Gooch and Jones — Estimation of Boric Acid. 39 



Obviously calcium oxide may be weighed with accuracy, 

 with or without boric acid ; but the fact remains that a less 

 hygroscopic absorbent — one requiring less care in the handling, 

 is to be desired. 



The use of Sodium Tung state as a Retainer. 

 In searching for a suitable material of less hygroscopicity to 

 replace calcium oxide as a retainer for boric acid, we have 

 found that sodium tungstate, fused with a slight excess of 

 tungstic acid over that contained in the normal tungstate (to 

 insure its freedom from carbonate), answers this purpose excel- 

 lently. This substance is definite in weight, not hygroscopic, 

 soluble in water, and recoverable in its original weight after 

 evaporation and ignition. To test its value as a retainer for 

 boric acid, portions of it — 4 to 7 grms. — were fused and 

 weighed in a 50 cm3 crucible, the tungstate was dissolved in 

 water and to it was added a known amount of a standard solu- 

 tion of boric acid. After diluting, mixing, evaporating, and 

 fusing the residue, the increase in weight should represent the 

 boric anhydride held by the tungstate. The results of the 

 accompanying table show how accurately the boric acid is 

 retained under these conditions : In experiments (3) to (7) the 

 tungstate, after its first weighing, was dissolved, transferred to 

 a larger platinum dish and mixed therein with the boric acid. 

 After evaporation to a suitable volume this solution of tung- 

 state and boric acid was transferred to the original crucible for 

 final evaporation and ignition. 



Na 2 W0 4 + W0 3 



B 2 3 



B 2 3 



Error 



taken. 



taken. 



found. 



in B 2 3 . 



grm. 



grm. 



grm. 



grm. 



6-5416 



0-1784 



0-1771 



— 0-0013 



7*3134 



0-1786 



0-1773 



— 0-0013 



5-5003 



0-0950 



0-0952 



+ 0-0002 



4-1394 



0-0944 



0-0944 



o-oooo 



7-5037 



0-2148 



0-2149 



+ 0-0001 



4-7744 



0-2718 



0-2702 



— 0-0016 



6-6470 



0-2503 



0-2487 



-0-0016 



It is plain that though the sodium tungstate does not hold 

 the boric acid with absolute accuracy the errors are not 

 unreasonable —0*0008 grm. in the mean. Upon substituting 

 the tungstate for calcium oxide as a retainer in the distillation 

 process, the results were likewise highly favorable. 



We used by preference the apparatus originally proposed, 

 excepting that the Erlenmeyer flask used as a receiver is fitted 

 tightly to the condenser and trapped with water bulbs. The 

 retort is made very easily from a 150 cm3 pipette and has the 

 special advantage that particles of the residue spattering dur- 



