Sentence:  Let me remark, that the great exercise used by these volunteer adventurers; their quantity of vegetable food; their <WSD>freshening</WSD> their salt provision, by boiling it in water, and mixing it with flour; their beverage of whey; and their total abstinence from spirituous liquors—are the happy preservatives from the scurvy, which brought all the preceding adventurers, who perished, to their miserable end. 
Meaning of the word marked with <WSD> tags:  To make less salty; to separate, as water, from saline ingredients.