TRANSACTIONS OF SECTION B. 599 



is berylliiim and calcium ; tliere is a somewhat greater difference between litliium 

 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 

 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 posi- 

 tion in tlie periodic scheme of the elements. The apparent difficulty is this: The 

 atomic weight of argon is 40 ; it has no power to form compounds, 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 4Q. 



Let us examine this contention. Taking the first row of elements, we have : 



Li = 7,Be = 9-8,B = ll, C = 12,N = 14,O = 16,F = 19,.P = 20. 



The differences are : 



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



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

 larities. Thus : 



(? = 20), Na = 23, Mg = 24-3, Al = 27, Si = 28, P = 31, S = 32, CI = 355, A = 40. 

 And the differences : 



3-0, 1-3, 2-7, 10, 30, 1-0, 3-5, 4-5. 



The same irregularity might be illustrated by a consideration of each succeed- 

 ing 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 weight than potassium by_0'9 

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

 follows argon in the table. Farther 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, 1 = 127. 



The differences are : — 



4-0, 2-0, 5-0, 1-5, 7-2, -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. Professor Brauner, indeed, has submitted tellurium 

 to methodical fractionation, with no positive results. AH the recent determina- 

 tions 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 irregulari- 

 ties. 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 con- 

 sideration. These are : Does some circumstance modify these ' combining propor- 

 tions ' 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,' unchange- 



