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Of Saltpetre

Saltpetre being the principal ingredient in fire-works, and a volatile

body by reason of its aqueous and aerial parts, is easily rarefied by

fire; but not so soon when foul and gross, as when purified from its

gross and earthy parts, which greatly retard its velocity; therefore,

when any quantity of fire-works is intended to be made, it would be

necessary first to examine the saltpetre; for if it be not well

cleansed from all impurities, and of a good sort, your works will not

have their proper effect.