90 LABORATORY WORK IN PHYSIOLOGICAL CHEMISTRY. 



(c) Phosphates. These are present combined with NH 4 , 

 Na, K, Ca, and Mg as primary, secondary, or tertiary com- 

 pounds. 



1. Make some urine alkaline with NH 4 OH. What is the 

 precipitate? Filter and to the clear filtrate add two drops 

 of BaCl 2 . .What is this new precipitate? Filter this off 

 through the same filter as the first and dissolve the whole 

 precipitate in dilute HN0 3 . Test for phosphates. 



2. Make the urine acid with acetic acid and add a few 

 drops of uranium nitrate solution. Of what is the precipitate 

 composed? 



3. Acidify the urine with a few c.c. of HN0 3 and add 

 some molybdic solution. Warm at 80 C. What is this 

 precipitate? 



4. Boil about 10 c.c. of the urine and add one-quarter its 

 volume of Fehling's solution. Notice the color of the pre- 

 cipitate. To what is it due? Then boil 10 c.c. of Fehling's 

 solution and add one-quarter its volume of urine. What 

 occurs? Contrast these two experiments. 



Write the equations for the reactions in the above experi- 

 ments. 



BASIC RADICALS. 



With the exception of NH 4 these have little or no chemi- 

 cal significance. The proof for the presence of ammoniacal 

 compounds will be taken up under the quantitative deter- 

 minations. 



