XXVlil CONSTITUTION OF CHEMICAL COMPOUNDS. 



According to this method we can build up an indefinite 

 number of compounds, all containing hydroxyl, and all 

 exhibiting certain common properties owing to the pre- 

 sence of this group. Although these compounds strictly 

 belong to the general heading bases, they have, as a class, 

 received a distinct name to designate some properties 

 which the bases do not possess in common with them. 

 They are called alcohols. 



The acids of carbon-compounds have an equally simple 

 constitution. Let us start again with CH 4 . Replacing 

 one atom by OH and two by 0, we obtain a compound 



OrC'rv -n- This is formic acid. Here we have an oxidized 



LJ.JtL. 



carbon-atom, and in combination wtih it a water-residue. 

 Again the hydrogen of the hydroxyl is the characteristic 

 ingredient of the compound, but its characterizing powers 

 have been imparted to it not alone by the fact that it is in 

 combination with oxygen, but that this group is in its 

 turn in combination with an oxidized carbon-atom. Organic 

 acids all contain the group 0:0.0. H, which may be looked 

 upon as a residue of formic acid. It is monovalent, and 

 can take the place of hydrogen in the most varied com- 

 pounds. It has received the name carboxyl. The con 

 sideration of organic acids may be still further simplified 

 by comparing them with certain derivatives of sulphuric 

 acid. When sulphuric acid, and a number of other acids 

 containing one hydroxyl-group, are allowed to act upon a 

 compound containing replaceable hydrogen-atoms, one of 

 the hydrox}d groups of the acid is given off in company 

 with one of the hydrogen-atoms of the other compound in 

 the form of water, and the two residues unite, thus: 



C 6 H 6 + SO 2 QH = C 6 H 5 .S0 2 .OH + H 2 0. 



Benzene. Sulphuric acid. 



The resulting compound may be called a substituted 

 sulphuric acid, one of its hydroxyls having been replaced 

 by a monovalent group. Now carbonic acid resembles 

 sulphuric acid in the fact that it contains 2(OH), and, 

 although the acid itself is unknown to us, we can, under 

 certain circumstances, induce a substitution similar to that 

 noticed in connection with sulphuric acid, and thus obtain 

 substituted carbonic acids, which are nothing but the so- 

 called organic acids : 



