340 CHEMICAL COMPOSITION OF MINERALS. 



1350, the atomic weight of silver, and so on. (See preced 

 ing table.) This process gives the relation, 

 0-0437 : 0-0146 : 0-0875, 

 and dividing each by the smallest, to simplify it. it becomes 



3:1:6, 

 which is therefore the number of atoms of each, silver, anti- 

 mony, and sulphur. The formula 3Ag4-lSb+6S, or Ag 3 

 SbS 6 , expresses this relation. 



As chemistry makes known a sulphuret of silver consisting 

 of 1 of sulphur to 1 of silver, and also a sulphuret of anti- 

 mony containing 3 of sulphur to 1 of antimony, the ingre- 

 dients are regarded as thus combined in the compound. The 

 3Ag take 3S, making 3AgS, and leave 3S for the lSb to 

 form l(SbS 3 ) ; so that Red Silver Ore is supposed to be rep- 

 resented by the formula 



3AgS+SbS 3 ; or Ag 3 Sb, 

 if the mark ( ' ) be used, as is common, for sulphur. 



2. An analysis of Feldspar gives in 100 parts, 



Silica 64-78, Alumina 18-38, Potash 16-84. 



Now if we ascertain the proportion of oxygen in these con- 

 stituents we learn the ratio of the constituents, since we know 

 that silica contains 3 of oxygen, alumina 3, and potash 1. 

 From the above table we find that 100 of silica contain 52*98 

 of oxygen; consequently if 100 give 52-98, the amount in 

 64-78 parts will be found by multiplying 52-98 by 64*78, 

 and dividing by 100 ; or what is equivalent, multiplying 

 0-5298 by 64'78. So in 100 parts of alumina the oxygen is 

 46-7 ; hence the oxygen in 18-38 parts of alumina will equal 

 18-38 X 46-7-7-100. In this way we ascertain that 



64-78 of silica contain 34-32 oxygen, ) or ^ ridiag { 12 

 18-38 of alumina " 8*58 " [ each by the J 3 



16-84 of potash » 2-86 " ) 8midIcst ' ( 1 



Hence the amount of oxygen in the potash, alumina, and 

 silica, is as 1:3:12. Now as each atom of silica contains 3 

 of oxygen, 12 atoms of oxygen correspond to 4 of silica: so 

 also 3 of oxygen for the alumina correspond for a like reason 

 to 1 of alumina ; and 1 of oxygen for the potash to 1 atom 

 of potash. The compound therefore contains 4 parts of silica 

 to 1 of alumina and 1 of potash. 



