200 SCIENTIFIC AMUSEMENTS. 



evolved upon the oxygen of the air in the flask; later on, when 

 the air has been all expelled, no more red colour is visible. 



Pill a cylindrical jar half full of nitric oxide at the pneumatic 

 trough, and then lift it up out of the water for a second or two, 

 so that the remaining water may run out and air take its place ; 

 dense red fumes will be visible. Lower the mouth of the jar 

 under water, and let the whole stand awhile ; the red fumes will 

 dissolve in the water, which will consequently rise in the jar 

 owing to the absorption. 



Instead of allowing air to enter, pass some oxygen into the jar; 

 the production of red fumes, and subsequent absorption of them 

 by the water and the consequent diminution in bulk of the gas, 

 will be still more marked. 



Combination of Gases with Solids or Liquids to form Gaseous 



Products. 



The burning away of charcoal in the air (or in oxygen, Expt. 

 224) affords an example of this class of action, the products of 

 combustion being not only gaseous at the temperature at which 

 the combination occurs (that of the burning charcoal), but also 

 remaining gaseous after cooling down to the ordinary temperature. 

 In all such cases it is evident that, although the solid matter has 

 become invisible, yet it has not been actually destroyed, but is 

 still present in a form capable of being rendered evident to the 

 sight by the use of appropriate tests, e.g., by lime water. In the 

 same kind of way when a candle burns, although the wax or tallow 

 disappears, yet it is not destroyed, but only converted into other 

 invisible forms of matter or gases. If a cold dry tumbler or 

 lamp chimney be held for a few moments over a burning candle, 

 it will become visibly bedimmed with dew ; this arises from the fact 

 that when chemical change takes place between the materials of 

 the candle and the air water is one of the products formed; owing 

 to the heat developed this is evolved in the form of vapour 

 or steam, which condenses as dew upon the comparatively cool 

 glass, just as dew is formed from the air upon a cooled surface in 

 Expts. 43 and 207. On putting a chimney over a moderator or 

 paraffin lamp, or over an argand gas burner, precisely the same 

 thing is seen, i.e., the cool chimney becomes dimmed with dew, 

 which speedily evaporates again as the glass gets hotter. 



On the other hand, Expt. 154 has shown that when a candle 

 burns the gas carbon dioxide, capable of making limewater turbid, 

 is also formed ; so that, on the whole, although the solid material 

 of the candle has disappeared during burning, yet we have in its 



