16 the cuvette carousel 16 preferably in the form of a wheel has about one hundred separate cuvettes 18 the inner wall of each cuvette 18 having an opening to allow transmission of light a small opening remains at the top of the cuvette 18 to allow the addition of reagent liquid and sample liquid a sample liquid arm 24 and a wash resource 26 are located proximate the sample cup carousel 12 and cuvette carousel 16 sample liquid arm 24 supports a conventional sample liquid probe 28 and an ultrasonic mixing mechanism 30 and is mounted to a rotatable shaft so that movement of sample liquid arm 24 describes an arc intersecting the three components 14 18 and 26 details may be found in u s pat no 4 863 693 assigned to the assignee of the present invention and incorporated herein by reference a liquid reagent arm 25 is mounted above cuvette carousel 16 for relative rotational movement with respect thereto to provide the capability to randomly dispose reagent arm 25 at any selected angular location above cuvette carousel 16 liquid reagent arm 25 also supports a conventional reagent liquid probe 27 adapted to draw reagent liquid from an appropriate reagent liquid cartridge 20 and deposit reagent liquid within a predetermined cuvette 18 probe 27 further comprises an ultrasonic mixing mechanism 31 included for hydrating aspirating dispensing and mixing reagents each of the ultrasonic mixing mechanisms 30 and 31 include a horn portion having an elongated shape and an associated pair of piezoelectric crystals and appropriate electronics the frequencies of oscillation are made to be.