Foam fraction as a function of gas velocity, for a 0.06% wt. SDS + 1.0%
wt. 1-Butanol solution, at a liquid velocity of 0.205 cm/s; without
particles (red, solid circles) and with resin coated or hydrophobic
sand from STIM-LAB 
= 2.65 g/cc;
mean size = 600-850 µm. The volume fractions are 10% (blue, open
circles) and 20% (green diamonds).