10 Mr. W. Sutherland on the 



Table II. 



Li. Na. K Eb. Cs. 



(N-l)B 3-6 4-65 8-00 114 15-6 



P 3-5 311 210 2-485 2375 



N 2*80 1-628 1430 1331 12785 



Ncalc 2-85 L63 1-47 132 1-26 



K 7-84 2-65 2-045 177 1635 



In the case of the Be family of metals there are special 

 circumstances to consider, the chief being the effect of their 

 divalency upon es for the atom of the metal in its compounds. 

 In "Further Studies on Molecular Force " (Phil. Mag. [5] 

 xxxix. p. 1) es/h for molecules is investigated under the 

 symbol (M 2 Z)*, and it is shown that in binary compounds of 

 the metals of the form RS n where R is an n-valent atom of 

 a metal and S is a halogen acting monovalently, (M 2 /)*/^ is 

 of the form F r /n + F s , whereas on the principle of additive 

 parameters for chemical equivalents the law would be that 

 (M*l)*/n should be of the form F r /n + ¥ s , where ¥ r and F s are 

 the parameters characteristic of the elements R and S, and 

 are proportional to es for the atoms of R and S respectively. 

 In "The Electric Origin of Molecular Attraction" (Phil. 

 Mag. [6] iv. p. 625) 1 have suggested that this remarkable 

 result is derived from the symmetrical arrangement with 

 regard to the centre of the atom of the n electric fields in an 

 %-valent atom. For the metals Be, Mg, Ca, Sr, and Ba the 

 values of F r /2 are given by 0*53 (4, 5, 6, 7, 8) with a 

 maximum error of 2 per cent, and an average error of 1 per 

 cent. (Phil. Mag. [6] iv. p. 642). For this family of metals 

 the values of B are reproduced in Table III. from Phil. Mag. 

 [5] xxxix. p, 26, along with the derived values of B 1/3 to be 

 compared with those furnished by the empirical formula 

 BV*=0'32 (4, 5, 6, 7, 8). 



Table III. 



Be. Mg. Oa. Sr. Ba. 



B 10 5-6 8-6 106 166 



BV3 l-o 1-78 2-05 2-20 255 



BV3calc 1-28 1-60 1-92 2*24 2-56 



The value of B for Be is very uncertain on account of its 

 smallness and the fewness of the suitable compounds whose 

 density has been measured. For the other metals of the 

 family the liability to error in the value of B is considerable, 

 for example the volume of a gramme-molecule of MgCl 2 is 

 43*6, which with 38 for Cl 2 , yields 5*6 for Mg, with danger 



