86 AN INTRODUCTION TO SCIENCE 



been verified in certain cases. New elements have been 

 found which have the atomic weight and the properties 

 foretold of missing members of the series. But what is to 

 be done in the event of several claimants demanding to be 

 admitted to the same place? This is a problem which 

 chemists have to face. A very rare metal, yttrium, has 

 been resolved by successive ' ' fractionations' ' into seven 

 metals (of which one, scandium, was wanted to fill a vacant 

 place in Mendele*efs table) which differ but very slightly 

 one from another. By fractionation, to take a simple 

 example, is meant such a process as forming a nitrate of 

 the metal, and then heating this salt to a certain tempera- 

 ture which is not sufficiently high to allow of the conversion 

 of the whole of the nitrate into oxide. Some is decomposed, 

 while the rest remains as nitrate, which, being a soluble 

 salt, can be dissolved in water. This dissolved nitrate is 

 crystallized and heated somewhat more strongly, and the 

 process repeated over and over again. And of the seven 

 new metals, the real yttrium, as judged by the spectroscope, 

 shows indications of being a mixture of five metals which 

 cannot be distinguished by chemical methods. It might be 

 inferred that this apparent multiplicity of metals could be 

 explained as due to the failure on the part of the chemist to 

 remove impurities ; but Sir William Crookes is not content 

 with this explanation. He believes that the chemical atom 

 of the element yttrium is not fixed ; that the number of pro- 

 tyle atoms which form its cluster varies, and that the five 

 "meta-elements" are, as it were, either trying to fix into 

 an element, or that, like a very rare species of animal (the 

 mud-fish, for example), which is dying out because it is not 

 fitted for its environment, it is exhibiting great variability 

 in its expiring efforts to hold its own against its better 

 equipped competitors. These far-reaching speculations of 

 Sir William Crookes bring the analogies of living phe- 

 nomena into the inanimate world. He speaks of the 

 origin, predominance and decay of the elements in the 



