CHEMICAL COMPOSITION OF MINERALS. ari 

Lithium | Li 7 | Silver Ag 108 
Magnesium _ Mg 24 | Silicon Si 28 
Mauganese Mn 90 | Sodium Na 23 
Mercury Hg 200 | Strontium Sr 87°6 
Molybdenum Mo 96 | Sulphur S 32 
Nickel Ni 58°8 | Tantalum Pa * 2 182 
Nitrogen N 14 | Tellurium Te tds 
Osmium Os 199°2| Thallium Tl 204 
Oxygen O 16 | Thorium Th 235 
Palladium Pd 106-6) Tin Sn 118 
Phosphorus P 31 | Titanium Ti 50 
Platinum Pt 197°6) Tungsten W 184 
Potassium K 39°1 | Uranium U 240 
Rhodium Ro 104°4; Vanadium V 51:2 
Rubidium Rb 85°4 | Yttrium a‘ 92 
Ruthenium Ru 104-4 | Zine Zn 65:2 
Selenium Se 79-4 ' Zirconium Zr 89°6 
The combining weights indicate the proportions in which the 
elements combine. Thus, assuming hydrogen, the lightest of 
the elements, to be 1, or the unit of the series, the combining 
weight of oxygen is 163 of iron, 56; of magnesium, 243; of 
sul phur, 02; and soon. When hydrogen and oxygen combine 
it is in the ratio of 2 pounds of hydrogen, or else 1 pound of 
hydrogen, to 16 pounds of oxygen, and two different compounds 
thus result. When oxygen and magnesium combine it is in the 
ratio of 16 pounds of oxygen to 24 of magnesium. Oxygenand 
iron combine in the ratio of 16 of oxygen to 56 of iron; or of 24 
of oxygen (14 times 16) to 56. Sulphurand oxygen combine in 
the ratio of 32 of oxygen to 32 of sulphur; or of 48 to 32 of 
sulphur. The combining weights are often called the atomic 
weights. 
The following is the manner of using the symbols: For the 
compound consisting of hydrogen and oxygen in the ratio of 2 
to 16, the chemical symbol i is H,O, meaning 2 of hydrogen to 1 
of oxygen. (This compound is water. ) For the compound of 
oxygen and magnesium just referred to, the symbol is MgO; 
for the two compounds of oxygen and iron, FeO, protoxide of 
iron; Fe,O,, sesquioxide of iron, the ratio of 1 to 14 being ex- 
pressed by 2 to 3; for the two compounds of sulphur and oxy- 
gen, SO, and SO. 
Some of the elements so closely resemble one another that 
their similar compounds are closely alike in crystallization and 
other qualities, and they are therefore said to be tsomorphous. 
This is true of iron, magnesium, calcium, and two or three 
other related elements, In one group of compounds of these 
bases, the carbonates, the crystalline form for each is rhombohe- 
