September 2, 1895.] 



KNOWLEDGE 



211 



the line had never been detected in the spectrum of any 

 constituent of our planet, and on this account the name 

 hilixtm was given to the element producing it, as being 

 entirely a solar element, although, as now appears, it is 

 pretty widely distributed in small quantities in certain 

 classes of rara minerals. This is the first instance on 

 record of an element known to exist in the sun being 

 subsequently discovered on the earth, though it will prob- 

 ably not be the last, for there are lines in the solar 

 spectrum which we are unable to i-eproduce from any 

 known ten-estrial element. One of these hypothetical ele- 

 ments, giving a line in the green portion of the spectrum, 

 forms a large part of the sun's corona, and is believed to 

 be a gas even Hghter than hydrogen. In a short note 

 upon helium, communicated to the Eoyal Society last May, 

 Mr. Lockyer says" ; — " We appear to be in presence of the 

 rem ciiisd, not of two or three, but of many of the lines 

 which, so far, have been classed as ' unknown ' by students 

 both of solar and stellar chemistry ; and if this be con- 

 firmed, we are evidently in the presence of a new order of 

 gases of the highest importance to celestial chemistry, 

 though perhaps they may be of small practical value to 

 chemists, because their compounds and associated elements 

 are for the most part hidden deep in the earth's interior." 

 The way in which the discovery of terrestrial helium 

 came about is interesting, and it may be recapitulated 

 shortly here. Argon, as everyone now knows, is an 

 extremely inert substance, and as a matter of fact there are 

 only two instances as yet of chemical combination on its 

 part, M. Berthelot having recently succeeded in forming 

 a hydrocarbon compound of argon by subjecting a mixture 

 of the latter with the vapour of benzene to the 

 influence of the silent electric discharge, and also in 

 inducing the gas to combine with carbon disulphide and 

 mercury under similar conditions. M. 15erthelot's experi- 

 ments were of necessity made with very small quantities 

 of pure argon — much too small to allow of anything more 

 than a qualitative observation ; they have, however, 

 established the important facts tbat argon can be made 

 to enter into chemical combination with other elements, 

 and can be regenerated from the compounds formed with 

 its initial properties intact. I In continuance of the search 

 after possible compounds of argon last spring, Prof. 

 Eamsay's attention was called by Mr. Miers, of the British 

 Museum, to the rare Norwegian mineral cleveite, which 

 consists mainly of uranate of lead associated with rare 

 earths, and which was said to give off two per cent, 

 of nitrogen when warmed with dilute sulphuric acid. 

 Thinking that this supposed nitrogen might very likely 

 be argon, he obtained some of the mineral and liberated 

 the gas from it. The spectroscopic examination of the 

 latter showed an extremely brilliant yellow line close to, 

 but not coincident with, the two yellow sodium lines 

 Dj and D,,. Not having at the time a spectrosi-ope 

 with which accurate measurements could be made, Prof. 

 Ramsay sent a Pliicker's tube of the gas to Mr. Crookes, 

 wbo found the wave-length of this new yellow line (D.j) 

 to be .587-45, the wave-lengths of the sodium lines being 

 Di = 589-.51, and Do^SSS-Ol. The spectrum of the gas 

 was, therefore, that of the solar element helium. 

 Profs. Runge and Paschen, of Hanover, have since 

 shown I that the yellow helium line is itself a double one, 

 its less refrangible component being much the weaker of 



* Jfature of May 16tli, 895. 



t Prof. Eamsay also appears to hare succeedci quite lately in 

 intlucing argon to combine ehemieallv, by making an arc with two 

 thin carbon rods in ' he gas (gee Chemical JVew.'.v of August 2nd, 1895). 



I Nature of June 6tb, 189.5. 



the two, while the stronger one is brilliant. They give 

 the following wave-lengths for these : — 



Strong component = 5875'883 

 Weak „ = 6876-206, 



Rowland's determination of Dj? being 5875-982. Lastly, 

 a week or two ago Dr. Huggins^ observed the double line 

 in the solar spectrum, stating at the same time that he 

 understood it had been already observed in the United 

 States by Prof. Hale. This would appear to make it 

 absolutely certain that solar and terrestrial helium are 

 identical. 



A large number of rare minerals have been examined 

 by Prof. Ramsay and his colleagues for helium, these 

 being described m detail in the memoir already referred 

 to at the beginning of this paper. The conclusion at 

 which they arrive is that helium is retained by minerals 

 consisting of salts of uranium, yttrium and thorium, but 

 whether its presence is conditioned by the uranium, the 

 yttrium, or the thorium has not yet been established. 

 None of the oxides of uranium, when heated in an 

 atmosphere of helium and allowed to cool, retain the gas ; 

 but similar experiments have not yet been made with 

 oxides of thorium and yttrium, or with a mixture of these 

 with uranium oxide. The miaerals which gave much the 

 best yield, and which, indeed, up to the present have been 

 the only available sources of helium, are cleveite, 

 broggerite, and the uraninite mveBtigated by Hillebrand. 

 Monazite, which also gives a good yield of helium, is a 

 phosphate of cerium, lanthanum and thorium, uranium 

 being absent. Being comparatively cheap, it would form 

 a more economical source of helium than either cleveite 

 or broggerite. 



On account of their rarity and cost, only small quantities 

 of the above-mentioned minerals could be used. To extract 

 the helium, from two to five grammes of the coarsely 

 powdered substance were heated in a small bulb of combus- 

 tion tubing, previously exhausted by a Toppler's pump. As 

 water vapour and carbon dioxide were often evolved at the 

 same time, a soda-lime tube and a tube filled with 

 phosphoric anhydride were frequently mterposed between 

 the bulb and the pump. After most of the gas had been 

 given off, the temperature was raised until the glass bulb 

 showed signs of collapsing. A further quantity of gas was 

 obtained by mixing the residue from the heated broggerite 

 or other mineral with hydrogen-potassium sulphate, and 

 re-heating. To get rid of the free hydrogen evolved in 

 most cases along with the helium (there was no chemically 

 combined hydrogen, i.,\, no hydride of helium), the gas 

 was sparked with oxygen, no alkali being present. The 

 excess of oxygen was then absorbed by alkaline pyrogallate, 

 and the gas transferred to a vacuum tube for spectroscopic 

 examination. This process of transference has proved 

 very convenient, and has prevented any waste whatever of 

 the gas. 



The apparatus "consists of a tube provided with a perfectly 

 fitting stopcock ; this tube is connected with a Toppler's 

 pump. The vacuum tube or tubes to be fitted are sealed to a 

 lateral branch above the stopcock. The lower part is bent 

 into a sharp (J and the end drawn out to a point and sealed. 

 The stopcock is then turned full on, and the whole tube is 

 completely exhausted, until the vacuum tube shows brilliant 

 phosphorescence, or, indeed, as often happens, ceases to 

 conduct the discharge ; the stopcock is then closed. A 

 mercury trough is placed below the bend of the tube, and 

 the latter is sunk until the closed end disappears below the 

 mercury. A small tube, which need not contain more than 

 1 c.c. of the gas to be i ntroduced into the vacuum tube, is 



§ L'hUustiphii-al Matjazine, July, 1893. 

 If CliMiincil A>!M of July l9th, 1895. 



