LAWS OF CHEMICAL COMBINATION. NOTATION. 35 



Examples of this law are abundant; to take the case 

 most familiar to us, iron and sulphur unite not only in the 

 proportions of atom to atom, but also of one atom of iron to 

 two atoms of sulphur consequently in the ratio of 56 parts 

 by weight to twice 32 parts. This is shown in the follow- 

 ing manner : 



. i unites with \ ... (to make > 



1 atom iron, weighing 



Fe, 56, , gj 



/ unites with \ ... (to mane \ 

 J 1 atom sulphur, i S hin * J a molecule, i 

 ( S, i 32 ' I FeS, ) 



1 atom iron, weighing j su lphur, i weighing] 



Fe > 56 ' I S 2 , i <* I FeS 2 , ) 



When there are two elements forming different com- 

 pounds, generally one remains the same in all the combina- 

 tions, while the other is varied, not irregularly, but regular- 

 ly. When two elements unite to form a series of com- 

 pounds, this law of multiples is very noticeable. Oxygen 

 and nitrogen furnish such a series, which you will find on 

 page 63. Sometimes the series is complete, as in the case 

 of the combinations of hydrogen with oxygen and chlorine, 

 which may be stated thus : 



Composition by weight 



Names. Formulae. Hydrogen. Chlorine. Oxygen. 



Hydrochloric Acid HC1 1 35.5 



Hypochlorous " HC1O 1 35.5 16X1=16 



Chlorous " HC1O 2 1 35.5 16X2=32 



Chloric " HC1O 3 1 35.5 16X3=48 



Perchloric " HC1O 4 1 35.5 16x4=64 



Here the proportions of oxygen, 16 xl, 16 x 2, 16x3, 16x4, 

 are respectively the multiples of 16 viz., 32, 48, and 64. 



The remaining law is that of Reciprocal Proportions, 

 which may be thus stated: If two bodies combine with a 

 third, the proportions in which they combine with that 

 third body are measures or multiples of the proportions in 

 which they may combine with each other. 



