THE CHEMISTRY OF TO-DAY. 593 



prophesied the discovery of elements then nnknown which would 

 fill these gaps. Not only this, but he boldly ventured to describe 

 some of these unknown elements in detail. At first no one was in- 

 clined to give serious consideration to the predictions ; certainly 

 no one dreamed that they would soon prove to be among the most 

 brilliant predictions ever recorded in the annals of science. With- 

 in a few years all three of the elements predicted by Mendelejeff 

 were discovered— the last one about two years ago. The first one 

 was discovered in France, and was hence called gallium ; the sec- 

 ond, discovered in Norway, is known as scandium ; and the third, 

 recently discovered in Germany, is the baby element germanium. 

 The descriptions given by Mendelejeff, eighteen years ago, are 

 found to agree marvelously well with the facts. These discoveries 

 have directed the attention of all chemists to the periodic law, 

 and have lent a new interest to the discovery of new elements. 

 There are undoubtedly others still undiscovered. Let us hope 

 that the next one may come to light in the New World, and that 

 we may thus have our own particular element, as France and Nor- 

 way and Germany have theirs. 



It is obvious from what I have already said that, to tell what 

 things are made of, is not so simple a matter as it might at first 

 appear. The best answer we can give, in any case, is lamentably 

 incomplete. But there is another side to the subject, one of fasci- 

 nating interest. Let me eiideavor to illustrate this by means of 

 another example. It has long been known that there are two sub- 

 stances, called respectively glucose and levulose, which are made 

 of the same elements, viz., carbon, hydrogen, and oxygen, in ex- 

 actly the same proportion by weight. Notwithstanding the fact 

 that these two substances have exactly the same composition, they 

 have markedly different properties. Chemistry abounds in simi- 

 lar examples. To account for these facts, chemists suppose that 

 the parts of which the two substances are made up are arranged 

 differently. An immense amount of work has been done during 

 the past half -century with the object of reaching conclusions con- 

 cerning what is called the constitution of chemical compounds, 

 and the results reached in this field have been brilliant in the 

 highest degree. By methods of the most refined character the 

 chemist of to-day is enabled to enter into the innermost recesses 

 of compounds, and trace out the connections which exist between 

 the constituent parts. Many of the most complex compounds 

 found in nature have thus been studied, their constitution deter- 

 mined, and methods have in many cases been devised by which 

 the substances found in nature can be built up in the. chemical 

 laboratory without the intervention of the life process. Among 

 recent achievements in this direction I may mention indigo. This 

 is remarkably complex, and for a long time it had baffled all 

 VOL. xxxiF. — 38 



