The main author, Smith, suggests that, since different metals have different thermal expansion coefficients, it should be possible to estimate the composition of a coin by measuring its thermal expansion. He suggests the design of an apparatus for carrying out such a study. In his rejoinder, Oddy points out several complicating factors that make such a technique impractical. He suggests, instead, that the coefficient of volume expansion of the alloy could be obtained by measuring the specific gravity at two different temperatures.