1 8 Operations used in Quantitative Analysis 



[20 



and allowed to burn quietly until the last spark dies out. Then 

 the burner is used to keep it red hot until all the carbonaceous 

 matter is burned off. The ash is then shaken out into the 



Fig. 



dish, and the last traces removed from the wire with a small 

 camel's-hair brush. Finally, any portions of the ash which may 

 have fallen on the tile are swept into the dish. The dish is 

 then ready for ignition and weighing. 



Exercise VII. — Carefully clean a platinum dish of the size de- 

 scribed in paragraph 17. Place it over an Argand, as in fig. 16, 

 until red hot. Remove it to a desiccator, and when quite cool 

 weigh it. Place the wet filter paper containing the sand which has 

 been washed in performing Exercise VI. in this dish, and heat 

 over an Argand turned down until the flame is as small as possible. 

 Whilst it is drying start Exercise VIII. When steam ceases to 

 come off, turn up the burner until the dish becomes red hot. The 

 paper will catch fire and burn. When nothing is left but the sand 

 and the white ash of the filter paper, remove to a desiccator, and 

 when cool weigh. Enter your results thus : 



Dish + sand + ash = 



Dish - 



Sand + ash = 



Filter ash = 



Sand = 



From this calculate what percentage of sand was contained in the 

 mixture dissolved in Exercise IV. 



