twice 

 16=32 to make carbonic acid, but it will not take up any- 

 thing between these weights. This same law holds true of 

 all the elements, each one having its own peculiar weight. 

 Nitrogen, for example, combines in weights of 14, or twice 

 14=28, or three times 14=42, &c. ; sodium in weights of 

 23, 46, and 69, &c. This is called the law of multiple pro- 

 portions^ which we owe entirely to Dalton, and it is a fact 

 about which all chemists agree. Dalton went on to try and 

 explain it by a theory which is still a matter of speculation, 

 and which some chemists do not receive. 



Dalton's Atomic Theory, 1808- — In order to explain why 

 each element should have its fixed weight in which it always 

 combines, Dalton imagined, as Democritus, Epicurus, Bacon, 

 and Newton had done before him, that all matter is com- 

 posed of tiny parts, or atoms ^ which are too small to be seen 

 and which cannot be divided. These atoms, which he 

 pictured to himself as round grains like very small shot, 

 would be of the same size in every substance, but not of the 

 same weight. Hydrogen atoms would be the lightest of 

 all, for hydrogen is the lightest substance known ; oxygen 

 atoms would be 16 times, and nitrogen 14 times, as heavy 

 as those of hydrogen. 



