384 PRINCIPLES OF CHE-MIST I! Y 



If the addition of CO 2 raises the basicity the removal of CO 2 lowers 

 it. Thus from the bibasic oxalic acid, C 2 H 2 O 4 , orphthalic acid, C 8 H )5 O 4 , 

 by eliminating CO 2 (easily effected experimentally) we obtain the 

 monobasic formic acid, CH. 2 O 2 , or benzoic acid, C 7 H 6 O 2 ., respectively. 

 The nature of carboxyl is directly explained by the law of substitution. 

 Judging from what has been stated in Chapters V. and VIII. concerning 

 this law, it should already be evident that CO 2 is CH 4) with the 

 exchange of H 4 for O 2 , and the hydrate of carbonic acid, H 2 CO 3 , is 

 CO(OH) 2 , that is, methane, where two parts of hydrogen are replaced by 

 two parts of the water radicle (OH, hydroxyl), and the other two by 

 oxygen. Therefore the group CO(OH), or carboxyl, HCO 2 , is a part 

 of carbonic acid, and is equivalent to (OH), and therefore also to H. 

 That is, it is a univalent residue of carbonic acid capable of replacing 

 one atom of hydrogen. Carbonic acid itself is a bibasic acid, both 

 hydrogen atoms in it being replaceable by metals, therefore carboxyl, 

 which contains one of the hydrogen atoms of carbonic acid, represents 

 a group in which the hydrogen is exchangeable with metals. And 

 therefore if 1, 2 . . . n atoms of non-metallic hydrogen are exchanged 

 1, 2 ... n times for carboxyl we ought to obtain 1, 2 ... n-basic 

 acids. Organic acids are the products of the carboxyl substitution of 

 hydrocarbons. 1 * If in the saturated hydrocarbons, C M H 2M+2 , one part 

 of hydrogen is replaced by carboxyl the monobasic saturated (or fatty) 

 acids, C n H 2w+l (CO 2 H), will be obtained, as, for instance, formic, 



18 If CO-2 is the anhydride of a bibasic acid, and carboxyl corresponds with it, re- 

 placing the hydrogen of hydrocarbons, and giving them the character of comparatively 

 feeble acids, then SO 3 is the anhydride of an energetic bibasic acid, and sulphoxyl, 

 SO. 2 (OH), corresponds with it, being capable of replacing the hydrogen of hydrocarbons, 

 and forming comparatively energetic sulphur oxyacids (sulphonic acids) ; for instance, 

 C 6 H 5 (COOH), benzoic acid, and C 6 H 5 (SO. 2 OH), benzenesulphonic acid, are derived from 

 C 6 H 6 . As the exchange of H for methyl, CH 3 , is equivalent to the addition of CHo, the 

 exchange of carboxyl, COOH, is equivalent to the addition of COo ; so the exchange of H 

 for sulphoxyl is equivalent to the addition of SO 5 . The latter proceeds directly, for 

 instance : C 6 H 6 + SO 3 = C H 5 (SO.,,OH). 



In Chapter VIII. we saw that the structure of hydrocarbons might and ought to be 

 represented by the presence of CH 3 , CHo, CH, and C radicles of methane, starting 

 from methane itself ; therefore the atoms of hydrogen are retained by separate atoms of 

 carbon, which refers also to OH, COOH, and other radicles. Although with one atom of 

 carbon, H 4 , H 3 , and H 2 , or several, CH 3 , Cl, &c., may be retained, yet not more than one 

 of hydroxyl may be retained, and therefore there is no alcohol CH 2 (OH)., or C 5 H 4 (OH) 4 . 

 The carboxyl, as well as the sulphoxyl, substitution of hydrogen in hydrocarbons, leads to 

 the formation of acids, because the derivative acids H 2 CO 3 and H 2 SO 4 are bibasic. 

 Nitric acid, being monobasic, is unable to form a similar radicle. Its radicle, NO 3 , does 

 not contain hydrogen, and does not produce acidity, but has the same relation to the 

 acid NO a (OH) as carboxyl to carbonic acid. 



As, according to the determinations of Thomsen, the heat of combustion of the vd/iotiM 

 of acids RCO-> is known where R is a hydrocarbon, and the heat of combustion of the 

 hydrocarbons R themselves, it may be seen that the formation of acids, RCO.>, from 

 R + CO 2 is always accompanied by a small absorption or development of heat. We give 



