80 CHEMICAL PROPERTIES OF MINERALS. 
The following are examples of the symbols of binary and 
ternary compounds ; 
1. Binary. 
1. Sulphides, Selenides.—Ag.S = silver sulphide; Ag,Se = 
silver selenide; PbS = lead sulphide; ZnS = zine sulphide ; 
FeS, = iron disulphide. 
2. Fluorides, Chlorides, etc.—Ca¥, = calcium fluoride; AgCl 
= silver chloride; AgBr = silver bromide; Agl = silver 
iodide ; NaCl = sodium chloride (common salt). 
3. Oxides. — Al,O,; = 3(Al,O) = aluminium sesquioxide ; 
As,O; = arsenic trioxide ; As,O; = arsenic pentoxide; BaO = 
barium oxide; B,O; = boron trioxide (boracic acid) ; CaO = 
calcium oxide (lime) ; CO, = carbon dioxide (carbonic acid) ; 
CrO, = chromium trioxide (chromic acid) ; Cu,O = copper sub- 
oxide; CuO = copper oxide; BeO = beryilium oxide; H,O = 
hydrogen oxide (water); FeO = iron oxide; Fe,O; = iron 
Sesqnioxide ; PbO = lead oxide; Li,O = lithium oxide; MgO 
= magnesium oxide; MnO = manganese oxide; Mn,0O, = 
manganese sesquioxide; MnO, = manganese dioxide; P,O; = 
phosphorus pentoxide ; K,O = potassium oxide 3 $10, = silicon 
dioxide (silica) ; Na,O = sodium oxide; SrO = strontium ox- 
ide ; SO, = sulphur dioxide (sulphurous acid) ; SO; = sulphur 
trioxide ; SnOQ, = tin dioxide; V,O; = vanadium pentoxide 
(vanadic acid); WO, = tungsten trioxide (tungstic acid) ; 
ZnO = zinc oxide ; ZrO, = zirconium dioxide. 
The composition of these compounds may be obtained from 
the table of combining weights, page 76. For example, with 
reference to the first of them (AgS), the table gives for the 
combining weight of silver (Ag), 108, and for that of sulphur,-32. 
The elements exist in the compound therefore in the proportion 
of 108 to 32, and from it the composition of a hundred parts is 
easily deduced. 
If the formula were (Ag, Pb)S, signifying a silver-and-lead 
sulphide, and if the silver and lead were in the ratio of 1 to 1, 
then half the combining weight of silver is taken; that is, 54, 
and half the atomic weight of lead, which is 103°5; and the 
sum of these numbers, with 32 for the sulphur, expresses the 
ratio of the three ingredients. 
For Al,O; we find the combining weight of aluminium 27.4 5 
doubling this for Al, makes 54:8. Again, for oxygen, we find 
16; and three times 16 is 48. 54-8 to 48 is therefore the ratio 
