Comprises a pair of graduated glass syringes of capacities 50 and 20cm3, both having finely ground pistons and providing a cross-sectional area ratio of 3:1 respectively. Both the syringes have loading platforms on their tops. A 3 way tap allows the syringes to be opened to the atmosphere, isolated or interconnected as desired. Both the pistons provided with limit-stop to prevent their complete ejection from the barrels. The thick walls of the syringes allow them to be capable of withstanding the pressures involved.