4 flow Ruft is generated on Iron. [Book VI, 



already united with oxygen, bu* which have a weaker 

 attraction for that principle than the body which is to 

 be acidified. It is upon this principle that metals are 

 deprived of oxygen, or reduced to the metallic ftate, 

 by heating them in contact with charcoal, tallow, &c. 

 In this cafe the inflammable fubftance having a ftronger 

 attraction for oxygen than the metal has, becomes oxy~ 

 ^genated ; while the metal, by being deprived of this 

 principle, is reduced to the metallic frate. Metals and 

 combuflible bodies may alfo be oxygenated in the hu- 

 mid way, by fubmitting them to the action of acids. 

 In this procefs the acid furnimes the oxygen, and is 

 therefore decompofed. The oxygenation of minerals 

 in the bowels of the earth is probably chiefly effected 

 by the decompofition of water, which is a compound 

 of hydrogen and oxygen. A procefs of this kind is 

 continually carried on before our eyes ; the ruft which 

 iron acquires by being expofed to damp air is an oxy- 

 genation of that metal. Other metals, however, have 

 lefs attraction for the principle of acidity, and this is 

 remarkably the cafe with the perfect metals, platina, 

 gold, and filver, which therefore do not become rufted 

 by expofure to air. 



In treating of ialts, I mail firft give an account of 

 the alkalis, next of the acids, and laftly of their com- 

 binations, or the neutral faits. I mail defer fpeaking 

 of the earthy and metallic falt's till the earths and me- 

 tals are defcribed. 



