Which preposition to use with hydrate

of Occurrences 2%

The object of adding this acid is to dissolve the hydrate of oxide of zinc formed during the electrolysis and deposited in a whitish stratum upon the surface of the copper.

for Occurrences 1%

"By the way, Senator," he said, "I'll do my best to arrange what you want regarding aluminium hydrates for the sake of the South, and I'll also stand with you for Altacoola for the naval base.

Which preposition to use with  hydrate