Abstract: A reagent container is described formed from two hemispherical shells (10, 12) of a material which is solid below reaction temperatures (typically at room temperatures) and which will melt below the reaction temperature to form a liquid seal over the melted reagents. The container is adapted to be fitted within a crucible-like structure (16) and heated to the reaction temperature within a suitable reaction chamber (typically pressurized) so that the pressures within the reagent container can be balanced.Other shapes of reaction container may be used such as cylindrical shapes, rectilinear shapes, and hemispherical shapes.Where the reagents are Gallium and Phosphorus the material from which the container is formed may be Boric Oxide.