6 Holt, The Boric Acids. ^ 



the orthoboric acid would otherwise lose its water on 

 heating. 



The following results were obtained : 



Orthoboric acid (H3BOJ melting point 169-170 . 



2H3BO3. BA >> M 158-159*- 



H30,. B„_0, „ „ 159-160*. 



2H30,.3BA M " 167-174°. 



H^BCK.aBA ,. >. 172-173'- 



2H30,,.5BA: » n 171-173"- 



H,B03.3B,0, „ „ 172-174". 



H3BO3.4BA " " I7I-I72^ 



H3BO3.5BP, „ „ 170-172". 



These results do not point to any definite compounds. 

 When boric anhydride is added to orthoboric acid, the 

 melting point of the latter compound is lowered. It 

 subsequently rises again and then remains approximately 

 constant. 



In all mixtures, containing more boric anhydride than 

 is represented by the composition HjEO^.B^Og, a small 

 portion of the mixture melted at 158 -159", the melting 

 points given above being those of the main mass of the 

 substance. It is possible that this is the result of imperfect 

 mixing of the constituents in the capillary tubes employed, 

 but more probably is due to the formation of two partially 

 miscible solutions. Mixtures richer in boric anhydride 

 than is represented by the composition H3BO3.4B2O3, 

 when melted remained on cooling in the vitreous meta- 

 stable state, for when heated to i lo'-i i S'' they gradually but 

 completely crystallised. Boric anhydride itself could not, 

 however, be obtained in the crystalline condition. In this 

 connection it is interesting to note that metaboric acid 

 apparently exists in both vitreous and crystalline states. 

 When orthoboric is heated in air for some time at 100° an 

 almost completely vitreous mass of the composition repre- 



