TIIE CHEMICAL ELEMENTS. The ultimate de composition of all known forms of matter has produced over seventy substances which could not be further decomposed, and which are there fore regarded as forming the qualitative basis of all things. None of the substances which we term elements has been broken up into different constituents or changed without gain of weight into some other substance, in :guy of the innu merable processes ever employed by man. More o•er, speetrose9pic study of the sun and the stars shows that the elements of the earth exist tin decomposed also in the heavenly bodies, in spite of the high temperatures prevailing on many of them. Of course it seems strange, and certainly 1104: not appeal to our imagination, that the universe should be made up of several kinds of matter essentially different from one another. We should like to think of the elements as repre senting outwardly different forms of some pri mary matter pervading all space and making up all things. As a matter of speculation, views of this nature are even now held by many emi nent chemists, although no actual step has yet been taken in the direction of making, them part of science. Vet the view that the chem i•al elements are related to one another in some mysterious way is supported not. only by specula
tion, but also by the fact, long known. that cer tain elements are quite similar in their proper ties. Chemists have well known for many de cades how very closely chlorine, bromine. and iodine resemble one another. Sodium and potas sium, too, are so much alike that for mot pur poses it makes no difference whether we use the hydroxide of the one (caustie soda) or the hydroxide of the other (caustic potash). A large number of facts of this nature have been systematized by Mendel(-IT and Lothar :Meye•. who have shown 11869) that not only the ele ments just mentioned. but the rest of the ele ments, too, can be arranged in groups. the members of which are quite similar in their properties. This remarkable relation, extending as it does to all the well-known dements, can hardly be considered accidental: it must have a cause, :ind that cause must lie in sonic hidden I chit ionship uniting the (dements themselves, and at the same time rendering them quite dis tinct from all other forms of matter—i.e. from substances that (.an be decomposed by the ordi 11.11'y physical and chemical agencies. See PERI owe LAW.