Nitroaniline-sulfuric acid compositions, a source of a new class of aphrogenic pyrostats (intumescent fire-quenching agents) have been studied. Thermogravimetric analysis of the compositions and their expansion products was carried out. The chemical compositions of the foams were determined, and considerable similarity was noted. Sulfur is present exclusively as sulfonic acid groups. Appreciable deamination occurs during expansion, particularly at higher acidic content. Sulfur dioxide and water are major gaseous constituents. Only 2- and 4-nitroanilines can be converted into voluminous foams; they behave like difunctional monomers. 3-Nitroaniline expands only slightly into brittle products; it acts like a trifunctional monomer.