42 Mr. William Sutherland on the 



Table XXXII. (continued). 



S. Se. P. Br. 



a m 4-2 72 42 63 



P m 1-97 4-2 1-83 325 



M/ Po 15-7 17-1 13-5 27 



M 2 / 2-1 4-5 22 62 



M 2 / from Ta. XXIX. . 63 100 44 70 



Ratio -33 '45 -50 -88 



Where two values of a m are given for one metal, they are 

 the result of different methods of measurement ; the data are 

 all Quincke's except one of the measurements for lead made 

 by myself. If matters were exactly as we suppose them to be, 

 in applying equations (9) and (19) the values of the ratio in 

 the last table ought to be 1, or a constant near to 1, such as 

 we found in the case of the binary compounds, while the 

 range in the actual values of the ratio is from *33 for S to 

 6'0 for K. In seeking for the reason for this discrepancy, we 

 must remember that in using the equation (19) of the capil- 

 lary method we have assumed that the characteristic equation 

 of the metals is on the same type as that of the element gases ; 

 but there is this distinction between the metals and the 

 element gases, that some of the metals, namely Na, K, Zn, 

 Cd, and Hg, are known to be monatomic in the vaporous 

 state, while the element gases are diatomic ; and it is exactly 

 for these metals and tin that the ratio in the last table has its 

 largest values, while the smallest values belong to S, Se, and 

 P; and S and P are well-known instances of exceptional 

 molecular complexity, their vapour-densities at low tempera- 

 tures being such as correspond to the formulas S 6 and P 4 . 

 It is therefore probable that the discrepancy has to do with 

 an effect of molecular complexity not taken account of in 

 equation (19). We saw that the distinction between the 

 diatomic element gases and compounds was expressed by 

 introducing the factor 2 into the left side of equation (2); 

 and if we suppose that amongst the elements the effect of 

 molecular complexity is to introduce into the right side of 

 the equation (19), namely 



a factor equal to the molecular complexity, defining the 

 molecular complexity of an element as the number of pairs 

 of atoms in its molecule, which is 1/2 for JNa, K, Zn, Cd, and 

 Hg, 2 for P, and 3 for S, then the values of MH by the capillary 



