8 Holt, The Boric Acids. 



that each might be considered to contain the same amount 

 of boric anhydride per c.c. of water. The freezing points 

 of these sokitions were the same and identical with that 

 of orthoboric acid, this condition remaining unchanged 

 whether the sokitions were very dilute or almost saturated. 



Solutions of orthoboric acid from 2'48 grs. in lOO c.c. 

 water to O'l gr. in lOO q..c. water gave depressions of the 

 freezing point in accordance with a molecular weight of 

 from 685 to 55 (theory for orthoboric acid (i2). The acid 

 was apparently- very little ionised. 



No solvent could be found for either boric anh}'dride 

 or the other boric acids, in which they did not undergo 

 change, so their molecular weights are unknown, but from 

 the fact that the\- are vitreous substances in some ways 

 analogous to the phosphoric and silicic acids, their mole- 

 cular weights are probabh" greater than those represented 

 by simple molecules. 



Orthoboric acid is readil)' soluble in hot glacial acetic 

 acid, from which it separates out unchanged on cooling. 

 Boric anhj'dride does not appear to be soluble in this acid. 

 It was hoped, by means of this difference in behaviour 

 towards glacial acetic acid to decide whether the meta 

 and pyro acids were mixtures of the ortho acid and boric 

 anhydride or not. 



Metaboric acid dissolves to a very slight extent in hot 

 acetic acid the solution depositing the ortho acid on 

 cooling, but the amount dissolved is far too small to 

 correspond with that required for the meta acid if this 

 compound were an equi-molecular mixture of the ortho 

 variety with boric anhydride. The pyro acid does not 

 seem to dissolve at all. 



From the experiments which have been described, the 

 following conclusions may be drawn : — 



