The hydrogen evolution method for the determination of uranium trifluoride which was developed by Manning, Miller and Rowan has been used for the determination of trivalent uranium in this laboratory for the past three years. The method has been applied to many different sample types supposedly pure UF3, mixtures of UF3 and UF4 and the large variety of mixtures of fluoride salts that have been investigated as possible nuclear fuels. These mixtures contained alkali metal, beryllium and zirconium fluorides. Several modifications have been made that have substantially improved the performance and ease of operation of the method. These improvements include the use of (1) an inexpensive, long-lasting source of pure carbon dioxide, (2) vacuum to assist in purging the system of gases that are insoluble in potassium hydroxide solution, (3) deaerated acid that has an extremely low quantity of non-absorbable gases, (4) slower flow rates of purging gas, (5) a sampling technique to minimize contamination, and (6) more dilute absorber solution to reduce film error. It is the purpose of this report to show the effect of these modifications and the applicability of the method various sample types that contain uranium trifluoride.