250 PHYSIOLOGICAL CHEMISTRY 



acid. Test with litmus and add more of the acetic acid if neces- 

 sary to produce a slightly acid reaction. Boil for a few minutes. 

 If the liquid does not become perfectly clear, add a few drops 

 more of the acid and boil again. Avoid excess of acid, which 

 will cause the liquid to become milky. Filter the clear liquid 

 from the coagulated proteins and test it for inorganic materials 

 as described below in Section III. 



10. Bone, Dissolve a small spoonful of bone ash in 100 c.c. 

 of water acidified with nitric acid. Is a gas given off? If so, 

 what substance is shown to be present in bone? (Remember that 

 in preparing the bone ash much C0 2 may have been driven off 

 by heating.) If the bone ash does not all dissolve, add more 

 nitric acid, or filter off the undissolved ash. Test the solution 

 for inorganic materials as described below in Section III. Be- 

 fore testing for calcium, neutralize the solution with ammonia 

 (litmus) and reacidify with 10% acetic acid, as calcium oxalate 

 is soluble in nitric acid. In case the phosphates thrown down 

 by the ammonia do not all dissolve on the addition of acetic 

 acid, the solution must be filtered before performing the calcium 

 test. 



III. Tests for Inorganic Materials. 



Use about 3 c.c. of the solutions prepared in Section II for 

 each test. Record results as , indicating absence ; +, indicating 

 traces; and -| |-, indicating much. If the liquid only becomes 

 cloudy, report +. If there is a distinct precipitate, report ++. 



11. Chlorides. Acidify with about % volume of cone, nitric 

 acid and add silver nitrate. The presence of much chloride is 

 indicated by a heavy white precipitate. If only traces are pres- 

 ent, the solution becomes cloudy and shows a bluish-white opal- 

 escence. Write the equation. Confirm the presence of chloride 

 by adding ammonium hydrate until the liquid reacts alkaline to 

 litmus. On adding this reagent, any precipitate of silver 

 chloride will dissolve, but if phosphates are present in quantity, 

 they will be thrown down. If a precipitate forms on the addi- 

 tion of ammonia, filter, and in the filtrate confirm the presence 



