FIXED ALKALIES. T75 



In order that soda may possess all the requisite strength, 

 it is necessary to separate it from the carbonic acid with 

 which it is always united, and by which its properties are 

 weakened. This is easily done by mixing quick-lime with 

 a solution of soda. The acid has so strong an affinity for 

 lime as to quit the soda to combine with it. The ley pro- 

 cured from this mixture is caustic, and leaves a burning 

 impression upon the tongue : the soda thus purified acts 

 more readily upon the bodies with which it combines. 

 This mode of preparation is indispensable when soda is to 

 be employed with oil in the manufactory of hard soap ; it 

 is useless when it is to be combined at a strong heat with 

 earthy bodies, as is the case in glass works. 



Davy discovered soda and potash to be metallic oxides, 

 or burnt metals; and Berzelius has proved that when 

 these two alkalies are pure, potash is composed of -^jy of 

 oxygen, and y^^j of potassium, and that soda was the result 

 of 74.42 of sodium in 100 parts, and 25.58 of oxygen. 



Besides the substances of which I have spoken, plants 

 contain certain salts, earths, and metallic oxides, which 

 have never been extracted, either for domestic purposes or 

 to be employed in manufactures : the existence of these 

 is however so constant, their proportions so little varied in 

 the same kind of plant, and their situations in the different 

 parts of vegetables so marked, that they must be regarded 

 as belonging essentially to vegetation, and not as being in- 

 troduced accidentally and without design into the organs 

 of the bodies in which they are found. 



The most abundant salts in plants are the sulphate of 

 potash, and common salt, the phosphates of lime, and the 

 nitrate of potash : the sulphate and muriate of soda do not 

 exist in any considerable quantity, excepting in marine 

 plants. 



Of the four earths procured from these plants by com- 

 bustion, the one most extensively found is silica ; next to 

 that comes lime, and afterwards magnesia and alumina. 



M. Th. de Saussure, in his highly valuable work upon 

 vegetation, has given us the results of the analytical inves- 

 tigations he has made for determining the quantity of 

 ashes, salts, earths, and metallic oxides, which are fur- 

 nished by an equal weight of a great variety of vegetables : 

 these results are as follows. 



