J 09 



n very stable configuration. If attempts to bring it to crystallisation 

 should succeed, a substance may be expected with a very high 

 refractivity and very great hardness, and with a still more consider- 

 able resistance against external intluences than any amorphous product 

 known so far. 



The difference with the way of binding of the carbon in diamond 

 is this that one of the bonds at the moment of its formation is not 

 quite equal to the other; when one considers, however, that this 

 difference has vanished after the two elements have combined, so 

 that it is impossible to decide which of the four was this particular 

 bond, the expectation is the more justified that crystallized boro- 

 nitrogen will have the character of diamond. 



It is seen that when represented in this way, the idea of the 

 valency l)egins to diffuse. The boron is more than tri-valent with 

 respect to the nitrogen, because the element lacks something. And 

 the nitrogen is more than tii-valent with regard to the boron, 

 because in the simple compound this element has something too 

 much. Combined they make, llierefore, the impiession of two tetra- 

 valent elements. Hence the valency is replaced by Wkhnkk's coor- 

 dination value, to which a firmer foundation is given by these 

 considerations. 



If it should appear, e.g. from the Röntgenograni, that the diamond 

 structure is applicable to the crystallized boro-idtrogen, this proves at 

 the same lime that a distinction between principal- and by-valencies 

 is not rational, and that polar and non-polar bonds should be sub- 

 stituted for this, ni which the non-polar bond is a connection between 

 two atoms, which in consequence of mutual repulsion of some such 

 bonds, has taken up a certain place in the molecule, whereas the 

 polar bond forms a connection between one of the atoms and a 

 rest, which will often consist of a multiple of atoms, but which, 

 also when it consists of only one atom, is not fixed to a definite 

 place of it. 



It is self-evident that in the first pei-iods, in which the atoms are 

 simply composed, the number of pairs of electrons will not be 

 greater than four, and the coordination-value will not exceed this 

 number. 



As the atoms get more complicated, the coordination-value can 

 also increase: we see this already happen in the second period in 

 aluminium, many compounds of which are known, in which this 

 element is bound non-polarly to six atoms. 



With regard to the other boron compounds, I will still draw 

 attention to additional compounds of the boric acid esters with 



