176 Gerhard fs Organic Chemistry. 



of oxygen found in the three classes. When a monobasic acid is 

 exposed to the joint action of heat and of a basic oxyd, as of lime 

 or baryta, it loses one equivalent of carbonic acid, and is transform- 

 ed into a compound which is either a hydro-carbon like benzene, 

 or a neutral oxygenized substance like phenol. This same de- 

 composition is often effected by heat alone, as when the vapor is 

 passed through an ignited tube. The bibasic acids under the 

 influence of heat, lose one or two equivalents of carbonic acid, 

 yielding in the one case monobasic acids, and in the other neutral 

 compounds like the previous class, which result perhaps from the 

 decomposition of the acids previously formed. Tribasic acids 

 in the same manner yield one equivalent of carbonic acid, and a 

 bibasic acid or two, and monobasic and perhaps a neutral com- 

 pound, with the elimination of three of carbonic acid. In many 

 of these reactions a portion of the oxygen and hydrogen is also 

 disengaged in the form of water. — (Precis, Vol. I, pp. 78-80.) 



The solubility of acids in water bears a certain relation to their 

 equivalents and to the amount of oxygen which they contain ; 

 in those containing atomically the same proportions it is inversely 



as 



mentioned on page 99. When the carbon is the same, the sol- 

 ubility increases with the amount of oxygen ; for example, the 

 tannic, coumaric, and cinnamic acids each contain C n H, : while 



«"i) 



the amount of oxygen is respectively six, three, and two equiv 

 alents. The tannic is very soluble in water, the coumaric slightly 

 so, and the cinnamic least of all. Similar relations are to be 

 observed in neutral bodies, and very often guide us in the ex- 

 amination of new and unknown substances. 



Coupled Salts. — We have already explained our author's use 

 of the term accouplement to describe certain combinations in 

 which an acid unites with an organic substance with the separa- 

 tion of the elements of water, and forms a compound in which 

 the peculiar properties of neither of its components are recog- 

 nizable. Those formed by a monobasic acid are neutral, but it 

 the acid is polybasic and combines with but one equivalent of 

 the organic substance, the result is a coupled add. Sulphuric 

 acid unites in this way with almost all organic substances ; with 

 alcohol it forms the sulpho-vinic acid ; it combines with the hy- 

 drocarbons, as napthaline and benzene, with sugar and starch, 

 with azotized bodies like indigo, and with acids, as the acetic 

 and succinic. Analysis demonstrates . that these combinations 

 contain the elements of one equivalent of organic matter, and one 

 of sulphuric acid minus the elements of one equivalent of water. 

 The baryta salts of all these acids are soluble in water ana 

 frequently in alcohol. The acids produced by the accoup- 

 ment of neutral substances with sulphuric acid are monobasic ; 

 those formed with a monobasic acid, as the acetic, are bibasic 



