The first letter--from Jefferson to Jenkins--was written on June 21, 1791, soon after Jefferson and Madison returned to Virginia. Jefferson writes: "According to my promise when I had the pleasure of seeing you at Hudson, I have examined my notes made when I was at Bordeaux and find that the lowest priced white wines of that canton cost 75 livres a ton. . . ." After providing the information about wine prices and referring Jenkins to "Mr. Fenwick, a native of Maryland, consul at Bordeaux for the United States," Jefferson says he has enclosed "one of my reports on the whale and cod fisheries" (Jefferson and Madison also visited New England on their northern tour) and asks Jenkins to critique it: "I . . . will be obliged to you if, in reading it, you will have a pen in your hand, and make notes, ever so roughly, of any errors you may discover in it, and any new facts you can furnish me with, and be so obliging as to send me the notes."
Jenkins responded on July 5, 1791. He acknowledges receiving the information about wine prices and concedes that French wines "might serve a good purpose" were it not for "that heavy Duty," but says that at present they "cannot answer for Distilling in this Country." Of Jefferson's report on the whale and cod fisheries, Jenkins says: "I find your information to be so good that I can bear no light on [it]."
Six months later, on November 7, 1791, Jenkins writes to Jefferson again. This time it is a letter of introduction for Cotton Gelston who has traveled to Washington "to obtain a Patent for Mr. Benjamin Folger, for securing an important discovery he hath made in manufacturing Whale Oil." He goes on to say: "I am fully convinced that the discovery is entirely new, and a very important one, and that it will prove highly beneficial to the United States."
The List of Patents Granted . . . from April 10, 1790, to December 31, 1836 shows that on January 2, 1792, Benjamin Folger was granted a patent for his method for "Cleansing whale oil."