OXYGEN AM) ITS SALINK Co.MIHNATIoNs 183 



be prolonged, and tin- draught of air be increased, 63 parts of copper 

 absorb 16 parts of oxygen, and form black oxide of copper. Some- 

 times to distinguish between the degrees of oxidation a change of 

 suffix is made in the oxidised element ic oxide naming the higher 

 degree of oxidation, and ous oxide the lower degree. Thus ferrous 

 oxide and ferric oxide are the same as suboxide of iron and oxide of 

 iron. This nomenclature is convenient in some cases, but cannot 

 always be employed. If an element forms one anhydride only, then it 

 is named by an adjective formed from the name of the element made to 

 end in ic and the word anhydride. When an element forms two 

 anhydrides, then the suffixes ous and ic are used to distinguish 

 them : ous signifying less oxygen than ic ; for example, sulphurous 

 and sulphuric anhydrides. 49 When several oxides are formed from the 

 same element, the prefixes mon, di, tri, tetra are used, thus : chlorine 

 monoxide, chlorine dioxide, chlorine trioxide, and chlorine tetroxide 

 or chloric anhydride. 



Chemical transformations of the oxides themselves are rarely 

 accomplished, and in the few cases where they are subject to such 

 changes a particularly important part is played by their combinations 

 with water. The majority of, if not all, basic and acid oxides combine 

 with water, either by a direct or an indirect method forming hydrates 

 that is, such compounds as split up into water and an oxide of the 

 same kind only. We already know that many substances are cap- 

 able of combining with water. Oxides possess this property in the 

 highest degree. We have already seen examples of this (Chap. I.) 

 in the combination of lime, and of sulphuric and phosphoric anhydrides, 

 with water. Hence the results of such combination are basic and acid 

 hydrates. Acid hydrates are called acids, because they have an acid 



49 It must be remarked that certain elements form oxides of all three kinds i.e., 

 indifferent, basic, and acid ; for example, manganese forms manganous oxide, manganic 

 oxide, peroxide of manganese, red oxide of manganese, and manganic anhydride, although 

 some of them are not known in a free state but only in combination. It is, then, always to be 

 remarked that the basic oxide contains less oxygen than the peroxides, and the peroxides 

 less than the acid anhydride. Thus they must be placed in the following general normal 

 order with respect to the amount of oxygen entering into their composition (1) basic 

 oxides, suboxides, and oxides; (2) peroxides; (8) acid anhydrides. The majority of 

 elements, however, do not give all three kinds of oxides, some giving only one degree 

 of oxidation. It must further be remarked that there are oxides fonned by the combina- 

 tion of acid anhydrides with basic oxides, or, in general, of oxides with oxides. For 

 every oxide having a higher and a lower degree of oxidation, it might be said that the in- 

 termediate oxide was formed by the combination of the higher with the lower oxide. But this 

 is not true in all cases for instance, when the oxide under consideration forms a whole 

 series of independent compounds for oxides which are really formed by the combination 

 of two other oxides do not give such independent compounds, but in many > 

 decompose into the higher and lower oxides. 



