444 Jones — Action of Carbon Dioxide on Soluble Borates. 



already formed was put to the test directly. A known amount 

 of barium hydroxide was taken in solution and to it added an 

 amount of boric acid very little in excess of that theoretically 

 necessary to form the barium metaborate. The solution was 

 evaporated to dryness and the residue ignited. The weight ob- 

 tained proved to be 0*0008 grin, less than the sum of the barium 

 and boric oxides taken, doubtless because the slight excess of 

 boric acid was somewhat volatile in the evaporation. The 

 mass, presumably barium metaborate, was now dissolved as 

 completely as possible in hot water, carbon dioxide was passed 

 through the solution, the whole was evaporated, and the resi- 

 due ignited and weighed. The increase in the weight showed 

 that carbon dioxide had been absorbed, while a corresponding 

 amount of boric acid had not volatilized. 





Ba(OH) 3 taken. 





Residue after 



Residue after C0 2 





Calculated as BaC0 3 . 



B 2 3 taken. 



ignition. 



treatment and igni- 





grra. 



grm. 



grm. 



tion. — s:rm. 



v.. 



0-8377 



0-2990 



0-9491 



— 0-9771 



After passing in carbon dioxide and igniting, the increase in 

 weight was 0*0280 grm., representing the gas absorbed less the 

 boric acid volatilized. 



It was plain that barium metaborate is decomposed in solu- 

 tion by carbon dioxide. The possibility remained, however, 

 that the action of carbon dioxide might be so regulated as to 

 leave the metaborate practically un attacked. In experiment 

 VI, therefore, carbon dioxide was passed above the stirred 

 solution until no further precipitate formed upon the surface, 

 the barium present being in excess of that required to form a 

 metaborate. 



Ba(OH) 2 taken. Weight of residue 



Calculated as BaC0 3 . B 2 3 taken, after ignition. B 2 3 found. Error, 



grm. grm. grm. grm. grm. 



VI.. 0-7094 0-2070 0*7710 0*1658 —0*0412 



The variation of this result from the theory shows that under 

 these conditions the metaborate is not unaffected by carbon 

 dioxide, the loss being due, of course, to the escape of boric 

 acid. 



An attempt was now made therefore to gauge the amount of 

 the carbon dioxide introduced by means of an indicator. In 

 experiment VI phenolphthalein was added to the solution of 

 boric acid containing an excess of barium hydroxide and the 

 current of gas was stopped when the color of the indicator 

 disappeared. 



