224 CERAMIC WARE. 



crockery. But what is clay ? That is a question I will now 

 proceed to answer. Chemically, pure clay may be said to be 

 nothing more than alumina combined with water : in chemical 

 language, ' hydrate of alumina;' alumina being, as we must 

 not forget, the rust or oxide of the not very rare metal alumi- 

 nium. But absolutely chemically pure clay that is to say, 

 pure alumina in combination with water does not occur in 

 nature. If we want it, we must produce it ; separate it from 

 one of the many compounds in which it exists. For present 

 necessities, that compound shall be the crystallised material 

 alum. 



If, then, a portion of alum be dissolved in water, and 

 hartshorn (ammonia) added to the solution, down goes alu- 

 mina. By a filter it may readily be collected; and when 

 washed, it may be regarded as the type of all clays that are 

 to be found existing in nature. As already stated, however, 

 nature gives us no absolutely pure clay, in the sense of pure 

 hydrate of alumina. Nature's very purest clays always hold 

 a portion of silica, or the matter of flint. And what is silica 

 what are flints I Why, silica is an oxide or combination of 

 oxygen with something ; that something, whether non-metallic 

 or a metal, chemists are not yet agreed upon among them- 

 selves. Those who choose to regard it as a metal, call that 

 something silicium ; whilst, on the other hand, those who be- 

 lieve the something to be non-metallic, denominate it silicon. 



No matter. The courteous reader, who, not being a che- 

 mist, may choose nevertheless to procure a specimen of silica, 

 can take a piece of rock crystal, then making it white hot, 

 throw it into cold water, and powder the shattered fragments. 

 The product of these operations may be regarded as pure 

 silica. Silica has many wonderful properties. Flints are 

 almost pure silica ; and insects are occasionally found in the 

 very middle of nodules of flint. How did they get there ? 



When the statement is made, that not only can the matter 

 of flints be dissolved and converted into a liquid, but can 



