ON NEUTRAL SALTS 189 



when they contain a certain quantity of water; but when 

 this is diminished, it is not impossible that an earth or a 

 metal should obtain the superiority, especially if the alkali 

 which is separated should at the instant of its separation 

 meet with a weaker acid with which it can unite. Such is 

 the aerial acid in this case, which is always present in 

 considerable quantities in cellars. 



It appears strange that the fossil alkali efflorescing 

 upon the iron plate should not be able to precipitate the 

 drops of the martial solution resting upon it. But the 

 cause is this, that the solution of iron in muriatic acid, 

 when it has become dry, strongly attracts moisture, and the 

 alkali which is then separated and effloresces, cannot after- 

 wards produce any effect upon it. 



If vegetable alkali, like the fossil, had the property of 

 efflorescing, the neutral salts into which it enters would 

 probably be decomposed in the same manner ; but as they 

 have not this property, this does not happen. 



