34 Gooch and Jones — Estimation of Boric Acid. 



Art. V. — The Estimation of Boric Acid ; by F. A. 

 Gooch and Louis Cleveland Jones. 



[Contributions from the Kent Chemical Laboratory of Yale University — LXXVIL] 



The estimation of boric acid by treating the salts of that 

 acid with sulphuric acid, distilling with methyl alcohol, evapo- 

 rating the distillate over magnesium oxide, igniting and weigh- 

 ing, was proposed by Rosenbladt* A little later, and without 

 knowledge of Rosenbladt's experience, a somewhat similar 

 process, f which consisted in the treating of the compound of 

 Doric acid with acetic acid or nitric acid, distillation with 

 methyl alcohol, evaporation of the distillate over calcium oxide, 

 and ignition of the residue, was described by one of us. In 

 the course of the development of this process, it transpired 

 that the insolubility of magnesium oxide retards the absorp- 

 tion of boric acid by that substance, and that the more soluble 

 calcium oxide retains boric acid more actively and is therefore 

 to be preferred. 



Points in the treatment upon which special emphasis was 

 laid in the original description of this process were the choice 

 of a suitable apparatus for the distillation, the employment of 

 a loosely stoppered receiver for the reception of the distillate 

 upon slaked lime, the careful removal of water from the sub- 

 stance in the retort before acidifying and treating with the 

 methyl alcohol, regulated use of acid, and care in the evapora- 

 tion and ignition. 



The attainment of good results in this process depends upon 

 attention to details. Modifications have been suggested by 

 several investigators. Thus, instead of igniting the calcium 

 oxide in a large platinum crucible, transferring it to the 

 receiver to hold the boric acid, and returning the calcium oxide 

 with the distillate to the same crucible for subsequent ignition 

 of the residue, as was originally proposed, Penfield:): prefers 

 to ignite the calcium oxide in a small crucible, to collect the 

 distillate in ammoniacal water, to evaporate the latter over the 

 calcium oxide in a large platinum dish, and to transfer this 

 residue back to the small crucible for the final evaporation and 

 ignition. Kraut§ suggests a modification of form in the appa- 

 ratus with no other essential change in conditions. Moissan|| 

 has suggested changes in the apparatus and avoids a transfer of 

 the calcium oxide — collecting the distillate by itself in a closed 

 receiver, trapped with an ammonia bulb to prevent the escape 

 of the boric acid from the distillate. Furthermore, Moissan's 

 process calls for the use of an amount of calcium oxide from 

 fifteen to twenty times greater than that theoretically required. 



*Zeitschr. fur Anal. Chem., xxvi, 21. f Am. Chem. Jour., ix, 23. 



% This Journal, xxxiv, 222. § Zeitschr. fur Anal. Chem., xxxvi, 3. 



I Compt. Rend , cxvi, 1084. 



