ALKALIES. POTASH. SODA. 63 



as to float on water. So great is the attraction between 

 potassium and oxygen, that it decomposes the water on 

 which it floats, unites with a portion of its oxygen, exhib 

 iting the singular appearance of a little fire on the water, 

 and forms potassa. 



219. In the ashes of kelp and of other plants growing 

 in the sea, and of some of those growing near the sea, 

 instead of potash, Soda is found, in the state of carbonate 

 of Sodium, a light metal somewhat similar to potassium, 

 and having nearly the same violent affinity for oxygen, 

 so as to take fire when placed on hot water. 



220. Alkali. The ashes of sea plants have long been of 

 value in commerce, from being used in the manufacture 

 of hard soap, and also of glass. These soda ashes are 

 called, in Spain, alkali, (Arabic al, the, kali, ashes,) which 

 name has thus been given to soda, and thence to potash 

 and ammonia, all which are called alkalies ; and all three 

 have very similar properties. They have a bitter, acrid 

 and burning taste, and the power of changing vegetable 

 blue colors to green, and pink to blue. 



221. They have also the remarkable property of uniting 

 with the acids, and thereby losing all their own peculiar 

 properties, and destroying those of the acids. Sulphuric 

 acid, for example, has the extreme sourness and corrosive 

 power with the other properties of the acids. Pure soda 

 has the alkaline properties just mentioned. But when 

 sulphuric acid is poured upon soda, it forms a new sub 

 stance, sulphate of soda, or Glauber s salts, which is called 

 a neutral salt ; a salt, because it looks very much like 

 common table salt, and neutral, because it has neither 

 the properties of an acid nor those of an alkali. 



It is in the state of neutral salts that most of the 

 mineral substances enter into the composition of plants. 



