The kieselguhrs or diatomaceous earths are composed essentially of more or less well crystallised silica, as well as a small quantity of alumina, iron oxide, and traces of other oxides. These earths are largely used as filtration aids; they can serve as supports for certain catalysts, and have also excellent calorifugic properties.

A study of different sorts of kieselguhrs used as supports for nickel and cobalt catalysts in the Fischer-Tropfsch synthesis has recently been carried out by Anderson et al. (1947). These authors find that a previous treatment of the raw kieselguhr by hot hydrochloric and nitric acids gives more active catalysts than those obtained using the same support untreated, and especially than those prepared from calcined kieselguhrs.