19, 20] Ignition of Precipitates 17 



19. A better plan is never to let a flame touch the platinum. 

 Whenever a precipitate is to be ignited, an Argand burner 

 should be used of one of the forms shown in fig. 16. 



The support for the capsule is made either of platinum 

 wire, or of iron wire round which has been fastened a strip 

 of platinum foil. Should a higher temperature be required, 

 as in the burning of CaC0 3 to CaO, a Fletcher muffle furnace 

 may be used (see fig. 17). 



BURNING THE FILTER 



20. This operation is carried out in several ways, but for 

 the purposes of this book only two need be described. 



(a) When the burning of the filter has no action on the 

 precipitate, the filter paper may be folded up whilst still wet, 

 placed in a platinum dish, and ignited very gradually over an 

 Argand. 



(b) In other cases the precipitate, dried as described in 

 paragraph 16, is removed as completely as possible from the 

 filter paper to the dish, and the paper burned in a coil of 

 platinum wire. 



If the wire be wound carelessly about the paper, it will 

 probably break after being used a few times, from being con- 

 tinually bent about in different ways. This is 

 avoided by winding the wire in a spiral around 

 a small cone of wood. When required for use 

 the wooden cone is removed and the filter folded 

 up and introduced into the spiral as in fig. 18. 



The operation of burning is shown in fig. 19. The spiral 

 of wire containing the filter is held over the platinum dish, 

 which stands on a glazed tile. Should the precipitate be dark 

 coloured, a white tile is used ; should it be light, a red one is to 

 be preferred. First the paper is ignited by the Bunsen burner, 



c 



