RUEHLE
ANL) Sxrocrcl titrated boric acid in aqueous magnesium chloride solutions, using the potcntiometric null point method. In the range of IO to 50 mg of boric acid the results wcrc satisfactory for their purpose, although errors of IO per cent or more were found when only IO mg of boric acid are present. HOL-LANDEH AND RIEMAN~, however, found that boric acid could be titrated in mannitol solutions using phenolphthalein as indicator.
The object of their study was to ascertain the correct amount of mannitol for this titration, but the concentrations of the boric acid solutions were reasonably high, 0.057M (3.4 g per liter).
In the present work it was proposed to determine boron, as boric acid anhydride, in solutions as low as 7.2-10 -'JI. A precision of 99.5 per cent was sought, and the solvent could bc cithcr water or dcutcrium osiclc.
Boric acid anhydride dissolves in water as H,BO, and in deutcrium oxide as D,BO,. Either form is expected to complex with glycerin or mannitol and react as a monobasic acid, but since the propertics of deutcrium oside differ from that of ordinary water it is clesirablc to investigate and to show that the potentiometric titration method is applicable. Titrations were performed in aqueous solutions as reference method, then duplicated in deuterium oxide. Both glycerol and mannitol were used as complexing agents; solutions were pm-boiled under rcflux and then helium was used to purge the solution and also to stir the solution. Nitrogen is unsatisfactory as a purge gas because it contains uncertain quantities of carbon dioxide.
APPARATUS AND ClIEJIICALS
Becktna?t $H meter fitted with glass and calomcl electrodes. ManlzitoZ (neutral, boric acid-free) -CH,OH -(CHOH), -CH,OH.