To John Lining9
Copy: Yale University Library; also draft (incomplete): American Philosophical Society1
New-York, April 14. 1757.
It is a long Time since I had the Pleasure of a Line from you. And indeed the Troubles of our Country, with the Hurry of Business, I have been engag’d in on that Account, have made me so bad a Correspondent, that I ought not to expect Punctuality in others.
But being just taking Passage for England, I could not leave the Continent,2 without paying my Respects to you, and at the same Time taking Leave to introduce to your Acquaintance a Gentleman of Learning and Merit, Col. Henry Bouquet,3 who does me the Favour to present you this Letter, and with whom I am sure you will be much pleased.
Mr. Professor Simpson of Glasgow, lately communicated to me some curious Experiments of a Physician of his Acquaintance, by which it appeared that an extraordinary Degree of Cold, even to Freezing, might be produced by Evaporation.4 I have not had Leisure to repeat and examine more than the first and easiest of them, viz. Wet the Ball of a Thermometer by a Feather dipt in Spirit of Wine, which has been kept in the same Room, and has of Course the same Degree of Heat or Cold. The Mercury sinks presently 3 or 4 Degrees, and the quicker if during the Evaporation you blow on the Ball with Bellows; a second Wetting and Blowing when the Mercury is down, carries it yet lower. I think I did not get it lower than 5 or 6 Degrees from where it naturally stood, which was at that time 60. But it is said, that a Vessel of Water being plac’d in another somewhat larger containing Spirit, in such a Manner that the Vessel of Water is surrounded with the Spirit, and both plac’d under the Receiver of an Air-pump, on Exhausting the Air, the Spirit evaporating leaves such a Degree of Cold as to freeze the Water, tho’ the Thermometer in the open Air stands many Degrees above the Freezing Point.
I know not how this Phenomenon is to be accounted for, but it gives me Occasion to mention some loose Notions relating to Heat and Cold, which I have for some Time entertain’d, but not yet reduc’d into any Form. Allowing common Fire as well as the Electrical, to be a Fluid, capable of permeating other Bodies, and seeking an Equilibrium, I imagine some Bodies are better fitted by Nature to be Conductors of that Fluid than others; and that generally those which are the best Conductors of the Electrical Fluid, are also the best Conductors of this; and e contra. Thus a Body which is a good Conductor of Fire readily receives it into its Substance, and conducts it thro’ the Whole to all the Parts; as Metals and Water do; and if two Bodies, both good Conductors, one heated, the other in its common State, are brought into Contact with each other, the Body which has most Fire, readily communicates of it to that which had least; and that which had least readily receives it, till an Equilibrium is produced. Thus, if you take a Dollar between your Fingers with one Hand, and a Piece of Wood of the same Dimensions with the other, and bring both at the same Time to the Flame of a Candle, you will find yourself obliged to drop the Dollar before you drop the Wood, because it conducts the Heat of the Candle sooner to your Flesh. Thus, if a Silver Teapot had a Handle of the same Metal, it would conduct the Heat from the Water to the Hand, and become too hot to be used; we therefore give to a Metal Teapot a Handle of Wood, which is not so good a Conductor as Metal. But a China or Stone Teapot being in some Degree of the Nature of Glass, which is not a good Conductor of Heat, may have a Handle of the same Stuff. Thus also a damp moist Air shall make a Man more sensible of Cold, or chill him more than a dry Air that is colder, because a moist Air is fitter to receive and conduct away the Heat of his Body. This Fluid entring Bodies in great Quantity, first expands them by separating their Parts a little, afterwards by farther separating their Parts, it renders solids fluid, and at length dissipates their Parts in Air. Take this Fluid from melted Lead, or from Water, the Parts cohere again, the first grows solid, the latter becomes Ice. And this is soonest done by the Means of good Conductors. Thus, if you take (as I have done) a square Bar of Lead, 4 Inches long, and 1 Inch thick, together with 3 Pieces of Wood planed to the same Dimensions, and lay them as in the Margin,
There is another curious Question I will just venture to touch upon, viz. Whence arises the sudden extraordinary Degree of Cold, perceptible on mixing some Chymical Liquors, and even on mixing Salt and Snow, where the Composition appears colder than the coldest of the Ingredients? I have never seen the chymical Mixtures made, but Salt and Snow I have often mixed myself, and am fully satisfied that the Composition feels much colder to the Touch, and lowers the Mercury in the Thermometer more than either Ingredient would do separately. I suppose with others, that Cold is nothing more than an Absence of Heat or Fire. Now if the Quantity of Fire before contain’d or diffus’d in the Snow and Salt, was expell’d in the Uniting of the two Matters, it must be driven away either thro’ the Air or the Vessel containing them. If it is driven off thro’ the Air, it must warm the Air, and a Thermometer held over the Mixture without touching it, would discover the Heat by the Rising of the Mercury, as it must and always does in warmer Air. This indeed I have not try’d; but I should guess it would rather be driven off thro’ the Vessel, especially if the Vessel be Metal, as being a better Conductor than Air, and so one should find the Bason warmer after such Mixture. But on the contrary the Vessel grows cold, and even Water in which the Vessel is sometimes plac’d for the Experiment, freezes into hard Ice on the Bason. Now I know not how to account for this otherwise than by supposing, that the Composition is a better Conductor of Fire than the Ingredients separately, and like the Lock compar’d with the Wood, has a stronger Power of Attracting Fire, and does accordingly attract it suddenly from the Fingers or a Thermometer put into it, from the Bason that contains it, and from the Water in contact with the Outside of the Bason, so that the Fingers have the Sensation of extream Cold, by being depriv’d of much of their natural Fire; the Thermometer sinks, by having part of its Fire drawn out of the Mercury; the Bason grows colder to the Touch, as by having its Fire drawn into the Mixture, it is become more capable of drawing and receiving it from the Hand; and thro’ the Bason the Water loses its Fire that kept it fluid, so it becomes Ice. One would expect, That from all this attracted Acquisition of Fire to the Composition, it should become warmer; and in fact, the Snow and Salt dissolves at the same Time into Water without freezing.8
I doubt whether in all this I have talked intelligibly; and indeed how should a Man do so, that does not himself clearly understand the Thing he talks of. This I confess to be my present Case. I intended to amuse you, but I fear I have done more, and tired you. Be so good as to excuse it, and believe me, with sincere Esteem and Respect, Sir, Your most obedient humble Servant
Endorsed in Stiles’ hand: Copy Mr. Franklin’s Letter to Dr. Lining. Apr. 14. 17579
9. On Dr. John Lining of Charleston, S.C., see above, V, 521 n.
1. The copy, in BF’s hand, is the one he sent to Ezra Stiles, June 2, 1757; see below, p. 233. Of the draft only the last leaf survives, containing less than a fifth of the text. The letter is printed as Letter XXVI in Exper. and Obser., 1769 edit., pp. 341–9. Significant differences are noted.
2. Exper. and Obser. reads: “But being about to embark for England, I could not quit the Continent.”
3. See the two letters immediately above.
4. Robert Simson (1687–1768), professor of mathematics at the University of Glasgow. His letter to BF has not been found, but the “curious Experiments” described were those of Dr. William Cullen (1710–1790), who became professor of medicine at Glasgow in 1751 and professor of chemistry at Edinburgh in 1755. His “Essay on the Cold Produced by Evaporating Fluids” was published in Edinburgh Philosophical and Literary Essays, II (1755), 145–75. Later Cullen became professor of physic at Edinburgh and was for years the mainstay of the Medical School there. BF met Cullen in Edinburgh in 1759. DNB under both Simson and Cullen; John Thomson, An Account of the Life, Lectures, and Writings of William Cullen, M.D. (Edinburgh and London, 1859), I, 53–7, 139–40.
5. Exper. and Obser. omits “square.”
6. For “that … Fire,” Exper. and Obser. reads: “That some bodies are almost wholly solid fire.”
7. For “shows by the Thermometer,” Exper. and Obser. reads: “has.”
8. Exper. and Obser. ends the letter here.
9. The draft is endorsed in BF’s hand: “Letter to Dr. Lining on Fire &c.”