232 INDUSTRIAL MINERALS DIAGRAM 19 



light, nearly unalterable, and very resistant ~at the highest tem- 

 peratures. 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 largo 

 quantity of the metal in proportion to the quantity of mercury 

 with which it is mixed, they forni'a paste which is called an amal- 

 gam. It is an amalgam of mercury and tin which is used to form 

 the silvering of mirrors. 



VEGETABLE SOIL. 



This is so called because it is the soil most favourable to the 

 growth of plants useful to man. 'It is formed naturally of 

 sand and clay, or the detritus of rocks mixed with an uncertain 

 proportion of organic matter yielded by all the animal and vege- 

 table substances which rot on its surface. The presence of these 

 organic matters is requisite to form a good vegetable soil. Dead 

 leaves, the fragments of plants which fall on the ground, and 

 soil drifted by the wind, all contribute to increase continually the 

 thickness of this vegetable layer. 



Many rivers overflow their banks at certain seasons of the 

 year, and cover broad plains with their waters, which there de- 

 posit the earth which they carry with them. Soil thus formed 

 of earth or sand brought down by the agency of water, is called 

 an alluvial deposit. 



