CHAP. x. THE GREAT PROBLEMS OF CHEMISTRY. 91 



inent due to its atomic weight did not accord with that 

 dependent on its chemical properties. But the general 

 symmetry of the whole arrangement was such that Men- 

 deleef predicted the future discovery of elements to fill 

 the gaps, and named the chemical and physical proper- 

 ties of these unknown elements. In a few years three 

 new elements were discovered gallium, scandium, and 

 germanium and they precisely filled up three of the 

 gaps in the system. Further research as to the atomic 

 weights of the elements that did not fit into the scheme 

 showed that errors had been made, that of uranium being 

 much too low, while in the cases of gold, tellurium, and 

 titanium it was too great. The remarkable success of 

 these predictions a success always considered the best 

 proof of the truth of a theory renders it almost certain 

 that the true relations of the elements have now been 

 approximately ascertained, while it strengthens the be- 

 lief of those who think that what we term elements are 

 not really so, but that their differences depend on special 

 modes of aggregation of a few simple atoms, whose co- 

 hesion is so strong that we are not yet, and perhaps never 

 shall be, able to overcome it. 



It is therefore by no means impossible, perhaps not 

 even improbable, that methods will be discovered of 

 either breaking up some of the elements and producing 

 new elements which are common to two or more of them, 

 or of solving the problem which occupied the alchemists 

 of the Middle Ages the transmutation of some of the 

 inferior metals into gold. Within the last few months 

 a well-known American chemist declares that he has 

 solved the problem of producing gold out of silver at a 

 comparatively small cost, and that when he has made a 



