134 BIOGRAPHIES OF SCIENTIFIC MEN 



of unstable dissociating compounds of the solvent with 

 the substance dissolved." This, he said, was one of 

 the several possible hypotheses. He also worked on 

 the laws of the expansion of gases at low tensions, 

 and as far back as the year 1861 he reached the idea 

 of the "absolute boiling-point" (the critical temperature 

 of Andrews) as that temperature at which a liquid cannot 

 exist as a liquid, but forms a gas that cannot pass into 

 the liquid state under any pressure whatever, and at 

 which the cohesion and the latent heat of evaporation 

 are both nil. 



His great book, The Principles of Chemistry, in two 

 large volumes, is a philosophical treatise, and its foot- 

 notes occupy the greater part of the work. 



In 1877 he published another book on the Naphtha 

 Production in America and the Caucasus. This led to 

 his journey to the petroleum fields of America at the 

 expense of the Russian Government ; and up to the time 

 of his death he was the leading expert in all conferences 

 on the mineral oil question in Russia. 



Mendeleeff was an indefatigable worker, even down 

 to the day of his death, and living only for science. 

 When, in 1887, there was a total eclipse of the sun, he 

 ascended in a balloon alone to make observations. Alone 

 he effected dangerous alterations in the balloon valves, 

 and wrote an account of his observations. 



Although elected a member of almost every scientific 



