BONE. 37 



oxalate is proof of the presence of calcium combined other- 

 wise than with phosphoric acid. 



(d) Magnesium. To 15 c.c. of the solution add a slight 

 excess of NH 4 OH. Then make the mixture acid with acetic 

 acid; this should dissolve the greater part of the precipitate. 

 The slight insoluble substance is to be filtered off, dissolved 

 in HC1 and tested for iron by means of potassium ferro- 

 cyanide. The acetic acid filtrate is treated with a few c.c. 

 of ammonium oxalate and the resultant precipitate filtered 

 off. This new filtrate is made alkaline and a few c.c. of a 

 disodium phosphate solution added. Why does a precipitate 

 at this point prove the presence of magnesium? Write the 

 equations. 



(e) Carbonates. Did you notice an effervescence when 

 you added HN0 3 after incineration? What was the cause? 



