August 19, 1897] 



NATURE 



iSi 



of this portion does not differ in any respect from the usua 

 spectrum of helium. 



As re-diffusion does not alter the density or the refractivity of 

 this gas, il is right to suppose that either one definite element 

 has now been isolated ; or that if there are more elements than 

 one present, they possess the same, or very nearly the same, 

 density and refractivity. There may be a group of elements, 

 say three, like iron, cobalt, and nickel ; but there is no proof 

 that this idea is correct, and the simplicity of the spectrum 

 would be an argument against such a supposition. This sub- 

 stance, forming by far the larger part of the whole amount of 

 the gas, must, in the present state of our knowledge, be regarded 

 as pure helium. 



On the other hand, the heavier residue is easily altered in 

 density by re-diffusion, and this would imply that it consists of 

 a small quantity of a heavy gas mixed with a large quantity of 

 the light gas. Repeated re-diffusion convinced us that there 

 was only a very small amount of the heavy gas present in the 

 mixture. The portion which contained the largest amount of 

 heavy gas was found to have the density 2-275, ^""^ il^s refractive 

 index was found to be o'i333. On re-diffusing this portion of 

 gas until only a trace sufficient to fill a Pliicker's tube was left, 

 and then examining the spectrum, no unknown lines could be 

 detected, but, on interposing a jar and spark gap, the well-known 

 blue lines of argon became visible ; and even without the jar the 

 red lines of argon, and the two green groups were distinctly 

 visible. The amount of argon present, calculated from the 

 density, was I "64 per cent., and from the refractivity 1-14 per 

 cent. The conclusion had therefore to be drawn that the heavy 

 constituent of helium, as it comes off the minerals containing it, 

 is nothing new, but, so far as can be made out, merely a small 

 amount of argon. 



If, then, there is a new gas in what is generally termed helium, 

 it is mixed with argon, and it must be present in extremely 

 minute traces. As neither helium nor argon has been induced 

 to form compounds, there does not appear to be any method, 

 other than diffusion, for isolating such a gas, if it exists, and 

 that method has failed in our hands to give any evidence of the 

 existence of such a gas. It by no means follows that the gas 

 •does not exist ; the only conclusion to be drawn is that we 

 have not yet stumbled on the material which contains it. In 

 fact, the haystack is too large and the needle too inconspicuous. 

 Reference to the periodic table will show that between the 

 elements aluminium and indium there occurs gallium, a sub- 

 stance occurring only in the minutest amount on the earth's 

 surface ; and following silicon, and preceding tin, appears the 

 element germanium, a body which h.\s as yet l^een recognised 

 only in one of the rarest of minerals, argyrodite. Now, the 

 amount of helium in fergusonite, one of the minerals which 

 yields it in reasonable quantity, is only 33 parts by weight in 

 100,000 of the mineral ; and it is not improbable that some 

 other mineral may contain the new gas in even more minute 

 proportion. If, however, it is accompanied in its still undis- 

 covered source by argon and helium, it will bea work of extreme 

 difficulty to effect a separation from these gases. 



In these remarks it has been assumed that the new gas will 

 resemble argon and helium in being indifferent to the action of 

 reagents, and in not forming compounds. This supposition is 

 worth examining. In considering it, the analogy with other 

 elements is all that we have to guide us. 



We have already paid some attention to several triads of 

 elements. We have seen that the differences in atomic weights 

 between the elements fluorine and manganese, oxygen and 

 chromium, nitrogen and vanadium, carbon and titanium, is in 

 each case approximately the same ?s that between helium and 

 argon, viz. 36. If elements further back in the periodic table 

 be examined, it is to be noticed that the differences grow less, 

 the smaller the atomic weights. Thus, between boron and 

 scandium, the difference is 33; between beryllium (glucinum) 

 and calcium, 31 ; and between lithium and potassium, 32. At 

 the same time, we may remark that the elements grow liker 

 •each other, the lower the atomic weights. Now, helium and 

 argon are very like each other in physical properties. It may 

 be fairly concluded, I think, that in so far they justify their 

 position. Moreover, the pair of elements which show the 

 smallest difference between their atomic weights is beryllium 

 and calcium ; there is a somewhat greater difference 

 between lithium and potassium. And it is in accordance 

 with this fragment of regularity that helium and argon 

 show a greater difference. Then again, sodium, the middle 



NO. 145 I, VOL. 56] 



element of the lithium triad, is very similar in properties both 

 to lithium and potassium ; and we might, therefore, expect that 

 the unknown element of the helium series should closely resemble 

 both helium and argon. 



Leaving now the consideration of the new element, let us 

 turn our attention to the more general question of the atomic 

 weight of argon, and its anomalous position in the periodic 

 scheme of the elements. The apparent difficulty is this : The 

 atomic weight of argon is 40 ; it has no power to form com- 

 pounds, and thus possesses no valency ; it must follow chlorine 

 in the periodic table, and precede potassium ; but its atomic 

 weight is greater than that of potassium, whereas it is generally 

 contended that the elements should follow each other in the 

 order of their atomic weights. If this contention is correct, 

 argon should have an atomic weight smaller than 40. 



Let us examine this contention. Taking the first row of 

 elements, we have : 



Li = 7, Be = 9-8, B = ii, C = I2, N = i4, = i6, F=I9, ? =20. 



The differences are : 



2-8, 1-2, i-o, 20, 2-0, 3-0, i-o. 



It is obvious that they are irregular. The next row shows 

 similar irregularities. Thus : 

 (? =20), Na = 23, Mg = 24-3, Al = 27, Si = 28, P = 31, 8 = 32, 



Cl = 35-5, A = 40. 

 And the differences : 



3-0, 1-3, 27, I-o, 30, I-o, 3-5,4-5. 

 The same irregularity might be illustrated by a consideration 

 of each succeeding row. Between argon and the next in order, 

 potassium, there is a difference of -0-9 ; that is to say, argon 

 has a higher atomic weiglit than potassium by 0-9 unit ; whereas 

 it might be expected to have a lower one, seeing that potassium 

 follows argon in the table. Further on in the table there is a 

 similar discrepancy. The row is as follows : 



Ag = 108, Cd = 112, In = 114, Sn = 119, Sb = 120-5, 

 Te = 127-7, I = 127. 

 The differences are : 



4-0, 20, 50, 1*5, 72, - 0-7. 



Here, again, there is a negative difference between tellurium 

 and iodine. And this apparent discrepancy has led to many and 

 careful redeterminations of the atomic weight of tellurium. 

 Prof. Brauner, indeed, has submitted tellurium to methodical 

 fractionation, with no positive results. All the recent deter- 

 minations of its atomic weight give practically the same number, 

 127-7. 



Again, there have been almost innumerable attempts to 

 reduce the differences between the atomic weights to regularity, 

 by contriving some formula which will express the numbers 

 which represent the atomic weights, with all their irregularities. 

 Needless to say, such attempts have in no case been successful. 

 Apparent success is always attained at the expense of accuracy, 

 and the numbers reproduced are not those accepted as the true 

 atomic weights. Such attempts, in my opinion, are futile. Still, 

 the human mind does not rest contented in merely chronicling 

 such an irregularity ; it strives to understand why such an 

 irregularity should exist. And, in connection with this, there 

 are two matters which call for our consideration. These are : 

 Does some circumstance modify these " combining proportions" 

 which we term "atomic weights " ? And is there any reason to 

 suppose that we can modify them at our will ? Are they true 

 "constants of nature," unchangeable, and once for all deter- 

 mined ? Or are they constant merely so long as other circum- 

 stances, a change in which would modify them, remain un- 

 changed ? 



In order to understand the real scope of such questions, it is 

 necessary to consider the relation of the "atomic weights" to 

 other magnitudes, and especially to the important quantity 

 termed " energy." 



It is known that energy manifests itself under different forms, 

 and that one form of energy is quantitatively convertib le into 

 another form, without loss. It is also known that each form of 

 energy is expressible as the product of two factors, one of which 

 has been termed the "intensity factor," and the other the 

 "capacity factor." Pro^. Ostwald, in the last edition of his 

 " AUgemeine Chemie," classifies some of these forms of energy 

 as follows : 



