Laivs of Molecular Force. 33 



The values for compounds of 0, S, CI, Br, and I have been 

 introduced into the table only to give an idea of the degree 

 of approximateness of the values in the table, for more accu- 

 rate values for these compounds have been already discussed. 

 First let us consider the values of M//o which may be taken 

 as M/3. 



These numbers show that in M/3 CH 2 has a value about 

 16*5, which is close to the limiting domain for CH 2 in the 

 organic compounds, though it ought to be larger, seeing that 

 the density p used in the organometallic compounds is not 

 the limiting density, but that of the liquids about 15° C. 

 We will take the value for H to be the same as in the organic 

 compounds, namely 4*5, and then CH" 3 is 21, C 2 H 5 is 37*5, 

 C 3 H 7 is 54, and C 4 H 9 is 70*5; with which we get the follow- 

 ing mean values of the atomic domains of the metals in the 

 organometallic compounds : — 



Zn. 



Hg. 



Sn. 



Pb. 



Si. 



P. 



As. 



Sb. 



28 



30 



49 



49 



42 



33-5 



27-5 



46 



Except for P and As, these domains are much larger than 

 in the inorganic compounds : for instance, the domain of 

 PbCl 2 is only 47*8, which is actually less than the domain of 

 Pb in the organic compounds. Of course the one number is 

 calculated for the solid state, and the other for the liquid, but 

 this could explain only a small part of the discrepancy. There 

 is no doubt that the metallic atoms occupy more space in the 

 organic than in the inorganic compounds ; in the inorganic 

 compounds Sb may be seen to have a domain about 20, while 

 in the organic compounds the value is 46. This is a very 

 significant fact, that seems not to have been noticed by those 

 who have occupied themselves with the question of molecular 

 domains (volumes). 



As regards (M 2 /)% we know that in organic compounds 

 CH 2 has a value '9, which is the value it possesses amongst 

 the chlorides, bromides, and iodides of the last table; but in 

 the metallic compounds the values are smaller. In the Zn 

 compounds 2CH 2 has the values 1*8 and 1*5, with Hg 1*7 and 

 1*2; in the Sn compounds 4CH 2 is 2 # 8 and 1*7, and in the 

 Pb compounds 2'4 : in every case the greater the number of 

 CH 2 groups the smaller the value of CH 2 ; the compounds of 

 S show the diminution clearly, for they give for CH 2 instead 

 of 1*8 the values 1'6, 1*5, 1*4. These results seem to show 

 that the approximate equation (14), used to calculate the 

 values of (M 2 /) 5 in Table XXV., gives less and less accurate 

 results the more complex the molecule becomes, but at the 



Phil. Mag. S. 5. Vol. 39. No. 236. Jan. 1895. D 



