250 THE URINE. 



present. The reaction which takes place may be represented by 

 the equation : 



C 6 H 5 .OH + 61 = C 6 H 2 .I 3 OH + SHI. 



Five hundred c.c. of urine are rendered feebly alkaline and 

 evaporated to about 100 c.c. Any acetone which may have been 

 present is thus removed. The residual fluid is acidified with sul- 

 phuric acid, so as to contain "> per cent, of the original volume, and 

 is then repeatedly distilled. The individual portions thus obtained 

 are shaken with calcium carbonate until the acid reaction has dis- 

 appeared, so as to remove any nitrous or formic acid that may be 

 present. The fluid is now again distilled, and the distillate treated 

 with a solution of 1 gramme of caustic soda and 6 grammes of lead 

 acetate in substance. The mixture is kept on a boiling water-bath 

 for about fifteen minutes. A portion of the lead oxide is thus dis- 

 solved by the phenol to form basic phenolates, while any aldehydes 

 or ketones that may have been formed from the small amount of 

 carbohydrates that are present in every urine escape. To remove 

 these entirely, the mixture is heated over a free flame connected with 

 a condenser until a few cubic centimeters of the distillate no longer 

 reduce an alkaline solution of silver nitrate. After five minutes 

 this point is usually reached. The fluid is then acidified with sul- 

 phuric acid as before, and is distilled, water being added from time 

 to time. The distillate is placed in a glass-stoppered bottle, treated 

 with a decinormal solution of sodium hydrate until the reaction is 

 markedly alkaline, and immersed in hot water. To the hot fluid a 

 decinormal solution of iodine is added in an amount Avhich should 

 exceed that of the alkali solution by 1 5 to 25 c.c. The bottle is 

 now closed at once, shaken, and set aside until cool. The solution 

 is then acidified with dilute sulphuric acid, and the excess of iodine, 

 which was not used in the formation of tri-iodophenols, retitrated with 

 a decinormal solution of sodium thiosulphate. One c.c. of the iodine 

 solution represents 1.567 milligramme of phenol, or 1.8018 milli- 

 gramme of cresol. As the latter predominates in the urine, it is best 

 to express the results in terms of cresol. Thus modified, the method 

 is also applicable in the presence of sugar. The older gravimetric 

 method, by which the phenols were isolated as bromine substitution- 

 products, has now been largely abandoned, as it has been shown 

 that the resulting precipitate is not of constant composition, and 

 contains variable amounts of dibromocresol, besides tribromophenol 

 and bromo-tribromophenol. 



Indoxyl Sulphate. The indoxyl sulphate which occurs in the 

 urine in combination with potassium and sodium is usually spoken 

 of as indiean, but should not be confounded with the vegetable indi- 

 can, which, as has been shown, is a glucoside of the composition 

 C 26 H 31 NO, 7 . The amount which is daily excreted by man is nor- 

 mally small, and corresponds to about 0.0066 gramme. Larger 

 quantities are observed when from any cause intestinal putrefaction 



