The Chemical Relations of Water 281 



ignite the hydrogen, which burns above the sodium 

 with a vivid yellow flame. (The colour is due to a 

 small quantity of sodium vapour being burnt together 

 with the hydrogen, and is not that of the flame of 

 burning hydrogen, as will be seen in later experiments.) 

 When the burning has finished, a small glassy ball of 

 molten sodium hydroxide may be seen floating on the 

 water. This is not in actual contact with the water at 

 first, but, as it cools, a point is reached at which con- 

 tact occurs, when the hot substance reacts with the 

 water with some violence.. Splashes of hot solution of 

 the hydroxide may be thrown to a short distance, hence 

 the observer should not stand too close to the trough 

 during this stage of the experiment. The student will 

 now realise the need for the precautions taken in 

 Experiment 117 with regard to avoiding the contact 

 of the sodium there used with wet bodies. 



Equation : 



Sodium + hydrogen hydroxide = hydrogen + sodium hydroxide 

 (water) (caustic soda) 



195. A few other metals, e.g. potassium and calcium, 

 also possess the power of turning out part of the hydro- 

 gen from cold water. Others, such as magnesium and 

 iron, will deprive steam of its oxygen, while, a third 

 group, of which copper and silver are examples, do not 

 act upon either water or steam. 



EXPERIMENT 130. Fig. 91 represents a long tube, 

 which may be of iron or porcelain, the interior of which 

 is loosely filled with clean iron filings, or with the 

 common small iron tacks, or with small clean screws. 

 The large flask contains water and is supported upon a 

 sand-bath over a Fletcher burner. The long tube rests 

 in an iron trough placed above a furnace consisting of 



