66 POPULAR SCIENCE MONTHLY. 



of Van t'Hoff. Electrolysis is no longer to be considered as a 

 separating process, but rather as a sorting of the ions, which receive 

 different electrical charges and concentrate at the two electrical 

 poles. The phenomena of freezing and boiling points in solutions, 

 and of the absorption of heat when solid salts are dissolved, all har-" 

 monize with the conclusions which have been reached. A com- 

 plete theory of solutions is yet to be proposed; but these new doc- 

 trines, which are true so far as they go, represent a long step in 

 the right direction. A final theory will include them, but they are 

 not likely to be set aside. 



As we near the end of the century we find one more discov- 

 ery to note, from a most unexpected quarter — the discovery of 

 new gases in the atmosphere. In 1893 Lord Rayleigh was at work 

 upon new determinations of density, with regard to the more im- 

 portant gases. In the case of nitrogen an anomaly appeared: 

 nitrogen obtained from the atmosphere was found to be very 

 slightly heavier than that prepared from chemical sources, but the 

 difference was so slight that it might almost have been ignored. 

 To Rayleigh, however, such a procedure was inadmissible, and he 

 sought for an explanation of his results. Joining forces with Ram- 

 say, the observed discrepancies were hunted down, and in 1894 the 

 discovery of argon was announced. Ramsay soon found in certain 

 rare minerals another new gas — helium — whose spectral lines had 

 previously been noted in the spectrum of the sun; and still later, 

 working with liquid air, he discovered four more of these strange 

 elements — krypton, xenon, neon, and metargon. By extreme ac- 

 curacy of measurement this chain of discovery was started, and, 

 as some one has aptly said, it represents the triumph of the third 

 decimal. A noble dissatisfaction with merely approximate data 

 was the motive which initiated the work. 



To the chemist these new gases are sorely puzzling. They come 

 from a field which was thought to be exhausted, and cause us to 

 wonder why they were not found before. The reason for the over- 

 sight is plain: the gases are devoid of chemical properties, at least 

 none have yet been certainly observed. They are colorless, taste- 

 less, odorless, inert; so far they have been found to be incapable 

 of union with other elements; apart from some doubtful experi- 

 ments of Berthelot, they form no chemical compounds. Under 

 the periodic law they are difficult to classify; they seem to belong 

 nowhere; they simply exist, unsocial, alone. ( Only by their den- 

 sity, their spectra, and some physical properties can these intract- 

 able new forms of matter be identified. 



In a sketch like this a host of discoveries must remain unnoticed, 

 and others can be barely mentioned. The isolation of fluorine and 



