FROM JOSEPH PRIESTLEY TO B. FRANKLIN.

New Experiments on Air.

DEAR SIR,

Calne, 26 September, 1773.

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 Optics, 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 lately made 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 liquor begins to boil, the vapor arises, and being received in a vessel filled with quicksilver continues in the form of air well 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.

* See above, p. 375.

This alkaline vapor, like the acid, is quickly imbibed by water, which thereby becomes spirit of sal volatile.

Nitrous air makes this alkaline vapor 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 effervescences 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 particularly happy in seeing you and Sir John Pringle at 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,

JOSEPH PRIESTLEY.

TO JOHN INGENHOUSZ.

Torpedo.- Magnetic Needle. Nairne's Electricai Machine.Magazines at Purfleet.

MY DEAR FRIEND,

London, 30 September, 1773.

I rejoiced as much as any friend could do at the news we received here from time to time of your success in your profession, and of the safe recovery of your illustrious patients of that most amiable family. But it grieved us all, at the same time, to hear that you did not yourself enjoy health in that country. Surely their known goodness will graciously give you leave of absence, if you have but the courage to request it, and permit you to come and reside in England, which always agreed well with your constitution. All your friends here will be made happy by such an event.*

I had purposed to return to America this last summer, but some events in our Colony affairs induced me to stay here another winter. Some time in May or June next I believe I shall leave England. May I hope to see you here once more?

I shall be glad to see the work of the Abbé Fontana on that disease of wheat. As yet I have not heard that it is come to England.

Sir William Hamilton writes from Naples, that after

* Dr. Ingenhousz was now residing at Vienna, whither he had gone to inoculate for the smallpox the Archduchess Theresa Elizabeth, the only daughter of the Emperor, and the Archdukes Ferdinand and Maximilian, the Emperor's brothers. He remained in that city several years. He was in England during a large part of the year 1779, when he published his work, entitled Experiments on Vegetables, &c. In the title-page of that work, he styles himself, "Counsellor of the Court and Body Physician to their Imperial Majesties."— Editor.

many experiments he has not been able to perceive any certain signs of electricity in the torpedo. It is perhaps best that there should be two opinions on this subject, for that may occasion a more thorough examination of it, and finally make us better acquainted

with it.

It is not difficult to construct a needle, so as to keep pointing to the meridian of any one place, whatever may be the variation in that place. But to point always to the meridian, wherever the needle may be removed, is, I apprehend, not possible.

Mr. Nairne has, as you have heard, finished a very fine electric machine. I have seen sparks from the prime conductor thirteen inches in length. He has added a large battery, and produces a discharge from it sufficiently strong to blast growing vegetables, as lightning is supposed to do. From a greater force used, perhaps some more discoveries may be made. I am much pleased with the account you give me of your new machine of white velvet rubbed upon hareskin.

Last year the Board of Ordnance applied to the Royal Society here for their opinion of the propriety of erecting conductors to secure the powder magazines at Purfleet. The Society appointed a committee to view the magazines, and report their advice. The members appointed were Messrs. Cavendish, Watson, Delaval, Robertson, Wilson, and myself. We accordingly, after viewing them, drew up a Report, recommending conductors to each, elevated ten feet above the roof, and pointed at the ends. Mr. Delaval did not attend; all the rest agreed in the Report, only Mr. Wilson objected to pointing the rods, asserting that blunt ends or knobs would be better. The work, however, was finished according to our direction. He

was displeased, that his opinion was not followed, and has written a pamphlet against points. I have not answered it, being averse to disputes. But in a new translation and edition of my book printed lately at Paris, in two volúmes, quarto, you will see some new experiments of mine, with the reasonings upon them, which satisfied the committee. They are not yet printed in English, but will be in a new edition now printing at Oxford, and perhaps they will be in the next Transactions.*

It has been a fashion to decry Hawkesworth's book; but it does not deserve the treatment it has met with. It acquaints us with new people having new customs, and teaches us a good deal of new knowledge.

Captain Phips has returned, not having been able to approach the Pole nearer than eighty-one degrees, the ice preventing.

M. Tremont, an ingenious young Italian, who was lately here, gave me a little spyglass of his making, upon Père Boscovich's principles, the ocular lens being a composition of different glasses instead of the objective. It is indeed a very good one.

Sir John Pringle is returned from Scotland, better in health than heretofore. He always speaks of you

* See these experiments in Vol. V. p. 435. A copy of M. Dubourg's French translation of Dr. Franklin's writings, above alluded to, was sent by him to Harvard College. The following complimentary vote of the Corporation was returned.

"At a meeting of the Corporation of Harvard College, May 31st, 1774. "Dr. Franklin having presented to our Library a French Translation of his Philosophical Writings in two volumes quarto, a copy which we receive with particular pleasure, as it is a testimony of the sense foreigners have of the merit of these writings, which must do honor to the country that gave him birth, as well as to every literary Society he is related to; Voted, that the thanks of this Board be given to Dr. Franklin for this valuable present, and that Dr. Cooper do transmit him a copy of this vote. NATHANIEL APPLETON, "Senior Fellow of the Corporation."