METALS AND THEIR^)RES. 39 



ties, the sulphur of the gas uniting with the silver to form 

 a sulphuret of that metal. This gas is also sometimes 

 generated about volcanoes. 



CHAPTER V. 



METALS AND THEIR ORES. 



65. Native Metals. A metal is said to occur native 

 when it is found either pure or mingled with some other 

 metal in the form of an alloy ; in other words, when it is 

 not united chemically with any other substance. 



66. Ores. When a metal is united chemically with 

 any substance, the compound is called an ore. The metal 

 is in this case said to be mineralized. The most common 

 of these compounds are sulphurets, oxyds, and carbon- 

 ates. The word ore is sometimes used in a less strict 

 sense for alloys, and even native metals are often termed 

 ores. On the other hand, it is proper to state that to 

 the compounds of some of the metals the term is not ap- 

 plied at all. I refer to the earths and alkalies, which are 

 combinations of certain metals with oxygen, to their 

 salts, and to the combinations of these same metals with 

 chlorine, iodine, etc. These metals, potassium, sodium, 

 etc., have been discovered comparatively at a recent date, 

 are never found native, and, when obtained by chemical 

 processes, are, most of them, preserved in their metallic 

 state with difficulty. You see, then, the propriety of not 

 calling their compounds ores. It is to the compounds 

 of the well-known metals only that the term is applied. 



67. Positions and Associations of Ores. The ores of 

 metals are sometimes scattered here and there in rocks, 

 in collections small and large ; but commonly they are 

 in veins, or lodes, as they are called, or in layers between 

 layers of rock. They are associated with quartz, carbon- 

 ate of lime, and various other minerals. Often two or 

 more different ores are mingled together. 



