A viscous similarity of mineral oils

Mineral oils manifest a striking 1similarity in their behavior such that: $\text{f(T)=}\text{1}\text{v}{}^{\mathrm{\ast }}\text{·}\text{dv}\text{dT}$ is quantitatively the same for all oils. From this relationship it is possible to reach the useful expression:which gives the viscosity v at any temperature T in the range $\text{T}{}^{\mathrm{\ast }}\text{−30°}\text{to}\text{T+50°}$ as a function of which numerically varies with ($\text{T−T}{}^{\mathrm{\ast }}$): $\text{v}{}^{\mathrm{\ast }}$ and $\text{T}{}^{\mathrm{\ast }}$ are the co-ordinates of a particular point on the v′ vs T curve. In the above expression v′ = v₀ + 0.8 where v₀ is the actual viscosity in cSt. The values of are shown graphically as a curve of . Some values of $\text{v}{}^{\mathrm{\ast }}$ and $\text{T}{}^{\mathrm{\ast }}$ for various viscosities and viscocity index levels are also given. The expected errors are less than 1%. Methods and means for calculating $\text{v}{}^{\mathrm{\ast }}$ and $\text{T}{}^{\mathrm{\ast }}$ are given.