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Le Roy will, I suppose, now confute this translator, for I have just seen a letter of his to Mr. Magelhaens, thanking him for sending so excellent an electrical machine to France, (it is one of the plate ones,) which he has improved so as to produce the positive and negative electricities separately or together at the same time. "De façon," says he, "qu'on peut faire toutes les expériences possibles sur l'une ou l'autre, de ces deux électricités. Enfin on étoit si eloigné de connoître les phénomènes de ces deux électricités ici, faute de machines commodes de les demontrer, que beaucoup des gens ont été étonnés de voir avec quelle évidence ils établissent la distinction de ces deux électricités," &c. This letter is of the 5th instant.

My best wishes attend you and yours. I am ever, with great respect, my dear friend,

Yours most sincerely,

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B. FRANKLIN.

FROM JOSEPH PRIESTLEY TO B. FRANKLIN

Experiments on Air.

Leeds, 3 June, 1772.

DEAR SIR,

You make me very happy by the near prospect of seeing you and Sir John Pringle at Leeds. I shall be entirely at liberty to receive you, and I hope you will contrive to stay as long as possible in this town and neighbourhood. I thank you for the Native of New England. I had casually seen the same paper, and

*

Probably alluding to a piece entitled Toleration in Old Englana and New England, and signed A NEW ENGLAND MAN. This piece was first printed in "The London Packet," June 3d, 1772. See Vol. II. p 112. EDITOR.

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was particularly struck with it, without having any suspicion of Poor Richard being the author of it. I am obliged to you for your advice with respect to the Dedication, and shall comply with it; but some other alterations, besides what you noted, must be made in it, if it be addressed to Lord Sandwich only.

I am intent upon the prosecution of my experiments on air, and since I wrote to you have observed several remarkable appearances. That very extraordinary kind of air, which Dr. Hales got from Walton pyrites, and which I had despaired of procuring, I get from all the metals I have yet tried, by means of spirit of nitre. It is quite transparent; but a mixture of it and common air is red for a considerable time, in which the whole quantity is greatly reduced in bulk. A mixture of this and fixed air is not turbid. This air alone is reduced above one half by a mixture of iron filings and brimstone standing in it, whereas common air is diminished. only about one fifth in the same process.

When I have the pleasure of seeing you, I shall acquaint you with some other remarkable properties of this new kind of air. In the mean time you will do me a very important service by procuring for me, and bringing along with you, a little of highly concentrated marine acid. There is none to be got here; and, using a weaker sort in the solution of gold, I was obliged to apply a considerable degree of heat, the consequence of which was, that, the acid menstruum suddenly boiling, my hands, face clothes, and the walls of the room have been great sufferers by it, as, I am afraid, I shall be able to show you. A pennyweight of gold, which I had bought for the purpose, was also lost.

As a reward for this damage, I preserved about three ounce measures of air extracted from gold, which I believe was never seen before, and have the prodigious

satisfaction of finding, that it has the very same properties with that which is produced from copper. If I had studied Poor Richard in time, I should not have indulged myself in these expenses; but bad habits are not easily corrected. If, however, the passion be not kept up by considerable success, frugality and an attention to a growing family will, at length, get the better of experimenting, and then I shall write nothing but Politics or Divinity, to furnish the Bishop of Llandaff with more quotations for his future invectives against the Dissenters.

The French translation of my "History of Electricity" I borrowed of Mr. Walsh; but, as it will be of some use to me in a future edition of my work, I think to purchase it. In the mean time Mr. Walsh will have no objection to your having it for what time you please, and I can give it to you when you are here.

I am surprised that the French electricians should not have been able to provide themselves with better machines. I am confident that plates will never answer so well as globes or cylinders. I am, with my respectful compliments to Sir John Pringle,

Dear Sir, yours sincerely,

JOSEPH PRIESTLEY. P. S. I wish you could bring Dr. Price with you.

FROM JOSEPH PRIESTLEY TO B. FRANKLIN.

Curious Experiments on Air, and Discoveries of various Properties.

Leeds, 1 July, 1772.

DEAR SIR,

I

presume that by this time you are arrived in London, and I am willing to take the first opportunity of

informing you, that I have never been so busy, or so successful in making experiments, as since I had the pleasure of seeing you at Leeds.

I have fully satisfied myself, that air, rendered in the highest degree noxious by breathing, is restored by sprigs of mint growing in it. You will probably remember the flourishing state in which you saw one of my plants. I put a mouse in the air, in which it was growing, on the Saturday after you went away, which was seven days after it was put in, and it continued in it five minutes without showing any sign of uneasiness, and was taken out quite strong and vigorous, when a mouse died after being not two seconds in a part of the same original quantity of air, which had stood in the same exposure without a plant in it. The same mouse, also, that lived so well in the restored air, was barely recoverable after being not more than one second in the other. I have also had another instance of a mouse living fourteen minutes without being at all hurt in little more than two ounce measures of another quantity of noxious air, in which a plant had grown.

I have completely ascertained the restoration of air, in which tallow or wax candles, spirit of wine, or brimstone matches, have burned out by the same means.

The nitrous air, which I showed you, I found to be an admirable test of air that is fit for breathing. It makes this air red and turbid, but no other that I have tried. I took air, in which a mouse had putrefied, which was in the highest degree noxious and fetid, and also a quantity of fixed air. The nitrous air, admitted to each of these kinds of air separately, made no sensible alteration in them; but, when they were mixed (which I discovered to make a wholesome air), the nitrous air male the mixture turbid and diminished the bulk of it, as in common air, though not in the same

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degree. A mouse put into this mixture lived five minutes without uneasiness, when, if it had been put into either of them separately a few minutes before, it would have died in a few seconds.

Air, that has passed through hot charcoal, has many, perhaps all the properties of air that has been diminished by other processes. It extinguishes flame, kills animals, and is not diminished or made turbid by a mixture of nitrous air.

But the observation, that pleases me more than any I ever made, is the diminution of air by the crystallization (I believe) of quicksilver and the nitrous acid. This effect both precedes and follows the generation of nitrous air from the same mixture. This I suspect to be the case with other crystallizations.

I have observed many other things, which I have not room to mention at present.

I am, with great respect, dear Sir,
Yours sincerely,

JOSEPH PRIESTLEY.

FROM JOHN WALSH TO B. FRANKLIN.*

Experiments for ascertaining the Electrical Properties of the Torpedo.

La Rochelle, 12 July, 1772.

DEAR SIR,

It is with particular satisfaction I make to you my first communication, that the effect of the Torpedo ap

* Mr. Walsh was the first person, who ascertained from a series of experiments, that the shock communicated by the species of ray-fish called the Torpedo, is the same as that derived from the Leyden jat when charged with electricity. He had received directions from Dr

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