1815.] Berzellus'i System of Mineralogy. 306 



minerals the silica performs the function of an acid, and tliat it is 

 chemically combined with the other earths or oxides which perform 

 the function of bases. According to this notion, which has like- 

 wise been advanced by Mr. Smitlison, the stony bodies are in reality 

 salts. But they are often of a more complicated nature than the 

 salts composed of the common acids and bases ; for in the siiiciates, 

 as Berzelius terms these stones, we find not only the combination 

 of silica with one base, but witli two, three, or four bases, and 

 often in various proportions, so as to constitute subsiliciates or super- 

 siliciates. 



If we suppose silica, alumina, magnesia, and lime, to be com- 

 posed of one atom of oxygen and one atom of base, as I have done 

 in the table published in the second volume of the Annals of Philo- 

 sophy J or of two atoms of oxygen and one aton) of base, as Ber- 

 zelius has done, it is obvious that the number of integrant par- 

 ticles in any stony body may be determined by ascertaining the 

 proportion which the oxygen of the various constituents bear to 

 «ach other. Thus suppose we examine a mineral composed of 

 silica and lime, and find that the oxygen in the silica is three times 

 as great as in the lime, it follows that the mineral is composed of 

 three integrant particles of silica and one integrant particle of lime; 

 so that it may be termed a trisiliciate. This is the mode v.-hich 

 Berzeliijs has taken to determine the constitution of the various 

 stony bodies. It has the advantage of being at once easy and accu- 

 rate, supposing us acquainted with the composition of the different 

 earths. 



Berzelius supposes silica to be composed of 50*36 silicon + 

 49*64 oxygen. If therefore we consider it as a protoxide, it follows 

 that the weight of an atom of silicon is 1-007, and the weight of 

 an integrant particle of siUca 2007. He considers alumina i;s 

 composed of 53-3 aluminum -|- 46'7 oxygen. The following table 

 exhibits the weight of an atom of the diifercnt bases according to 

 the analyses employed by Berzelius in this work. 



Weight. Weighr. 



Silicon 1-007 Silica 2*007 



Aluminum .... 1-141 Alumina 2*141 



Magnesium.... 1*631 Magnesia 2*631 



Calcium 2-.571 Lime 3*.571 



Barium 8*523 Barytes 9*523 



This table will enable the reader to calculate the composition of 

 the diflerent stony bodies, which have been subjected to an accu- 

 rate analysis. For exam|)le, xchnalsteln, or lalile spar, is a hydr&ns 

 b'tsUiciate oj lime', somnite, or nephcime, \s a silicia/e of uluwina ) 

 one of the species of calamine analyzed by Smithson,' and com- 

 posed of silica and oxide of zinc, is a siliciute of zinc; cerile is a 

 ulicialt/ of leriuw. Berzelius gives examples of more complex 



Vol. V. N" IV IT 



