OP ARTS AND SCIENCES. 167 



V. 



A METHOD FOR THE SEPARATION AND ESTIMATION 



OF BORIC ACID, 



WITH AN ACCOUNT OF A CONVENIENT FORM OF AP- 

 PARATUS FOR QUANTITATIVE DISTILLATIONS. 



By F. a. Gooch. 



Presented June 16, 1886. 



In all successful methods for the estimation of boric acid, its compara- 

 tive isolation is a necessary preliminary. Fortunately the removal of 

 nearly everything w^hich interferes seriously with the proper execution 

 of methods is not particularly arduous, but, of ordinarily occurring 

 substances, two, silica and alumina, — both very commonly associated 

 with boric acid, — are especially annoying in this regard. In the sep- 

 aration of alumina the trouble lies in the tendency of the precipitated 

 hydrate to carry and retain boric acid,* so that the two cannot be 

 parted by means of ammonia or ammonia salts ; with silica, the diffi- 

 culty is in removing it completely. The volatility of boric acid stands, 

 of course, absolutely in the way of treating with acid and evaporating 

 to dryness, and every chemist knows the vainness of attempting to 

 precipitate silica by means of ammonia, ammonia salts, or zinc oxide 

 in ammonia. In Stromeyer's method f the presence of silica is pe- 

 culiarly harmful, since in passing to the condition of potassium fluo- 

 silicate this substance nearly quadruples its weight, and to free the 

 potassium fluo-borate from contaminating fluo-silicate requires, accord- 

 ing to Fresenius,! at least six treatments by solution in boiling water, 

 the addition of ammonia, and evaporation to dryness. Wohler § recom- 

 mends evaporating the hydrochloric acid solution to dryness in a flask 

 fitted to a condenser, collecting the distillate, reuniting the latter with 

 the residue, and filtering from silica ; and the operation is successful so 

 far as the complete removal of silica is concerned, but the alumina, if 



* Wohler, Ann. d. Chem. u. Pharm., cxii. 268. 



t Ann. d. Chera. u. Pharm., c. 82. 



X Quant. Chem. Anal., p. 424. 



§ Handbook of Mineral Analysis, under Datholite. 



