地壳中九十二种不同的元素有些是常见的,有些是难得见的,除了在化学实验室中可以听到它们的名字以外,恐怕就没有人提到了。这并不是因为它们没有用处,亦不是因为地壳中所有的量特别的小,而是因为不集中在一处生产,工业上不值得提炼的缘故。譬如镓Ga,知道的人就是很少,其实要比银多一百五十倍,比汞多三十倍,然而银汞已出名了好几百年或一二千年,并且使用的量亦是不少,完全是由于它们的矿在世界上各地有多量的发见。镓的少见是因为散布各处,没有集中的矿量,若是这些少见元素有相当易采的矿,就在工 Ninety-two different elements of the crust are somewhat common and some are rare, except for those who can hear their name in the chemical lab, and nobody is mentioned. This is not because they are of no use, neither because the crust is exceptionally small in all but because it is not concentrated in one place of production, industrially worthless. Gallium Ga, for example, is rarely known. In fact, it is one hundred and fifty times more than silver and thirty times more than mercury. However, silver and mercury have been known for hundreds or thousands of years and are not used in any amount Fewer, simply because of how much their mines have seen throughout the world. The rare gallium is scattered throughout the country, there is no concentration of ore, if these rare elements are quite easy to mine, on the work