274 PHYSIOLOGICAL CHEMISTRY 



magnesia mixture to the filtrate. Observe a precipitate due to 

 alkali phosphates. The fairly soluble alkali phosphates are pre- 

 cipitated as magnesium ammonium phosphate. 



(c) SULPHATES. Sulphur is present in three forms: In- 

 organic sulphates, ethereal sulphates, and unoxidized sulphur in 

 organic combination. To determine unoxidized s,ulphur, it is 

 necessary first to fuse with an oxidizing agent. 



(1) Inorganic Sulphates. To about 10 c.c. of urine add 2-3 

 drops of concentrated HC1 and barium chloride in excess. The 

 inorganic sulphates are precipitated as barium sulphate, which 

 will settle to the bottom as a whitish layer on standing. 



(2) Ethereal Sulphates. Filter off the precipitated barium 

 sulphate. If the filtrate does not come through clear, mix with 

 it a small amount of bismuth subnitrate and filter repeatedly 

 through the same filter. The bismuth subnitrate stops the larger 

 pores of the filter paper, thus helping to keep back the fine par- 

 ticles of barium sulphate. To the clear filtrate add about 2 c.c. 

 cone. HC1 and boil for some minutes. Ethereal sulphates are 

 split up in this process, and since there is still excess of barium 

 chloride, a second "crop" of barium sulphate is obtained. As 

 the amount is small, it may not be seen until the test has stood 

 for a few minutes, when the precipitate will form a film or layer 

 of deposit at the bottom of the tube. 



(d) CARBONATES. Evaporate 10 c.c. urine (Hood) to dryness 

 on the water bath. Add 10% H.C1. Observe the evolution of 

 carbon dioxide from the decomposed carbonates. 



(e) AMMONIA. To about 10 c.c. urine in a test tube, add so- 

 dium carbonate until alkaline. Moisten a piece of red litmus 

 paper with distilled water and hang in the mouth of the tube. 

 The paper will be turned blue by the ammonia liberated. 



(f) In addition to the above inorganic materials, urine con- 

 tains vaying amounts of sodium, potassium, calcium, magne- 

 sium, iron, fluorine, nitrates, silicates, traces of hydrogen perox- 

 ide, and dissolved gases, e. g., C0 2 , N 2 , and 2 , besides a pos- 

 sible number of casual constituents which may be taken in the 

 food and gotten rid of by way of the kidneys. 



