278 THE URINE. 



precipitate. The uric acid remains, and from its arnmoniacal solu- 

 tion the kynurenic acid is then precipitated by acidifying with hydro- 

 chloric acid. 



The crystals are soluble in alcohol and melt at 253 C. On 

 evaporating a bit of the material with hydrochloric acid and potas- 

 sium chlorate on a porcelain plate a reddish residue is obtained, 

 which principally consists of tetrachloro-oxykynurin. When this 

 is moistened with ammonia a brownish-green color develops, and on 

 standing this soon passes into a fine emerald green. 



The Fatty Acids. 



The Volatile Fatty Acids. The volatile fatty acids which may 

 be isolated from any urine, and which are especially abundant in 

 that of herbivorous animals, are normally derived from the intestinal 

 tract, where they are principally formed during the process of carbo- 

 hydrate fermentation ; a certain fraction, however, is also referable 

 to albuminous putrefaction. These acids are acetic acid, formic acid, 

 propionic acid, and butyric acid. 



The non- volatile acids, capric acid and caprylic acid, have further 

 been found in the urine of herbivorous animals. 



In man about 0.05 gramme of volatile fatty acids is excreted in 

 twenty-four hours. Especially large amounts, such as 3 grammes pro 

 die, have been found in the urine of the goat. In various diseases 

 larger amounts have also been encountered in man, but it is still an 

 open question whether they are then derived from the intestinal 

 tract exclusively. From decomposing urine a larger quantity can 

 be obtained than from fresh urine. This is no doubt owing to the 

 fact that every urine contains a small amount of carbohydrates, 

 which yield fatty acids on bacterial decomposition. Old diabetic 

 urine is hence especially rich in such acids. The higher fatty acids 

 are normally not observed in the urine, but traces may appear under 

 certain pathological conditions. 



Isolation and Quantitative Estimation. To isolate the volatile 

 fatty acids the collected urine of twenty-four hours is acidified with 

 phosphoric acid in the proportion of 10 : 100, and distilled in a cur- 

 rent of steam so long as the distillate shows an acid reaction. This 

 is then neutralized, evaporated to dryness, and the residue extracted 

 with alcohol. Traces of sodium chloride, which are formed on the 

 addition of the alkali, owing to the presence of a little hydrochloric 

 acid that has passed over, remain behind. The alcoholic solution 

 is then evaporated to dryness, the residue is dissolved in a little 

 water, acidified with sulphuric acid, and set aside in the cold, when 

 traces of benzoic acid are precipitated. The filtrate is neutralized 

 with a solution of sodium carbonate and extracted with ether, which 

 removes the phenols. The solution is now acidified with sulphuric 

 acid and is again distilled in a current of steam, when the volatile 

 fatty acids pass over. Their presence can be established according 



