Fifteen samples 'of clays and shales from the Adelaide area were selected from a total of 84 as representing material of possible value for the manufacture of light- weight aggregate. A detailed examination of the bloating._x000D_
characteristics of these revealed four likely to be suitable._x000D_
for expansion.' in a rotary kiln. One of these, a Tapley. Hill shale., was-fired in an 8 in. diameter rotary kiln, but con- tinuous bloating without ring formation in the kiln was not achieved. Steam,,-oxygen,, sulphur dioxide and carbon dioxide have been, suggested. as the agents of bloating. An examina- tion of .. the evidence : `leads to the conclusion that carbon dioxide derived from. carbonate minerals is likely to be the principal bloating agent. Attempts to bloat clays by the addition of mica were.not successful.