The compounds of the following metals and semi-metals have fewer applications, but are well known, and are somewhat frequently met with in nature, although in small quantities:—
| Beryllium, | Be | = | 9. | Palladium, | Pd | = | 107. | |
|---|---|---|---|---|---|---|---|---|
| Titanium, | Ti | = | 48. | Cerium, | Ce | = | 140. | |
| Vanadium, | V | = | 51. | Tungsten, | W | = | 184. | |
| Selenium, | Se | = | 79. | Osmium, | Os | = | 192. | |
| Zirconium, | Zr | = | 91. | Iridium, | Ir | = | 193. | |
| Molybdenum, | Mo | = | 96. | Thallium, | Tl | = | 204. |
The following rare metals are still more seldom met with in nature, but have been studied somewhat fully:—
| Scandium, | Sc | = | 44. | Germanium, | Ge | = | 72. | |
|---|---|---|---|---|---|---|---|---|
| Gallium, | Ga | = | 70. | Rubidium, | Rb | = | 86. | |
| Yttrium, | Y | = | 89. | Cæsium, | Cs | = | 133. | |
| Niobium, | Nb | = | 94. | Lanthanum, | La | = | 138. | |
| Ruthenium, | Ru | = | 102. | Didymium, | Di | = | 142. | |
| Rhodium, | Rh | = | 103. | Ytterbium, | Yb | = | 173. | |
| Indium, | In | = | 114. | Tantalum, | Ta | = | 183. | |
| Tellurium, | Te | = | 125. | Thorium, | Th | = | 232. |
Besides these 66 elements there have been discovered:—Erbium, Terbium, Samarium, Thullium, Holmium, Mosandrium, Phillipium, and several others. But their properties and combinations, owing to their extreme rarity, are very little known, and even their existence as independent substances29 is doubtful.
It has been incontestably proved from observations on the spectra of the heavenly bodies that many of the commoner elements (such as H, Na, Mg, Fe) occur on the far distant stars. This fact confirms the belief that those forms of matter which appear on the earth as elements are widely distributed over the entire universe. But we do not yet know why, in nature, the mass of some elements should be greater than that of others.30
The capacity of each element to combine with one or another element, and to form compounds with them which are in a greater or less degree prone to give new and yet more complex substances, forms the fundamental character of each element. Thus sulphur easily combines with the metals, oxygen, chlorine, or