The escape at the moment of the eruption in Vesuvian lava flow of a Thorium volatile component has been deduced on the basis that the presence of Mesothorium I(²²⁸Ra) in lava flows is limited to only few years after the eruption. In the same way, the excess of ²²⁶Ra ($m_{Ra}$) in the specific mass relative to the ²³⁸U content, is a proof of the escape also of a volatile component of the Uranium. The presence of volatile components of the ²³⁸U and ²³²Th series in magmas was already called for in order to justify some peculiar behaviour in the magmatic evolution and in the eruptive dynamics. The experimental data consist of measurements of total gamma ray radioactivity and recently of gamma ray spectrometry of lava samples erupted from 1631 to 1944. The time-variation of a fraction of the ²²⁶Ra excess was considered as indicating a continuous decreasing of the ²³⁸U magmatic content. The above results suggest, on the basis of justified assumptions, the magmatic contents of ²³⁸U, ²³²Th, free ²³⁶Ra, in equilibrium with the other components of their families. The obtained values, relative to 1944, are: \begin{equation*}m_{U} = 3.28 \times 10^{-5} gr/gr \quad,\quad m_{Th} = 4.90 \times 10^{-5} gr/gr,\end{equation*}\begin{equation*}\frac{m_{Th}}{m_{U}} = 1.50 \quad,\quad m_{Ra} = 1.47 \times 10^{-12} gr/gr.\end{equation*}