PYREX® Barrett Distilling Apparatus with Stopcock and 24/40 Standard Taper Joints This PYREX® distilling apparatus is for determining water content in petroleum or bituminous products. It is graduated upwards from the stopcock to 3mL in 0.2mL divisions, and from 3mL to 20mL in 0.5mL divisions. For replacement stopcock plugs, see No. 7680. For replacement retaining clips, see No. 7280. Reference: Barrett method B-2.