AN UNDISCOVERED GAS. 251 



We first directed our attention to the sources of helium — minerals. 

 Almost every mineral which we could obtain was heated in a vacuum, 

 and the gas which was evolved examined. The results are interesting. 

 Most minerals give off gas when heated, and the gas contains, as a rule, 

 a considerable amount of hydrogen, mixed with carbonic acid, question- 

 able traces of nitrogen, and carbonic oxide. Many of the minerals, in 

 addition, gave helium, which jjroved to be widely distributed, though 

 only in minute proportion. One mineral — malacone — gave appreciable 

 quantities of argon, and it is noteworthy that argon was not found 

 except in it (and, curiously, in much larger amount than helium) and 

 in a specimen of meteoric iron. Other specimens of meteoric iron were 

 examined, but were found to contain mainly hydrogen, with no trace of 

 either argon or helium. It is probable that the sources of meteorites 

 might be traced in this manner, and that each could be relegated to its 

 particular swarm. 



Among the minerals examined was one to which our attention had 

 been directed by Professor Lockyer, named eliasite, from which he said 

 that he had extracted a gas in which he had observed spectrum lines 

 foreign to helium. He was kind enough to furnish us with a specimen 

 of this mineral, which is exceedingly rare, but the sample which we 

 tested contained nothing but undoubted helium. 



During a trip to Iceland, in 1895, 1 collected some gas from the boiling 

 springs there; it consisted, for the most part, of air, but contained some- 

 what more argon than is usually dissolved when air is shaken with 

 water. In the spring of 1896 Mr. Travers and I made a trip to the 

 Pyrenees to collect gas from the mineral springs of Cauterets, to which 

 our attention had been directed by Dr. Bouchard, who pointed out that 

 these gases are rich in helium. We examined a number of samples from 

 the various springs, and confirmed Dr. Bouchard's results, but there 

 was no sign of any unknown lines in the spectrum of these gases. Our 

 quest was in vain. 



We must now turn to another aspect of the subject. Shortly after 

 the discovery of helium its spectrum was very carefully examined by 

 Professors Iiung§ and Paschen, the renowned spectroscopists. The 

 spectrum was photographed, special attention being paid to the invisible 

 portions, termed the "ultraviolet" and "infrared." The lines thus 

 registered were found to have an harmonic relation to each other. They 

 admitted of division into two sets, each complete in itself. ISTow, a 

 similar process had been applied to the spectrum of lithium and to that 

 of sodium, and the spectra of these elements gave only one series each. 

 Hence, Professors Eunge and Paschen concluded that the gas, to which 

 the provisional name of helium had been given, was, in reality, a mix- 

 ture of two gases, closely resembling each other in properties. As we 

 know no other elements with atomic weights between those of hydrogen 

 and lithium, there is no chemical evidence either for or against this 

 supposition. Professor Eunge supposed that he had obtained evidence 



