20] Burning the Filter 19 



Exercise VIII. — Whilst the ignition described above is going 

 on, filter off the alumina precipitate obtained in Exercise V., wash- 

 ing it thoroughly by decantation. Dry in the arrangement de- 

 scribed in paragraph 16, and burn it as described in paragraph 20 £, 

 first weighing the dish as in Exercise VII. Finally, ignite the 

 dish and precipitate, cool in a desiccator, and weigh. Enter the 

 results just under the entry for Exercise V., and calculate the 

 percentage of Al 2 O s which you have precipitated out of the 

 ammonia alum. 



