Gooch and Jones — Estimation of Boric Acid. 37 



fluosilicate, the inaccuracy of the dried paper filter, and the 

 obvious uncertainty of success in an attempt to wash a mixture 

 of acid potassium fluoride and potassium borofluoride in potas- 

 sium acetate and alcohol, so that the one shall be rendered 

 entirely soluble while the other remains sensibly unaffected, — 

 besides these objections, there is the theoretical probability that 

 boric acid must be lost by volatilization during the evaporation 

 of the solution of the mixed salts in the presence of free hydro- 

 fluoric acid. This last point was put to the proof by submit- 

 ting to distillation in a platinum retort a mixture of equal 

 quantities of borax and potassium hydroxide with an excess of 

 hydrofluoric acid, collecting the distillate in potassium hydrox- 

 ide, evaporating it to dryness and testing it for the presence of 

 boric acid. When this residue from the evaporated distillate 

 was treated with sulphuric acid and methyl alcohol, the burn- 

 ing alcohol vapor gave plainly the green flame of boric acid. 

 Another portion showed clearly the presence of boric acid 

 when acidulated with hydrochloric acid tested with turmeric 

 paper. JS o boric acid could be detected in any of the reagents 

 used. It is plain, therefore, that boric acid does volatilize 

 upon the evaporation of a mixture of potassium fluoride and 

 borofluoride in acid solution. The amount of such loss is dis- 

 closed in the record of the following experiment. Portions of 

 a standard solution of boric acid, prepared by dissolving a 

 known weight of anhydrous boric oxide in a liter of water, 

 were mixed with a solution of potassium hydroxide (free from 

 silica and standardized by conversion to the chloride) in the 

 proportions to form the potassium borofluoride, and an excess 

 of hydrofluoric acid was added. The mixture was evaporated 

 -and the residue was dried and weighed at 100°, the whole opera- 

 tion being conducted in platinum. 



HKF 2 





KFBF 3 





Error in 



Error in 



equivalent to 



B 2 3 



theoretical 



KPBF 3 



terms of 



terms of 



KOH taken. 



taken. 



weight. 



found. 



KFBF 3 . 



B 2 3 . 



grm. 



.grm. 



grm. 



grm. 



grm. 



grm. 



0-3531 



0-1582 



0-5701 



0-5580 



— 00121 



— 0-0033 



0-3192 



0*1430 



0-5154 



0-5100 



-0-0054 



— 0-0015 



0*3192 



0-1430 



0-5154 



0-5030 



— 0-0124 



— 0-0034 



0-3192 



0-1430 



0-5154 



0-5088 



— 0-0066 



— 0-0018 



0-3192 



0-1430 



0-5154 



0-5114 



— 0-0040 



—o-ooii 



In experiments (1) to (3) the volume of the solution evapo- 

 rated was about 50 cm3 . In experiment (4) this volume was 

 reduced about one-half before acidifying with hydrofluoric acid, 

 while in experiment (5) the solution was diluted about one-half 

 before adding the hydrofluoric acid. It is plain, therefore, 

 that in this single step of Thaddeeff's process there is a con- 

 siderable error of deficiency. On the other hand, the errors 

 for the full process as laid down by Thaddeeff have been in 



