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在十九世纪中叶,化学元素之为大家所熟知的大约有五十余种,这些元素大多是用当时进步的分析化学方法来发现的。到了1869年,俄国大化学家门特雷业夫于担任彼得格勒大学的化学教授时,提出了著名的元素的周期律,并根据这个周期律而造成一个周期表,把错综复杂的元素排列成为有系统的表式。根据这一个表,他指出在当时没有发现的若干元素,并预测这些元素中之三种,即到后来被发现的锗、钪、和镓的物理的和化学的性质(这些性质后来都被——证明与门氏的预测相符合)。同时,门氏亦曾在周期表内预测另一种元素的存在和这种元素的性质,
In the middle of the nineteenth century, there were about fifty kinds of chemical elements known to all of us. Most of these elements were discovered by the analytic chemistry that was advanced at that time. By 1869, the great Russian chemist Mentreyev, as professor of chemistry at the University of Petrograd, proposed the periodic law of the famous elements and, according to this periodic law, created a periodic table that arranged the intricate elements into System of the table. Based on this table, he pointed out several elements that were not found at the time and predicted three of these elements, the physical and chemical properties of germanium, scandium, and gallium that were later discovered (these were later - - Proof and door’s prediction is consistent). At the same time, Men’s also predicted the existence of another element and the nature of this element in the periodic table,