176^ 



GOLD. 



between steel-grey and silver-white, and its ductility and 

 malleability arc very great. From late improvements in the 

 process of bringing it to a pure and malleable state, its price 

 has been diminished, and its utility is becoming more gene- 

 rally acknowledged. Facts are continually brought to light 

 by means of platina instruments, which^ without it, might 

 perhaps ever have escaped notice. 



Questions. — 1. What are the four classes of minerals? 2. What 

 are earthy minerals and how are they divided ? 3. What is said of 

 the diamond ? 4. What are saline minerals ? 5. Inflammable ? 6. 

 Metallic ? 7. To what do salt-springs owe their origin ? 8. What is 

 said of mineral coal ? 0. What is said of platina ? [Note. The 

 United States possess abundant sources of some of the most useful 

 minerals, and of the stones used in jewelry.] 



LESSON 78. 



Gold. 



In'got, a mass of metal. Nitro-muriafic acid is formed by mixing 

 one part of nitric and four parts of muriatic acid ; it was known 

 to the ancient alchymists, and called aqua regia. 



Gold is never found in a mineralized state ; but it occurs 

 native in many parts of the world, generally alloyed with a 

 little silver or copper, and commonly in the form of grains. 

 Most of the gold of commerce is obtained at present from 

 Africa and the continent of America. It is the heaviest of 

 all metals except platina, and although its tenacity is such 

 that a wire of one tenth of an inch in diameter will support a 

 weight of five hundred pounds without breaking, yet it possess- 

 es less tenacity than iron, copper, platina, or silver. It is duc- 

 tile and malleable beyond any known limits. The method 

 of extending it used by gold-beaters, consists in hammering 

 a number of thin rolled plates between skins or animal mem- 

 branes, upon blocks of marble fixed in wooden frames. A 

 grain of gold has been extended to more than forty-two 

 square inches of leaf, and an ounce, which, in the form of 

 a cube, is not half an inch either high, broad, or long, is 

 beaten under the hammer into a surface of one hundred and 

 forty-six and a half square feet. There are gold leaves not 

 thicker in some parts than the three hundred and sixty- 

 thousandth part of an inch ; but on the wire used by the 



