VIU CHEMICAL SYMBOLS. 



of Iron combined witli one of Oxygen. A dashed letter indicates a double 

 atom of the substance — tlius, Pe means two atoms of Iron combined with 

 three of Oxygen. A general formula has sometimes been given when one 

 or more of the elements are replaced by others in variable proportions, or 

 for species which include several important varieties, as Melinophane, 

 p. 12, Allanite and others, p. 14, Pyroxene, p. 11, Araphibole and Peridot, 

 p. 12, &c. In these formulae R represents all the bases composed of one 

 atom of an element and one of Oxygen, and fi all those composed of two 

 atoms of an element and three of Oxygen. Thus the general formula for the 

 family of the Chlorites, p. 17, is 5R3 Sif + 3R Si| + 12H, which means that 

 the mineral contains five atoms of a compound made up of three atoms of 

 proto-base combined with three-quarters of an atom of silicic acid, plus 

 three atoms of a compound of one atom of sesqui-base combined with three- 

 quarters of an atom of silicic acid, plus 12 atoms of water. In Chlorite 

 and Pennine the proto-bases are Magnesia and Iron, but in Clinochlore 

 Magnesia only ; in Chlorite and Clinochlore the sesqui-base is Alumina 

 only, while in Pennine it is Alumina and Iron. It will thus be seen that 

 a large figure written as a co-efiicient refers to the whole of the member to 

 which it is prefixed, while a small figure written as an exponent refers only 

 to the symbol to which it is attached. Thus 5R*Si| means five atoms of 

 "S? Si|, while R' means simply three atoms of S. When the symbols are 

 written together the substances are in chemical combination — thus As S 

 which is the formula for Realgar, p. 2, characterizes that mineral as a 

 sulphuret of Arsenic. When one element is combined with several these 

 are placed in brackets and each symbol is followed by a comma — thus 

 Smaltine (Co, Fe, Ni) As^, p. 4, is an Arseniuret of Cobalt, Iron, and Nickel. 

 In this case the proportions of Cobalt, Iron, and Nickel are not stated. In 

 the formula of Eisennickelkies (JNi -f- ^Fe) S, p. 3, a sulphuret of Nickel 

 and Iron, the proportions are stated. The general formula in this case 

 would be RS; one-third of R is Nickel, and the other two-thirds Iron. 

 When more than one element is combined with several others, both mem- 

 bers are written in brackets; thus Glaucodot (Co, Fe) (S, As)^, p. 4, is a 

 Bi-sulpho-arseuiuret of Cobalt and Iron. In some instances, as Bismuth 

 Silvei', p. 1, no formula has been given, but simply an enumeration of the 

 elements of which the mineral is composed ; in this case each symbol is 

 followed by a comma. 



When the water of a mineral has not been determined, it has been 

 written Aq. instead of H. , 



