212 



KNOWLEDGE. 



[September 2, 1895. 



tbeu placed over the closed end of the bent tube, and the 

 mercury trough is lowered. The sealed end is then broken 

 by pressing it against the interior of the gas tube, when 

 gas enters up to the stopcock. On carefully opening the 

 stopcock a trace of gas is passed into the vacuum tube ; 

 this gas is then pumped out and collected below the 

 delivery tube of the TOppler's pump. One such washing 

 with gas is usually sufficient. The stopcock is again 

 opened, and a sufficient amount of gas introduced into the 

 vacuum tube to show the spectrum. The vacuum tube is 

 then removed by sealing, and the gas still remaining iu 

 the bent tube may be transferred to the pump and collected. 

 It is seen that this method permits of the filling of a 

 vacuum tube absolutely without loss, and — it may be 

 added — with great expedition." 



It is further interesting to notice at this point that the 

 discoverer has also found small quantities of argon and 

 helium in the gas obtained by heating in vacuo a piece of 

 a meteorite found in Virginia, the argon being present in 

 relatively much larger amount than the helium. This is 

 the first time that argon has been found in any extra- 

 terrestrial substance ; it has not yet been recognized in the 

 sun. This particular investigation showed very clearly 

 how little reliance is to be placed on the evidence of the 

 spectroscope as to the presence of anyone gas in a mixture 

 where other gases predominate. Thus, the characteristic 

 spectrum of argon is almost completely masked by the 

 presence of a few parts per ceut. of nitrogen or of hydrogen, 

 and that of helium is similarly affected, although to a less 

 degree. The author suggests that in future much attention 

 should be paid here to the relative conductivities of gases. 



The spectrum of helium is chai-acterized by five very 

 brilliant lines, which occur in the red, the yellow, the 

 blue-green, the blue, and the violet. The double yellow 

 line, D,, which is the most characteristic, has been 

 already referred to in detail. No one who has seen this 

 spectrum is ever likely to forget its extraordinary brilliancy. 

 An exhaustive study of it is being made by Mr. C'rookos. 

 With regard to the spectrum. Prof. Eamsay and his 

 coadjutors point out *' that at least two of the Imes i;i 

 the spectrum of helium, seen with a wide dispersion prism, 

 are coincident with two of the argon lines. These occur 

 in the red, and comprise one of each of the two pairs 

 of characteristic argon lines. . . . We may say that if 

 not absolutely identical, the lines are so near that it is not 

 possible with the means at our disposal to recognize any 

 difference in position. But the relative brilliancy is by no 

 means the same. One of the argon lines, rather faint, is 

 coincident with the prominent red of the helium spectrum, 

 and one of the strong red argon lines is coincident with a 

 faint red line in the helium spectrum." 



Next to the spectrum, the property of helium which it 

 was of most interest and importance to determine wag the 

 density. Unfortunately, most of the minerals employed as 

 a source gave such a minute yield, amounting usually to 

 only a few cubic centimetres, that a determination of 

 density was in their case out of the question. Very 

 careful estimations were, however, made with the gas from 

 clcveite and from br()ggerite. Even here the quantity of gas 

 available was but small, the capacity of the bulb used for 

 most of the weighings being only about thirty-three cubic 

 centimetres. But care in manipulation and the use of a 

 very sensitive balance by Oerthng made it possible, even 

 under these conditions, to arrive at results nearly 

 approaching to accuracy. The original paper must be 

 consulted for all the precautions taken to purify the 

 helium, whose density was in question, from every trace 

 of hydrogen sulphide, carbon dioxide, sulphur dio.xide, 

 hydrogen and nitrogen. Let it suffice to give here the 



results of three determinition^, of which " ths mean may 

 be taken as approximately correct to within 0-05 " : — 



Density. 

 G-as from bi'oggcrite by lieatiug ... ... ... 2'152 



Ctixs from brciggerifce with liydrogeQ-pota.ssium 



sulphate ... ... ... ... ... ,.. 2 1S7 



Gas from cleveite ... ... ... ... ... 2 205 



Mean 



2181 



(the density of oxygen being taken as IG). All these three 

 samples were then mixed together, and the whole treated 

 again for the absorption of any traces of hydrogen and 

 nitrogen remaining, after which the density was found to 

 be 2-218, i.e., it remained substantially unaltered. A 

 determination in another sample gave the figure '2'13i}. 

 Helium is thus, next to hydrogen, the lightest of all known 

 elements. 



Again, as in the case of argon, it has been found to be 

 a mowitomic gas, the ratio of the specific heat at constant 

 volume to that at constant pressure being l-l)32 (another 

 determination gave 1-G52) — a sufficiently close approxima- 

 tion to the theoretical number 1-6G. 



Helium is very sparingly soluble in water, 100 volumes 

 of the latter at 18'2'' C i.e., at about the ordinary tempera- 

 ture, dissolving only 0-73 volumes of helium. This is the 

 lowest solubility yet recorded for any gas, and it points to 

 the boiling temperature of liquid helium being very low. 

 Prof. Olszewski, of Grac3W, has undertaken to make 

 experiments on the temperature of liquefaction of helium, 

 " and it will be interesting to learn whether its boiling 

 point does not lie below, or at least as low as that of 

 hydrogen. For their molecular weights are not very 

 different, and helium is a monatomic gas, a condition 

 which appears to lower the boiling point." 



So far, but few attempts have been made to induce 

 helium to enter into chemical combination with other 

 elements, but those experiments which have been tried 

 have all proved ineffectual. Like argon, it is not attacked 

 by oxygen in presence of caustic soda under the action of 

 the electric discharge, this forming in fact a good method 

 of removing all impurities other than argon. Further, 

 like argon, it is not affected by red-hot magnesium, and 

 it is not oxidized by copper oxide at a red heat. No 

 method has yet been found by which helium and argon 

 can be separated from one another. 



Towards the close of their paper, the authors draw some 

 general conclusions, so far as their present knowledge of 

 the subject warrants this. " It cannot be doubted that a 

 close analogy exists between argon and helium. Both 

 resist sparkmg with oxygen in presence of caustic soda; 

 both are unattacked by red-hot magnesium; and, if we 

 draw the usual inference from the ratio between their 

 specific heats at constant volume and at constant pressure " 

 (the significance of which, however, is by no means uni- 

 versally conceded, not, for instance, by ^^leudeli'eff), " both 

 are monatomic gases. These properties undoubiedly place 

 them in the same chemical class, and differentiate them 

 from all known elements." The properties of helium 

 itself not having yet been sufficiently investigated, the 

 authors proceed to discuss those of argon, with the view 

 of seeing how far these corroborate the deduction that the 

 latter is a monatomic element, and the conclusion at wliich 

 they arrive is that, while the considerations referred to 

 cannot be accepted as evidence, they are corroborative of 

 the conclusions as to the monatomiclty of argon. " If 

 they apply to argon, thi-y apply with equal force to helium ; 

 and if they are accepted, it follows that the atomic weight 

 of helium is 4'26," tliat of argon being 30-8. 



With regard to the question, why is not helium, like 

 argon, present in the air ? the authors are inclined to 



