104 



of the penta-valeiit boron, in wliicli one of tlie lionds is polar 

 (see fnrther). 



The non-acid complexes agree with this, the acid ones, which 

 are formed with the poly-hydroxy compounds, the hydroxy 1 groups 



Fig 9. 

 Potassium boro pyro catechate. 



of which have a favourable position, are derivatives of the penta- 

 valent element. Let ns choose as an example potassium boro pyro 

 catechate. 



The four oxygen atoms of the two pyro catechol rests are bound 

 to the boron atom. This cannot take place, however, until one elec- 

 tron of a metal or of an H-atom has been ceded to the complex. 

 When this has once been accomplished, it is immaterial for the 

 potassium (or H-) atom, where this electron is to be found in the 

 complex; in view of the telia-valency of the carbon, of the bi- 

 valency of the oxygen, and of the mono-valency of the complex, 

 the boron may here be assumed as penta-valent ; one of these bonds 

 is then polar (Fig. 9). 



The four non-polar bonds, just as in the carbon atom — will be 

 grouped as a tetrahedron, so that we may already expect o|)tical 

 activity in mono-derivatives of the pyro-catechol. These complex 



