From Joseph Priestley
ALS: American Philosophical Society
Calne 14. Oct 1773.
If I had had a frank for Mr. Johnson, I should not have given you this trouble; but Ld. Shelburne is not at home, and my covers for him are expended.9
I hope you received my letter, in which I gave you some account of my discovery of an alkaline air,10 tho’ I have not had the plea[sure of] hearing from you since. I am still busy in examining its properties and affinities, some of which are curious enough. The most remarkable observation I have made is of the manner in which it affects alum put into it. This substance absorbs it very fast, and then comes out perfectly white, and altogether unlike what it was; but I have not yet examined it any farther.1
I have also found that this alkaline air is slightly inflammable. This is not observed without attention, for a candle dipped into it goes out several times before there is much appearance of its inflammability. This, however, agrees with the opinion of chymists, that volatile Alkali contains phlogiston.
As you have not written to me, I hope you are planning an excursion to Calne, along with Sir John Pringle, or some of our friends. This would make me very happy. I am, with great respect, Dear Sir, yours sincerely
Endorsed: Dr Priestley. Oct. 1773
9. Priestley was in frequent touch with Joseph Johnson, the London bookseller and publisher, for whom see above, XI, 258 n. BF had the franking privilege for receiving and sending letters because he was a postal official, and Shelburne because he was an M.P. (ibid., pp. 39 n, 257 n). Priestley, having run out of his patron’s covers, was thriftily enclosing a communication for BF to forward to Johnson.
10. Above, Sept. 26, where Priestley discussed his chemical discoveries at greater length and most of the terms used here are explained.
1. Alum is a mineral salt, aluminum sulphate combined with either potassium or ammonium; our conjecture is that Priestley was using the latter combination. For a more detailed description see his Experiments and Observations on Different Kinds of Air (2nd ed., corrected; 3 vols., London, 1775–84), I, 174.