SOME PHYSICAL PROBLEMS 



It is this lack of combining power, of course, that 

 explains the non-discovery of these elements during all 

 these years, for the usual way of testing an element is 

 to bring it in contact with other substances under con- 

 ditions that permit its atoms to combine with other 

 atoms to the formation of new substances. But in 

 the case of new elements such experiments as this have 

 not proved possible under any conditions as yet at- 

 tained, and reliance must be had upon other physical 

 tests such as variation of the bulk of the gas under 

 pressure, and under varying temperatures, and a 

 study of the critical temperatures and pressures under 

 which each gas becomes a liquid. The chief reliance, 

 however, is the spectroscope the instrument which 

 revealed the presence of helium in the sun and the 

 stars more than a quarter of a century before Professor 

 Ramsay ferreted it out as a terrestrial element. Each 

 whiff of colorless gas in its test-tube interferes with 

 the light passing through it in such a way that when 

 viewed through a prism it gives a spectrum of alto- 

 gether unique lines, which stamp it as krypton, neon, 

 or zenon as definitely as certain familiar and more 

 tangible properties stamp the liquid which imprisons 

 it as mercury. 



Queries Suggested by the New Gases 



Suppose that a few years ago you had asked some 

 chemist, "What are the constituents of the atmos- 

 phere?" He would have responded, with entire confi- 

 dence, " Oxygen and nitrogen chiefly, with a certain 

 amount of water-vapor and of carbonic-acid gas and a 

 trace of ammonia. ' ' If questioned as to the chief prop- 



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