With this I return you Mr. Winthrop’s letter, according to your desire, thanking you for your endeavours to serve me in America, though I find, as I was apprehensive, that the scheme would not answer. Please to return my thanks to the professor for his candid and judicious remarks on my History of Opticks, which will be much improved by them, if it should come to a second edition.

Dr. Price will have informed you, that I have resumed my experiments on air, and with a good prospect of success. Since that I have been much more successful; but in a letter I can only confine myself to the heads of things.

The most important of the observations I have made lately is of an alkaline, corresponding to my acid air, of which an account is given in what I have already printed. This I get by treating a volatile alkali in the same manner in which I before treated the spirit of salt. As soon as the liquid begins to boil the vapour arises, and being received in a vessel filled with quick-silver, continues in the form of air, not condensed by cold.

I imagined that a mixture of this alkaline with acid air would make a neutral, and perhaps a common air; but, instead of that, they make a beautiful white salt of a very curious nature. It immediately deliquesces and even wholly disappears upon being exposed to the open air, and if it be in a dry and deep vessel, where moisture cannot easily come at it, it wholly evaporates in dense white clouds, occasioning a very strong smell.

This Alkaline vapour, like the acid, is quickly imbibed by water, which thereby becomes Spirit of Sal Volatile.

Nitrous air makes this alkaline vapour turbid, and perhaps generates a different salt; but I have not yet made a tenth part of the experiments that I propose to do with this new kind of air.

I have just found that spirit of wine yields air also, which is probably pure phlogiston, but I have not yet made one experiment with it.

If volatile alkali, liquid or solid, be exposed to nitrous air, during its effervescence with common air, the vessel is presently filled with beautiful white clouds; and the salt is tinged blue. This explains the constitution of nitrous air, but I have no time for reasoning.

This experiment appears to great advantage when a vessel, no matter how large, containing the smallest portion of volatile alkali, fluid or solid, is opened in a quantity of nitrous air, for the whole is filled almost instantly with dense white clouds.

Report says that you are about to leave us, at least for a time. If this be true, I shall be very sorry; as it will deprive me of one of the greatest satisfactions that used to make my annual visits to London agreeable. If you should leave England before winter, I should think myself very happy in an opportunity of seeing you before your departure. As I cannot conveniently come to London, I should be peculiarly happy in seeing you and Sir John Pringle, in my new situation; and I flatter myself that I could amuse you with some of my new experiments. If you can oblige me so far, give me a line to acquaint me with your intention, that I may be sure to be at home when you come. I am, Dear Sir, yours sincerely