The absolute density of Standard Mean Ocean Water (SMOW) has been determined over the range 1 °C to 40 °C by weighing a hollow sphere of known volume in air-free water samples of measured isotopic content. The volume of the sphere as a function of temperature is known as a result of a combination of interferometric and mechanical measurements. The measured densities are tabulated. A formula (as proposed by Thiesen et al) and a fifth-order polynomial in temperature have been fitted to the tabulated data by least-squares analysis. The density calculated from the polynomial is estimated to have a standard uncertainty ranging from 0,64 parts in 106 at 15 °C to 1,4 parts in 106 at 1 °C and 40 °C. Comparisons are made with published data.
The results of the four absolute determinations of the density of mercury since 1945 are discussed. When reduced to a common temperature scale the values differ by more than the claimed uncertainties. Results are presented of a comparative measurement of the density of two further samples of mercury in terms of a reference sample. The density difference is determined by measuring the change in apparent mass of a tungsten carbide block when fully immersed in each mercury sample. The standard deviation of the measured density difference between the samples and the reference was found to be 4 x kg/m3. The values obtained show significant differences in density, and the possible cause, i.e. variation in the isotopic ratios between samples, is discussed. We confirm that the density of mercury must be measured if it is required to be known to better than a few parts in lo6.
The results of a series of comparative density measurements on various mercury samples are presented together with a comment on the long term stability of the density of mercury.
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