CERAMIC WARE. 223 



and the marvellous change effected upon it by oxygen ; de- 

 scend we now to earth once more, with the intent of scruti- 

 nising, as a chemist would scrutinise, the changes that have 

 ensued. The chemical scrutiny over, let us classify our mate- 

 rials ; as it behoves those who, waiting humbly and reverently 

 upon Nature, implore her to reveal her mysteries. This 

 chemical scrutiny over, the result will be made apparent that 

 the metallic 'rusts,' as I have called them, but which the 

 chemist terms < oxides,' will admit of division into the three 

 following classes : 



1. Those which are alkalis, as potash, soda, lithia. 



2. Those which are earths, as lime, magnesia, alumina, &c. 



3. Those which are neither alkalis nor earths, in which 

 list are comprehended the majority of metals. 



Proceeding thus, our scheme of investigation begins to 

 unfold itself clearly. We soon perceive that every metal 

 admits of reference to one of three classes, viz. : 



1. Kaligenous (alkali-making). 



2. Terrigenous (earth-making), 



3. Calcigenous (calx-making). 



The next important point to which attention should be 

 directed is this, viz. : the rusts or oxides of all metals com- 

 prised in the first and second classes are always white ; 

 w^hereas calcigenous rusts or oxides are in most instances 

 coloured. To impress this fact on the mind, let the point be 

 remembered that potash and soda (both rusts or oxides of the 

 first class) are white ; that lime, magnesia, and alumina (ex- 

 emplars of the second class) are also white ; but as for metals 

 of the third class, their oxides present us with a variety of 

 colours, either of themselves or in their compounds: as is 

 sufficiently testified by the tints displayed on the surface 

 of china. Each one of these lovely colours is produced by 

 oxides of the third or calcigenous class of metals. 



6 Earthenware' is a household word. Each and every 

 one of us knows that clay holds some immediate relation to 



