]24 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1918. 



donbtedly the uranium comprised in these ores is continually de- 

 generating and forming the helium as it does so. 



Thus the dreams of the old alchemists bad almost come true. For 

 centuries they had endeavored to transmute the chemical elements, 

 thus to produce the precious metals, such as gold and silver. In this 

 they had always failed. But nature, that more powerful alchemist, 

 had now revealed its secret that the chemical elements are not im- 

 mutable but may be transmuted one into the other. Unfortunately 

 for commercial applications, no processes have ever been discovered 

 by means of which the change of radium and its associates into 

 helium and other metals can either be hurried or retarded. Nature 

 retains full control of the apparatus. Hitherto man has been unable 

 to usurp the government of it. 



Among the properties of helium has been noted its chemical inert- 

 ness. In other words, no combinations of helium with other chemical 

 elements can be made. This means that helium can not be burned. 

 We well know that hydrogen burns with tremendous energy in 

 oxygen or in air, but nothing of the kind takes place with helium. 

 By no process whatever can helium be burned. Another most inter- 

 esting physical property of helium gas is the extreme difficulty of 

 liquefying it. During the nineteenth century almost all of the so- 

 called permanent gases were liquefied. Hydrogen resisted the attack 

 the longest, but even hydrogen was at last liquefied and even solidi- 

 fied. Helium, however, resisted that degree of cold and pressure to 

 which hydrogen had yielded itself as a liquid, and it was only in 

 1908 that Kamerlingh Onnes, the distinguished Dutch physicist, suc- 

 ceeded actually in liquefying helium. The temperature at which he 

 arrived in this process was but 4° C. above absolute zero, that unique 

 beginning of all motion of the molecules and of properties of many 

 kinds. Measured on the absolute centigrade scale, the temperature of 

 the sun is about 6,000° to 7,000°; that of the earth about 285°; 

 freezing water, 273° ; liquid oxygen, 90° ; liquid hydrogen, 20° ; and 

 liquid helium, 4°. 



Onnes was able to reach almost to 2° absolute by employing helium 

 in a special way, and employed this new extreme of cold to test the 

 electrical and other properties of metals. Very extraordinary results 

 were found. Tin, lead, and mercury (which is a solid, of course, at 

 these temperatures) suddenly lost their properties of electrical re- 

 sistance. Thus a thread of mercury that measured several hundred 

 ohms at room temperatures, at 2? 45 Abs. C. had so little electrical 

 resistance that it could not be detected, and certainly less than 

 t o.ooo i ooo.oo ' o °f what it had at the temperature of freezing water. 

 Probably this curious sudden change of electrical behavior occurs 

 with other metals, too. 



