118 ACIDS OF THE ACETIC SERIES. 



at 141 C., and may be separated from formic and acetic acid 

 by taking advantage of the superior solubility of its lead salt 

 in cold water. 



It occurs in small quantities in sweat, in the contents of the 

 stomach, and in diabetic urine when undergoing fermentation. 

 It is similarly produced, mixed however with other products, 

 during alcoholic fermentation. 



It is stated to have been found occasionally in normal urine. 



Butyric acid. C 8 H 7 . COOH. 



There are two possible isomeric acids of the general formula 

 8 H 7 . COOH, the normal or primary, CH 8 . CH 2 . CH 2 . COOH and 

 iso- or secondary, CH(CH 3 ) 2 . COOH. 



Normal butyric acid. An oily colourless liquid, with an odour 

 of rancid butter, soluble in water, alcohol, and ether, boiling at 

 162 C. 



Found in sweat, the contents of the large intestine, faeces, and 

 in urine. It occurs in traces in many other fluids, and is plenti- 

 fully obtained when diabetic urine is mixed with powdered chalk 

 and kept at a temperature of 35 C. It exists, in union with gly- 

 cerin as a neutral fat, in small quantities in milk, and gives the 

 characteristic odour to butter which has become rancid. 



It is the principal product of the second stage of lactic fermen- 

 tation (see p. 105), and is ordinarily prepared from this source. 



Isobutyric acid. Occurs in fasces and among the putrefactive 

 products from proteids, also in certain fruits such as the banana. 



Valeric or Valerianic acid. C 4 H 9 . COOH. 



Four isomeric forms of this acid exist. Of these the one here 

 described is the isoprimary CH(CH 8 ) 2 CH 2 . COOH. (Isopropyl- 

 acetic acid.) 



An oily liquid, of burning taste and penetrating odour as of de- 

 caying cheese ; soluble in 30 parts of water at 12C., readily soluble 

 in alcohol and in ether. Boils at 175 C. 



It is found in the solid excrements, and is formed readily by 

 the decomposition, through putrefaction, of impure leucin, am- 

 monia being at the same time evolved ; hence its occurrence in 

 urine when that fhiid contains leucin, as in cases of acute atrophy 

 of the liver. 



Caproic acid. C 5 H U . COOH. 



Caprylic acid. C 7 H 15 . COOH. 

 Capric (Eutic) acid. C 9 H 19 . COOH. 



These three occur together (as fats) in butter, and are con- 

 tained in varying proportions in the faeces from a meat diet and 



