LABORATORY PRACTICE 



323 



Experiment No. 24 

 Testing for Phosphoric Acid 



Dissolve 0.5 gm. bone ash in 15 cc. H 2 O and 3 to 5 cc. HNO 3 and 

 filter. To the warm filtrate add 5 to 7 cc. ammonium molybdate 

 and shake. The yellow precipitate formed is ammonium phospho- 

 molybdate. See Experiment No. 19. 



In a test tube heat 0.5 gm. of bone ash with 20 cc. distilled 

 H 2 O ; filter. To the warm filtrate add 5 cc. ammonium rnolyb- 

 date and shake. Note the result as compared with that when 

 HNO 3 was used with the distilled water. What does the result 

 show ? 



Experiment No. 25 

 Preparation of Acid Phosphate 



Place 100 gms. bone ash in a large lead dish. Add slowly and 

 with constant stirring 100 gms. commercial 

 sulphuric acid, using an iron spatula for the 

 purpose. Transfer the mixture to a wooden 

 box and allow it to act for about three days. 

 Then pulverize and examine. The mixing of 

 the acid and phosphate should be done in a 

 place where there is a good draft. Test 

 gm. for water soluble phosphates as directed 

 in Experiment No. 24. 



Experiment No. 26 



Solubility of Organic Nitrogenous Compounds 

 in Pepsin Solution 



Prepare a pepsin solution by dissolving 

 5 gms. of commercial pepsin in a liter of 

 water, adding I cc. of strong HC1. Place in 

 separate beakers 0.5 gm. each of dried blood, 

 tankage, and bone ash. Add 200 cc. of pep- 

 sin solution to each and place the beakers in a 



FIG. 60. Determining 

 Digestibility of Organic 

 Nitrogen in Acid Pepsin 

 Solution. 



