40 



Gooch and Jones — Estimation of Boric Acid. 



ing distillation are easily washed from the walls of the vessel 

 by a slight rotary motion of the retort. It was found that 

 special care should be taken to give the tungstate ample time 

 for contact with the distillate before exposing the latter to 

 atmospheric evaporation. The distillate was received, there- 

 fore, in a dilute solution of sodium tungstate placed in the 

 receiver, cooled by ice and trapped with water, and the mix- 

 ture was well stirred, allowed to stand one-half hour, evapo- 

 rated to small volume in a large dish, and transferred to the 

 crucible in which the tungstate had been originally weighed. 

 After thorough drying the residue was ignited to fusion and 

 weighed. When acetic acid was employed in the retort, caro 

 was taken in the ignition to expose the fused mass freely to 

 the air (by causing it to flow upon the sides of the crucible) 

 until the color of the cooled tungstate was white, in order that 

 the reducing effect of the acetate might be eliminated. In the 

 experiments recorded in the following table the tungstate was 

 used in the receiver to retain the boric acid distilled as usual 

 with methyl alcohol, from the borates treated with acetic acid, 

 nitric acid or sulphuric acid, in amounts regulated by the use 

 of phenolphthalein as an indicator. 



2 wo 4 +wo 3 



B 2 3 



B 2 3 





taken. 



taken. 



found. 



Error 



grm. 



grm. 



grm. 



grm. 





With Nitric Acid. 





8-5516 



0-1582 



0-1572 



—o-ooio 



4-9639 



0-1329 



0*1323 



— 0-0006 



80033 



0-1267 



0-1256 



—o-ooii 





With Acetic 



Acid. 





4-9658 



0-1434 



0-1418 



— 0-0016 



6-0289 



0-1431 



0-1433 



+ 0-0002 



4-6797 



0-1589 



0-1587 



— 0-0002 



4-0013 



0-1433 



0-1422 



— 0-001 I 





With Sulphuric Acid. 





6-3439 



0*1582 



0-1579 



-0-0003 



8-8227 



0-1582 



0-1577 



— 0-0005 



10-1516 



0-1265 



0-1264 



-o-oooi 



6-5738 



0-1392 



0-1390 



— 0-0002 



Excessive use of acid is disadvantageous, and this is espe- 

 cially true in the case of sulphuric acid ; for, if this acid is 

 carried over with the methyl alcohol, as it is at 100° if present 

 in appreciable excess, a part of it, at least, is held permanently 

 by the tungstate to increase the apparent weight of the boric 

 acid to be estimated. 



The manipulation of the tungstate presents no difficulties, 

 and the results obtained by its use are reasonably accurate. 



