408 PRINCIPLES OF CHEMISTRY 



atomicity of the elements. Hydrogen is taken as the representative 

 of the univalent elements, giving compounds, RH, R(OH), R 2 O, RC1, 

 R 3 N, R 4 C, &c. Oxygen, in that form in which it gives water, is the 

 representative of the bivalent elements, forming RH 2 , RO, RC1 2 , 

 RHC1, R(OH)C1, R(OH) 2 , R,C, RON, etc. Nitrogen in ammonia is 

 the representative of the trivalent elements, giving compounds RH 3 , 

 R 2 O 3 , R(OH) 3 , RC1 3 , RN, RHC, &c. In carbon is expressed the 

 properties of the quadrivalent elements, RH 4 , RO.,, RO(OH) 2 , R(OH) 4 , 

 RHN, RC1 4 , RHCU, &c. We meet with these forms of combination 

 or aspects of union of atoms in all other elements, some being analogous 

 to hydrogen, others to oxygen, and others to nitrogen or to carbon. 

 But besides these quantitative analogies or resemblances, which 

 are foretold by the law of substitution (Chapter VI.), there exist 

 among the elements qualitative analogies and relations which are not- 

 exhausted in the compounds of the elements which have been con- 

 sidered, but are most distinctly expressed in the formation of bases, 

 acids, and salts of different types and properties. Therefore, for a 

 complete study of the nature of the elements and their compounds it 

 is especially important to become acquainted with the salts as sub- 

 stances of a peculiar character, corresponding with acids and bases. 

 Common table salt, or sodium chloride, NaCl, may in every respect be 

 taken as a type of salts in general, and therefore we will pass to the 

 consideration of this substance, of hydrochloric acid, and of the base 

 sodium hydroxide, of the non-metal chlorine, and the metal sodium, 

 which correspond with it. 



Sodium chloride, NaCl, or the familiar table salt, occurs in the 

 primary formations of the earth's crust, 2 from which it is washed away 

 by the atmospheric waters, and is held in small quantities in all waters 

 flowing through these formations, and is in this manner collected in 

 the oceans and seas. The immense mass of salt in the oceans has been 

 accumulated by this process from the remote ages of the earth's crea- 



2 The primary formations are those which do not bear any distinct traces of having 

 been deposited from water (have not a stratified formation, contain no remains of 

 animal or vegetable life), occur under the sedimentary formations of the earth, and uiv 

 everywhere uniform in composition and structure, which is generally distinctly crystal 

 line. If the origin of the earth were of a molten nature, the first primary formations 

 are those which formed the first solid crust of the earth. But even with this hypothesis 

 of the earth's origin, it is necessary to admit that the first aqueous deposits must have 

 re-formed the crust of the earth, and therefore under the head of the primary formations 

 must be understood the most ancient of the products of decomposition (mostly by atmo- 

 spheric, aqueous, and organic agency, &c.), from which all the rocks and substances of 

 the earth's surface have arisen. In speaking of the origin of one or another substance, 

 we can only, on the basis of facts, descend to the primary formation, of which granite, 

 gneiss, and trachyte may be taken as examples. 



