Volume II Part 26 (1/2)

_To Dr Lining, at Charleston_

ON COLD PRODUCED BY EVAPORATION

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 engaged in on that account, have ht not to expect punctuality in others

But, being about to eland, I could not quit the continent without payingleave to introduce to your acquaintance a gentle and merit, Colonel Henry Bouquet, who does me the favour to present you this letter, and hom I am sure you will be ow, 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, ht be produced by evaporation 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 dipped in spirits of hich has been kept in the saree of heat or cold

The rees, and the quicker if, during the evaporation, you blow on the ball with bellows; a second wetting and blowing, when the et it lower than five or six degrees from where it naturally stood, which was at that ti placed in another so spirit, in such a manner that the vessel of water is surrounded with the spirit, and both placed under the receiver of an airpu, leaves such a degree of cold as to freeze the water, though the ther point

I know not how this phenoivesto heat and cold, which I have for some time entertained, but not yet reduced into any for common fire, as well as electrical, to be a fluid capable of perine 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 electric 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 through the whole to all the parts, as ood conductors, one heated, the other in its coht 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 equilibriuers with one hand, and a piece of wood of the sa both at the saed 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 becoive to a ood a conductor as ree 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, entering bodies in great quantity, first expands the their parts a little; afterward, by farther separating their parts, it renders solids fluid, and at length dissipates their parts in air Take this fluid froain; the first grows solid, the latter becoood conductors Thus, if you take, as I have done, a square bar of lead, four inches long and one inch thick, together with three pieces of wood planed to the same dimensions, and lay them on a smooth board, fixed so as not to be easily separated or moved, and pour into the cavity they form as much melted lead as will fill it, you will see the melted lead chill and become firm on the side next the leaden bar some time before it chills on the other three sides in contact with the wooden bars, though, before the lead was poured in, they ree of heat or coldness, as they had been exposed in the same room to the same air You will likewise observe, that the leaden bar, as it has cooled the melted lead more than the wooden bars have done, so it is itself more heated by the melted lead There is a certain quantity of this fluid, called fire, in every living hu in due proportion, keeps the parts of the flesh and blood at such a just distance from each other, as that the flesh and nerves are supple, and the blood fit for circulation If part of this due proportion of fire be conducted away, by means of a contact with other bodies, as air, water, or metals, the parts of our skin and flesh that coreeable, and give that sensation which we call cold; and if too much be conveyed away, the body stiffens, the blood ceases to flow, and death ensues On the other hand, if too much of this fluid be communicated to the flesh, the parts are separated too far, and pain ensues, as when they are separated by a pin or lancet The sensation that the separation by fire occasions we call heat or burning

My desk on which I norite, and the lock of my desk, are both exposed to the saree of heat or cold: yet if I lay my hand successively on the wood and on the metal, the latter feelsa better conductor, it more readily than the wood takes away and draws into itself the fire that was in ly, if I lay one hand part on the lock and part on the wood, and after it had laid on some time, I feel both parts with my other hand, I find the part that has been in contact with the lock very sensibly colder to the touch than the part that lay on the wood How a living animal obtains its quantity of this fluid, called fire, is a curious question I have shown that soer than others; and I have so body had so out of the air, or other bodies, the heat it wanted Thus row hot in the bent or hammered part But when I consider that air, in contact with the body, cools it; that the surrounding air is rather heated by its contact with the body; that every breath of cooler air drawn in carries off part of the body's heat when it passes out again; that, therefore, thereit, or otherwise the anirow cold; I have been rather inclined to think that the fluid _fire_, as well as the fluid _air_, is attracted by plants in their growth, and becomes consolidated with the other reat part of their substance; that, when they coested, and to suffer in the vessels a kind of fermentation, part of the fire, as well as part of the air, recovers its fluid, active state again, and diffuses itself in the body, digesting and separating it; that the fire, so reproduced by digestion and separation, continually leaving the body, its place is supplied by fresh quantities, arising from the continual separation; that whatever quickens the motion of the fluids in an animal quickens the separation, and reproduces more of the fire, as exercise; that all the fire e, existed in the only discovered when separating; that soreat deal of solid fire; and that, in short, what escapes and is dissipated in the burning of bodies, besides water and earth, is generally the air and fire that before ine that animal heat arises by or from a kind of fermentation in the juices of the body, in the sa for distillation, wherein there is a separation of the spirituous from the watery and earthy parts And it is remarkable, that the liquor in a distiller's vat, when in its best and highest state of ferree of heat with the human body: that is, about 94 or 96

Thus, as by a constant supply of fuel in a chimney you keep a warm room, so by a constant supply of food in the stomach you keep a warm body; only where little exercise is used the heat may possibly be conducted away too fast; in which case such ainst the effects of an immediate contact of the air, as are in themselves bad conductors of heat, and, consequently, prevent its being coh their substance to the air Hence what is called _warmth_ in wool, and its preference on that account to linen, wool not being so good a conductor; and hence all the natural coverings of animals to keep them warm are such as retain and confine the natural heat in the body by being bad conductors, such as wool, hair, feathers, and the silk by which the silkwor, thus considered, does not _ the too quick dissipation of the heat produced in his body, and so occasioning an accumulation

There is another curious question I will just venture to touch upon, viz, Whence arises the sudden extraordinary degree of cold, perceptible onsalt and snohere the coredients? 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 redient would do separately I suppose, with others, that cold is nothing more than the absence of heat or fire Now if the quantity of fire before contained or diffused in the snow and salt was expelled in the uniting of the two h the air or the vessel containing theh the air, it must warm the air, and a ther it, would discover the heat by the raising of the mercury, as it must and always does in waruess it would rather be driven off through the vessel, especially if the vessel bea better conductor than air; and so one should find the basin warrows cold, and even water, in which the vessel is sometimes placed for the experiment, freezes into hard ice on the basin Now I know not how to account for this, otherwise than by supposing that the coredients separately, and, like the lock co fire, and does accordingly attract it suddenly froers, or a thermometer put into it, from the basin that contains it, and from the water in contact with the outside of the basin; so that the fingers have the sensation of extre deprived ofpart of its fire drawn out of theits fire drawn into theit froh the basin, 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 dissolve at the sa

B FRANKLIN

_Peter Franklin, Newport, Rhode Island_

ON THE SALTNESS OF SEAWATER

London, May 7, 1760

It has, indeed, as you observe, been the opinion of soreat naturalists, that the sea is salt only from the dissolution of mineral or rock-salt which its waters happen to ranted that all water was originally fresh, of which we can have no proof I own I am inclined to a different opinion, and rather think all the water on this globe was originally salt, and that the fresh water we find in springs and rivers is the produce of distillation The sun raises the vapours from the sea, which fors and rivers are formed of that rain As to the rock-salt found inits saltness to the sea, it is itself drawn from the sea, and that, of course, the sea is now fresher than it was originally This is only another effect of nature's distillery, and ht be performed various ways

It is evident, from the quantities of seashells, and the bones and teeth of fishes found in high lands, that the sea has forher than it now is, and has fallen away froh lands, or they have been lower than they are, and were lifted up out of the water to their present height by sohty force, such as we still feel some remains of hole continents are moved by earthquakes In either case ithills, , and the fluid part drying away in a course of years, would leave the salt covering the botto afterward to be covered with earth fro through that earth Or, as we know from their effects that there are deep, fiery caverns under the earth, and even under the sea, if at any time the sea leaks into any of them, the fluid parts of the water h sorees and continual accretion, becoth be filled, and the volcano connected with it cease burning, assuch cavern, find e call a salt- the salt-mines at Northith ht up with him out of the mine

B FRANKLIN

_To Miss Stephenson_

SALT WATER RENDERED FRESH BY DISTILLATION--METHOD OF RELIEVING THIRST BY SEAWATER

Craven-street, August 10, 1761

We are to set out this week for Holland, where we ain before the coronation I could not go without taking leave of you by a line at least when I am so many letters in your debt