Fire and Heat 115 



The study of water may be carried on in several ways. Two 

 are suggested here. The first is strikingly brilliant, and may 

 be done accurately with the aid of a delicate balance. The 

 experiment is instructive also without weighing. 



Exercise. Cut off and, if practicable, weigh accurately a small 

 piece of magnesium ribbon. Burn it in the air, on a piece of asbestos 

 paper, and weigh the product. Oxygen in the air unites, as you 

 know, with burning substances and forms oxids. In this instance 

 the product of combustion is magnesium oxid. The additional weight 

 shows the quantity of oxygen combined with it in burning. But the 

 principal point is that oxygen is indispensable in burning magnesium. 



Fill a beaker about two thirds full of water, and cover closely with 

 a heavy piece of asbestos paper, through which is made a slit just large 

 enough to admit the magnesium ribbon. Boil the water until the 

 air is expelled from the beaker by the steam, and then insert the 

 ribbon which you have lighted by the fire of the burner. The mag- 

 nesium ribbon continues to burn just as freely as it did in the air. 

 The product is identical with the product of magnesium burned in 

 air, that is, magnesium oxid. Where is the oxygen necessary for 

 burning obtained? What conclusion can you draw as to one of the 

 constituents of water? 



Another interesting phenomenon may be observed if the room is 

 darkened during the experiment. Above the asbestos and about the 

 slit is a flame, which evidently is not altogether due to the burning 

 magnesium. The magnesium is deep in the steam and above it is a 

 space through which no flame is carried. But outside is this ghost of 

 a flame. Now if one substance contained in water is oxygen, as your 

 observation shows, another substance seems to burn when it comes 

 into contact with the oxygen in the outer air. The union of the oxy- 

 gen from water with the burning magnesium must have set free the 

 other substance, or substances, which are apparently combustible. 



Caution. The intense brilliancy of the flame makes it necessary 

 to wear blue glasses to protect the eyes. To see the flame burning 

 above the slit, hold a strip of cardboard between the magnesium and 

 the eyes. 



Exercise : The decomposition of water. We may analyze water 

 into its constituents by passing through it an electric current, a pro- 

 cess known as electrolysis (electro-lysis, meaning to loosen or dissolve 

 by electricity). A comparatively simple apparatus can be made. 

 The materials needed are a granite or porcelain dish about six inches 



