66 CHEMISTRY POR AGRICULTURAL STUDENTS 



to the compounds, regarding them both as hydrates of metallic 

 oxides, e.g. MO.HgO, and as metallic hydroxides, e.g. M(0H)2, 

 where M stands for any metal uniting with oxygen in single 

 combining proportions. Arrange them in groups of mono-, di-, 

 and tri-hydroxides. 



The result of these calculations will show that the assump- 

 tion on which they were founded was perfectly justified. In- 

 deed, it may now be surmised that, not only do elements in 

 general unite in the proportion of their combining weights, or 

 in simple multiples of them, but that the proportion in which 

 a compound unites with another compound is the sum of the 

 combining weights of its elements or a multiple thereof. 



XVI. THE NON-METALLIC ELEMENTS: 

 SULPHUR 



It has been found that non-metallic elements are characterised 

 by forming anhydrides, i.e. oxides which, when combined with 

 water, form acids; whereas metals form basic oxides which 

 combine with water, forming basic hydrates. The elements 

 which are non-metallic in this sense are further characterised 

 by absence of metallic lustre. In this respect oxygen must be 

 classed as a non-metaUic element; indeed, in that it forms 

 compounds with hydrogen and the metals, it may be regarded 

 as a typical non-metal. Just as the properties of oxygen and 

 the oxides have been studied, so we have now to study the 

 properties of the remaining non-metallic elements and their 

 compounds with hydrogen and the metals, in addition to the 

 compounds they form with oxygen, the acids formed by the 

 union of the oxides with water, and the salts formed by union 

 of acidic with basic oxides. 



