THE BUTYRIC ACID GROUP. 33- 



also are oenanthylic acid=C 14 H 13 O 3 . HO, acetate of oxide of amyl= 

 C 10 H n O.C 4 H 3 O 3 , caproate of oxide of methyl^C^O.C^I^Og, 

 and valerianate of oxide of ethyl=C 4 H 5 O.C 10 H 9 O 3 C 14 H 14 O 4 . 



Most of these acids were formerly called volatile fatty acids 

 from having first been made known through the decomposition of 

 many fats ; but this designation ought no longer to be retained, 

 because while a large number of these acids cannot be prepared 

 from fats, others again may be obtained with equal facility, as 

 educts and products of many other animal or vegetable substances. 

 Thus, for instance, butyric acid, which was formerly regarded as the 

 representative of these acids, may be as easily obtained by the 

 putrefaction or artificial oxidation of albuminous substances, or by 

 the fermentation of sugar and starch, as by the saponification of 

 butter. 



Before we enter upon the consideration of the individual acids 

 belonging to this group, we must draw attention to some of the 

 relations possessed in common by all of them, and which depend 

 upon the substances with which they are intimately connected, upon 

 the series of homologous bodies from which they are either pro- 

 duced, or into which they are converted under like conditions, 

 and more especially upon their chemical constitution. 



We would first draw attention to the fact that by following 

 the theory of organic radicals, we discover a number of bodies 

 which may be regarded as lower stages of oxidation of the carbo- 

 hydrogen radical of these acids. Thus we have bodies of the 

 general formula C^H^O-f HO[= (CH) n O 2 ] and C n H n-1 O 2 +HO 

 Q=(CH) n O 3 ], The substances composed in accordance with the 

 first of these formulae have been named oxides of the radicals of the 

 acids, or more commonly aldehydes. These .bodies are for the most 

 part liquid, very volatile, and oxidise rapidly when exposed to the 

 air, becoming thus converted into their corresponding acids. Up to 

 the present time, the following bodies of this classhave been accu- 

 rately studied. 



Aldehyde of acetic acid C 4 H 3 O.HO. 



Aldehyde of metace tonic acid .... C 6 H 5 O.HO. 

 Aldehyde of butyric acid C 8 H 7 O.HO. 



The stage of oxidation=C n H n __ 1 O 2 .HO, existing between these 

 oxides and the acids in question, is only found in a few cases ; as 



Acetylous acid C 4 H 3 O 2 .HO. 



(Enanthylous acid C 14 H 13 O 2 .HO. 



Moreover they are rapidly oxidised by the air, and converted 

 into the corresponding acids. 



D 



