Faraday to Jean-Baptiste-André Dumas   14 December 1844

Royal Institution London | 14, Dec 1844

Most kind & dear friend

Your letter¹ has touched me deeply, for it brings with it a flood of that which I value more than honors, even though they be national (as those you refer to truly are:) it brings me kindness & affection and that from the men of whom as regards both powers of the mind & thoughts of the heart I know of none who rank higher. Of yourself, I had seen enough in personal intercourse & by your letters to make me trust I had a share in the latter: and of M Arago I had heard enough to make me think how happily his friends must be joined in thought with him: but I did not feel that circumstances had given me any reason to suppose that I was more than formally known to him. For, my dear friend, however well he may have thought of my scientific endeavours or however high such may rise in any individual it does not follow that honor, probity, good feeling & the qualities of the heart should rise with them. But now his acts make me think that M Arago looks a little beyond the limit which I had placed between myself & him & across which I did not feel emboldened to pass: and the character of friend in which he has always appeared to me will now be exalted in my mind by a feeling which I durst not before attach to it. I have not many friends in the world (by friend I mean one at thoughts of whom the heart rejoices) probably because I go very little into the world; but now I shall be bold to put M Arago in the number.

If I understand your letter rightly you wish me to send you an abstract of my late & present experiments on the condensation & solidification of bodies usually gaseous² and this I do with very great pleasure, though I have not succeeded yet in my desire, which was to condense Hydrogen oxygen & Nitrogen & to see if hydrogen or nitrogen were metals or what they were: but now you must act for me[.] Such an honor as that you refer to, comes with so much more beauty & glory when it is conferred by the dignified, deliberate, & spontaneous act of the body, that if the presentation of my results to the Academy were to appear as if done with a consciousness of their thoughts, or as an asking on my part for such honor, I should feel ashamed of myself; - both for appearing to think I was worthy of it; or for presuming in the least degree to think that such a body in such an act could or ought to be moved by such a motive; or turned by any thing from their great purpose of approving that which was excellent. The honor you have already given me by putting me second is more than I deserve. However in all this I leave myself in your hands and for you to present my results (if when you see them you think fit) is a pleasure so great, that if not before the election, perhaps it may happen afterwards.

As for the results they are soon told, though I have been more than six months engaged in them. You remember M. G. Aime's³ experiments (Ann de Chemie 1843. VIII.)⁴ in the depths of the Sea where great pressure was put on certain gases: the results could not be looked at in the compressed state & they were made at common temperatures. You remember also M Cagniard de la Tours experiments on ether⁵ &c in which he shews that at a certain temperature the liquid becomes vapour without increase of bulk. Now if this disliquifying point⁶ is, as it appears to be, lower with the more vaporous & lighter bodies existing as gases then there can be little or no hopes of liquifying such substances as hydrogen oxygen or nitrogen &c at any pressure whilst retained at common temperatures; for their disliquifying points are almost certainly below common or even considerably depressed temperatures. Here therefore you have the key to my course of proceedings. I first sought for a very low temperature and for this purpose used Thilorier's⁷ beautiful bath of solid Carbonic acid & ether⁸ - but then I worked with this bath under the vacuum of the air pump keeping up a continual exhaustion the while, & reduced the temperature so low that the carbonic acid of the bath was not more volatile than water at the temperature of 30˚C; for the barometer of the air pump was 28.2 inches - the external barometer being 29.4 inches. This being done I next succeeded in fitting and adjusting together by caps & stopcocks small brass & glass tubes so that I could by means of two successive pumps force in & compress different gases up to a pressure of 40 atmospheres, & at the same time submit them to the intense cold in the air pump and look at & examine the effects. As I expected the cold produced many results which the pressure never could have given and especially in the solidification of bodies usually gaseous. These I will now hastily give you[.]

You remember the gases formerly condensed. You I believe added to their number Arseniuretted hydrogen⁹. It is very probable that M. Aime may have condensed olifiant gas & fluosilicon down below; - if at least water was kept from the latter. For myself the following are my present results Olifiant gas is condensed into a beautiful clear colourless transparent fluid - but did not solidify - it dissolves resinous bituminous & oily bodies - Hydrosodic acid may be obtained pure either in the liquid or the solid state - solid hydrosodic acid is very clear colourless & transparent with generally a few fissures running through it looking very much like ice - Hydrobromic acid may also be obtained either as a limpid colourless liquid or as a clear transparent solid body - these two acids require careful pressuration & rectification by distillation in closed vessels & under pressure before they can be obtained in the pure & colourless state. - Fluosilicon was condensed into the liquid state but at the very lowest temperature was exceedingly fluid & thin like hot ether; it then indicated a pressure of about 9 atmospheres & showed no sign of solidification - it was clear & colourless. - Fluoboron & Phosphoretted hydrogen have both presented me with results of condensation but you know how needful it is for a philosopher to repeat his experiments again & again that he may be quite firm on his ground & I am now waiting for Carbonic acid to repeat these very experiments - Muriatic acid easily liquefies at less than 1 atmosphere of pressure but does not solidify[.] Sulphurous acid of course freezes[.] Sulphuretted hydrogen becomes a solid and then appears as a white crystalline translucent mass looking rather like congealed nitrate of ammonia or camphor than like congealed water - Carbonic acid when thus rendered solid from the fluid state without being dispersed into snow is a very beautiful substance clear as crystal so that I have at times been in doubt whether the tube was full or empty of it & have to melt it so that by the joint pressure of liquid & solid I might know the solid was there. The solid Carbonic acid has a pressure of 6 atmospheres so that we easily perceive how liquid C.A. becomes solid when let out into the air - Euchlorine is a beautiful orange red crystalline body very brittle & presenting no signs of explosive power in that state - Nitrous oxide. This gas you will remember I condensed formerly. I see by the Journals that lately M Natterer¹⁰ has repeated the experiment using a pump for the compression & has obtained the liquid in open air¹¹. I also have condensed it into a liquid by my pumps but I have also rendered it solid by the cold bath[.] It was then a beautiful clear crystalline colourless body but in that state its vapour had not the pressure of 1 atmosphere and this result accorded with other experiments in which having opened a vessel containing the fluid a part evaporated cooling the rest but not solidifying it. The cold produced by this evaporation is very great & this was shewn by putting the tube & its contents into a bath of solid carbonic acid & ether in the air; this bath which so instantly freezes mercury seemed like a vessel of hot fluid to the former & instantly made its contents boil violently[.] Hence I propose to use fluid nitrous oxide in further experiments on hydrogen oxygen & nitrogen for by placing a nitrous oxide bath in an air pump & exhausting the air & gas we may sink as far below the Carbonic acid bath in vacuo as that is below the same bath in air - Cyanogen freezes as Bunsen¹² has shown already¹³ - Ammonia perfectly pure & dry may be obtained as a solid white translucent crystalline substance heavier than the fluid ammonia & having very little smell because of the low pressure of its vapour at that temperature[.] Arsenuretted hydrogen and Chlorine would not change their fluid for the solid state - Alcohol became thick like cold oil but would not crystallize neither would caoutchoucene nor camphine nor oil of turpentine but they were thickened - Nitric oxide & carbonic oxide shewed no signs of liquefaction at the lowest temperature & a pressure from 30 to 35 atmospheres[.]

I have many other results as to the pressures of the vapours of these different bodies at different temperatures and also as to the temperatures of the liquifying points of the solid mentioned but you know how often such results should be repeated to afford any useful degree of certainty - this it is which has kept back the announcement of the above conclusion for some time & I am still repeating before I am willing to publish the numbers. - And now my dear friend I send this to you & if you should not think fit to communicate it at once I shall still think I may consider the research as taking date from this time for your knowledge & judgement of it are to me as valuable as that of half the world.

Will you thank M.M. Becquerel & Chevreul as they ought to be thanked for all their kindness on my behalf. I can only say as I said before that I esteem their thoughts for me as of far more value than what these thoughts & exertions may produce as to the honor; though none can esteem that more highly as an honor than I should. With profound respects to Madame Dumas & earnest feelings of grateful affection to Yourself.

I am Most Truly Yours | M. Faraday