Afurnace wall is to consist of a series of 7 in. of kaolin firebrick (k = 0.100 btu/hr ft∙°f), 6 in. of kaolin insulating brick (k = 0.12 btu/hr∙ft∙°f), and sufficient fireclay brick (k = 0.54 btu/hr∙ft∙°f) to reduce the heat loss to 100 btu/hr∙ft2 when the face temperatures are 1500 °f and 100 °f respectively. what thickness of fireclay brick should be used? if an effective gap of 1/8 in. can be incorporated between the fireclay brick and the insulating brick when installing the wall without impairing its structural support, what thickness of insulting brick will be required?