CHEMISTRY OF THE EARTH 83 



that sometimes the atoms unite in the ratio 

 of one to one, at other times two to one, or 

 three to one, or even as in the case of carbon 

 and hydrogen, four to one. 



As there are eighty or more forms of ele- 

 mental matter, and as there may be from two to 

 as many as six or seven different elements, and 

 these in different arrangement and numbers of 

 atoms, in the compounds, it follows that the 

 number of chemical compounds is legion. For 

 out of twenty-six letters in the alphabet any 

 number of words may be formed, and three 

 or four words on the back of an envelope will 

 take a letter safely to one of many million 

 individuals. And, as the individuals are 

 arranged in countries and communities and 

 families, so also the groups of chemical com- 

 pounds are related and organised and arranged, 

 and a great part of the science of chemistry 

 consists of the study of their organisations 

 and relationships. 



Space forbids us entering into details of 

 such study, it will be sufficient for our present 

 purpose to point out that these elements 

 unite with one another with very varying 

 degrees of intensity, or as the chemist ex- 

 presses it, possess varying chemical affinities 

 for one another, and, secondly, that in uniting 

 they possess different valencies, or chemical 



