NUMBER OF ELEMENTS AND COMPOUNDS 



107 



decay, part of the hydrogen and sulphur they contain is given off as 

 hydrogen sulphide. The gas burns in air, giving water and sulphur 

 dioxide (cf. 105). It is present in the mineral waters known as 

 "sulphur" waters. 



114. Number of Elements and Compounds. The 



total number of compounds known is very large : probably 

 several hundred thousand. All of these are made of 

 80 or 90 elements. Most com- 

 pounds contain only 2, 3, or 4 

 of these elements, and only 

 about 30 elements are at all 

 common (Fig. 89). We may 

 compare the formation of com- 

 pounds out of elements with the 

 making of the many words of 

 our language out of its 26 let- 

 ters. In the following table Abundance of F t 8 E 9 ; ements in ^ 

 we have the names of some 



compounds formed out of the elements we have been 

 studying. 



