Junk 13, 1895] 



NA TURE 



16- 



the two spectra upon a very large scale. The upjjer is the spcc- 

 iriiin of the blue light ; the lower is the spectrum of the red light ; 

 anil it will be seen that they differ very greatly. Some lines are 

 common to both ; but a great many lines are seen only in the 

 red, and others are .seen only in the blue. It is astonishing to 

 notice what trilling changes in the ccmditions of the discharge 

 bring about such extensive alterations in the spectrum. 



One question of great importance, upon which the spectrum 

 throws light is, Is the argon derived Ijy the oxygen method 

 really the same as the argon derived by the m,ignesium method ? 

 By Mr. Crookcs' kindness I have had an opportunity of examin- 

 ing the spectra of the two gases side by side, and stich examina- 

 tion as I coidtl make revealed no difference whatever in the two 

 spectra, from which, I suppose, we may conclude either that the 

 gases are absolutely the same, or. if tliey are not the same, that 

 at any rate the ingredients Ijy which they differ cannot be present 

 in nn>re than a small jiroportion in either of them. 



My own observations upon the spectrum have been made 

 princi|)ally at atmospheric pressure. In the ordinary process 

 '^f sparking, the pressure is atmospheric ; and, if we wish to 

 look at the spectrum, we have nothing more to do than to 

 include a jar in the circuit, and put a direct-vision prism to the 

 eye. .\t my request, Prof. Schuster examined some tubes con- 

 taining argon at atmospheric pressure prepared by the oxygen 

 method, and I have here a diagram of a characteristic group. 

 He also placed upon the sketch some of the lines of zinc, 

 which were very convenient as tlirecting one exactly where to 

 look. (See Fig. i.) 



43 



44 45 



46 



I 



47 



48 49 



5000 



I 



^ 



jyon 



-> M^d 



J' 



inc 



7(ydrocic7i 



ur 



Fig. 



Within the last few days, Mr. Crookes ha.s charged a radi- 

 ometer with argon. When held in the light from the electric 

 lamp, the vanes revolve rapidly. Argon is anomalous in many 

 res|>ects, but not, you see, in this. 



Next, as to the density of argon. Prof. Kanisay has made 

 numerous and careful observations upon the density of the 

 gas prepared by the magnesium method, and he finds a density 

 of about I9'9 as compared with hydrogen. Equally satisfactory 

 ob.servalions upon the gas derived l.)y the oxygen method ha\''' 

 not yet l)een made, but there is no reason to sujipose that the 

 ticnsily is different, such numbers as 197 having been obtained. 



One of the most interesting matters in connection with argon, 

 however, is what is known as the ratio of the specific heats. I 

 must not stay to elaborate the i^uestions involved, but it will be 

 known to many who hear nie that the velocity of sound in a gas 

 ilc|H'nds u]Kin the ratio of two specific heats— the specific heat 

 of the gas measured at constant pressure, and the specific he.it 

 measured at constant volume. If we know the density of a gas. 

 and also the velocity of sound in it, we are in a pfjsition to infer 

 this ratio of specific he.ats ; and by means of this method. Prof. 

 Ramsay h.-is determined the ratio in the case of argon, arriving 

 at the very remarkable result that the ratio of specific heats is 

 represented by the number I "65, approaching very closely to the 

 theoretical limit, i '67. The number 1 •67 would indicate that 

 the gas has no energ)- except energj' of translation of its 

 molecules. If there is any other energy than that, it would 

 show itself by this number dropping below i '67. ( )rdinary gases, 

 oxygen, nitrogen, hydrogen, tvc, do drop below, giving the num- 

 ber I '4, Other gases drop lower still. If the ratio of specific 

 heats is 1-65, pr.actically I'67, we may infer then ihal llie wliole 



NO. 1337, VOL. 52] 



energy of motion is translational : and from that it would seem 

 to follow by arguments which, however, I must not stop to 

 elaborate, that the gas must be of the kind called by chemists 

 monatomic. 



I had intended to say something of the operation of 

 determining the ratio of specific heats, but time will not allow. 

 The result is, no doubt, very awkward. Indeed I have 

 seen .some indications that the anomalous properties of argon 

 are brought as a kind of accusation .against us. But we had the 

 very best intenticms in the matter. The facts were too much 

 for us ; and all we can do now is to apologise for ourselves and 

 for the gas. Several questions may be asked, upon which I 

 should like to say a word or two, if you will allow me to 

 detain you a little longer. The first question (I do not know 

 whether I need ask it) is. Have we got hold of a new gas at 

 all ? I had thought that that might be passed over, but 

 only this morning I read in a technical journal the suggestion 

 that argon was our old friend nitrous oxide. Nitrous 

 oxide has roughly the density of argon ; but that, as far as I 

 can see, is the only i>oint of resemblance between them. 



Well, supposing that there is a new gas, which I will not stop 

 to discuss, because I think the spectrum alone would be enough 

 to prove it, the next question that fii.ay be asked is. Is it in the 

 atmosphere? This matter naturally engaged our earnest atten- 

 tion at an early stage of the inquiry. I will only indicate in a 

 few words the arguments which seem to us to show that the 

 answer must be in the affirmative. 



In the first place, if argon be not in the atmosphere, the 

 original discrepancy of densities which formed the 

 starting point of the investigation renains unex- 

 plained, and the discover}' of the new gas has been 

 made upon a false clue. Passing over that, we have 

 the evidence from the blank experiments, in which 

 nitrogen originally derived from chemical sources 

 is treated either with oxygen or with magnesium, 

 exactly as atmospheric nitrogen is treated. If we 

 use atmospheric nitrogen, we get a certain propor- 

 tion of argon, about I per cent. If we treat 



chemical nitrogen in the same way, we get, I will 



nf)l say absolutely nothing, but a mere fraction of 

 what we should get had atmospheric nitrogen been 

 the subject. \'ou may ask, why do we get any 



fraction at all from chemical nitrogen? It is not 



difficult to explain the small residue, because in the 

 manipulation ol the gases large quantities of water 

 are userl ; and, as I have already explained, water 



rlissolves argim somewhat freely. In the processes 



of manijiiilation some of the argon will come out of 

 solution, and it remains after all the nitrogen has 

 been consumed. 

 Another wholly distinct argument is founded upon the method 

 of diffusion introduced by Ciraham. (Iraham showed that if 

 you pass gas along porous tubes you alter the composition, if 

 the gas is a mixture. The lighter constituents go more readily 

 through the pores than do the heavier ones. The experiment 

 takes this form. A numlier of tobacco pipes — eight in the .actual 

 arrangement — are joined together in .series with indiarubber 

 junctions, and they are jnit in a space in which a vacuum can be 

 made, so that the S]iace outside the porous pipes is vacuous, or 

 ap|iroxiniateIy so. Through the pipes <irdinary air is led. 

 One end may be regarded as open to the atmosphere. The 

 other end is connected with an aspirator so arranged that the 

 gas collected is only some 2 per cent of that which leaks through 

 the porosities. The case is like that of an Australian river drying 

 up almost to nothing in the course of its flow. Well, if we 

 treat air in that way, collecting only the small residue which is 

 less willing than the remainiler to penetrate the ]Kirous walls, 

 and then prepare " nitri>gen " from it by removal of oxygen and 

 moisture, we obl.ain a gas heavier than atmospheric nitrc^en, a 

 result which proves that the ordinary nitrogen of the atmo.sphere 

 is not a single body, but is cajiable of being divided into parts 

 by so simple an agent as the toliacco pipe. 



If it be admitted that the gas is in the atmosphere, the further 

 question arises as to its nature. 



At this point I would wish to say a word of explanation. 

 Neither in our original announcement at Oxford, nor at any 

 time since, until January JI, did we utter a word suggesting that 

 argon was an element ; and it was only after the experiments 

 upon the specific heats that we thought that we had sufficient to 

 go upon in order to make any such suggestion in public. I will 



