A rack for holding at least one vessel for agitation of the vessel, said rack comprising:
- resilient clamping means comprising resilient members formed of resilient material for holding said vessel to said rack, positive-action movable means attached to said clamping means for moving said resilient members against the vessel at a position remote from the bottom thereof to resiliently hold the vessel vertically in place, laterally movable agitating means for engaging the vessel near the bottom thereof for imparting a lateral movement to the bottom of said vessel, said clamping means clamping said vessel to said rack and defining a null point while said lateral movement is imparted to said vessel, said rack further comprising a frame, said clamping means comprising three clamping members, a first of the clamping members being arranged in the frame between the second and third clamping members, the first clamping member having a respective resilient edge at each of two opposite sides thereof, the second clamping member having a resilient edge facing one of the resilient edges of the first clamping member and the third clamping member having a resilient edge facing the other resilient edge of the first clamping member and lateral shifting means comprising means for laterally shifting the second and third clamping members between positions sufficiently spaced from the third clamping member so that a vessel received between the first and the second clamping members or between the first and the third clamping members is not clamped therebetween and positions in which the clamping members are sufficiently close to each other that a vessel received between the first and second clamping members or between the first and the third clamping members is clamped therebetween, said clamping means further comprising a shaft, handle means rigidly mounted on the shaft for facilitating manual rotation of the shaft, a cross bar rigidly mounted on the shaft, first and second lever arms each pivotally connected near one end to the cross bar at a point near a respective end of the cross bar and each pivotally connected near the other end to a respective one of the first and second clamping members, one of the lever arms extending upwardly from the cross bar and the other lever arm extending downwardly from the cross bar, whereby a vessel received between the first and the second clamping members or between the first and the third clamping members is clamped therebetween when the shaft is rotated sufficiently that a line connecting the points of pivotal connection of the lever arms to the cross bar has rotated from an orientation non-parallel in a first rotational sense to a plane common to the resilient edges of the second and third clamping members to an orientation non-parallel in a second rotational sense to said common plane.