Complex sentence: The Gallery was unlucky not to have been founded around an existing collection, but through diligent and skilful purchase, by the time it opened it had 125 paintings, in 1866 an annual purchase grant was established and by 1891 space was already limited.
Split into simpler sentences: The Gallery was unlucky not to have been founded around an existing collection, but through diligent and skillful purchase, by the time it opened it had 125 paintings. In 1866 an annual purchase grant was established and by 1891 space was already limited.