CONSTITUTION OF CHEMICAL COMPOUNDS. XXV 



Acids are usually derived from the so-called metalloids ; 

 bases from the metals. When acids act upon bases, salts 

 are formed, water being given off, thus : 



H.O.O.S.O.O.H and K.O.H give H.O.O.S.O.O.K and 

 H.O.H. 



H.O.O.S.O.O.H and 2(K.O.H) give K.O.O.S.O.O.K and 

 2(H.O.H). 



Now, if we examine these formulae, we see that the salt 

 may be considered either as the base, in which the original 

 hydrogen is replaced by the acid-residue, or as the acid, in 

 which the original hydrogen is replaced by the base residue 

 or metal. As the latter is the simpler view, it is the one 

 usually held, though be it remembered, that it is imma- 

 terial, for the constitution of the salt, which of the two 

 views is held. 



Compounds similar to salts in their constitution are 

 anhydrides and metallic oxides. In the former two acid- 

 residues, in the latter two base-residues, are employed in 

 the formation. 



OrN.O.H + OrN.O.H = 0:N.O.(N:0) + H.O.H, 

 K.O.H + K.O.H = K.O.K + H.O.H, 



H.O.Ca.O.H + H.O.Ca.O.H = Ca'^'Ca -f 2(H.O.H), 



H.O.O.S.O.O.H -f H.O.O.S.O.O.H = S^'^S + 

 2(H.O.H). 



It is, however, probable that in such cases as the two 

 latter, the product splits up into two molecules, and the 

 union of the atoms takes place in a different manner in 

 consequence : 



ca;0- Ca = 2(0*0), 



The compounds of carbon resemble those of other ele- 

 ments, but, owing to certain properties of the element, 

 variations are met with in this connection that require 

 special notice. 



For one group of carbon-compounds, marsh gas, CH 4 , is 

 the mother substance. From this, other substances con- 

 taining only carbon and hydrogen can be obtained, thus : 

 C 



