CHAP. X.] PHENYL-ACETIC AND PHENYL-PROPIONIC ACIDS. 431 



The relative proportion of x the acids present depends on the 

 length of time during which the process of decomposition has been 

 going on, phenyl-propionic acid being first formed. In the early 

 stages, phenyl-acetic acid may be absent. 



Besides being found amongst the products of the decomposition of 

 albumin and gelatin by anaerobic bacteria (Nencki 1 ), these acids 

 have been detected in the contents of the rumen of the ox (Tappeiner 2 ). 



Method of The liquid products of putrefaction are distilled to 



separation 3 . one-sixth of their original volume and the residue is 

 still further concentrated, then treated with alcohol and the alcoholic 

 extract is filtered from insoluble matters. The alcoholic filtrate is 

 evaporated to dryness, and the residue having been treated with 

 water and rendered strongly acid, by means of sulphuric acid, is 

 shaken up with ether. The ethereal solution is allowed to evaporate, 

 and the residue is treated with solution of caustic soda until the 

 reaction is alkaline. The liquid is heated, so as to dissolve the 

 sodium soaps of the higher fatty acids and the hot, turbid, solution is 

 precipitated by means of barium chloride. The mixture is filtered 

 and the clear filtrate is evaporated to dryness, acidulated with hydro- 

 chloric acid, and extracted with ether. The ethereal solution is now 

 evaporated to dryness, when an oily residue is left, consisting of 

 volatile acids, oxy-acids, skatol-carbonic acid, succinic acid, &c. This 

 residue is distilled in a current of steam, the distillate being collected 

 in a solution of sodium hydrate. This alkaline solution is now con- 

 centrated, acidulated with hydrochloric acid and shaken up with 

 ether. The residue left on evaporating the ether is distilled, and the 

 fractions which distil at a temperature above 260 are collected 

 apart ; these fractions contain phenylpropionic and phenylacetic 

 acids. In order to separate the two acids, the oily liquid is rubbed up 

 with zinc oxide and water, and the magma is boiled, with considerable 

 quantities of water, and filtered whilst yet hot. The insoluble matter 

 contains the phenylpropionate of zinc, whilst the filtrate contains 

 zinc phenylacetate, which separates out on cooling. By decomposing 

 the respective zinc salts the pure acids are obtained. 



Chemical Phenylpropionic acid crystallises in long slender 



needles. Its melting-point is 47 48 C. and it boils 

 at about 280 C. Phenylacetic acid crystallises in broad leaflets. 

 Its melting-point is 76'5 C. and it boils at 62 C. In accordance 

 with their constitution, neither acid gives a red colouration or pre- 

 cipitate when heated with Millon's reagent. 



1 Nencki, ' Untersuchungen iiber die Zersetzung des Eiweisses durch anaerobe 

 Spaltpilze,' Monatshefte f. Chem. Vol. x. (1889), pp. 306 and 908. 



2 Tappeiner, Zeitschriftf. Biol. Vol. xxn. p. 236. 



3 Although the Author has carefully studied all the original papers bearing on this 

 subject, in his description of the methods of separation of these bodies, he has availed 

 himself of the succinct account given in Hoppe-Seyler's Handbuch, <&c. 6te Auf. Berlin, 

 1893, p. 180. 



