  A lithium-based radiochemical detector is aimed primarily to detect neutrinos
from CNO cycle what will provide a direct proof of its existence and will be a
stringent test of the theory of stellar evolution. Another task which can be
solved by this experiment is to measure a mixing angle $\theta_{12}$. The
sensitivity of a lithium experiment to $\theta_{12}$ was calculated by
Monte-Carlo following the proposed original technique which can be used as a
complimentary one to a chi-square technique usually applied to this task. It is
shown that the accuracy of measurement of the mixing angle in solar neutrino
experiments is principally limited by the accuracy of a lithium experiment due
to the limiting uncertainty of the energy generated in a pp chain.
