A reagent cartridge for reacting a soluble reagent with a fluid diluent is disclosed having a fluid inlet for accepting a diluent and fluid outlet for expelling a solution. The cartridge casing also has fluid manifolds adjacent to the inlet and the outlet for directing fluid in a radial direction from the inlet to the outlet. The casing further defines a receptacle for a soluble reagent. A volumetric compensation means for volumetrically compensating for dissolution of the reagent upon introduction of the diluent into the fluid inlet is provided. The volumetric compensation means can take the form of a resilient sponge material having a compressed volume and an expanded volume, wherein the expanded volume is up to at least 500% of the compressed volume. The volumetric compensation means can also take the form of resilient coil springs. In other embodiments, a fluid permeable pressure plate is positioned adjacent to a free end of the coil spring and the reagent is positioned against the pressure plate. A method for obtaining injectable quality intravenous solutions in the field using the reagent cartridge is also disclosed.