436 PEACTICAL PHYSIOLOGY 



about 10 per cent, of the total sulphate excretion. The neutral 

 sulphur is present in organic compounds, such as cystin. 



EXPERIMENT IV. Place about 10 c.c. of urine in a test tube and 

 dilute with water to about 20 c.c. Add about 2 c.c. of hydrochloric 

 acid (1 part HCl(conc.) + 4 parts water), and then drop by drop about 

 2 c.c. of 5 per cent, solution of barium chloride. A white precipitate of 

 barium sulphate forms, due to the presence of inorganic sulphates. 

 After allowing the test tube to stand for a few minutes, filter and boil 

 the clear filtrate with a few drops more of hydrochloric acid and barium 

 chloride solution. There is another precipitation of barium sulphate 

 due to ethereal sulphates which have been decomposed by boiling with 

 hydrochloric acid. 



Quantitative determination. There is no volumetric method, that is even 

 approximately accurate, available for this purpose, so that it is necessary that a 

 good analytical balance be at command. For accurate work it is further necessary 

 that great care be exercised in carrying out the processes, for the final precipitates 

 are otherwise apt to be quite impure and the estimation inaccurate. 



The following processes have been worked out by Folin, and the directions 

 must be implicitly followed. Protein must be removed if present. This is best 

 done by boiling the urine acidified with acetic acid in a flask, cooling and 

 filtering. 



EXPERIMENT V. Inorganic Sulphates. 25 c.c. of urine are diluted with 100 

 c.c. of water in an Erlenmeyer flask (of 250 c.c. capacity) and 10 c.c. of dilute 

 hydrochloric acid (1 part HC1 (con.) to 4 parts water) added. A burette contain- 

 ing a 5 per cent, solution of barium chloride is then placed over the mouth of the 

 flask and 10 c.c. of the reagent allowed to drop into the contents of the flask at a 

 slow rate (not quicker than 5 c.c. per minute). 1 The flask must not be shaken 

 until after the end of an hour, 2 when it is shaken and the precipitate collected on 

 an asbestos mat in a Gooch crucible, washed with about 250 c.c. cold water, dried 

 and ignited. In doing this, the flame must not be applied directly to the per- 

 forated bottom of the crucible, but the crucible must be laid on a crucible lid or 

 specially fitting platinum bottom. The crucible must also be covered with a lid 

 during the ignition. Ten minutes' ignition is sufficient. 



EXPERIMENT VI. Total Sulphates (Inorganic and Ethereal). By boiling 

 the urine with acid, nearly all of the ethereal sulphates are decomposed. 25 c.c. 

 urine are mixed with 20 c.c. of dilute hydrochloric acid (1 : 4) in an Erlenmeyer 

 flask of about 250 c.c. capacity, and, after covering the mouth of the flask with a 

 watch-glass, gently boiled for 20 to 30 minutes. The flask is then cooled in 

 running water, its contents diluted with distilled water to about 150 c.c. and 

 10 c.c. of 5 per cent, solution of barium chloride added, and the further procedure 

 followed as above described. 



EXPERIMENT VII. Ethereal Sulphates. It is sufficiently accurate to calcu- 

 late this as the difference between I. and II. If a direct estimation is desired as a 



J More rapid addition of the reagent causes the results to be too high, i.e. 

 produces an impure precipitate. 



2 Shaking the solution too soon will lower the result, because the precipitate 

 will lose sulphuric acid during ignition. 



