Uhmm.. i faced some problem with my experiment of finding the thermal conductivity of glass..i hope that someone can help me. May i know the extimation of the thermal conductivity of a boiling tube?? isit the same as the thermal conductivity of pyrex glass?? when i want to find the radius of the boiling tube, should i take the reading of the external diameter divided by 2 or the internal diameter divided by 2?? and about the thickness of the boiling tube, its the external diameter deduct the internal diameter then divided by 2 isit?? i will really appreciate your help..