Analytical 



tible of quantitative application. Physiological tests can 

 supply roughly quantitative information in some cases at 

 high dilutions, but are of little critical value in distinguishing 

 the constituents of mixtures. 



Phenyl-acetic acid. — Steenbock (191 2) has described a 

 method for the estimation of phenyl-acetic acid in urine in 

 presence of benzoic acid. He treats the urine with caustic 

 soda with addition of hydrogen peroxide, extracts the benzoic 

 and phenyl-acetic acids with ethyl ether, dries, and weighs 

 after subhmation. The sublimate, of weight S grams, is 

 titrated with N /20 NaOH, requiring n ml. The phenyl-acetic 

 acid content in grams is then: 



136 {S — o-oo6i n) 



The acid is oxidized to benzoic acid by strong oxidizing 

 agents. It has a beautiful rose-like odour. For other tests, see 

 the chemical handbooks. 



Phenyl-propionic acid. (^-phenyl-propionic acid). — For 

 tests see chemical handbooks. It has a pleasant, sweet odour. 



Phenyl-pyruvic acid (not shown to be a growth substance) 

 has been found in the urine of a small proportion of mental 

 defectives by Foiling (1934). Urine containing this substance 

 gives a deep green colour on addition of ferric chloride solu- 

 tion. For other properties and quantitative methods, see the 

 paper by Penrose and Quastel (1937). Like homogentisic 

 acid (see infra) phenyl-pyruvic acid is a product of incomplete 

 metabolism; its source appears to be dietary phenyl-alanine. 

 It is fairly easily decomposed under alkaline conditions in the 

 presence of bacteria in urine, but the products of such 

 decomposition are not known. 



p-hydroxy -phenyl-acetic acid. — With ferric chloride solution, 

 its solution gives a faint violet colour, quickly becoming 

 greyish-green. 



p~hydroxy -phenyl-propionic acid (P-(4-hydroxy-phenyl)- 

 propionic acid). — Said to occur in urine. The cupric salt is 

 difficultly soluble in water and alcohol, but is soluble in ether. 

 (Hlasiwetz, Journ. prakt. Chem. (i), 72, 401 ; from Beilstein's 



121 



