234 INDUSTRIAL MINERALS DIAGRAM 20. 



Aluminium. This metal is not found pure in the bosom of 

 the earth. It is extracted by very complicated processes, from 

 alumina, which forms the base of clay. It is white, exceedingly 

 light, nearly unalterable, and very resistant at the highest 

 temperatures. Much use will certainly be made of it in the 

 arts, but it is only a few years since they have been able to 

 prepare it. 



Mercury. Mercury, or quicksilver, is a metal which is liquid 

 like water. It is found in a pure state in some mines, and in 

 others it is extracted by different processes. Mercury can be 

 boiled and reduced to a state of vapour, like water, but these 

 vapours are dangerous, and seriously affect the health of the 

 workpeople employed in the numerous industries where mercury 

 is used. Mercury has the power of dissolving gold and other 

 metals, just as water dissolves sugar. When there is a large 

 quantity of the metal in proportion to the quantity of mercury 

 with which it is mixed, they form a paste which is called an 

 amalgam. It is an amalgam, of mercury and tin which is used 

 to form the silvering of mirrors. 



METEORIC STONES. 



This name is given to stones which sometimes fall from the 

 sky, and they are also called aerolites. But it must not be sup- 

 posed that these stones are common, and this origin has been 

 wrongly ascribed to many fossils. True meteoric stones have 

 always an irregular shape, and are generally of a black colour. 

 The shooting stars which are seen at night are meteoric stones 

 passing through the air, very few indeed of which, however, 

 reach the earth in the form of stones, being nearly always 

 reduced to an impalpable dust in the highest regions of the 

 atmosphere. 



