Abstract: Means for reducing intersample contamination in an automatic chemical testing apparatus, in which liquid from a sample is aspirated from a sample source into a reservoir, and aliquots of the sample are each dispensed into individual reaction containers for analysis by well-known means. A cylindrical reservoir is utilized with a piston therein shaped for pushing out virtually all of the remaining sample from the cylinder after dispensing the sample liquid through a hollow needle, communicating with the cylinder. A solid pin coaxially mounted within the piston is projected through the needle and has minimum clearance therewith, for pushing remaining sample out of the needle. The portion of the pin projecting through the needle is retracted into the piston prior to aspiration of liquid from a next sample.

Abstract: In an automatic chemical analyzer, a reagent dispensing system is provided for delivering reagent from containers in a reagent compartment to reaction stations. A mounting block assembly is formed with a first bore therethrough for providing a reagent flow path whose direction of flow is regulated with check valves. A second bore normal to the first bore and communicating therewith is provided for receiving a piston having travel-limiting radial flange means formed at the end thereof remote from the first bore. A solenoid is mounted to the block having a plunger for activating the piston.