108 LABORATORY WORK IN PHYSIOLOGICAL CHEMISTRY. 



Quantitative Estimation. 



The procedures for the determination of these various 

 units rest upon the following facts: 



Boiling the urine with dilute HC1 liberates all the sul- 

 phate radicles present in such a form that they may be 

 precipitated with BaCl 2 as BaS0 4 . This gives the amount of 

 total sulphate. If acetic acid be used instead of HC1, the 

 resulting precipitate with BaCl 2 will be made up of the pre- 

 formed or sulphate-sulphate. This may be filtered off and 

 the filtrate treated as for the total sulphates, the result being 

 the amount of ethereal sulphates present. The difference 

 between this and the total will be the amount of the pre- 

 formed sulphate. 



TOTAL S0 3 . 



In a beaker place 50 c.c. of filtered urine and dilute with 

 100 c.c. of water, adding 5 c.c. of HC1. Heat to boiling, add 

 very slowly 20 c.c. of the BaCl 2 solution and allow it to cool 

 and stand covered in a cool place for 24 hours. Filter through 

 a small ash-free filter; the precipitate must be removed quan- 

 titatively from the beaker to the paper by means of warm 

 water. Now wash the white precipitate with water until the 

 washings give no test for chlorine; then dry at 100 C. 

 When dry, slip out the paper from the funnel, fold it up so 

 that the contained sulphate cannot fall out and place it in a 

 porcelain crucible which has previously been ignited and 

 weighed. Ignite the paper in 'the crucible carefully and 

 burn until the residue becomes white. Cool the crucible and 

 weigh. The difference in the two weights will give that of the 

 BaS0 4 from 50 c.c. of urine, from which may be calculated 

 the S0 3 in the total 24-hour sample. 



