The tubular reactor is a silicone tube with 3 mm internal diameter, and was changed for each experiment to avoid errors that could result from the presence of CaCO 3 precipitates formed on the inner walls in a previous experiment. The residence time (τ ) of the precipitates in the reactor was kept low, such that the mixture being fed into the stirred Ca(OH) 2 solution mostly contains amorphous CaCO 3 . 44 τ was calculated from the total volumetric flowrate (Q) and reactor length (L): τ = πd 2 L 4Q . In this study, τ ≈ 9 s, and is equivalent to L = 30 cm. Also, flow through the tubular reactor is laminar, with Reynolds number Re ≈ 120 at 25 • C. Equal volumes of the precipitants are reacted in each experiment. The time (t) required to deliver the desired precipitants volume (V P ) are also calculated from the flowrate (Q P ) of either precipitant: t = V P /Q P . For instance, 50 mL of each precipitant would flow through the tubular reactor in 400 s.