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irreproducibility of determinations by the hydrogen
evolution method. In the analyses of some of the
NaZrF,-UF, samples, low results were obtained
because the samples were not completely dissolved
in 6 N HCI.
The methylene blue procedure requires less
operational time than the hydrogen evolution
method, and, for the samples which have been
tested, it appears to give results of comparable
precision and accuracy. Tests are being conducted
to determine the extent of the reactions between
methylene blue and uranium hydride, uranium
metal, and other metallic contaminants of the
fluoride samples.
In order to carry out subsequent determinations
of the total uranium concentration on the same
ples, the final solutions from the methylene
blue determination were titrated with oxidizing
agents. Titrations with Ce(lV) and Fe(lll) solu-
did not yield stoichiometric end points.
gh the reaction with K,V,O, was extremely
slow, two well-defined potentiometric end points
were obtained when the solutions were titrated
slowly. The second of these end points corre-
sponded to the reoxidation of methylene khite to
methylene blue plus the oxidation of the U(IV) to
U(VI). The stoichiometry of the first break in the
potential curve has not yet been accurately de-
fined, but it appeqrs to be consistent with the
oxidation of U(IV) to U(V). Further investigation
is under way to elucidate the nature of these
changes in potential.
Determination of Oxygen in Fluoride Fuels
Rep. Sept. 10, 1954, ORNL-1771, p 148.
PERIOD ENDING DECEMBER 10,1954
is used, a concentration of 1% water corresponds
to 235 rng of oxygen. From the above linear
relation the calibration curve can be extended to
concentration ranges too low for direct measure-
ment by weighed primary standards.
At the temperatures at which liquid HF could be
safely maintained in the reaction vessel, the rote
of the reaction between metallic oxides such as
UO, and HF was found to be too slow for applica-
tion to analytical measurements. The oxides were
found to react rapidly with fused KHF, according
to the postulated reaction
4KHF, + UO, --+ UF, + 4KF + 2H,O
The procedure has been modified accordingly to
carry out the dissolution of the sample in molten
KHF,.
In the revised procedure, the sample is mixed
with about five times its weight of arihydrous
potassium fluoride, KF, in a platinum crucible.
The crucible is then placed in the reaction vessel
and the KF is converted to the acid salt by trans-
ferring a portion of the HF acid from the conduc-
tivity cell to the reaction vessel. After the excess
HF has been returned to the cell, the KHF, is
fused by heating the reaction vessel to about
300T. The water is then transferred to ,the cob-
ductivity cell for measurement by repeated distilla-
tions with portions of HF.
Because part of the KF was carried over to the
cell during the distillation, the original apparatus
was modified by placing a silver-lined vessel,
which is similar in design to a Kieldahl trap,
directly above the reaction vessel. The revised
procedure is now being tested on pure samples of
ted for the deter-