present invention however in one preferred embodiment the valve 12 is a pair of simultaneously actuated three way valves type 075t3wmp12 32 from biochem valve corporation east hanover nj with an injection loop between the common valve port of each valve as shown schematically in fig6 all of the above valves operate on 12 volts dc and although the timer provides such voltage output an external 12 volt dc power supply was used to prevent overloading the capacity of the timer itself the automatic valves can be operated by any suitable means other than directly by electrical solenoids such as by pneumatic means in addition if desired pressure regulators can be used in the compressed air system shown in fig1 to deliver different air pressures to the different points of use e g the reagent reservoirs 20 and 21 could be pressurized to different pressures if desired referring now to fig2 therein is shown a detailed view mostly in section and partly in full of the reactor 10 the reactor 10 includes a 1 5 milliliter capacity disposable polypropylene microcentrifuge tube 50 elkay products shrewsbury ma with its top rim cut off and potted in epoxy resin 51 inside a.