84 the motors 86 being connected for example by a connecting rod 88 to each aliquot vessel array 42 as seen in fig6 a each aliquot vessel array 64 has a protruding and downwardly projecting zero backlash hitch 100 described hereinafter adapted to secure aliquot vessel array 64 to a pin portion 101 of connecting rod 88 fig7 is a plan view of the aliquot vessel array 64 useful in practicing a first embodiment of the present invention showing spatial relationships between parallel first and second side wails 90 and 91 extending lengthwise along the longer orthogonal edges 92 of a generally rectangular aliquot base plate 93 an ordered array of open wells 64 w is formed between the pair of parallel side walls 90 and 91 and separated therefrom by notched side flanges 94 front orthogonal edge 95 and rear orthogonal edge 96 of base plate 116 are further seen to be formed mutually parallel to one another with a zero backlash hitch 100 formed in the central region 97 of the front shorter perimeter portion 98 between the array of open wells 64 w and front orthogonal edge 95 an important feature of the aliquot vessel array 64 is the zero backlash hitch 100 formed in the central region 97 of the front shorter perimeter portion 98 between the shorter orthogonal edge 95 and the array of open wells 64 w sectional line 7 a u2014 7 a in fig7 a is enlarged to show details of zero backlash hitch 100 comprising an opening 101 in base plate 93 and a pair of semi circular sleeves extending downwardly a frontal sleeve 102 formed to slant backwards from the front of aliquot vessel array 64 towards a rear sleeve 104.