DISCOVERY 



315 



Helium 



By A. S. Russell, D.Sc. 



Sludenl o/ Christ Church, Oxford 



The gaseous element, helium, which has recently been 

 brought into public notice bj- wTiters endeavouring to 

 explain how the accident to the airship R38 might 

 have been avoided, has had a curious and interesting 

 history. Few of the elements have caused more 

 surprises in the scientific world than this one, and none, 

 by the mere fact of its existence, b\^ its possession of 

 certain properties and total lack of others, has had so 

 important and far-reaching an effect upon present-day 

 knowledge of the constitution of matter. 



In describing this element I find it most convenient 

 to treat it under seven headings, the subject matter of 

 each of which is summarised below. 



I. Helium was discovered in the sun, and much 

 later on the earth. 



II. The discovery of helium and argon led to the 

 isolation of four more inert gaseous elements. 



III. It has been experimentally proved that the 

 atom of helium is " inside " the atoms of certain heavy 

 atoms. 



IV. It is firobable that the atom of helium may be 

 a constituent of many of the chemical elements. 



V. The liquefaction and solidifying of helium have 

 led to the coldest attained temperatures. 



VI. Helium, a thing of purely scientific interest, 

 became a necessity for balloons in war. It will become 

 of increasingly practical importance for balloons and 

 airships according as sources from which it may be 

 isolated are explored. 



I 

 Helium was first heard of in 1868, when it was dis- 

 covered in the luminous atmosphere of gas which 

 surrounds the sun. During a total eclipse this atmo- 

 sphere was examined by a spectroscope and a new 

 yellow spectrum-line, called the D3 line, was observed. 

 It had not been observed on the earth ; nevertheless, 

 the new spectrum-line was so characteristic as to leave 

 no doubt that it came from a new element. For 

 twenty-si.x years nothing was known about this ele- 

 ment except its spectrum-lines and the fact that it 

 existed in the sun and in certain stars ; but towards the 

 end of 1894 Sir William. Ramsay showed conclusively 

 that it existed in a rare mineral on the earth. This 

 discovery was just missed five \-ears earlier by a well- 

 known American mineral-analyst. Prof. Hillebrand. 

 In working up a specimen of the mineral pitch-blende 

 (from which we get radium), Hillebrand obtained a gas 

 which he supposed to be nitrogen, for so it appeared to 

 be when tested by the ordinary methods ; but one or 



two curious happenings that occurred during his experi- 

 ments led him to suggest to his assistant jocularlj- that 

 possibly they might be also dealing with a new element. 

 The matter, however, was not pursued farther. 



In 1894 the gaseous element argon had been dis- 

 covered in the atmosphere by Lord Rayleigh and Sir 

 William Ramsay, and the latter in searching for new 

 sources of this gas had his attention called to the 

 " nitrogen " which Hillebrand had prepared from 

 pitchblende. It was suggested that this might contain 

 argon. Ramsay repeated Hillebrand's work, proved 

 as Hillebrand had done that it contained some nitrogen, 

 but found by the spectroscope that most of the gas was 

 not nitrogen, and not argon, but the long-awaited 

 helium. 



It is a curious thing that often when an element has 

 been discovered, no matter how difficult it had been to 

 detect in the first instance, it is immediately found 

 nearly everywhere without much difficulty. The 

 explanation is simply that when keen and active minds 

 have been told to look for something new, and given 

 the necessary information to recognise it, it is largely 

 a matter of their looking hard enough to find it. 



Helium was soon found to be a constituent, but 

 always in small quantity, of the atmosphere, of a 

 certain class of rocks, of many mineral springs, of the 

 sea, and of the natural gas that comes out of the ground 

 chiefly in America. It is also found in the hotter stars 

 and in meteorites ; so that it is widely distributed. 



II 



A development of great theoretical interest in 

 chemistry arose from the discovery of these two gases, 

 argon and helium. These gases were found to possess 

 no chemical properties, i.e. they refused to combine 

 even under most favourable conditions with other 

 elements. This was strange and novel behaviour, and 

 it set many minds thinking. Now this refusal might 

 arise for one of two reasons : (i) because these elements 

 were completely inert and lacked the power of uniting 

 with other elements ; or (2) because they were so very 

 active that each gas was wholly occupied in combining 

 among itself, and so had neither opportunity nor 

 " desire " to combine with other elements. The first 

 of these views was adopted, and it is important 

 because it had an interesting consequence. For if 

 argon and helium are inert elements they arc unique, 

 i.e. they form a group by themselves. But in the 

 Periodic System of classification such a group, if like 

 other groups, has six members. It followed therefore 

 that, if a new group of elements existed, and if two of 

 them had ahead}' been isolated, four remained to be 

 found. The truth of this view was borne out by 

 experimental work. Tlu'ee of the four — neon, kryp- 



