Thermal diffusivity measurements of seven igneous rocks were made to temperatures of 400°C and pressures of 200 MPa. The measuring method was based on the concept of cylindrical symmetry and periodic heat pulses. The seven rocks measured were Westerly (Rhode Island) granite, Climax Stock (Nevada) quartz monzonite, Pomona (Washington) basalt, Atikokan (Ontario, Canada) granite, Creighton (Ontario, Canada) gabbro, East Bull Lake (Ontario, Canada) gabbro, and Stripa (Sweden) granite. The diffusivity of all the rocks showed a positive linear dependence on inverse temperature and, excluding the East Bull Lake gabbro, showed a linear dependence on quartz content. (Quartz content varied from 0 to 31% by volume.) Diffusivity in all cases rose or remained steady with increasing confining pressure. The pressure effect was strongest at lowest pressures and vanished by levels between 10 and 100 MPa, depending on rock type. The pressure effect (measured as a percentage change in diffusivity) is stronger in the four rocks of granitic composition than in the three of basaltic composition. Our results agree well with existing thermal diffusivity measurements at atmospheric pressure.

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An improved version of the comparative method thermal conductivity apparatus was designed. I t s accuracy was determined by measuring the conductivity of alumina with standards made of the same alumina and by cross-checking the conductivities of alumina, forsterite, Pyroceram Code 9606, and zirconia. The thermal stabilities of Pyroceram Code 9606 and zirconia were examined to establish their values as thermal conductivity reference materials. It was concluded that : (1) With this apparatus accurate thermal conductivity data can be obtained and (2) Pyroceram Code 9606 can be recommended for use as a primary standard for the low thermal conductivity range.

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A novel thermal diffusivity apparatus is described. It is based on the concept of an infinite cylinder and the measurements can be performed in transient and periodic temperature modes. Its ability to perform measurements on electrically conductive, medium range thermal diffusivity solids, as well as its accuracy of measurement, was established by measuring thermal diffusivity of an Armco iron specimen.