Automatic pipettor

Claim 2

Apparatus in accordance with claim 2 additionally comprising a magnetically operable electrical control means arranged adjacent said annular member and substantially in alignment with said first and second probe members; magnet means arranged in a receptacle of said annular member adapted to actuate said magnetically operable switch when substantially in alignment therewith; third probe member adapted to contain liquid supportably engaged by said second arm member being continually moveable in the same manner as said second probe member; a vessel adapted to contain a reference liquid; third pump means communicating with said reference liquid vessel cooperatively engaged to said third cam means to cause reference liquid to be drawn into said third pump means whenever said second probe member is in its first dwell position and to be dispensed from said third pump means whenever said second probe member is in its second dwell position; eighth electrical control means arranged adjacent said fourth cam member and adapted to be actuated thereby for a predetermined interval and transmit an electrical control signal for such interval whenever said second probe member is in its second dwell position and while an electrical signal is applied thereto; second electrically operable valve means in communication with said third probe member, said third pump means and said reference liquid vessel being electrically connected to said eighth electrical control means and being adapted to provide communication between said third pump means and said third probe member upon application of said electrical control signal thereto; ninth electrical control means adapted to be actuated upon actuation of said magnetically operable electrical control means to remove any control signal applied to said first electrically operable valve means and apply a corresponding electrical control signal to second valve means.