Kaolinite- and halloysite-potassium acetate complexes were synthesized by cogrinding with solid potassium acetate (mechanochemical intercalation). The efficiency of mechanochemical intercalation was compared to the intercalation in solution and by homogenization. The effects of ageing and grinding parameters (grinding time, sample:grinding body mass ratio (SGMR), rotational speed) and the humidity on the intercalation were studied. The degree of intercalation increased exponentially with ageing of the samples prepared by mechanochemical and homogenization techniques. For the mechanochemical and homogenization techniques the required amount of potassium acetate per gram of kaolin (∼0.4 g/g) was two orders of magnitude lower than that for the solution intercalation (78.6 g/g). The highest degree of intercalation (86%) and the lowest structural deformation were achieved by the mechanochemical method (¼ h of co-grinding with 1:2 SGMR at 300 rpm), followed by 16 h ageing at 57% relative humidity.

The argument by Burkart et al. in the target article relates to fluid (not general) intelligence: a domain-general ability involved in complex, novel problem solving, and strongly related to working memory and executive functions. A formative framework, under which the general factor of intelligence is the common consequence, not the common cause of the covariance among tests is more in line with an evolutionary approach.

We welcome Blair's argument that the relationship between fluid cognition and other aspects of intelligence should be an important focus of research, but are less convinced by his arguments that fluid intelligence is dissociable from general intelligence. This is due to confusions between (a) crystallized skills and g, and (b) universal and differential constructs.