Johann Gottlob Leidenfrost

27th November 1715 -2nd December 1794 Duisburg

&

The Leidenfrost Phenomenon

The Leidenfrost Phenomenon with water.

This site is to make available the appropriate pages of Prof. Dr.

Leidenfrost’s work , De Aquae Communis Nonnullis Qualitatibus Tractatus

(1756), and also the relevant pages in translation relating to the Leidenfrost

Phenomenon.

Also here is an account of this author’s discovery of the emission of

electrically charged solute particles from drops undergoing Leidenfrost

boiling, plus some more recent photographs of water drops on a metal

surface at about 800 degrees C.

Dr. Colin Pounder

June 21st 2008.

Here translated into English for the first time

By Carolyn S.E. Wares from the 1756 Latin edition

Published at Duisburg on the Rhine by Herman Ovenius.

Copyright, 1964, by Carolyn S. E. Wares.

Copyright,2006, Carolyn Sue Embach, All Rights Reserved.

ON THE FIXATION OF WATER IN

DIVERSE FIRE

XV

1. An iron spoon of any size, well polished within and free from rust and dirt, is

heated over glowing coals until it glows with light. To this glowing spoon, removed

from the coals. send through a glass tube of suitable length, of which the other end

finishes in a very narrow capillary canal, one drop of very pure distilled water.

However the water which I have used was certainly as pure as can be made through

distillation. It dissolved whole nitrous crystals of mercury without color, nor did

mercury precipitate in any way, nor was it disturbed by alkalis. Moreover the water

which I mostly used runs into a protected pool, now and for 6 and some odd years. No

disturbance was noticed in all this time. Even with ordinary non-distilled water one is

allowed to assume a nearly similar event. In any case such a tube as I have just

described is right to use so that one drop always equal to another falls from the small

opening, nor does varying in the magnitude of drops make a difference in the

experiment. This drop which first fell upon the glowing iron is divided into a few little

globes, which nevertheless after a little while are collected in one great globe again. At

the instant when the drop touches the glowing iron, it is spherical. It does not adhere to

the spoon, as water is accustomed to do, which touches colder iron. Nevertheless in the

first moment of contact the glowing iron around the drop is black, indeed very black in

a space which is greater, the brighter the iron, as if the matter of light and fire from the

glowing iron suddenly was snatched into the water.

2. If then the spoon remains motionless, this water globule will lie quiet and without any

visible motion, without any bubbling, very clear like a crystalline globe, always spherical,

adhering nowhere to the spoon, but touching it in one point. However, although motion

is not visible in the pure drop, nevertheless it delights in a very swift motion of turning,

which is seen when a small colored speck, for example some black carbon, adheres to

the drop. For this is turned around the drop with a wonderful velocity, and it shows the

same sight as the drop of silver upon a little tub, which as long as it is polluted with

particles of litharge shows its own gyration by a most rapid circular motion of these,

until deeply cleansed from these it emits most beautifully the customary splendor. For

if Astronomy concludes correctly from the motion of the spots of the sun alone that

gyration of the sun around the axis, it is permitted so also to Chemistry to form a

similar conclusion from similar phenomena. Moreover, however, this drop only

evaporates very slowly. For if you turn to a pendulum indicating seconds with its

oscillations, at least 34 or 35 seconds, that is it runs a little over half a minute of an hour

before the whole drop disappears. Which at last exceedingly diminished so that it can

hardly any more be seen, with an audible crack, which with the ears one easily hears, it

finishes its existence, and in the spoon it leaves a small particle of earth.

3. While these things are done, the glowing spoon ceases to glow and becomes cooler.

Therefore as soon as the first drop disappears, send another drop similar to the first

through the same glass tube to that same spoon, which

with similar phenomena will disappear in 9 or 10 seconds. But there is this difference;

this other drop in this case is divided into more globules than the first. which return

into one globe with more difficulty, but they are moved from here to there and as if

dancing they produce a whistle with their motion in the spoon.

4. Meantime while the iron is cooled more, after the second drop has evaporated, then

let go a third, which, with a great motion of globules greater certainly than can be called

boiling, it will disappear within the space of three seconds. I observed nothing

remaining of solid, earthy matter in the second and third drops, as from the first drop

unless there was a manifest impurity in the spoon.

5. If then you put in the fourth drop with the same precautions, this is no longer rolled

into a globe, but adheres to the spoon and makes a damp spot in it and with a whistle

surges into a true motion of boiling, and thus foaming into vapors it will depart very

swiftly inside the space of one second or even swifter, and leaves nothing which is in

any way sensible of earth or of solid matter.

6. If after this you send down successively the fifth, sixth, seventh, and more drops to

the same spoon now cooled enough so that it can be touched with the fingers with no

harm, it will be evident to the eyes that because the spoon is cooler, the drop falling

imparts a greater moist spot to the spoon, and adheres to it a longer time before it is

evaporated.

7. If in the place of one drop you put in the spoon glowing well several drops, for

example six seven, eight, ten, it also makes a globe, but not perfect, the top depressed,

nevertheless very transparent. And not less than for one drop slowly expiring without

any boiling motion, thus so that some 10 drops stand through two and more minutes in

the fire. And they leave a portion of earth, especially if the spoon is left over the fire, so

that it doesn't cool too fast.

8. In the same way I compared a deep orichalch phial, the bottom segment of which

was spherical, the inside polished. When heated until it glowed, over burning coals, it

affected the drops of water in a similar manner, as had the iron spoon.

1), If an iron or copper vase is not pure, but is mixed with iron rust, the experiment

either does not succeed or not accurately, because the verdigris and rust impedes the

attachment of the water, as will be seen. If this vase is not of pure enough metal, if it is

heated red hot, after a great quantity of water (for example 10 drops and more) is

poured in at one time, all impurity is rapidly rubbed off by the motion of this water, so

that afterward the experiment can be undertaken without disturbance.

10. A little piece of ice is swiftly dissolved on glowing iron, and then it shows the

same phenomena as does simple water.

XVI

From this observation various things are understood. First, it is certain that fire brings

about the volatility of water, but not by boiling waters. For at first the abundance of

vapor increases with the degrees of heat until we come to a certain point, namely, to

that at which water boils. For when the heat increases more, beyond the point at which

water is accustomed to boil, the drops of water stand there for a longer time, or, what is

the same thing, they evaporate more slowly there. If then the fire is increased more, the

water is exhaled much less, and the hotter the iron is and the closer to the fire, so longer

do the drops adhere to it. That is, it is evaporated slower so that finally in great heat,

such as that of glowing iron, it may be made attached a long time, at least through 34

seconds, and its small part supports for a long while the power of a high heat. Nor do I

doubt, if in the experiment a great mass of iron of notable thickness, which therefore

does not emit heat so swiftly, is used, then, sufficiently great quantities of water can

assume a greater attachment in that same way as this. However, there is no opportunity

to try this with large masses. In the second place it appears that the degree of fire at

which the water is most of all evaporated is that at which it boils. Third it is manifest

that the fire protects the immediate contact of bodies, because the water does not

dampen the fiery iron, nor adhere to it. Whence the idea that the drop of water attracts a

great part of the fire out from the surface of the glowing iron and it releases the iron

from brilliance to motion. Fourth the very hot water endures without any boiling

motion. Wherefore it is necessary that at the instant of time in which a drop falls upon

the burning iron, all enclosed air is suddenly expelled. Or, what is more probable, the

air in such heat is fixed and loses a part of its elasticity. From this, in such a fire the

water droplet is left most clear on top, although its transparency is disturbed on account

of the many bubbles in the motion of boiling. Fifth, it is correctly concluded from the

perfect spherical figure of the droplet and from its whirling motion that the mutual

adhesion of the water particles among themselves is greatly increased in such a fire so

that in truth the cohesion of water thus is made greater in heat than in cold. But really

thus the sixth of these observations suggests that water is changed into earth by a large

fire, because always after the complete evaporation of the drop some terrestrial matter

remains in the heated vessel. This has not escaped the notice of the distinguished

investigation according to the warning of Boerhaave. For into such fire because of the

very light atmosphere all the dust from the surrounding air easily flies together, and it

can enter these hanging drops, unless other circumstances advocate the contrary, a

subject which we will not discuss.

XVII

In order to avoid all deceit, the experiment is varied:

1. If you loose a drop of moderately distilled spirit of wine from the same glass tube

onto an iron spoon glowing with light, this also is altered into a similar crystal globe as

soon as it touches the surface of the iron. And in the same way, provided chat it is kept

from the name of coals or a lamp which happens to be there, even if it remains in the

strongest heat of the glowing iron, nevertheless it does not seize the flame (i.e. does not

catch fire). Rather in all these things it is similar to water; it holds itself and stands fixed

around 30 seconds or more in this extreme heat. Finally it gradually leaps apart with a

small noise, and leaves a small piece of dry earth, which is burned tip a little after by the

heat of the iron. And the likeness of carbon or soot glows for a short time, then it splits

into white ashes.

2 While the spoon is held over the burning coals the drop of spirit of wine falling takes

up t1he flame easily, because it attracts it from the coals, and then it holds it in the

bottom of the spoon (i.e. catches fire falling through the flames into the spoon and then

continues to burn in the spoon). This can be prevented if at the moment at which the

drop is let loose, you remove the iron from the coals, or in some other way cover the

flame of the coals. However, when once the flame takes hold, it does not stop burning

until all the true spirit has been consumed, because it is done quickly in such a small

drop. However in the moistness from this spirit which remains in the bottom of the

spoon after the extinction of the flame. the resemblance of simple water is fixed in a

long enough interval of time. Afterward it flies into several pieces with a noise and

vanishes.

3. However when I have very carefully repeatedly distilled this true alcohol or spirit of

wine, in very tall glass jars. I put one drop into the glowing vase, and I set it afire with

the flame of a small piece of paper moved close with the hand. This alcohol burns up

swiftly in deep (lam.es, and no vestige of a water residue remains. Truly if the same

alcohol is protected from the flame, it has the appearance of common water and for a

long time the clear globe resisted the actions of the fire. If 8, 10, or several drops are

dropped into such a spoon, they conduct themselves similarly, but then they can with

difficulty be protected from the flame.

XVIII

I do not understand the spirit of wine in these phenomena. Why does a drop of it not

take hold of the flame spontaneously in a very hot iron spoon and in a very warm

atmosphere, when nevertheless it is inflamed easily from another burning body? In

itself it is clear that the weakness alone of the air is not at fault, because in that same

atmosphere flame persists, if this has been excited before with another flame. I learn

however from this phenomenon that great heat does not destroy spirit of wine, nor does

it change into its parts, unless the flame approaches. For according to others the spirit

through flame can be changed into water, as can be read in Boerhaave's Chemiae.

Wherefore it is no wonder that the spirit of wine can be burned from the steaming

aeolipile, and therefore it is not rightly concluded from the spirit of wine to water,

which I pointed out previously. contrary to Wolf (Para. VII). However many drops of

spirit of wine I have burned up thus on burning iron without inflammation, always a

small portion of earth remains. But this little piece contains fixed phlogiston. Wherefore

at first it wholly exhales liquid, the appearance of soot or carbon springs forth for a

moment, then it changes into white ashes. When on the other hand I investigated in a

similar manner a drop of pure water, a portion of earth remained, which was not

burned. Therefore it contained no phlogiston. However, I confess, several times

(although rarely) in drops of water that I used a small portion of earth remained

glowing, perhaps a little dust of the wood coals over which the iron vessel was held

having gotten into the water, which is able to appear after a quick movement. Perhaps

nevertheless another cause exists which I do not know, therefore I conclude nothing

from this phenomenon. I am able to do so if the next experiment is performed.

XIX

I show a new method by which the most perfect goodness of alcoholic wine can be

determined.

The learned men know that such a mark of character of great goodness is to be desired

in alcohol: that which in no way is affected by heat is also thought to be of the greatest

use in chemical solutions. That common method which the medicine vendors use for

lighting ashes with wine spirits works upon the said defects so that the deed does not

appear to be a confutation. However, the brilliant Parisienne chemist, Gothofred the

younger, describes a praiseworthy method for the whole thing in a writing for the

Academic Royale Parisienne in 1718, in which the spirit of wine is evaluated by measur-

ing the quantity of superfluous water, burning it (of course) in a narrow cylindrical

vessel placed in cold water, for after the final fire the water left in a cylindrical vessel

may be reduced for measurement more easily than in any other. Nevertheless not even

with this very accurate proportion is it determined, although granted that in common

practice his method suffices for the most part. For burning spirit of wine heats the water

mixed in it, and by this same heat the greater part of it diminishes into exhalation.

Gothofred himself in his other calculations in his proposed commentary thought that

very pure alcohol is half part water but for my part I do not think so. Because if I held

such alcohol in a torch the flame burns very slowly and from its vapor water can be

collected. For alcohol, while it is burned, is not made pure, but truly is destroyed and is

dissolved into its primary ingredients of mixture water and pure phlogiston. Therefore

water is not drawn from the spirit through flame, but the whole spirit is changed and

converted into water, as I have said (XVIII). Similarly compared is another thing from

his thesis: when quicklime begins to increase in the distilling spirit, demonstrated over

abundantly by its watery proportion, so quicklime purifies in the same way the spirit of

wine for a certain portion but destroys the greater portion. Therefore, so that we might

be certain that nothing in the spirit of wine clings to excess water, it is necessary to

arrange the thing so that at the same time that the spirit flies off the water is fixed and

impeded in its evaporation.

It is so done with a degree of heat which has alighted glowing iron. For if in the sprit

of wine a little water is mixed, this after the conflagration of the first is completed will

cling or is moved long and evidently enough so that it can be seen under the form of

little clear globes in the glowing spoon. So the pure spirit will be totally consumed so

that no liquid remains. From this you are certain that the spirit of wine is pure alcohol.

A drop of it dropped upon a glowing iron vessel must catch fire, for if after the flame is

spent nothing remains of water. that is the best spirit nor is it able to hold any other im-

purity. And such a spirit in the Reaumur thermometer rising encheiresin more easily for

giving judgment on the solutions of bodies makes the decision more certain.

XX

Similarly it happens in the same way with other and greater spirituous compositions

in the described liquors. If a drop of spirit of sal ammoniac for example prepared with

the spirit of wine is placed on a burning iron vessel in some way the first outside is

covered. through itself probably. It is not burned. but the large globe makes much foam

as if supported by tenacious bubbles and it exceeds the mass of the original drop in the

vicinity of some hundred each. When, however, this drop is set afire by a flame from a

flap of paper moved towards it. it burns as does the spirit of wine. After the last flame it

leaves a very clear drop of water fixed for a long time in the fire. But if the spirit of sal

ammoniac was prepared with urine and quicklime and water in a manner similar to

that described above, this never would take fire, but nevertheless foamed and formed

large bubbles, which disappeared after a while. It left a particle of water resting in the

hot vessel for a long time. In several other saline liquids I tried similar things, and with

few exceptions I saw the same phenomena, in the reckoning of which I will not be long,

because nothing now can be taught unless the known nature of simple water is

worthwhile to tell over.

XXI

If a drop of olive oil or some other fatty material is put into a very hot iron spoon it

never is rolled into a ball but widely adheres to the glowing iron as if it moistened it. If

it is put on a fire, in a moment of time (even without the external flame moved towards

it), it emits a flame and a great denseness, in which a little while after vanishing it leaves

copious black carbon in the hot vessel. Afterwards the image of a coal grows red, and

shows copious white embers (earth, in truth).

XXII

Water does not boil in the heat of glowing iron (XV. No. 1) or, what is the same thing,

the air leaving does not form bubbles. Both of these phenomena are possible either

because the air enclosed in water is not emitted, or (if it leaves) it flees insensibly. In the

first case it is necessary that air be fixed with water through fire in some violent way. In

the latter clearly the viscous-ness of water is such in that immense heat that it may not

require a bubble to rise. This also is true, as the following experience shows: if you

apply a cold body for example an iron staff to drops of water clinging without any

boiling motion in the fiery heat of glowing iron, or if you move a cold pebble towards it,

or even if you drop a water drop from the burning metal swiftly into another less

heated vessel, this quickly will boil, and with a boiling motion it vanishes swiftly into

the air. Whence it is established that water in great heat does not give up its dry air, but

retains it, since after this if the heat is diminished to the point that it can be let out, then

the air (clinging fixed with the water between the spaces of water in great heat) is

yielded.

XXIII

It follows that in the great heat of glowing iron not all the liquid but only the simple

water and the more fixed air is made so. For the spirit of wine swiftly disappears. On

the other hand the composition is inflammable, with a water portion left over (XVII).

The spirit of sal ammoniac equally with wine as with urine is expanded, inflated,

burned in its born essence, swiftly evaporated truly it discharges the more fixed water

contained in itself (XX). Olive oil needs to be protected from the flame. It is not changed

into a globe. It is attracted by the burning iron. It is very quickly changed into carbon

and ashes (XXI). But simple water alone, or that which does not cling in other liquids to

that water mixture, is rounded into a globe by the fire. It does not boil, it shines and for

such a paucity of matter clings fixed for a very long time. That same water there fixes

the enclosed air. For by water it is done, rather than by the vehemence of the fire, thence

it is clear, because the spirit of sal ammoniac in such a heat does not fix its contained air,

but permits its great expansion in very ample bubbles (XX). However, we conclude that

some air can be fixed because certain minerals, namely limestone then melted slabs next

a red cinnabar made from lead solidified a long time by fire then lime of antimony and

perhaps several similar ones, are made heavier by fire. We know absolutely that the

acquired weight from fixed air in the mixture can be determined through the Hales

experiments in Stat. Veget.

XXIV

Therefore, it has been sufficiently shown that water made volatile is increased with

degrees of heat until it comes to that point at which water boils and all very swiftly is

evaporated. Then truly if the heat excites more strongly I diminish the volatility of that

same water and increase its fixation by the added heat My hope now will be to answer

the same objection which can turn away that whole observation: obviously in a great

heat water tends to evaporate less, not because it is more fixed when in such heat but

because the expelled air does not require the atmosphere to be made lighter by the

exhalation of water particles lifting into the air. For there is a certain hydrostatic law: a

lighter body in a specific fluid. with a specific gravity, that has great inequality in the

proportion of the weight of the fluid to the ascending body ascends with greater

swiftness and force. Which thing can be seen by all: water in an atmosphere very

rarefied through heat ought to be evaporated less swiftly. But in truth it is evident to me

that this objection may be made of nothing in the case presented to evaluate. For (1) it

has been sufficiently demonstrated by distinguished Hamberger in Phys. 47'7, that the

exhalation of vapors in no way is done according to hydrostatic laws; (2) not yet have

we explored to what degree the atmosphere can be rarefied in the dry heat of glowing

iron; (3) in the same degree of fire mercury exhales, much heavier than water: (4) a

flame in this degree of fire can be aroused as we see, from the spirit of wine (XVII, No.

2) or from the spirit of sat ammoniac (XX) and from fat (XIX); where there is a flame,

however, it is necessary that sufficient air enter there; (5) it has been shown besides

(XIII) that water expires in the Boyle vacuum. And the learned Krafft observed

concerning the exhalations of water in free air and in vacuum, that there is hardly any

difference by reason of the quantity given in time. If therefore water in a place empty of

air and coolness exhales swiftly, I do not see why it could not ascend in equal swiftness

in free air if rather rate and heated. Which reasons contributed also dissolve the

opposing fact, so that by nothing can the verisimilitude be overcome. Nevertheless I dig

out as the whole deep basis for my argument another experiment I have investigated in

w1hich it is proven with certainty that a drop of water in the heat of glowing iron is

made more fixed not because of the atmosphere's failing but from the action of the fire.

Namely: either a little piece of lead or tin is put into an iron spoon glowing with light. It

quickly melts there and is spread. To this liquid metal of lead or tin carefully place a

drop of simple water through the glass tube described above so that it will not fall on

the convex surface of the metal. You will see this drop, hanging over the lead, dispersed

within 6 or 7 seconds. Which water if joined to the lead in the bottom of the iron spoon

and therefore laid down in the same atmosphere, it remained more than 34 seconds.

Also if one places another drop of water in that glowing vessel that is put so that it is

touched to the lead and so it will not hang over it, you will observe that as the surface of

the lead touches it, it flies away with a light motion, and it emits a noise as if the body

were dashed against something cold, and then more swiftly with many that if it does

not touch lead. Truly, very surely, no one knows the nature of these things. The heat of

the melted lead is much less than of glowing iron, wherefore the melted lead in respect

to the glowing iron is called a cold body. And above this cold or medium warm body, a

drop of water more swiftly exhales than if it is placed above burning iron, even though

the ratio of the atmosphere on both sides will be very perfectly equal. Therefore the

rarity of the atmosphere is not the cause of a greater fixation of water in a larger fire.

XXV

Therefore, I dare to propose this new thermometry to the physicists and learned men of

Chemistry, so that in measuring large degrees of heat it will be done equally certain as

with an ordinary thermometer in measuring lesser degrees. For it is known that until

now with those thermometers that we used, they indicated the degree of heat through

the degree of expansion, as much as the enclosed liquid undergoes. Formerly it was

established that all the liquid especially is incited into a motion of boiling and its heat is

expanded as swiftly as its degree of expansion and cannot be measured better.

From such a thing water and the spirit of wine boil on a small fire to the point that they

are not able to measure great degrees of heat. Just then the mercury was added to these,

for which often a greater fire is made before it will boil.

But in truth also mercury was despised and shunned for this too much, although from

its moderate expansion the heats of metals and melted salts we might be able to find

out. Therefore in its place learned Muschenbroek substituted another instrument, which

he called the pyrometer, whose construction is such that it is a solid body, such as an iron

rod, as long as its extended length shows in proper indication those degrees for various

degrees of heat. Since such a very ingenuous instrument is greatly used in physical

things and it can measure higher than all others, so the remaining kinds of

thermometers can be altogether tested by this thermometer, and also a convenient

degree scale is assigned to each. Where however a different degree must be measured

in vessels of burning or melted metals or salts, because of its structure the pyrometer is

applied with difficulty, in which cases I propose that a method more deserving be

devised.

XXVI

1. So let the vessel be hot iron and in addition let it have the degree of heat of boiling

water. Onto this a small drop of water put out boils and flies apart completely within

one second, or even faster. This lowest and first degree of heat is agreed upon and

measured.

2. It is established that with lead in a small trough, of which the greater the mass the

better, into which you pour a pure water drop of an equal magnitude as before, the

water will not boil, but is evaporated within 6 or 7 seconds.

3. The lead is excited by the heat so that it boils [the Germans say treiberi (drive, push)] ;

a drop of water then let loose will not fly apart until after 14 seconds or more.

4. The iron glows so that the whole is made alight: a drop of water in that will be

retained through 30 seconds.

5. If then you stir the iron in a furnace anemio with a big fire. a similar drop will he

fixed for 34 or 35 seconds. And in this degree of heat the iron remains until melted. For

if you detain for several hours a little iron vessel in this same high heat, so that it is

made near to melting, nevertheless the water will not be able to be made more fixed in

this unless at the most it is detained for 35 seconds.

6. If in this same iron vessel greatly heated and nearly melted you place one grain of

mercury, this flies apart within about 18 seconds. However, in those that I used, three

water drops were equal to two grains. Therefore two or three grains of mercury flew

apart within 12 seconds. Therefore it is in that degree of fire that the fixation of water is

to the fixation of mercury as 35 to 12 or as 3 to 1 in nearness. That is remarkable enough.

For with the first, as they say, nothing has been learned easily----to be able to make a

drop of very pure water without any mixture as in free air, with the action only of the

approaching fire, ever is made repeatedly more fixed than an equal quantity of

mercury.

And also with this second method many bodies of metals, earths, salts, and minerals

can be explored as to the degree of heat. For as in former times we measured from space

in the use of the thermometer, so here in time.

XXVII

However the fixation of water does not increase in infinity with the increasing heat,

For iron and copper as long as they burn fix water. Especially in fact they did not fix it

more, rather they changed that very drop of water brought together with them with

such violence into an elastic state, that such impetus was perhaps not to be found

elsewhere on the surface of the earth. Why do you wonder therefore that nature rejoices

in changes as the beautiful cycle of all things"! Certainly water at the degree of heat 32°

Fahrenheit (when it forms ice) is a solid and rigid form and is the same if that heat

increases It is dissolved not into a liquid form, but is changed into elastic vapors, and

grows in volatility to the degree 212 of the same thermometer, evidently when it boils.

And the fixation again increases with the degree of heat of glowing with-light iron.

Then again it was fixed with the iron at a great volatility and elasticity. Who however,

determines what was done formerly? Meanwhile from these which formerly I have

investigated, it is plain that in the scale of heats, a new fixed point ought to be put,

namely that of iron glowing-with-light. When therefore formerly none other than three

fixed and constant points of heat were known, namely of salt ice, of natural congelation,

and of boiling water, to these this fourth can be joined not unsuitably at the end. For

nothing more certainly helps scientists than to have a constant terminal, from which

you can measure others. This maxim of Archimedes : Give me the foot that I might

measure (da possim figore pendem).

XXVIII

Readers, you do not see me advising that which I indicated in the two preceding para-

graphs unless there are possible plans for a thermometer of its kind. How to put

together a table of many mineral bodies having their degrees of heat wasn't permitted

formerly among my other works, my leisure being small. Meanwhile I show that many

chemical phenomena proven by this method are able to be explained. Pure earth and

potter's earth evidently never acquire great heat. For a baked dish or similar earthen

vessel, heated for a long time and very shiny on a high fire in a furnace anemio, is made

very hot but nevertheless it is not much hotter than water in the boiling state. A drop of

water is fixed at a minimum when poured into such a melting pot, so that in a moment

of time it boils and is evaporated. Again that which I asserted in XXIV is confirmed by

such phenomena, namely that the fixation of water does not depend on the lightness of

the atmosphere for the most part. For if the baked dish melting pot and the iron vase

glow on that same fire, nevertheless a drop of water boiling in the former is evaporated

quickly. However, in the latter it is fixed for a long time. Next the reason is clear also

why pieces of earth cannot be found. They endure the fire whole if they are pure.

Obviously because they do not attract fire unless to a certain degree and that is why

such convenient instruments are made from these discovered minerals. A flint stone,

however, made very hot (as much as melted earth) fixed a drop of water much longer.

Moreover, several times it seems to me that concerning the experiment described above

on Glowing iron in various masses of heated iron (which by chance fortune had offered

as an instrument for economic items) the fixation of water did not succeed and I

marveled until I observed that these masses of iron had been spread over scores. For

with those separated with a hammer, the undertaking soon succeeded. Wherefore

scores of iron with common potter's earth and also with simple water assumed the same

degree of heat, not greater. Silver has a melting heat less than that of burning iron, but

never accurately determined. Alkaline salt glowing but not yet melted into a liquid will

resolve distilled water, wherefore from these things and through this method nothing

can be explained. But as soon as they are melted into a liquid, they make a drop of

water dropped in very elastic and nearly give the impression of melted copper.

Wherefore it follows that this salt is made very hot in a state of fusion, and it is clear

from these things why the flowing motion of the said chemicals is seen : because it is

obvious that they incite an immense fire in a brief period of time and they pass beyond

extreme so that even metals are not able to dissolve because of another reason than

maximum heat alone. Concerning boiling oil perhaps an exception must beset down

from the general rule. since they drive off with great impetus water poured onto them.

Whence nevertheless it is not probable that it has same degree of heat as melted copper.

About these things and several others which I tried by this method, I am now (when it

is permitted to write about these things) more certain than at that time. For more than

any other thing it seems probable that the magnitude of the water drops could not

always have been very perfectly equal.

XXIX

And also, while I might occupy myself more strongly with the phenomena in these

descriptions of water in fire, more often I tried to find out also whether water in this

state was impeded in its evaporation by fire according to the Amontonian rule. The

truth remains that even though water has been more fixed nevertheless it stays at the

same temperature. Easily one sees (no matter who) that through the thermometer used

it can be determined when their masses and, the proximity of the very hot metal will

not permit their application when compared with a few water drops which have been

tried. Nor have I described all of the methods which someone ingenious has supplied so

that I might make use of these toward one goal. I tell only about those which succeeded.

It is known that mercury cooked in water does not fly apart, even if a very strong fire is

applied, unless after the water touching it has evaporated. When therefore I mixed a

very small drop of quicksilver with a drop of water in a heated iron spoon, immediately

the mercury was seen in infinitely small balls distributed throughout the water, as if it

were dissolved. But afterwards when all the water was evaporated, the mercury

showed itself conspicuously in the spoon. and it flew apart following the water. When

therefore I showed formerly (XXVI, No. 6) that mercury in the heat of burning iron is-

more volatile than water, the same is true when it lies in water. It does not fly apart

before the evaporation of this. Water is seen in its greater fixation, nevertheless, not to

reach the degree of heat which is required so that mercury might be made volatile.

Therefore it is seen that water fixed on glowing iron is not any hotter than boiling

water, hence I conclude that the Amontonian rule probably remains true in this case

also.

Similarly, I poured drops having remained for some seconds in the heat of burning

iron from the iron spoon immediately into another vessel. And in that way with

repeated diligence I collected a great abundance of this water consumed from that, so

that I might inquire whether its sensible qualities had been altered. However I acquired

nothing by this operation unless very pure and clear water which was changed through

cold into ice as well as other water. It dissolved salts, it did not cling to oil. On the other

hand, if from that very hot ladle I poured such drops over various refines and other

bodies not easily soluble by water, I observed nothing that I could not expect from

boiling water. Whence again I conclude that the rule of learned Amontonius is probably

true, unless the water can be heated to a certain degree. However, my investigation is

debated for truth.

XXX

Before I continue to the following things, I ought to describe another kind of experiment

with common water upon a strong fire, about which at first I intended to investigate

whether a small portion of earth always remains manifest after a drop is evaporated in

a glowing iron spoon, and whether this earthy portion is born from the water itself or

whether it ought to be ascribed to other causes. I prepared for myself some little twisted

glass vessels, which had a circumference about the size of a chicken egg. Into one of

these washed and purified twisted vessels I accurately dropped out one ounce of very

pure distilled water. Into the mouth of the vessel I put another glass receptacle firmly

without mastic but nevertheless sized to the vessel. I made it firm without mastic so that

I might have less fear of the glass breaking. Thus, I set the so-constructed vessel in the

said furnace. Learned Teichmeyer gives a description of it in The Chemistries, and more

accurately B. Schultz in his posthumous work (Der Chemischen Bersuche, under the name

taken from the covers) where it is evident that the jar or iron or baked earth was placed

in a furnace anemio so that its aperture was not on the top but to the side of the furnace,

just as the domestic arch is usually placed in the furnace. Into this jar (which in my

furnace was fashioned from earth) I placed over a small portion of mud a twisted

vessel, and swiftly thus I made it firm so that it could not easily be dislodged or turned

around, Before I put the vessel into the furnace I had already made a fire, so that the jar

with the mud might be heated lightly. Also it had been turned correctly, set, and placed

immovably. I placed an iron vessel within the furnace. and I built up the fire as large as

I could so that within a brief time the pot and mud began to glow with light. And after a

brief time the twisted vessel glows and quivers. While the fire increases so swiftly, a

good quantity of water in the semblance of vapor is propelled with impetus into the

receptacle. where it is condensed at last into water again. Especially when the heat

comes to the degree when now the jar and mud and twisted vessel deeply and utterly

burn, then the water which is in the bottom of the twisted vessel jumps up and (because

of the described structure of the furnace one can observe it with the eyes) it is

evaporated gently and slowly, and at last is very fixed. Thus, so that on this fire about a

drachma through half an hour and more perhaps without any fume or vapor and

without any motion of boiling appearing. When then you build up the fire so that the

glass melts and seems to approach near to fusion, then the twisted vessel with a great

noise suddenly flies apart and is diffused into fragments. The water from the broken

vessel flowing over the glowing mud extinguishes it with a hiss. For truly if you take

the broken bottom of the vessel from the furnace and consider it with attention, you will

find a considerable portion of white earth.

XXXI

This experiment (XXX) succeeded correctly for me many times but it lacked success

several times for it is difficult to make the twisted vessel firm so that it stands

completely immovable in the furnace. For if it is agitated or moves even a little then

water clings to the bottom and to the sides of the burning vessel so that this is now

ruptured before it will have reached full heat and eludes the hope of the experimenter. 1

declined to omit this experiment, imperfect and not -repeated-enough as it is, until I

thought of investigating water by a better and more certain method in enclosed heated

vessels. Perhaps nevertheless it will give an opportunity to others, something for better

experimenting, for which reason I am pleased to add it. However it seems from this that

now I have probably taught further above (XXVI) how water committed to a larger fire

than of burning iron (for example fused copper or fused glass or beginning to be

melted) does not remain more fixed, but at most the elastic vapors are perhaps changed

into elastic air. For the same reason a new probability of the Amontonian law is clear:

that water obviously even if it is made more fixed in such a fire is nevertheless not

hotter. Because after the broken vessel extinguishes the underlying glowing sand with a

hiss. plainly besides the cold water (or lighter-heated) is able to hold itself, wherefore in

its nature and its heat it is not seen then to be much changed. There will be another

occasion, however. for speaking about the fixed part of earth remaining in the bottom.

XXXII

Now the reason for other changes is to show in what manner water, a body in a very

fluid state, is made firm. But for this end it is not yet applied to common experience.

From Aristotle, whose hypotheses I have shown today in two former experiments (III).

it is known that the possibility of the change of pure and simple water into a firm

visible body could be demonstrated. Another is Boyle_ in whom if the method is

correct, it is established that water is frequently changed by distillation into true fixed

earth, see his translation On the origins of form, experiment 9. Another is the marvelous

man Helmont, who in wondrous genius teaches that all solid parts of plants and

perhaps of animals as well are born from very pure water alone. He fed a tree of five

pounds with the nourishment of water alone to the weight of 169 pounds, see his tract

On the complexities and mist. Elements, section number 30.

XXXIII

Again the experiment of Boyle succeeds from no one's opinion, since it is perhaps

length of patience which one requires to carry out the annoying labour. Perhaps also

because on the authority of Boerhaave, who accuses it of fallacy, since he affirmed that

an earthy portion left by distillation in single atmospheric parts and an abundance of

terrestrial dust (which is always flying through the air of a chemist's laboratory and

adhering continuously to the vessels and to the liquids) must be its origin. With such an

objection the Boerhaavian idea has not very much probability, because such a portion of

terrestrial dust is required for explaining the Boyle phenomenon. It never flies in quiet

air, nevertheless if one wishes to investigate more deeply the truth or falsity of its

presence, I urge him to commence with the distillation not in large vessels but in small,

not in abundant water but in a small or medium portion of it, and not on a slow- or little

fire but on the biggest one on which vessels can be heated safely, in the method which I

have described (XXX). Do it thusly because of an enlarged fire a greater portion of earth

is anticipated and because a better atmosphere and more certain dust can be enclosed in

a small vase. For me certainly there always remained in the water so tested some white

earth, even much more abundant than it is permitted to deduce from the atmosphere.

XXIV

However the experiment of Helmont on the growth of plants through water alone

repeated infinitely always correctly succeeds, nevertheless better in one kind of plant

than in another. Learned Woodward opposed these experiences set down by Helmont

with great zeal in the English Philosophical 7"rarisactinns, year 1699. number 253, where

he purposes to demonstrate that the plants do not increase from water, but from the

portion of earth which usually always occupies the water. And which, if it stands in a

quiet way; gently is put aside in the form of living wood. For true vegetable material

has those living wooden stalks. And he shows in this that plants are nourished more

richly with water, with which principle they overflow, much more as it pleases a plant

to grow from such peculiar material (so created by God). In Woodward more modern

physics is applied to it, as is clear from the systems here and there. Nevertheless the

endeavor of the illustrious Eller outdoes it and he also shows in his communication to

the Royal Academy of Berlin that this green wood matter is least common with water,

but is sprung from a very subtle phlogiston mixture through the solar rays.

XXXV

It is also permitted to consider in passing that Woodward, while he denies Helmonta

will not show the state of the controversy and would combine the two propositions

with themselves, the one of Helmont, who asserts that the solid vegetable parts are born

from water. But in the same piece in which he describes the experiment on the willow,

he denies with abundance the Aristotelian dictum of transformation. If, therefore,

Woodward thinks that the earthy parts of vegetables also are born from the earthy

particles of water, it is just so with Helmont, because it is easily conceded that there is a

very small quantity of earth in all plants, this which before was concealed in the water.

Whence, however, is born the great long part of solids remaining in vegetables which

are not earth and also do not lie in such form in water? Therefore, Woodward did not

distinguish between a solid or a firm body in general, and a terrestrial body in

particular. On the contrary, if he had examined that same green material as he calls

earth and which he thinks is intermixed with all water, he could easily have seen that it

was not earth, but richness or fat. And also while he concedes that structures do not

increase from such earthy matter, he proposes to himself that these are nourished from

earth. This is a contradiction.

They are also less distinguished by him in turn than the great Boerhaave does, a man

beyond my praise, and one of those who ought to be venerated since through them it appears not

to be a vile thing to be a human. However as Boerhaave was the leader of Europe it easily

happens that what he said wrongly and also that which he advanced less accurately are

accepted as axioms. Among these I refer to his theory which he zealously teaches on the

solid substance of vegetables and animals, to which very pure earth is joined by glue

alone not in the way in medical institutions, but in chemistry and they see who wish to

think that the proposition is not far from truth that in lesser animals there is no sensible

earth, little in the greater and there it clings only in the bones.

However, in cremated bones changed through fire the lime is not the same matter as of

living fibres, but rather it fills the interspaces of the vital fibres, dead matter in that

living body and remaining destitute of life ; however the solid living fibres have been

destroyed by the magnitude of the fire.

Bodies are born from the albumin of an egg without any addition except heat,

membranes, cartilages, bones, and true solid parts. For also if I do not deny that

something of earth is required in the mixture of solid parts in the vegetable and animal

kingdom, nevertheless I think it can be demonstrated in respect to those left more

formally than materially for the necessary firmness, and it profits little as it would be an

enemy to life because it is lacking in elasticity. However in this passing note I have said

that I might show that the reasonings of Woodward detract nothing from the Helmont

experiments.

……………………………………………………………………………………….

.

My Investigation of the Leidenfrost

Phenomenon

The Forms of Boiling

Basically there are four forms of boiling:-

1. Nucleate boiling - The one most people are familiar with in making drinks, washing pots

and clothes and cooking. When the temperature of water, say in a saucepan, begins to rise small

bubbles of dissolved gases are released. As temperature increases bubbles will be seen at the

bottom and on the sides near the bottom of the pan. Here a sharp point or protrusion of the pan

surface serves as a nucleate point at which the temperature is highest and the water vapourises.

No matter how well polished a surface may appear an electron micrograph will reveal in fact the

surface is - as someone well described it - full of mesa like protuberances.

Increasing temperature sees more vapour bubbles until finally these are breaking free and the bulk

water is boiling with bubbles forming on the pan surfaces and on any nuclear material - dust -

pollen grains - in the water.

2. Flash boiling - at a surface temperature higher than that for nucleate boiling , water

poured on the surface is vapourised, with much noise, into steam. This form of boiling is used in

certain boilers for rapid steam production.

3.Transition boiling - on a surface higher than for flash boiling a water breaks up into

many tiny droplets which bounce on the hot surface and vapourise noisily into steam.

4.Film boiling - The Leidenfrost Phenomenon - When a surface is at a much

higher temperature than that of boiling water (100 degrees C) water will first contact the surface and

lift clear to hover on its own vapour layer. Vapourisation of a water drop takes minutes as against

seconds for lower surface temperatures.

Investigations into the forms of boiling have been unable to establish precise transition points of

surface temperature at which one form will change to the next form. For the most part this is due to

surface conditions and the thermal conductive properties of the material from which the hot surface

is made.

The Leidenfrost Phenomenon. Anyone who worked at the blacksmith`s forge when cooling iron in

the trough, the housewife preparing to smooth clothes first spat on the flat iron taken from near the

fire to test the temperature and those who observed lava pouring into the sea saw the strange

phenomenon of large drops of water swishing about on molten lava.

Professor John Tyndall succeeded Michael Faraday at the Royal Institution in London, England. In his

book Heat A Mode of Motion he included demonstrations of the Leidenfrost Phenomenon.

Tyndall`s illustration of the setting up of a Leidenfrost drop

I used shallow stainless steel dishes or a piece of brass about 5 inches (10cm) diameter and 1/2 inch

(1cm approximately) in thickness with a shallow depression machined into it. Heat was supplied

from a large electric boiling ring which could be adjusted to vary the temperature of the brass dish.

A 1.5 ml drop of distilled water on a surface at 600 degrees C.

Drops were placed from a glass pipette or from hypodermic syringes. On initial contact they hissed

very briefly as a series of separate drops rushed around on the hot surface before all coalescing into

one drop.

The hot surface causes vapourisation from the underside of the drop. The steam forms a layer which

lifts and supports the drop above the hot surface - in the manner of a Hovercraft.

Although this drop, photographed at 1/1000s appears to be stationary, there are convection

currents within the water and across its surface. There is rapid movement of vapour up and over the

drop. A speck of Balsa wood or a few spores of Lycopodium dropped on to the surface show this to

be the case.

(These photographs date from the 1970s C.P.)

Objectives of my Investigation:-

I set out to study the behaviour of drops - Measure the time drops of

different volumes took to evaporate - measure the thickness of the

supporting vapour layer and watch for any differences between drops

of distilled water and others made from saline solution.

(1/1000s exposure)

Some drops suddenly change from the drop shape and make a beautiful rosette - here sketched by

Tyndall. Some give out a fluttering sound and, more rarely, a musical note.

When such a drop is photographed, to record the rosette as this one was, it is disappointing.

Examination of many such drops reveal that first of all a circular drop takes on an elliptical shape.

Then it becomes an oscillating curvilinear polygon. Persistence of vision makes the drop look as

Tyndall drew it.

Drops above about 2.5ml in volume describe all manner of shapes on the hot surface and the

supporting vapour layer bulges upwards as the dome of a bubble.

The vapour layer lifting the drop centre into a dome.

(White dot is reflected flash- dotted lines are brass surface at 600 deg C)

This does not always occur, then again there may be several such domes in a large drop i.e. up to

the 10ml limit I put on my work.

The upper surface of a drop is often covered with wavelike disturbances. Sometimes a circular drop

will have circular waves coming from the centre - as if a stone has been dropped into a pool of

water - and these flow outwards and disappear under the drop.

The differences in drop thickness as it glides on the hot surface. Condensing steam vapour rises up

and over the drop. (1/1000s exposure)

The Vapour Layer

Drops used were at the average salinity 3.5% of the worlds seas and oceans.

I used three approaches to measuring the thickness of the supporting vapour layer. Apart from the

very smallest volumes, which take on a nearly spherical shape, drops will have a concave base. The

part of the layer of particular interest is at the bottom edge from which steam is escaping and

keeping the drop from touching the hot surface. The first approach used photography.

Photography

Tyndall was able to see the light of a glowing filament (a-b left) through the vapour layer beneath

the suspended drop.

Part of an enlarged photograph of a Leidenfrost drop.

Photographs were taken of drops and enlarged. A scale placed vertically on the brass surface was

photographed. Direct measurements were made at equal intervals along the base of the drop to

determine the thickness of the vapour layer.

The vapour layer was found to be 0.06mm for most of the length of the drop edge except in places

where the edge curved upwards and the gap was 0.26mm.

The flow of vapour from the supporting layer considered as the escape

of fluid from an orifice.

The rate of escape of a fluid from an orifice is governed by the geometrical shape of the orifice and

the area of discharge. This method determined the vapour layer at the drop bottom edges to be

0.06mm

(Published values for the Coefficient of discharge (Cd) used were often for large hydraulic

engineering projects. In order to check these applied to the very small scale Leidenfrost drops the

following experiment was made:-

Air was released, through a rectangular slit of similar area (4 sq mm) and aspect ratio to that of a

2ml drop having a vapour layer thickness of 0.06mm, from a spherical balloon, to deliver air at

constant pressure for a decreasing volume. Air pressure was measured with a U tube manometer and

balloon volume determined from radius measured with external calipers as air was released over 5

second intervals.

The Cd values were in the same range as those used in the vapour layer measurements determined

by flow from an orifice.

A Capacitance Method

This is Tyndalls version on Poggendorf`s suggestion to demonstrate the existence of an insulating

vapour layer. If the drop touches, or is made to touch the surface, the circuit is completed and the

Galvanometer needle turns.

This gave me the idea to try and measure the capacitance of the capacitor made up of the drop and

heated surface as plates and the vapour layer as dielectric.

For several approaches and other investigations e.g. volume to area changes due to evaporation, the

drop area needed to be determined.

Measuring Drop Base Area: -

Sheets of glass had mm graph paper glued to one face. The opposite face was coated with Vaseline

rendered smooth in a flame. A drop was carefully set up on the greased surface and had the

appearance of a Leidenfrost drop. The area was measured by the method of counting squares. For

the drop volumes used - 2ml and less - the method proved okay.

Measuring Capacitance:-

Remember this investigation was carried out in the early 1970s. The only capacitance bridge was a

valve version unable to go into low pf regions. So all capacitance had to be measured against a

standard capacitor the value of which had then to be deducted from the measured value. (It may be

of some historic interest to tell you that the digital calculator appeared - fixed decimal point version

- at this time -oh to have had available all the marvellous digital meters we now have.)

With area known, capacitance measured and a dielectric value for air the only unknown was the plate

separation distance = the vapour layer thickness. This varied all over the place and I did not find it

came within acceptable ranges of that measured by the other methods. There are several reasons

not least of which was the means of measuring capacitance! The whole vapour layer was involved not

just that at the drop edge. The dielectric for the steam layer was assumed from dry air and now I feel

it was probably wrong.

A Summary of Results

For drops of 3.5%NaCl and of volumes 1ml and less:-

Area of drop exposed to heated surface Ab = (190± 4)V sq m

Vapour layer pressure = 51.57 Pa

Vapour layer thickness at drop edge 0.06 mm

Vapour flow rate from drop edge Q = Cd Ao = sq root of (2(pp ml per second

(Where Cd is co-efficient of discharge; Ao is the area of the annulus of the vapour escape - area of

orifice; (p1-p2) is pressure excess in vapour layer = 51.57Pa; is density of vapour (assumed to be

that of air)

Area of orifice of escaping vapour Ao = 2 r d ........(r to be determined from Ab, d = 0.06 mm)

Total evaporation to related to drop volume t = (V/ 7.4 x 10¯9) raised to the 1/2.4 ....... seconds

Drop volume to total evaporation time (t) ....V = 7.4 x 10¯9 x t raised to the 2.4 power .... litres

Evaporation rate dV/dt = 1.68 t (to the 1.4) x 10¯5 ...... ml per second

Some recent photographs June 2008

These were taken yesterday June 24th with a compact digital camera. The

old brass plate

heated by gas and tapwater drops deposited by syringe. Forty years on

and I still find them impressive and fascinating.

Colin Pounder Discovers Charged Solute

Specks

from Leidenfrost Boiling

This was undertaken to investigate the origin of electrical charge resulting in lightning in volcanic

clouds i.e. Volcanic Lightning. It was initiated by the emergence of Surtsey off Iceland in 1963. The

investigation formed the major part of the thesis for Ph.D. of the Open University by myself as the

first part-time student researching Physics. It took 6½ years in an improvised home laboratory using,

for the most part, improvised apparatus and whilst pursuing the full time vocation of a Primary

School Master.

Apparatus for measuring charge on a Leidenfrost drop. On the left is the electrometer - centre is a

probe made from the body of a spark plug to withstand heat and remain insulated and connected to

the meter via a screened coaxial connection - right is a dish on a hotplate. In front is the brass used

for most of the investigation of drops.

During the later stages of investigating drop behaviour and shortly after devising this probe set up

to measure capacitance I decided to examine drops to see if there was any electrical activity. One of

the earlier investigators had stated that the Leidenfrost drops did not produce any electricity. (That

was with water).

I wanted to extend the lifetime and in effect magnify the droplets of transition boiling which

Blanchard had found produced charge which charged the clouds at Surtsey. So to do this I now used

only saline solution drops (3.5%NaCl). This is the average salinity of the seas and oceans.

To measure out the correct volume I used either a pipette or calibrated syringes. Drops of solution

behaved as did those of distilled water, forming rosettes sometimes, waves on the surface on

occasions, or just remaining stationary.

With the apparatus shown above I found that saline solution drops produced electric charge but

intermittently. A flick of the electrometer needle -back to zero - another flick and so on getting

faster until the drop shrank and just a pellet of salt was left stuck to the probe.

I would let a drop diminish in size then add more solution. In this way I could feed a drop for many

minutes and the remaining salt was a dome like that of a drop. I tend to observe for one particular

item at a time. So once I had noted the electricity I wondered why it was generated in pulses and

watched drop carefully for some change in behaviour.

I discovered that a saline solution drop would slowly diminish in size, as you would expect, when

suddenly it went "Crack!" sometimes broke up and reformed or just sort of shook all over and settled

down again. This was when electricity registered on the electrometer.

Goodness knows how many drops I watched and how many wonderful notions (the correct term is

hypotheses) I had to explain this. For some reason I had the feeling that many of these drops had

waves passing over the surface. Maybe if I could measure wavelength then I would find something.

I made a stroboscope from a disc of black card driven by a small model motor fed from a battery

through a rheostat. With a photocell opposite a light and the disc with its slots interposed I could

switch on and off a Dekatron timing unit and so determine the speed of the stroboscope.

As a light source for the stroboscope I used a slide projector. For hours I watched drops and waves

but none ever strobed to a standstill. In the heat of that unventilated room and bent over the table

staring at that flickering light my back ached intolerably. I gave up. Switched off the little motor and

sat down in a chair with a great sigh of relief from back pain.

The last of the drops cruised around on the hot surface and went "Crack" a few times then left a bit

of salt. It was then I noticed on the black card of the strobe curved streaks of white. The disc was

about half a metre from the dish. I tasted the curved white streaks - they were salt. As I was

wondering how the salt had got from the drop to the disc - remember my mind was set on

something to do with waves on the drop surface - I stretched back in the chair and saw what looked

like tiny brilliant white stars slowly coming down from the ceiling and lit up by the slide projector

light.

I cannot describe what I felt, wonder, awe, a sense of the beauty of these tiny specks of light. Now,

as far as I am aware, I was the first person ever to see the salt specks from salt water undergoing

Leidenfrost boiling.

(Later Blanchard would confirm he and Woodcock had never seen them. The salt on slides was in

`misshapen lumps`.) I was the first to see the electrically charged salt specks from sea water contact

with a heated surface -in Nature - lava.

We had a Total Eclipse of the Sun on Wednesday (11th August 1999). The feeling so many people

felt is similar to what I felt alone that night. For billions of years something has been happening and

for that `one moment in annihilations waste`, as an individual, a person can say, "I experienced that

for myself alone".

Here is a brief outline of the results:-

Salt specks from Leidenfrost boiling.

At first to get a look at the tiny specks of salt I listened from a drop to go Crack then waved a

microscope slide about horizontally and hoped for the best. This picture and the next show some

results.

The specks are spherical and hollow

I surmised that the drop fired off droplets of solution and that as these floated in the air they

evaporated off water. Their solution would become more concentrated and a skin of salt would form

which trapped concentrated solution inside. Continuing evaporation through the skin made this

rigid. A slower rate of crystallisation would continue inside the droplet/speck. This would produce

larger crystals which lined the inside of the skin. The solution remaining inside the droplet would

come under ever increasing pressure until it burst out through the surface - making the small exit

hole. The speck would dry out and float in the air like a miniature geode charged with electricity.

To examine this idea I drew out glass tube in a flame to about the diameter of a human hair and

suspended a droplet of salt solution on it and fixed it under a microscope. I broke a torch bulb to

make a small electric one bar electric fire which I fed from a battery via a rheostat. I brought the tiny

glowing element near to the droplet and watched crystalline salt form on part of the surface. This

spread slowly to enshroud the droplet. After a while the salt coated droplet broke open and left a

near spherical salt speck with an exit hole.

I also prepared bowls of saturated salt solution and examined the surface layers of crystalline

material - fine on the surface where more rapid evaporation took place - large cubic crystals into the

liquid under this surface.

Initial & final stages from microscopic investigation of the formation of ‘geode’ like salt specks.

A droplet on glass drawn out to about the diameter of a hair.

A Salt speck produced by heated element held near the above droplet.

The Salt Specks in glorious close up

Salt specks from Leidenfrost boiling. 10 microns diameter photographed under an optical

microscope. The surface is of fine crystalline salt the inside walls are covered with larger crystals

which formed more slowly due to slowed evaporation. The opening is where solution was expelled

by the inward acting pressure as internal crystals formed.

When the drop made a loud crack droplets were emitted from one place i.e. not all over the drop. I

caught droplets from such emissions on to slides blackened with candle smoke. I could then count

the discs made by impacted droplets and get some idea of the number given off each time.

The probe used to detect and measure charge, via the electrometer, was now connected to a pulse

counter. Each time droplets were emitted a pulse was registered. In this way it was possible to gain

an estimate of the number of droplet/speck emissions from drops of particular volumes.

The number of emissions from a drop of initial volume 1ml 3.5%NaCl solution ranged from 613 to

2,777. The average = 1,444.

From this it was possible to determine that from a 1 ml drop of 3.5%NaCl solution some 6 x 105

specks are emitted.

Counts etc were all plotted as histograms and emissions to drop size, speck numbers to drop size,

duration of speck emissions , equations derived, etc., were made.

Electrical

The average charge per particle emission ranged from 0.1 x 10-10 Coulombs to 0.5 x 10 -10C.

From which an average charge per particle of 10 -14C to 10 -13C with a net +.

This is very high . Usually in spraying, raindrop break up and suchlike the charges are in the 10 -19C

and net -.

Dark Field Ultramicroscope

I constructed a dark field ultramicroscope. This consisted of an insulated case with two microscope

slides - rendered conducting on one surface by a molecular layer of tin - in parallel about ¼inch

apart. The halogen projector shone directly in to the camera with a strobe disc interposed. A small

black disk and various lenses gave a cone shaped shadow into the space between the parallel plates.

The camera was focused on a weighted hair hung in the gap. The conducting slides were connected

to a high voltage battery pack. The depth of field was virtually zero.

Through the camera a black disc is seen surrounded by brilliant light. Any dust - Lycopodium pollen

was used in trials - falling into the dark disc area lights up as a point of light. By projecting the

negative on to a squared screen the rate of fall due to gravity may be calculated, any deflection

towards a plate due to the particle carrying its own electrical charge may be measured. Hence the

size and the charge of each individual speck may be determined.

Salt specks from Leidenfrost boiling in the field of the ultramicroscope.

Dotted tracks are small sized specks, dashes are larger & moving more quickly, discs are out of

focus specks and not used.

Three thousand slides were taken originally and the tracks measured by hand as described.

Other materials were used for the heated surface and other

aqueous solutions - spring water -sea water (same as NaCl) -

rainwater - water filtered after mixing with volcanic ash - pumice

and powdered lava -were investigated - all produced electrically

charged solute particles.

Summary of electrical properties of Leidenfrost

drops.

Leidenfrost boiling of saline solution (and other aqueous solutions) produces electricity.

A Leidenfrost drop has a net negative polarity, the opposite polarity of charge is assumed on the

particulate cloud.

Average charge per particle all radii is 10 -14Coulombs

Charge on 10 micron particles is 10 -14C to 10 -17C

Charge increases with particle radius.

Particle emission from drops.

Evaporation/vapourisation is most from nearest to the hot surface.

As this takes place the drop becomes more and more saturated with salt (or other solute). For NaCl

when the 3.5% concentration reaches about 36% solid solute crystallises on the surface. For most

Leidenfrost drops this is on the underside. When this layer grows over a sufficient area the vapour

support layer is shut off! The drop crashes on to the hot surface the temperature of which is several

hundred degrees.

At least two things happen - the crystalline salts decrepitates into charged fragments - some of the

drop solution is flash boiled into steam. Both are directed by the `walls` of hot surface and drop

above to hurtle outwards from beneath the drop and into the air/atmosphere -where the droplet and

speck formation then take place.

The form of charging is tribo-electric - frictional electricity both in decrepitation and in the material

sliding across the surfaces on its way out into the air where it forms highly charged particles.

To examine this Professor Bill Bright (Southampton University) arranged for me to use a high frame

speed camera and here are some results from the film:-

Time between frames is 3 x 10-3 seconds

A Saline Solution drop Leidenfrost Boiling -emitting

Triboelectrically charged material

Another saline drop undergoing Leidenfrost Boiling and

emitting electrically charged material which will form charged

solute specks.

The high charge on each speck means that less of them need to

accumulate high values of electrical charge in a cloud.

Most volcanoes are phreatic which is to say they have

water either in crater lakes, as junior water in the rocks

of the magma chamber, as internal lakes in caverns (See

Humboldt`s exploration of the Andes) and or in contact

with the waters of the sea. At times of eruption the

solution contact with hot lava produces billions of

highly electrically charged specks into the clouds

associated with the volcano. This electricity discharges

as Volcanic Lightning. There is reason to believe that the

same process may also be involved in earthquake lights.

This page is presented as an acknowledgement to my wife and

family’s support and encouragement and in respect to:-

Dr. C.E.R. Bruce

Professor Dr. W.A. Bright

&

Professor Dr. J.G. Leidenfrost.

SEMPER FIDELIS