208 CHEMISTRY. 



the air the oxide absorbs moisture, and very shortly becomes 

 potassium hydrate. It can not be kept in the air at all, and 

 is ordinarily kept in naphtha for the same reason that it is 

 received into that liquid when it is made. It is so soft that 

 it can be worked by the fingers like wax. 



285. Potassium Set on Fire by Water. When a little 

 piece of this metal is thrown upon water it instantly decom- 

 poses the water, taking the oxygen to itself to form an ox- 

 ide. Hydrogen, the other ingredient of water, being set 



free, immediately takes fire, Fig. 86, from the 

 heat which is produced by this sudden union 

 of the oxygen and potassium. The flame of 

 the burning gas is of a beautiful violet color. 

 Fig. so. rpjjjg j s Because the heat changes some of the 

 metal into vapor, and this rises with the burning hydrogen. 

 As the metal burns it runs about on the surface rapidly. 

 This is owing to the hydrogen gas which is constantly devel- 

 oped from the water, the steam produced from the water by 

 the heat, and the vapor of the metal. These act on the lit- 

 tle bit of potassium as the gases of burning powder do on 

 a rock. The motion is irregular, because the production of 

 the gas and steam and vapor is going on upon all sides of 

 the piece of metal. The results of this energetic action are 

 potassium hydrate and free hydrogen ; the latter, however, 

 immediately burns, i. ., unites with oxygen, forming water. 

 K+H 2 O=:KHO+H and H 2 +O=H 2 O. The same phenom- 

 ena and results occur if potassium be thrown upon ice. So 

 strong is its attraction for oxygen that the coldness of the 

 ice makes no difference. 



286. Caustic Potash. What is commonly termed caustic 

 potash is a hydrate of potassium, KHO. So strong is the 

 disposition of the oxide of potassium to become hydrated, 

 that the anhydrous oxide can be obtained only by exposing 

 the metal potassium to air or oxygen that is perfectly dry. 



