The aggregation of kaolinite

A series of fractions of kaolin [smaller than 0.5, 0.5–1, 1–2.5, 2.5–5, 5–10 and 10–20 μ in equivalent Stokes' diameter (E.S.D.)] separated by sedimentation have been investigated by measuring the specific surface area, S A , by gas sorption, the heat of immersion in carbon tetrachloride, the bulk volume, V , and the apparent density in various liquids; the ‘percentage floating in air after five seconds,’ f , has also been determined by dropping down a long glass tube. The value of S A agrees reasonably with the specific area, S D , calculated from the E.S.D. for the 0.5, 0.5–1, and 1–2.5‐μ fractions, but S A / S D then increases with increasing E.S.D. to nearly 4 for the 10–20‐μ fraction; moreover both V (whether measured ‘in air’ or ‘ in vacuo ’) and f have maximal values for the 1–2.5‐μ fraction. The results point to the existence of two types of aggregate : ( a ) temporary and loose aggregates in the three smallest particle sizes, and ( b ) ‘booklets’ in the three largest sizes.