PHYSIOLOGICAL CHEMISTRY 



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 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'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. 



Procedure. Place 25 c.c. of urine in a 200-250 c.c. Erlenmeyer flask, add 

 20 c.c. of dilute hydrochloric acid 2 (i volume of concentrated HCl to 4 volumes of 

 water) and gently boil the mixture for 20-30 minutes. To minimize the loss oi 

 water by evaporation the mouth of the flask should be covered with a small watch 

 glass during the boiling process. Cool the flask for 2-3 minutes in running water, 

 and dilute the contents to about 150 c.c. by means of cold water. Add 10 c.c, 

 of a 5 per cent solution of barium chloride slowly, drop by drop, to the cold solu- 

 tion. 3 The contents of the flask should not be stirred or shaken during the addi- 

 tion of the barium chloride. Allow the mixture to stand at least one hour, then 

 shake up the solution and filter it through a weighed Gooch crucible. 4 



Wash the precipitate of BaSO 4 with about 250 c.c. of cold water, dry it in an 

 air-bath or over a very low flame, then ignite, 5 cool and weigh. 



Calculation. Subtract the weight of the Gooch crucible from the weight of 

 the crucible and the BaSO 4 percipitate to obtain the weight of the precipitate. 



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



2 If it is desired, 50 c.c. of urine and 4 c.c. of concentrated acid may be used instead. 



3 A dropper or capillary funnel made from an ordinary calcium chloride tube and so 

 constructed as to deliver 10 c.c. in 2-3 minutes is recommended for use in adding the barium 

 chloride. 



4 If a Gooch crucible is not available, the precipitate of BaSO 4 may be filtered off upon 

 a washed filter paper (Schleicher & Schull's, No. 589, blue ribbon), and after washing the 

 precipitate with about 250 c.c. of cold water the paper and precipitate may be dried in an 

 air-bath or over a low flame. The ignition may then be carried out in the usual way in the 

 ordinary platinum or porcelain crucible. In this case correction must be made for the 

 weight of the ash of the filter paper used. 



6 Care must be taken in the ignition of precipitates in Gooch crucibles. The flame 

 should never be applied directly to the perforated bottom or to the sides of the crucible, since 

 such manipulation is invariably attended by mechanical losses. The crucibles should 

 always be provided with lids and tight bottoms during the ignition. In case porcelain Gooch 

 crucibles, whose bottoms are not provided with a non-perforated cap, are used, the crucible 

 may be placed upon the lid of an ordinary platinum crucible during ignition. The lid 

 should be supported on a triangle, the crucible placed upon the lid and the flame applied 

 to the improvised bottom. Ignition should be complete in ro minutes if no organic matter 

 is present. 



