118 ACIDS OF THE ACETIC SERIES. 



alkali (formation of iodoform) and colour-reactions with sodium nitro- 

 prusside and fuchsin 1 . 



Propionic acid. C 2 H 5 .COOH. 



This acid closely resembles the preceding one. It possesses a very 

 sour taste and pungent odour; is soluble in water, boils 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 3 H 7 . COOH. 



There are two possible isomeric acids of the general formula 

 C 3 H 7 . COOH, the normal or primary, CH 3 . 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 plentifully 

 obtained when diabetic urine is mixed with powdered chalk and kept 

 at a temperature of 35 C. It exists, in union with glycerin 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 fermentation 

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



Isobutyric acid. Occurs in faeces 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 de- 

 scribed is the isoprimary CH (CH 3 ) 2 CH 2 . COOH. (Isopropyl-acetic acid.) 



An oily liquid, of burning taste and penetrating odour as of decaying 

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

 and in ether. Boils at 175 C. 



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

 composition, through putrefaction, of impure leucin, ammonia being at 

 the same time evolved ; hence its occurrence in urine when that fluid 

 contains leucin, as in cases of acute atrophy of the liver. 



1 Consult Neubauer und Vogel, Harnanalyse, S. 31. 



