CHEMICAL COMPOSITION OF MINERALS. 79 
antimony, boron, columbium, tantalum, vanadium, gold. For 
example, for arsenic there are the compounds As,S, As,S., 
As,O,, As,O;, etc. Another characteristic of these elements of 
the hydrogen, sodium, chlorine, and arsenic groups is that the 
number of equivalents of the acidic element in the compounds 
into which they enter is, with a rare exception, odd, and of the 
], 3, 5, ete., series, and on this account they are called in 
eat aay pertssads ; while the other elements, in whose com- 
pounds their number is of the 1, 2, 3, etc. (or 2, 4, 6) series, 
are called artiads. An apparent exception exists under the 
_artiads in the sesquioxides, but this does not alter the general 
character of the series. 
The facts above cited sustain the general statement that 
Ca,, Me,, Mn,, Zn,, Fe,, Al, He, Mn, have equivalent combin- 
ing values, and hence in minerals often replace one anotlier 5 
and so also Ca, Mg, Mn, Zn, Fe, K,, Na,, Li,, H., may replace 
one another. Similarly, also, As,, or Sb, replaces S in some 
minerals. 
With reference to the classification of minerals the elements 
may be conveniently divided into two groups: (1) the Acidic, 
and (2) the Basic. The former includes oxygen and the ele- 
ments which were termed the acidifers and acidifiable elements 
in the old chemistry. They are those which have been called 
in mineralogy the mineralizing elements, since they are the 
elements which are found combined with the metals to make 
them ores, that is, to mineralize them. The basic are the rest 
of the elements. The groups overlap somewhat, but this need 
not be dwelt upon here. 
The more important of the acidic elements are the following 
oxygen, fluorine, chlorine, bromine, iodine, sulphur, selenium, 
tellurium, boron, chromium, molybdenum, tungsten, phosphorus, 
arsenic, antimony, vanadium, nitrogen, tantalum, columbium, 
carbon, silicon. 
Again, among the compounds of these elements occurring in 
the mineral kingdom there are two grand divisions, the binary 
and the ternary. The binary consist of one or more elements 
of each of the acidic and basic divisions, and the ternary of one 
or more elements of each of these two classes, along with oxy-. 
gen, fluorine, or sulphur as a third. The binary include the 
sulphides, arsenides, chlorides, fluorides, owides, etc., and the 
ternary the sulphates, chromates, borates, arsenates, phosphates, 
silicates, carbonates, etc., and also the sulph-arsenites and sulph- 
antimonites, in which a basic metal (usually lead, copper, sil- 
ver) is combined with arsenic or antimony and sulphur. 
