88 Helium, a Gaseous Constituent of certain Minerals. [May 2, 



This table may be taken as giving the most striking lines of helium. 

 Those which at once catch the eye are first the yellow line D 3 , wh ich 

 enormously surpasses the rest in brilliancy. Next in intensity, but 

 still brilliant, is the violet line ; next the peacock-green, and fin ally 

 the red. All other lines are comparatively faint. 



That the argon spectrum is reproduced with variations in the 

 helium-tube might lead to the conclusion that argon is present in the 

 helium. But that argon was derived from atmospheric sources or 

 from the water is excluded by the method of extraction. Even sup- 

 posing that a few cubic centimetres of air had entered by leakage, 

 the amount of argon contained therein, compared with the large 

 volume of the helium, would make it practically impossible that the 

 spectrum of argon should be visible. But there is no reason to suspect 

 such a leakage. On the other hand, the helium spectrum reproduces 

 one of the characteristic red lines of argon more intensely than it is 

 seen in the argon-tube ; and the other is absent. The faint orange-red 

 line,* a faint blue-green, and three violet lines are also present in both. 

 Can it be that both these gases are mixtures ? That there is no helium, 

 or at least no gas giving the line D 3 in atmospheric air is certain, 

 for its brilliancy would lead at once to its detection in the spectrum 

 of atmospheric argon if it were present. 



8. General Remarks. 



So far as these experiments go, they show that a gas can be 

 extracted from cleveite, and probably from some allied minerals, 

 lighter than any known gas except hydrogen. "Whether or not this 

 gas is a mixture or a single substance remains undecided. The fact 

 of its spectrum possessing some of the lines of argon and not others 

 may point to the conclusion that argon is a mixture, but until some 

 methods of fractionation have been tried it is premature to speculate. 

 Only one remark may be permitted of a speculative nature : the 

 general similarity of helium (applying this name to the gas from 

 cleveite) to argon, in not being affected either by red-hot magnesium 

 or by sparking with oxygen in presence of potash, makes the infer- 

 ence probable that they belong to the same natural group. If the 

 atomic weight of argon be 20 (a supposition which may be supported 

 by some lines of argument), then, on subtracting 16, which is the 

 average difference between the atomic weights of members of the 

 first line, beginning with lithium and continued to fluorine, and the 

 second line, beginning with sodium and ending with chlorine, the 

 number 4 is obtained ; and this closely approximates to the found 

 density of helium, if that number is not too high. On the other hand, 



* Subsequent experiments have shown that this line is strong in helium near the 

 negative electrode. 



