36 Gooch and Jones — Estimation of Boric Acid. 



Following are determinations made by this method with the 

 use of acetic acid. 



CaO taken. 



B 2 3 taken. 



B 2 3 found. 



Error. 



grm. 



grm. 



grm. 



grm. 



0-9977 



0-2065 



0-2062 



— 0-0003 



1-0220 



0-2067 



0-2070 



+ 0-0003 



1-3717 



0-2077 



0-2075 



— 0-0002 



1-1310 



0-1791 



0-1795 



+ 0-0004 



The results of the preceding table, as well as those of the 

 investigators mentioned, are a sufficient answer to the criticism 

 of Reischle,* that acetic acid and nitric acid do not liberate boric 

 acid in the distillation process so that good results may be 

 obtained. Moreover, it has been shown by one of usf that 

 even carbonic acid is strong enough to bring about complete 

 volatility of boric acid with methyl alcohol. 



The use of Calcium Oxide as a Retainer. 



Quite recently Thaddeeff;); has advocated the abandonment 

 of calcium oxide as an agent for holding boric acid in the 

 evaporation of alcoholic and aqueous solutions on account of 

 the hygroscopic nature of the oxide and the consequent diffi- 

 culty of securing it in definite conditions for weighing, and 

 proposes, instead of using calcium oxide, to retain and estimate 

 boric acid in solution by converting it into the form of potas- 

 sium borofluoride. 



In the final modification of Thaddeeff's method the proposal 

 is made to liberate the boric acid from its compounds by sul- 

 phuric acid, to volatilize it in methyl alcohol with the aid of a 

 current of dry air, to catch the distillate in potassium hydrox- 

 ide, to treat the mixture of hydroxide and borate with hydro- 

 fluoric acid in excess and evaporate in the steam bath, to digest 

 the residue of fluoride and borofluoride at normal temperatures 

 for two hours with 50 cm3 of a potassium acetate solution (sp. gr. 

 1*14) and for twelve hours more after adding 100 cm3 of ethyl 

 alcohol (sp. gr. 0*805), to filter on paper, wash the residue with 

 62-72 cm3 of alcohol (sp. gr. 0*805), dry at 100° and weigh as 

 potassium borofluoride, after which the borofluoride is to be 

 dissolved in boiling water and tested with calcium chloride for 

 possible contamination by the presence of a fluoride. Plainly 

 ThaddeefFs procedure presents at the outset difficulties ; for 

 besides the inconvenience of conducting long digestions with 

 reagents of regulated strength, the difficulty of procuring 

 hydrofluoric acid free from silica, which if present (as it 

 usually is, in the so-called chemically pure hydrofluoric acid of 

 commerce) would be retained in the borofluoride as potassium 



*Zeitschr. fur Anal. CLem., xxvi, 512. 

 f Jones, this Journal, v, 442. 

 JZeitschr. fur Anal. Chem., xxxvi, 568. 



