US Patent No. 8,227,400 B2; S.C. Johnson has patented a substrate that can actively dispense a volatile air treatment chemical upon being heated. The substrate is comprised of granular sand particles adhered together to form a body having a network of pores and volatile air treatment chemical disposed in the pores. The substrate has a first end and a second opposed end; and the average size of the granular particles adjacent the first end is sufficiently less than an average size of the granular particles adjacent the second end such that the first end tends to wick air treatment chemical toward the first end as air treatment chemical is dispensed from pores of first end. The substrate can deliver a first burst of the volatile air treatment chemical from the first end when the substrate is heated adjacent the first end. If thereafter the substrate is allowed to cool, it can deliver a second burst of the volatile air treatment chemical from the first end when the substrate is heated for a second time adjacent the first end, even without refreshing the substrate from an external reservoir supply of the air treatment chemical between the first burst and second burst, the second burst comprising volatile air treatment chemical that has been wicked toward the first end from elsewhere in the substrate. The granular particles comprise sand and a binder.