Priestley describes his recent experiments on 'the purification of the atmosphere by vegetation', using water plants. He now believes that all plants emit air 'in a dephlogisticated state'. Priestley seeks advice from Mr Keir on testing for the presence of nitrous acid in vitriolic. The letter also includes family news and greetings. Letter from Joseph Priestley to Reverend Mr Scholefield
Sends sample of "Noah's Bacon"; thanks da Costa for presentation of emeralds to Warrington Academy; mentions his anxiety as the time approaches for his election to the Royal Society. Note in another hand: "Dr Priestley to Mr Da Costa". Letter is on backing sheet, watermarked 1820 and bearing brief biographical details of Priestley. Letter from Joseph Priestley to Emanuel da Costa