596 KEPORT— 1897. 



My assistant, Mr. Morris Travers, has indefatigably aided me in a search for 

 this unknown gas. There is a proverb about looking for a needle in a haystack ; 

 modern science, with the aid of suitable magnetic appliances, would, if the seward 

 ■were sufficient, make short work of that proverbial needle. But here is a supposed 

 unknown gas, endowed no doubt with negative properties, and the whole world to 

 find it in. Still, the attempt had to be made. 



We first directed our attention to th& 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, questionable traces of nitrogen, and carbonic oxide. 

 Many of the minerals, in addition, gave helium, which proved to be widely dis- 

 tributed, though only in minute proportions. One mineral — malacone — gave appre- 

 ciable 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 tc which our attention had been 

 directed by Professor Lockyer, named eliasite, from which he said that he haid 

 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 exceed- 

 ingly 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 somewhat move 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 Oauterets, 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 Runge 

 and Paschen, the renowned spectroscopists. The spectrum was photographed, 

 special attention being paid to the invisible portions, termed the ' ultra-violet ' and 

 ' infra-red.' The lines thus registered were found to have a harmonic relation to 

 each other. They admitted of division into two sets, each complete in itself. 

 Now, 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 Runge and Paschen concluded that the gas, to which the provisional 

 name of helium had been given, was, in reality, a mixture 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 Runge supposed that he had 

 obtained evidence of the separation of these imagined elements from each other by 

 means of diffusion ; but Mr. Travers and I pointed out that the same alteration of 

 spectrum, which was apparently produced by diffusion, could also be caused by 

 altering the pressure of the gas in the vacuum tube ; and shortly after Professor 

 Runge acknowledged his mistake. 



These considerations, however, made it desirable to subject helium to system- 

 atic diffusion, in the same way as argon had been tried. The experiments were- 

 carried out in the summer of 189G by Dr. Collie and myself. The result was 

 encouraging. It was found possible to separate helium into two portions of 

 different rates of diffusion, and consequently of different density by this means. 

 The limits of separation, however, were not very great. On the one hand, we 

 obtained gas of a density close on 2-0 ; and on the other, a sample of density 2'4 



