106 



We are now able to bring some order in the inorganic derivatives 

 of boron. 



The volatile boric acid and its esters are, as was stated above, 

 derivatives of tri-valeni boron, and as sucli, somewliat nnsatnrated. 

 It will try to supply the deficiency by complex formation. 



Ai'k,hb.\ch's investigations ') iiave brought to light that when an 

 insuHicient quantity of a base is distributed between boric acid and 

 arsenic acid there is formed far more borate than was to be expected 

 according to the dissociation constant of boric acid. Complexes must 

 1)6 formed which are much more strongly acid than boric acid in 

 diluted aqueous solution. 



Hence in virtue of 3 tiie added bases cause the quantity of poly- 

 boric acid ion to increase. 



This is corroborated by an investigation of P. Mülleh '), who 

 could shake out but very little boric acid from a mixture of borate 

 and boric acid with amyl alcohol, though the free acid is easily 

 dissolved in it, evidently l)ecause the boric acid was bound with 

 formation of poly-borates in consequence of the above-mentioned 

 kation-action. 



These stronger poly-boric acids will be derivatives of penta-valent 

 boron, and accordingly in the symbol a place may be assigned to the 

 metal atoms which piomote this phenomenon, next to the boron 

 atom. 



The nietaborates then have the composition AJ(BO,), born.v has the 



.0— B— 0. 



formula: ()B<^ /BO, while potassium penta borate 



Na \0— B— 0^ Na 

 KB^Oj (see Hermans, following communication), which crystallizes 



OBOv .OBO 

 beautifullv from formic acid, possesses the constitution /'^\ 



OBO/ I \0B0 

 K 

 all assumed to be anhydrous. 



There are described a great number of poly-borates ; on the con- 

 dition that the number of penta-valent boron atoms be taken the 

 same as the number of positive metal valencies, their contiguration 

 can be easily constructed. 



Boric acid (inhydride is distinguished from boric acid by its slight 



1) Zeitschr. anorg, Ch. 37 353. 



2) Abegg Handbuch III. I p. 32 (1905). 



