Annual Report of the Council. xlix 



elements then unknown. Within twenty years the discovery of 

 gallium, germanium, and scandium gave the most striking con- 

 firmation to his prophecies — a confirmation which assisted 

 materially in winning for his periodic system that assured place 

 in chemical theory it now holds. Later work has done little to 

 alter it ; much to confirm its essential principle. 



At times Mendeleeffs genius in evolving theories was only 

 equalled by his ingenuity in defending them against experimental 

 attack. His persistent devotion to the Mendeleeff-Gerhardt 

 Law — that gases combine only in equal volumes — is a striking 

 example of this. 



His boldness and originality are still further shown in his 

 ■" Principles of Chemistry " — a chemical text-book in no ordinary 

 sense of the words, but a detailed exposition of the facts on 

 which the periodic system is based. It abounds, too, in ideas 

 stimulative of research. 



His numerous papers on the properties of solutions give 

 abundant evidence of Mendeleeffs experimental ability ; and it 

 is interesting to note that it was his study of the densities of 

 mixtures of alcohol and water — work done for the Russian 

 Government for excise purposes — which led him to regard solu- 

 tions as " strictly definite, atomic, chemical combinations at 

 temperatures higher than their dissociation temperatures." 



Even this short account of Mendeleeffs life would be incom- 

 plete without some reference to his influence on the Russian 

 petroleum industry. He made many journeys to the Caucasus 

 and investigated at length the distribution and capacity of the 

 Baku oil wells. His theory of the origin of petroleum is 

 characteristic of the man. Petroleum, he declares, is continually 

 being formed by the interaction of steam and metallic carbides 

 below the surface of the earth, and the supply would therefore 

 seem to be endless. Whatever may be thought of so bold a 

 theory, there can be no doubt that the Baku petroleum industry 

 owes its present position to Mendeleeff. 



As a theorist he will be remembered, not only for his contri- 



