It is to be understood, of course, that my inven tion, inasmuch as it is'not limited to on cracking equipment or limited t9 vessels containing liquids at relatively high temperatures, may have blocks similar to the blocks 9 composed of any suitable material, for instance, a material which is non-corrosive,-or if the vessel 1 is to contain such fluids as acids or the like, the material of which sai