442 Jones — Action of Carbon Dioxide on Soluble Borates. 



Aet. LV. — The Action of Carbon Dioxide on Soluble 

 Borates; by Louis Cleveland Jones. 



[Contributions from the Kent Chemical Laboratory of Tale University.— LXX.] 



In a process for the separation and estimation of boric acid 

 devised by Morse and Burton,* the liberation of carbonic, 

 silicic and boric acids from a mixture of inorganic salts is 

 effected by the action of sulphuric acid, using tropaeolin 00 

 as an indicator of acidity. In the solution thus prepared, con- 

 taining in free condition only carbonic, silicic and boric acids, 

 the silicic acid is dehydrated and made insoluble by anhydrous 

 copper sulphate. The boric acid is then extracted with abso- 

 lute alcohol. To this alcoholic solution of boric acid, a known 

 amount of barium hydroxide solution is added in excess over 

 that required to form a barium metaborate, BaB 2 4 . Carbon 

 dioxide is then passed into the solution in accordance with the 

 hypothesis that the excess only of barium is acted upon. The 

 aqueous mixture of barium metaborate and barium carbonate 

 is evaporated and the residue is heated to a constant weight 

 over a triple burner. From the following proportion the boric 

 acid present may be calculated. The molecular weight of 

 boric acid — the molecular weight of carbon dioxide : the mole- 

 cular weight of boric acid = the total weight found — the theo- 

 retical weight of barium as carbonate: the weight of boric acid 

 present. It is obvious, inasmuch as the difference between the 

 calculated weight of the barium as carbonate and the actual 

 weight of the residue is multiplied nearly three times to get 

 the boric oxide, that the actual error of the process, whatever 

 it may be, is magnified three-fold by the method of computa- 

 tion. 



I have made a study of this method applied to pure boric 

 acid, but have been unable to obtain results similar to those of 

 Morse and Burton. 



For this investigation boric acid of standard strength was 

 made by dissolving in a given amount of water a known weight 

 of anhydrous boric oxide, prepared by igniting over a blast 

 lamp boric acid several times recrystallized and washed. A 

 solution of barium hydroxide was filtered free from carbonate 

 and then standardized by precipitation as carbonate and also 

 by the Phelps method with iodine.f To a measured amount 

 of the boric acid solution an excess of barium hydroxide was 

 added, carbon dioxide passed, and the whole evaporated and 

 by successive ignitions brought to a constant weight. Below 

 are tabulated some of the results : 



* Am. Chem. Jour., x, 154. f This Journal, ii, 70. 



