107 



volatiliti : this furnishes a sufficient ground for assuming this suh- 

 stance to be strongly polymerized. This may possibly be explained 

 from the tendency of the boron atoms of one molecule to form 

 non-polar bonds with pairs of electrons of the oxygen atoms of 

 other molecules. It is possible to form an idea of this polymer by 

 imagining the anhydride molecules to be built up in columns, in 

 which alternately the oxygen atoms have penetrated into the outer 

 shells of the lioron atoms, thus contributing to the completion 

 of the "octet". There are enough free atoms left at the oxygen 

 atoms to render the easy hydration to boric acid comprehensible. 



The how hydrogen compounds. From the place of the boron in 

 the system it was to be expected that the atïinity of the H should 

 be slight. The interesting investigations by Stock and his pupils ') 

 have really proved that these compounds are formed in very small 

 quantities from magnesium boride, and are very unstable. At first 

 B,H, and B^Hi, were separated as gaseous boro-hydrogens, and 

 later B^H^ besides higher boro-hydrogens. Stock is of opinion that 

 the boron must be assumed to be tetra-valent in these compounds. 



He, therefore, tried to prepare halogen boron compounds BX,, in 

 which he did not succeed, which is, indeed, not astonishing in 

 view of what precedes; such a combination can only be realized 

 when at the same time an electron is added. 



The BjHj obtained by him is not necessarily a derivative of 

 tetra-valent boron; the BH,, which would; have to be formed in 

 virtue of the tri-valency of the boron, is evidently so unstable that 

 two molecules inter-penetrate, in which, however, one of the 

 B-atoms must more or less change into the ion-condition. It is 

 actually immediately adopted by KOH with formation of KBOH, 

 (propably a mixture or combination of KBOH, and KBOH^i and H,. 

 Accordingly it is a compound with tri- and penta-valent boron, 

 which through this makes the impression of being a derivative of 

 the tetra-valent element (see the symbol on the following page). 



Nor need the second gaseous boro-hydrogen B^Hi„ possess a tetra- 

 valent boron. In this two BH, -groups can be bound to each other, 

 each of them bearing a BH3-group, while besides two H-atoms have 

 passed into the kation-condition, and the rest, therefore, forms a 

 bi-valent anion. The B^H,, which is, moreover, the most stable boro- 

 hydrogen '), can certainly, not consist exclusively of tetra-valent 

 boron atoms. If it is assumed that one of the boron atoms is bound 



1) Berichte 54 A 142-158 (1921). 

 «) Berichte 54 A 155 (1922). 



