Physical properties of heavy-oxygen water. Absolute viscosity of H ₂¹⁸O between 15 and 35°C

The absolute viscosity of highly enriched heavy-oxygen water, H ₂¹⁸O, has been measured at 5°C intervals between 15 and 35°C, using a semi-automatic closed viscometer of the suspended-level type. A linear extrapolation was performed to determine the viscosity of 100% heavy-oxygen water, based upon the measured viscosity of natural water and that of a highly enriched heavy-oxygen water sample. The effect of isotope substitution on the viscosity of natural water has been analyzed for both H ₂¹⁸O and D₂¹⁶O. The viscosity ratio at 25°C for H₂¹⁸O/H₂¹⁶O is 1.0536, whereas that for D₂¹⁶O/H₂¹⁶O is 1.2316.