THE METALS: THE METALLIC OXIDES 55 



and in its producing moisture on the sides of the tube, when 

 burnt, has the gas the properties of hydrogen? Now test the water 

 in the dish with red Utmus paper. Has it become alkaline, thus 

 showing that the metallic oxides, potash and soda, have been 

 formed and are dissolved in the water ? Does 

 Potassium + oxide of hydrogen = oxide of potassium + hydrogen? 



The vapours of many metals and of their volatile compounds impart 

 characteristic colours to non- luminous flames. Thus, among other 

 metals : — 



Sodium imparts a yellow colour. 



Potassium ,, violet ,, 



Calcium ,, red ,, 



Strontium ,, criinson ,, 



Barium ,, green ,, 



These colours are best observed by heating a little of the compound on the 

 end of a platinum wire in the Bunsen flame. As many compounds are not 

 volatile, it is best to moisten the substance on the wire with hydrochloric 

 acid, volatile salts being thus produced. As potassium compounds are very 

 often impure with sodium compounds, it is best to examine the flame for 

 potassium through a solution of indigo, the blue of which absorbs the 

 yellow of the sodium. These coloured flames are useful for detecting and 

 identifying the metals in minerals, mineral waters, etc. This is best done 

 by examining the spectra by means of the prism of a spectroscope, in which 

 advantage is taken of the different refrangibilities of different coloured rays 

 of light in order to decompose the light emitted by each incandescent 

 vapour into its component colours. By this means it is possible to identify 

 the metals with certainty even in complex minerals. 



The metals calcium, strontium, and barium are so costly that 

 their oxidisability cannot be practically investigated in this 

 course. They assume a position, however, intermediate be- 

 tween the metals just studied and those next referred to. 



Take pieces of magnesium ribbon and zinc foil. Note that 

 in the air at ordinary temperatures the surface has very slowly 

 become tarnished, but that the film of oxide gradually formed 

 has preserved the metal beneath from further oxidation. Place 

 each in a test-tube of water, and note that no gas is evolved, 

 and therefore no oxide formed, even when the water is heated 



