Examples from the Web for protoxide
As the last, but submitting oxide of chromium for the protoxide of copper.Cooley's Practical Receipts, Volume II|Arnold Cooley
A natural clay containing about 18% of protoxide and carbonate of iron.
By digestion with acids, it is dissolved into salts of the protoxide.
It consists of silica 25; protoxide of manganese 60; water 13.A Dictionary of Arts, Manufactures and Mines|Andrew Ure
All other acids dissolve its salts to protoxide, the hydrochloric acid producing chloric gas.