Abstract: Correns and Lippmann have extended the work carried out in England on swelling chlorites by some investigations on Keuper clays.
Dietzel has succeeded in showing that the infrared absorption band of kaolinite at 2.7µ has two peaks which can be correlated with two different kinds of (OH) groups in the structure.
The “fire-clay” type of clay mineral has been found in Grossalmeroder clay by Lippmann and in Frantex clay from Provins by von Engelhardt. In Frantex clay especially the layer sequence is highly disordered. Halloysite is distinguished from these minerals by its greater layer spacing and metahalloysite by its tubular morphology.
Winkler has studied the particle size distribution of numerous brick clays and has established that the mineral must have a certain proportion of fine and coarse clay and fine sand, but also a very smooth particle size distribution curve from the finest to the coarsest particles if the clay is to be suitable for thin-walled ware.
The clay mineral section of the Deutsche Keramische Gesellschaft tested various methods for quantitative clay mineral analysis. More than 20 laboratories used the following methods: x-ray analysis, dilatometer analysis, D.T.A., dehydration curves, microscopic analysis, and the determination of free silica by solution in phosphoric acid.
By the investigation of mixtures made up of the purest quartz, feldspar, halloysite, illite, kaolinite, montmorillonite and “fire-clay” mineral, the correct values were found for the most part within a few percent.
In the investigation of natural clays, greater differences were found, amounting to as much as 10 percent. Von Engelhardt especially investigated the errors arising with Geiger counter x-ray equipment.