Brimstone is an archaic name for sulphur. These particular specimens are a by-product of the the oil & gas refining process. Hydrogen Sulphide is one of the contaminants removed during fractionation. This is coverted into elemental sulphur by the Claus process which involves the oxidation of H2S to form Sulphur Dioxide (SO2). A further reaction between the two compounds ( comproportionation) produces Sulphur. It is used in the manufacture of fertilizers, pesticides & in the chemical & pharmaceutical industry. These specimens are available in two sizes only. Each one supplied in a labelled card tray.