THE RECENTLY DISCOVERED GASES AND THEIR RELA- 

 TION TO THE PERIODIC LAW. 1 



By William Ramsay. 



Gentlemen : It is well known to you all how the remarkable obser- 

 vation of Lord Rayleigh that nitrogen from the atmosphere possesses a 

 greater density than that prepared from ammonia or nitrates led to the 

 discovery of argon, a new constituent of the air. I need not say that 

 had it not been for this observation the investigations of which I shall 

 speak this evening would never have been carried out, at least not by 

 me. You also, doubtless, will remember that the search for some com- 

 pound of argon was rewarded, not by the attainment of the quest, but 

 by the discovery,in cleveiteaud other rare uranium minerals, of helium, 

 an element whose existence in the chromosphere of the sun had already 

 been suspected. And, further, I hardly need to recall to your minds 

 that the density of helium is in round numbers 2, and that of argon 20, 

 and that the ratio of specific heats of both these gases, unlike that of 

 most others, is 1.66. 



From these figures it follows that the atomic weight of helium is 4 

 and that of argon 40. It is true that in many quarters this conclusion- 

 is not admitted, but I have always thought it better to recognize the 

 validity of the theory of gases and accept the logical deductions than 

 to deny the truth of the present theories. The only reason for not 

 admitting the correctness of these atomic weights is that that of argon 

 is greater than that of potassium, but this is no severer attack upon the 

 validity of the periodic law than the accepted position of iodin after, 

 instead of before, tellurium. As a matter of fact, all the more recent 

 determinations of the atomic weight of tellurium give the figure 127.6, 

 while that of iodin remains unchanged at 127. 



Since these new elements form no compounds, it is not possible to 

 decide the question by purely chemical methods. Were it only possible 

 for us to propare a single volatile compound of helium or of argon our 

 problem would be solved. In spite of many attempts, I have not been 



'Address delivered by Prof. William Ramsay before the Deutschen chemischen 

 Gesellschaft, December 19, 1898. Translated by J. L. H. Printed in Science, Vol. 

 IX, No. 217, February 24, 1899. 



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