['Moreover', ',', 'the', 'only', 'assumptions', 'are', 'chemical', 'reactions', 'between', 'the', 'gas', 'and', 'the', 'solid', 'forming', 'volatiles', ',', 'the', 'loss', 'of', 'these', 'volatiles', 'from', 'the', 'material', 'and', 'the', 'two', 'stated', 'boundary', 'conditions', 'of', 'gas', 'influx', 'at', 'a', 'single', 'outer', 'surface', 'and', 'the', 'possibility', 'of', 'reactions', 'throughout', 'the', 'bulk', '.']