23-26] IGNITION AND SUBLIMATION II 



cased so as to contain water. The latter on being boiled 

 keeps the interior of the oven approximately at a tempera- 

 ture of too° C. The arrangement shown at (a) is for 

 maintaining the water at a constant level. 



A more rapid way of drying precipitates is to open out 

 the filter-paper containing the precipitate on a piece of wire 

 gauze, and hold it some distance above the Bunsen flame. 



23. Ignition. — Frequently substances require to be 

 heated strongly or ignited. This is best performed in a 

 small test-tube called an ignition-tube (6) or on a piece of 

 platinum foil 2 in. x 1 in., the latter being held in the 

 flame by means of crucible tongs. 



Experiment. — Heat a little solid manganese sulphate in 

 an ignition-tube ; the substance will turn black, due to the 

 production of the oxide. 



24. Fusion. — On ignition some substances melt or 

 fuse; occasionally other substances are added before 

 fusion. 



Experiment. — Heat a mixture of sodium carbonate and 

 potassium nitrate with a trace of manganese dioxide on 

 platinum foil ; a green mass will be produced. 



25. Sublimation. — On heating, some substances go off 

 in vapour, but condense again on a cool surface. 



Experiment. — Heat a little ammonium chloride in an 

 ignition-tube held in a horizontal position. The salt will 

 totally sublime and condense again as a white solid in the 

 cold part of the tube. 



26. Flame Colorations. — Certain substances when 

 heated in a colourless flame, such as the Bunsen or blow- 

 pipe flame, give a distinct coloration to the flame. 



Experiment. — Clean a piece of mounted platinum wire 

 (7) by heating it in the blowpipe flame, moistening it with 

 hydrochloric acid, reheating, and repeating the operation if 

 necessary. Take up a little calcium chloride by means of 

 the loop and hold in the flame. A red coloration will be 

 given to the flame. 



