Dissolution tester

A dissolution tester comprising:

• a constant-temperature-water tank provided on a base and containing constant-temperature water;
• a head disposed above the constant-temperature-water tank, which moves up and down relative to the base;
• a support arm for supporting the head so as to allow free movement up and down relative to the base;
• a vessel comprising a main body having a bottom and a top opening for inserting a sample and a test liquid, and an outwardly projecting flange disposed around the entire circumference of a peripheral wall defining the top opening of the main body, a desired portion of the main body being immersed into the constant-temperature water inside the constant-temperature-water tank;
• a water-tank lid which is provided at a top opening of the constant-temperature-water tank, which is provided with a retaining hole having an inner diameter that is slightly larger than the outer diameter of the main body of the vessel and that is slightly smaller than the outer diameter of the flange of the vessel, and which holds the vessel by catching the projecting flange of the vessel at the retaining hole such that the desired portion of the vessel is immersed in the constant-temperature water inside the constant-temperature-water tank;
• a vessel lid which can be attached to and removed from the top opening of the vessel, wherein the lid prevents evaporation of the test liquids in the vessel, when the lid is attached to the top opening of the vessel, which moves up and down relative to the vessel, said vessel lid including a tapered portion having a bottom diameter that is smaller than a top diameter thereof which serves to position the vessel relative to the lid as the lid is being attached to the vessel;
• and
• a lid-moving shaft which is suspended from a lower part of the head and which is aligned with and secured to a center of the vessel lid to move up and down together with the vessel lid,
• wherein, by moving the lid-moving shaft starting from a position where the vessel lid is raised above the vessel and separated therefrom, when the vessel lid is lowered using the lid-moving shaft to cause the tapered portion of the vessel lid to come into contact with the top opening of the vessel, the vessel is made to move within a predetermined range in the planar direction of the water-tank lid such that the center axis of the lid-moving shaft and the center axis of the vessel are aligned and the vessel lid closes the vessel.