MOLECULAR VOLUME 



685 



electrical properties. So too do molecular volumes show con- 

 clusively that changes have taken place. Several writers show 

 this to be the case by summing up the A.V.'s in the free state 

 and finding out the nature of the differences, M.V. — 5"V a . 

 This certainly indicates that changes have taken place, but we 

 are left in the dark regarding the nature of such changes. This, 

 no doubt, is because these writers are unwilling to make the 

 assumption that 



M.V. = S(A.V.) 



Thus E. Vanstone, in a paper entitled " A Physico-chemical 

 Study of the Mercury-sodium Alloys or Amalgams," and read 

 before the Faraday Society, March 14, 191 1, gives data which 

 show the existence of the compounds Na 3 Hg, Na 3 Hg 2 , NaHg, 

 Na 7 Hg 8 , NaHg 2 , and NaHg 4 as crystalline solids. Volumetric 

 evidence is here given that they are divisible into two classes. 

 The first four are additive as regards volume, and made up from 

 the combined volumes of Na = 21*64 an d Hg = 9*04. The free 

 values are Na = 23*786 and Hg = 1476. Na thus contributes 

 23*786 — 21*64 = — 2*146 to the contraction, and Hg 14*76 — 

 904 = — 5*72, per gramme atom. 



The remaining compounds, NaHg 2 and NaHg 4 , are different. 

 The columns marked * are additional to those given by the 

 author of the paper (E. Vanstone), and are based upon the prin- 

 ciples set forth in the present one : 



The observed and calculated values agree so well, that it cannot 

 be doubted that the explanation given of the reason for the 

 changes in volume is the correct one. 



The combined volume of Na is very similar to that in the 

 free state, but the free and combined volumes of mercury are 

 very different. 



In the next group the state of things is very different : 



M.P. [NaHg 2 ] 43*14 = 3 x 14*38 



M.P. [NaHg 4 ] = [NaHg] . 3 Hg = 30*99 + 3 x 14*38 = 74-13 



Observed 74-07 



