THE EARTH. 26? 



grosser substances as are exposed to its influence ; 

 for scarcely any substance is found capable of re- 

 sisting the corroding qualities of the air. The 

 air, say the chemists, is a, chaos furnished with 

 all kinds of salts and menstruums ; and therefore 

 it is capable of dissolving ah 1 kinds of bodies. It 

 is well known, that copper and iron are quickly 

 covered, and eaten with rust, and that, in the 

 climates near the equator, no art can keep them 

 clean. In those dreary countries, the instru- 

 ments, knives, and keys, that are kept in the 

 pocket, are nevertheless quickly incrusted ; and 

 the great guns, with every precaution, after some 

 years become useless. Stones, as being less 

 hard, may be readily supposed to be more easily 

 soluble. The marble of which the noble monu- 

 ments of Italian antiquity are composed, although 

 in one of the finest climates in the world, show the 

 impressions which have been made upon them by 

 the air. In many places they seem worm-eaten by 

 time, and in others they appear crumbling into 

 dust. Gold alone seems to be exempted from this 

 general state of dissolution ; it is never found to 

 contract rust, though exposed ever so long : The 

 reason of this seems to be, that sea salt, which is 

 the only menstruum capable of acting upon, and 

 dissolving gold, is but very little mixed with the 

 air ; for salt being a very fixed body, and not apt 

 to volatilize and rise with heat, there is but a small 

 proportion of it in the atmosphere. In the elabo- 

 ratories and shops, however, where salt is much 

 used, and the air is impregnated with it, gold is 

 found to rust, as well as other metals. 



