The Importance of Clay- The Element of Alumina

Every one knows that common substance called clay, which is so easily mixed into a paste with water. But every one does not consider perhaps what an important part in agriculture and industry this familiar substance performs.

All soils that are of value for the production of vegetables contain clay. The principal element of this substance--alumina--is necessary to the development of plants; and its presence is necessary to retain the humidity of soil that is indispensable to vegetable life.

To indicate the importance of clay in the industrial world it is only necessary to say that tiles, bricks, pottery, from the coarsest kind to the finest Sevres ware, are almost exclusively formed of this substance.

And what is clay?

To answer this question categorically is impossible, because there are comprehended under that name a multitude of mixtures, whose composition is extremely variable; but the only fact important for us to know here is that the principal constituent element of clay is alumina.

In these modern times industry has been enriched by an important conquest, aluminium, that new metal which, whether used alone or in combination with other metals, lends itself with complete success to the manifold wants of the industrial arts. It is a discovery and creation for which our epoch is indebted to the French chemist M. Henri Sainte-Claire Deville.

If this metal is combined with the oxygen of the air, the metal disappears, and is transformed into the rust of aluminium; exactly as the brilliant and metallic iron is transformed into iron rust under the same conditions; only that aluminium rust is white instead of red. This white rust is pure alumina.

Now this alumina exists in a prodigious quantity, not only in vegetable mould, but also in a large portion of the rocks of our globe. Generally it is mixed with iron rust, which gives it a red colour, or it may be with other substances; but it now and then occurs in abborute purity; and it is always possible to extract pure alumina from any kind of clay.

If we ask now what is the composition of the precious stones such as sapphires, rubies, topaz, emeralds, aquamarines, and tourquiose, we are answered--they are formed of alumina nearly pure. Besides this they contain only some faint traces of foreign matters, generally of the oxide of iron.

Notwithstanding the minute quantities, these foreign matters are very important, because it is to their union with alumina that the precious stones we are considering owe their remarkable colour, and consequently a great part of their commercial value.