TOINE 563 



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

 20 c.c. of dilute hydrochloric acid 1 (i volume of concentrated HC1 to 4 volumes of 

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

 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. 2 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. 3 



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

 air-bath or over a very low flame, then ignite, 4 cool and weigh. 



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

 the crucible and the BaSo4 precipitate to obtain the weight of the precipitate. 

 The weight of SOa 5 in the volume of urine taken may be determined by means of 

 the following proportion. 



Mol. Wt. Wt. of Mol. wt. 



BaSO 4 : BaSO 4 : : SO 3 : x(wt. of SO 3 in grams). 



Representing the weight of the BaSO 4 precipitate by y and substituting the proper 

 molecular weights, we have the following proportion: 



2 33 -43 : y : : 80.06 : x (wt. of SO 3 in grams in the quantity of urine used). 



Calculate the quantity of SO 3 in the twenty-four-hour specimen of urine. 



To express the result in percentage of SO 3 simply divide the value of x, as just 

 determined, by the quantity of urine used. 



i 



Interpretation. The total sulphate excretion (ethereal and inorganic 

 sulphates) by a normal adult on a mixed diet is usually between 1.5 and 

 3.0 gram of 80s with an average of about 2.0 gram. The sulphuric 

 acid is derived but to a slight extent ordinarily from ingested sul- 

 phates, being mainly dependent on the sulphur of the protein ingested 

 and will consequently vary widely with the protein content of the diet. 



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



2 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. 



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

 a washed filter paper (Schleicher & SchiilTs, 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. 



4 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 10 minutes if no organic matter 

 is present. 



6 It is considered preferable by many investigators to express all sulphur values in terms 

 of S rather than SO 3 . 



