562 PHYSIOLOGICAL CHEMISTRY 



Procedure for Total Volatile 'Phenols. The second filtrate from the Folin- 

 Denis procedure is treated as outlined by Folin and Denis for the deconjugation 

 of phenols and then extracted with ether as in Tisdall's procedure for free volatile 

 phenols (see above). 



Interpretation. Results for total phenolic substances obtained by 

 this method are at least 50 per cent lower than those recorded by 

 Folin and Denis. By the Tisdall method only a small fraction of 

 the volatile phenols are found to be excreted in the free state. The 

 substances causing the difference in results by the two methods remain 

 undetermined. For additional notes on interpretation see Folin-Denis 

 method p. 561. 



Oxalic Acid 



SalkowsM-Autenreith and Earth Method. Principle. The oxalic acid is pre- 

 cipitated by means of CaCU. From the solution of this precipitate in hydrochloric 

 acid the oxalic acid is extracted with ether and reprecipitated as calcium oxalate. 



Procedure. Place the 24-hour urine specimen in a precipitating jar, add an 

 excess of calcium chloride, render the urine strongly ammoniacal, stir it well, and 

 allow it to stand 18-20 hours. Filter off the precipitate, wash it with a small 

 amount of water and dissolve it in about 30 c.c. of a hot 15 per cent solution of 

 hydrochloric acid. By means of a separatory funnel extract the solution with 150 

 c.c. of ether which contains 3 per cent of alcohol, repeating the extraction four or 

 five times with fresh portions of ether. Unite the ethereal extracts, allow them to 

 stand for an hour in a flask, and then filter through a dry filter paper. Add 5 c.c. 

 of water to the filtrate, to prevent the formation of diethyl oxalate when the solu- 

 tion is heated, and distil off the ether. If necessary, decolorize the liquid with 

 animal charcoal and filter. Concentrate the filtrate to 3-5 c.c., add a little calcium 

 chloride solution, make it ammoniacal, and after a few minutes render it slightly 

 acid with acetic acid. Allow the acidified solution to stand several hours, collect 

 the precipitate of calcium oxalate on a washed filter paper, 1 wash, incinerate strongly 

 (to CaO), and weigh in the usual manner. 



Calculation. Since 56 parts of CaO are equivalent to 90 parts of oxalic acid, 

 the quantity of oxalic acid in the volume of urine taken may be determined by 

 multiplying the weight of CaO by the factor of 1.6071. 



Interpretation. From 15-20 mg. of oxalic acid are excreted by a normal adult 

 on an ordinary mixed diet. It arises from oxalates of the food ingested and from 

 fat and protein metabolism. It is increased by the ingestion of apples, grapes, 

 cabbage, etc., although most of the ingested oxalate is destroyed. It is increased 

 in disturbances of metabolism associated with decreased oxidation, according to 

 certain observers. The term "oxaluria" has been largely a misnomer. 



Sulphur 

 (a) Gravimetric Procedures 



I. Total Sulphates. Folin 1 s Method. Principle. The sulphuric 

 acid of the conjugated sulphates is set free by boiling with acid. The 

 total sulphates are then precipitated with barium chloride. 

 1 Schleicher and Schiill, No. 589, is satisfactory. 



