This observation is consistent with the pinhole being too large. Under these conditions, the specimen can be depleted prior to reaching the boiling
point. The resulting endotherm can be shallow with a significantly
reduced leading edge from which the onset tangent cannot be accurately extrapolated. These results suggested that optimum pinhole
size selection requires balancing pre boiling vaporization from a pinhole that is too large and self-pressurization from a pinhole that
is too small.