Michael Faraday · Public domain edition · 111 cards · 32 chapters
Michael Faraday's 1861 lectures use the candle to demonstrate the principles of natural philosophy, tracing combustion, capillary action, and the properties of tallow, wax, and stearin. This deck covers his accounts of candle manufacture, flame structure, fuel transport, and his arguments about observation and experimental reasoning.
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Chapter 1 · Question
What does Faraday claim a candle's phenomena illustrate about natural philosophy?
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Chapter 1 · Answer
The author argues that there is no law governing any part of the universe that does not come into play and get touched upon in the phenomena of a candle. He calls it one of the best and most open doors into the study of natural philosophy, preferring the subject to any newer topic.
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Section 14 cards
What does Faraday claim a candle's phenomena illustrate about natural philosophy?
The author argues that there is no law governing any part of the universe that does not come into play and get touched upon in the phenomena of a candle. He calls it one of the best and most open doors into the study of natural philosophy, preferring the subject to any newer topic.
Chapter 1
How were 'dips' candles manufactured, according to Faraday?
Dips were made from lengths of cotton cut off and hung up by a loop, then dipped into melted tallow, taken out and cooled, and re-dipped until tallow accumulated around the cotton. Faraday shows these as the common commercial candles, alongside tiny miners' candles rated 20 to 60 to the pound.
Chapter 1
Why were small candles used by miners, and what replaced them?
The author explains that miners once made their own small candles, 20 to 60 to the pound, because it was supposed that a small candle would not so soon set fire to the fire-damp in coal mines as a large one, and also for economy. They were later replaced by the steel-mill, then the Davy-lamp and other safety-lamps.
Chapter 1
How does Faraday describe the conversion of tallow into stearin?
The fat or tallow is first boiled with quick-lime and made into a soap; the soap is then decomposed by sulphuric acid, which takes away the lime and leaves the fat re-arranged as stearic acid, while glycerin—described as absolutely a sugar or similar substance—is produced. The oil is then pressed out, impurities carried off, and the remainder melted and cast into candles.
Chapter 1
Section 24 cards
Why can wax candles never be cast, and how are they made instead?
The author states wax cannot be cast despite melting easily. Instead, cottons with metal tags at the ends are hung on frames and carried to a heater where wax is melted. A man pours wax down each wick in turn, giving repeated coats until the required thickness is reached. The candles are then taken down, rolled on a fine stone slab, the conical top moulded by shaped tubes, and the bottoms cut off and trimmed.
Chapter 2
How are moulded tallow candles made, and why do they fall out of the moulds?
Moulds are fastened in a frame, and a plaited wick is threaded through each, pegged at the bottom to stop fluid running out and held taut by a bar across the top. Melted tallow fills the moulds; once cool, excess tallow is poured off at one corner, cleaned away, and wick ends cut. The candles are cone-shaped, narrower at the top, so their form and shrinking mean a little shaking makes them tumble out.
Chapter 2
What does Faraday say about ornamental and coloured candles?
He shows coloured candles using mauve, magenta, and other recently introduced chemical colours, plus varied forms including a fluted pillar and candles by Mr. Pearsall ornamented with designs that glow as they burn. The author argues that all that is fine and beautiful is not useful: the fluted candles, pretty as they are, are bad candles because of their external shape, and refinement means sacrificing a little in utility.
Chapter 2
How does a candle differ from a lamp, and what does Faraday call the wonderful thing about a candle?
With a lamp, oil is put in a vessel with moss or prepared cotton, and the flame burns only in the part of the wick above the oil. Faraday says the more wonderful thing about a candle is that it is a solid substance with no vessel to contain it: how does this solid get up to the place where the flame is, and once made fluid, how does it keep together?
Chapter 2
Section 34 cards
What forms the cup at the top of a burning candle, and why does it matter?
Faraday explains that the ascending current of hot air cools the outer edge of the wax while the inner part melts, forming a cup. If the cup is not horizontal, the fluid runs away in guttering. A well-formed cup is essential to good burning, and he argues that utility, not appearance, is the true beauty of a process.
Chapter 3
Why does Faraday say a pretty, irregularly shaped candle burns badly?
Irregular or intermittent shapes cannot form the nicely leveled edge of the cup, so the stream of air is uneven and the candle gutters. Faraday argues that the best-looking candle is often a bad burning one, and that the perfection of a process—its utility—is the better point of beauty about it.
Chapter 3
How does fuel reach the flame, according to Faraday?
By capillary attraction, the kind of action that makes two things which do not dissolve in each other still hold together. Melted tallow ascends the cotton wick as water creeps up a finger or soaks a towel. Particles follow by mutual attraction and are gradually burned as they reach the flame. Faraday notes the name came from old times, before the real power was understood.
Chapter 3
What does Faraday want his audience to do when a new result occurs?
He tells them they come to be philosophers, and that whenever a result happens, especially if it is new, they should ask 'What is the cause? Why does it occur?' He adds that the greatest mistakes and faults with regard to candles, as in many other things, often bring instruction which would not be received if they had not occurred.
Chapter 3
Section 44 cards
Why does a candle go out when turned upside down?
The author explains that the only reason a candle does not burn down the side of the wick is that the melted tallow extinguishes the flame. When a candle is turned upside-down, the fuel runs onto the wick and puts it out, because the flame has not had time to make the fuel hot enough to burn as it does when carried in small quantities up the wick.
Chapter 4
What does Faraday's blown-out candle experiment demonstrate about the fuel?
Faraday argues the fuel exists in a vaporous condition. If you blow a candle out cleverly, without disturbing the surrounding air, you can see vapour rise from it. Holding a lighted taper two or three inches from the wick sends a train of fire through the air to the candle. If the vapour is allowed time to cool, it condenses into a liquid or solid, or the stream is disturbed.
Chapter 4
According to Hooke's drawing, what surrounds and shapes the flame?
Hooke's drawing of a lamp flame, which Faraday says applies to a candle, shows a quantity of unseen matter rising about the flame and the surrounding atmosphere essential to it. A current is formed that draws the flame out and upward to a great height. Faraday notes the flame is really drawn out by this current, which also supplies air and cools the sides of the cup of melted fuel.
Chapter 4
What does the shadow of a candle flame reveal about its bright and dark parts?
Faraday throws the flame's shadow on a screen using sunlight, then the voltaic battery and electric lamp. The shadow shows the candle and wick, a darkish part, and a more distinct part. Curiously, what appears as the darkest part of the flame in the shadow is in reality the brightest part, and the ascending current of hot air streams upward, drawing out the flame and supplying it with air.
Chapter 4
Section 54 cards
Why do flames normally rise, and how can Faraday make one burn downward?
Faraday explains that flames rise because of the draught of air by which combustion is formed. By blowing the flame down, he changes the direction of the air current and makes the flame travel downward into a little chimney. He notes that later lectures will show a lamp where the flame goes up and smoke goes down, or the reverse, demonstrating that flame direction can be varied.
Chapter 5
How does Faraday use the game of snapdragon to illustrate the philosophy of flame?
Faraday describes snapdragon as a beautiful illustration of flame: the dish holds the spirit, the raisins act like wicks, and the air creeping irregularly over the dish's edge breaks the flame into tongues. Each tongue has an independent existence, so he says you have a multitude of independent candles. He recommends warming the dish, plums, and brandy for proper play.
Chapter 5
What does Faraday say about the apparent shape of a large, lively flame?
Faraday argues that a large flame does not keep a uniform shape but breaks out with a power of life, as when a cotton ball soaked in spirit burns with rising tongues of flame. He insists a flame of that shape is never so at any one time: it consists of many different shapes succeeding each other so fast that the eye takes them all in at once.
Chapter 5
What does Faraday propose to examine first in a candle flame, and with what apparatus?
Faraday arranges apparatus including a glass tube, which he puts into the middle of the flame—the part old Hooke represented in the diagram as rather dark, visible at any time if you look at a candle carefully without blowing it about. He says they will examine this dark part first, to learn what happens in each part of the flame and where the candle goes.
Chapter 5
Section 63 cards
Where is the heat of a candle flame located, according to Faraday's paper experiment?
Faraday argues the heat is not in the inside of the flame but in a ring where chemical action occurs, where air and fuel meet. Holding paper across the flame burns it in two places, leaving the middle little burnt. He recommends this as a good experiment to try at home with quiet air in the room.
Chapter 6
Why does a candle under a jar go out, though the jar is still full of air?
Faraday demonstrates that a candle burns nicely in a jar of air at first, then fades and goes out. It is not that the jar lacks air, since it is as full as before, but that it lacks pure, fresh air. The air has been partly changed, and insufficient fresh air remains for combustion.
Chapter 6
What happens when a flame is given too little air, as with the obstructed Argand lamp?
Faraday shows that obstructing air to the Argand lamp makes it burn poorly and smoke, while opening a passage to the middle of the flame, as Argand did, makes it burn beautifully. He argues larger wicks need a larger supply of air, or combustion is imperfect and soot—charcoal or carbon—flies off.
Chapter 6
Section 74 cards
What contrast does Faraday demonstrate by burning gunpowder with iron filings?
Faraday mixes gunpowder with iron filings and ignites them to show two kinds of combustion: the gunpowder burns with a flame, while the iron filings burn without producing flame. He argues that on these distinctions depend all the utility and beauty of flame used for illumination, whether the fuel is oil, gas, or candle.
Chapter 7
What happens when a glass tube is dipped into the brightest part of a candle flame?
A black vapour, not the earlier white vapour, comes through the tube. It is as black as ink, and when a light is applied it does not burn but extinguishes the light. Faraday identifies these particles as the smoke of the candle, the same carbon that exists in the candle itself.
Chapter 7
According to Faraday, why does a candle flame give off light?
The author argues that whenever a substance burns without becoming vaporous, whether it becomes liquid or stays solid, it becomes exceedingly luminous. The candle's brilliancy is owed to solid particles in the flame: heat decomposes the wax vapour, freeing carbon particles that rise heated and glowing before entering the air.
Chapter 7
What does the hydrogen and oxygen experiment show about heat versus light?
Hydrogen burning in oxygen produces far greater heat than a candle yet very little light, because it lacks particles that stay solid. Holding lime, which will not burn or vaporise, in that flame produces the intense lime-light, almost equal to sunlight. Faraday argues light depends on solid particles retaining heat, not on heat alone.
Chapter 7
Section 83 cards
What happens to a gas flame when air mixes with it before the carbon separates?
Faraday demonstrates that adding air to a gas flame causes the carbon to burn before it is set free as solid particles, so the flame becomes pale and blue rather than bright. He shows this with a wire-gauze cap over the jet, and by blowing on a bright gas flame. The difference is solely due to the solid particles not being separated before the gas burns.
Chapter 8
What experiments does Faraday use to show that burning substances produce solid particles?
Faraday burns phosphorus under glass and shows the smoke consists of solid particles. He ignites a mixture of chlorate of potassa and sulphuret of antimony with sulphuric acid, and burns zinc filings in a hot crucible, producing a woolly solid. He also re-ignites carbon smoke particles in a hydrogen flame to show they glow when heated.
Chapter 8
What does Faraday conclude causes the dimness on a cold spoon held over a candle?
Faraday states that the dimness is caused by water produced during combustion. He notes that the products of the candle make the jar's sides cloudy and dim the light behind it, and that a cold spoon or silver dish held over a candle becomes dim in the same way. He promises to show next time that this water can be made to assume liquid form.
Chapter 8
Section 91 cards
How does Faraday use potassium to test for water?
Faraday uses potassium, a substance discovered by Sir Humphry Davy, as a test for water because it has a very energetic action upon it. When thrown into water or placed on a drop, the potassium lights up, floats about, and burns with a violent flame, visibly showing the presence of water.
Chapter 9
Section 104 cards
What happens to water when it freezes in sealed iron bottles, and why?
Faraday fills strong cast-iron bottles completely with water, excludes air, and screws them tight. When the water freezes in a mixture of salt and pounded ice, the ice occupies a larger bulk than the water, so the expansion bursts the iron vessels apart. He notes the same freezing occurs naturally outdoors in Canada or the North.
Chapter 10
Why does ice float on water, according to Faraday?
Faraday asks the audience to think it through: ice floats because the ice is larger in bulk than the quantity of water that produced it. Since the same amount of matter occupies more space as ice, the ice weighs lighter than the water, and the heavier water supports it. He illustrates with a boy who falls through a hole and tries to get back onto the ice to float him up.
Chapter 10
What happens when steam in a closed tin flask is condensed by cold water?
Faraday closes a tin flask full of steam and pours cold water over the outside. The steam returns to liquid water, a vacuum forms inside, and the vessel immediately collapses inward. He contrasts this: had he kept heat applied with the stopper closed, the vessel would have burst outward. He uses this to show the water remains water through both changes.
Chapter 10
According to Faraday, where does the water produced by a burning candle come from?
Faraday states the water is not present in the candle beforehand, nor in the air around it that is needed for combustion. It comes from their conjoint action: part from the candle and part from the air. He says this must be traced so the chemical history of a burning candle can be understood, and he asks the audience to reason it out from what he has already told them.
Chapter 10
Section 112 cards
How does Faraday compare potassium, iron, and zinc in their action on water?
Faraday presents them as differing in degree of intensity but acting on water in the same general manner. Potassium burns beautifully on water, using the water in place of air. Iron filings or turnings change more slowly, becoming rusty. Zinc, burned over the candle, shows a sort of combustion halfway between potassium's action on water and iron's action, leaving a white ash.
Chapter 11
What test shows the gas from steam over iron is not steam?
The gas is passed through water after leaving the iron barrel, lowering its temperature, yet it does not change back into water—whereas steam condenses when cooled. Applying a light to the jar's mouth makes it ignite with a slight noise. Steam puts out a fire and does not burn, so the burning proves the substance is not steam.
Chapter 11
Section 123 cards
Why is hydrogen called an element, and why is a candle not one?
Faraday classes hydrogen among the elements because nothing else can be gotten out of it. A candle is not elementary because carbon and hydrogen can be obtained from it, or at least from the water it supplies. The name hydrogen means the element which, in association with another, generates water.
Chapter 12
Why does Faraday fill the hydrogen phial nearly, but not quite, full?
The evolved gas is very combustible and explosive to a considerable extent when mixed with air. If a light were applied to the pipe before all the air had been swept out of the space above the water, it might lead to harm. Filling nearly full limits that air space while leaving room for the gas.
Chapter 12
What demonstrations show that hydrogen is lighter than the atmosphere?
Faraday blows soap bubbles with hydrogen through a tobacco-pipe connected to the generator; unlike bubbles blown with warm breath, they rise to the roof, carrying much of a hanging drop. He also inflates collodion and thin-membrane balloons that float until the gas escapes, noting balloons were formerly filled with hydrogen.
Chapter 12
Section 133 cards
How does the weight of a cubic foot of hydrogen compare with water?
Faraday's table gives a pint of hydrogen as three-quarters of a grain and a cubic foot as one-twelfth of an ounce, while a pint of water weighs 8,750 grains and a cubic foot of water weighs almost 1,000 ounces. He uses these figures to show the vast difference between the weight of a cubic foot of water and a cubic foot of hydrogen.
Chapter 13
What is the sole product of hydrogen's combustion, and why is it unique?
When hydrogen burns it produces water only, and nothing solid is formed during or after combustion. Faraday notes that a cold glass held over the flame becomes damp, showing water produced immediately in appreciable quantity. He states it is important to remember that hydrogen is the only thing in nature which furnishes water as the sole product of combustion.
Chapter 13
What does Faraday plan to use the voltaic battery for next?
Faraday demonstrates the voltaic pile's power, producing a brilliant flash and burning an iron file with it. He calls it a chemical power and says that when they next meet he will apply it to water to pull the water to pieces, to see what else is in water besides hydrogen, since passing water through the iron tube did not return the full weight of water as steam.
Chapter 13
Section 144 cards
What happens when both battery poles touch the moistened paper, and what does Faraday demonstrate?
When both platinum poles contact the moistened paper simultaneously, a brown spot appears under each pole, showing something is pulled apart from the white paper. Faraday then traces the word "juvenile" on the paper with a terminal wire, demonstrating that the effect can be used to write. Neither pole alone produces any visible action.
Chapter 14
What happens to platinum plates dipped in the copper solution with and without the battery connected?
Without the battery, the platinum plates come out as clean and white as they went in. When connected to the battery and dipped into the copper-nitric acid solution, one plate becomes coated with copper while the other stays clean. Reversing the plates' sides transfers the copper coating to the other plate, showing the same copper put into the solution can be taken out again.
Chapter 14
Why does Faraday argue the gas produced from water is not steam?
Faraday notes the gas appears to boil up famously, but the vapour collected in the jar remains unchanged instead of condensing as steam would. Since it stands over the water without condensing, it must be a permanent gas. He then shows the gas burns with an explosion, and that it can burn without air, unlike a candle.
Chapter 14
What does Faraday conclude when the collected gas is ignited by an electric spark in the closed vessel?
The gas burns with a flash of brilliant light but no sound, since the vessel confines the explosion. After ignition the gases disappear, their place is filled by fresh gas rising, and drops of water trickle down the vessel's sides. Faraday concludes the gas formed from water by the battery changes back into water under the spark's influence.
Chapter 14
Section 154 cards
In Faraday's electrolysis experiment, what volume ratio of gases came from water?
Faraday states that electrolysing water yields two volumes of hydrogen to one volume of the gas that burns it, oxygen. In the apparatus, the jar over one pole filled about twice as fast as the other. He notes both gases are colourless and stand over water without condensing, and that the oxygen is a very heavy body compared with hydrogen.
Chapter 15
How does Faraday identify the two gases produced from water?
He tests the faster-filling gas by holding the jar inverted and applying a light; it burns with a pale flame, matching hydrogen's known qualities. The other gas will not burn itself but makes a lighted splinter of wood burn far better than air would, identifying it as oxygen. Together the two would form an explosive mixture.
Chapter 15
What methods does Faraday demonstrate for obtaining oxygen?
He notes oxygen can be gotten from the air by complicated and difficult processes, but demonstrates better ones. Heating black oxide of manganese red-hot in an iron retort releases oxygen. Mixing chlorate of potassa with oxide of manganese (oxide of copper or iron would do as well) evolves oxygen with far less than a red heat, even a common spirit-lamp sufficing.
Chapter 15
Why must the first portion of gas be discarded when preparing oxygen?
Faraday explains that if too small a charge is used, the first portion of gas evolved will be mixed with the air already present in the retort, diluting it. The first portion must therefore be thrown away. He sets the first jar aside as containing air plus the first oxygen, and proceeds with experiments on the later, purer gas.
Chapter 15
Section 164 cards
How do the weights of equal volumes of hydrogen and oxygen compare, per Faraday?
Faraday states a pint of hydrogen weighs three-quarters of a grain while the same volume of oxygen weighs nearly twelve grains. A cubic foot of hydrogen weighs one-twelfth of an ounce; a cubic foot of oxygen weighs one ounce and a third. So although water yields twice the volume of hydrogen as oxygen, the weights differ greatly because hydrogen is a very light gas and oxygen is heavy.
Chapter 16
What happens when a candle or lamp burns in oxygen instead of air?
Faraday shows a candle burning in a jar of oxygen with a vigour resembling the light at the poles of a voltaic battery, yet producing the same water and the same phenomena as burning in air. He also feeds oxygen to a deliberately badly burning lamp; the combustion is greatly accelerated, and when the oxygen flow is shut off the lamp relapses to its former dimness.
Chapter 16
How does Faraday demonstrate oxygen's effect on burning iron, sulphur, and phosphorus?
Faraday attaches a piece of wood to an iron wire, lights the wood, and lowers both into a jar of oxygen; the wood ignites the iron, which burns brilliantly and continues as long as oxygen is supplied, even a bar as thick as his wrist would burn. Sulphur burns with far greater intensity in oxygen than in air, and phosphorus gives a glorious light, with solid particles going off.
Chapter 16
How does Faraday show oxygen supporting the combustion of hydrogen?
Faraday mixes one volume of oxygen with two volumes of hydrogen, the proportion in which they occur in water, and blows soap bubbles with the mixture through a tobacco-pipe into soap-suds. He explodes a bubble on the palm of his hand rather than firing it from the pipe, since the explosion would pass up and blow the jar to pieces. The gases unite with the utmost readiness.
Chapter 16
Section 173 cards
Why does potassium decompose water, and what is set free?
Potassium decomposes water because it finds oxygen in the water and combines with it, setting the hydrogen free; the freed hydrogen then burns. Faraday notes the affinities are so strong that a piece of potassium placed on ice will set it alight, producing a sort of volcanic action—an example of how greatly results are modified by circumstances.
Chapter 17
How does the test-gas reveal oxygen in air?
The test-gas reddens when oxygen is present. Mixed with air over water, it produces the same reddening as with pure oxygen, proving oxygen is in the air. Shaking with water absorbs the red gas, so more test-gas can be added until nothing reddens—showing something else in the air is left untouched.
Chapter 17
Why does a candle burn differently in oxygen than in air?
The chapter poses this as a key question about the nature of the atmosphere but defers the full answer. It shows air contains oxygen yet also something else: when phosphorus burns in a jar, the condensed smoke leaves gas unburnt—gas that neither phosphorus nor the reddening test-gas can touch, and which is not oxygen yet is part of the atmosphere.
Chapter 17
Section 184 cards
What proportions of oxygen and nitrogen make up atmospheric air by bulk and by weight?
By bulk, air is 20 parts oxygen to 80 parts nitrogen; by weight, 22.3 parts oxygen to 77.7 parts nitrogen, out of 100. Faraday notes this is a true analysis as regards the quantities of the two gases, and that 5 pints of atmosphere contain only 1 pint of oxygen and 4 pints of nitrogen.
Chapter 18
Why does Faraday argue nitrogen is essential rather than a useless part of air?
The author argues nitrogen moderates combustion: in pure oxygen, iron grates and locomotive fires would burn furiously, since iron is more combustible than coal. Nitrogen lowers the oxygen's action to something moderate and useful, and also disperses candle fumes through the atmosphere to serve vegetation. In its ordinary state nitrogen is inactive and safe, combining only under intense electric force.
Chapter 18
How does Faraday demonstrate the weighing of gases using the copper bottle?
He balances an air-tight copper bottle with a stop-cock on a balance, then pumps twenty measured volumes of air into it, and the bottle sinks, showing added weight without added bulk. Opening the bottle into a jar of water releases the compressed air, and the bottle rebalances against the original weight, confirming the experiment. A cubic foot of air weighs 1⅕ ounce.
Chapter 18
What weights does Faraday give for nitrogen, oxygen, and air per pint and cubic foot?
A pint of nitrogen weighs 10⁴⁄₁₀ grains, or 1⅙ ounce per cubic foot. Oxygen is heavier: 11⁹⁄₁₀ grains per pint and 1¾ ounce per cubic foot. A pint of air weighs about 10⁷⁄₁₀ grains, and a cubic foot 1⅕ ounce. Faraday adds that the air in his lecture room weighs above a ton.
Chapter 18
Section 194 cards
What happens to a bladder stretched over a glass when air is pumped from beneath it?
The bladder is pushed inward more and more by the weight of the atmosphere pressing down on it, and eventually it is driven in and breaks with a loud report. Faraday uses this to show that the air above presses on objects when the air beneath is removed.
Chapter 19
What does Faraday's two hollow brass hemispheres demonstration show?
When the air inside is exhausted, the two halves cannot be pulled apart even by two people, because every square inch of surface sustains about fifteen pounds of atmospheric weight. While air remains inside, the halves separate easily. This demonstrates the pressure of the atmosphere.
Chapter 19
How does the upside-down tumbler experiment keep water from falling out?
A wine-glass is filled or half-filled with water, a flat card is placed on top, and the glass is turned upside-down. The water stays in because the air cannot get in; capillary attraction around the edge keeps the air out. The card and water remain in place.
Chapter 19
What does the quill popgun experiment demonstrate about confined air?
A pellet is pushed to one end of a tube and a second pellet inserted, confining the air between them. Faraday says it is impossible to drive the second pellet close to the first by force, because the compressed air drives the front pellet out with force like gunpowder, which partly depends on the same action.
Chapter 19
Section 203 cards
How does Faraday demonstrate the elasticity of air using a bladder and bell-jar?
He confines air in a bladder inside a bell-jar and removes the outside atmospheric pressure. The bladder then expands larger and larger until it fills the whole bell-jar, showing air's elasticity, compressibility, and expansibility to a great extent—a property Faraday says is essential for the purposes it serves in the economy of creation.
Chapter 20
What happens when lime-water is exposed to the air collected from a burning candle?
The lime-water turns milky, forming a white powder like whitening or chalk. This does not happen with ordinary air, whose oxygen and nitrogen leave lime-water clear. The chalk is the lime combined with a product from the candle—the same substance that issues from chalk heated red-hot in a retort with moisture.
Chapter 20
What does Faraday conclude about the non-condensable product issuing from the candle's chimney?
The current from the chimney can blow out a flame, which one might attribute to nitrogen not supporting combustion. But Faraday shows the bottle collecting this air contains more than nitrogen: it turns lime-water milky, producing chalk. He traces this substance to the same material released from chalk heated red-hot with moisture in a retort.
Chapter 20
Section 214 cards
Where in nature does Faraday say carbonic acid is found in abundance?
Faraday states that carbonic acid is found in great abundance in all limestones, chalks, shells, and corals, where it is fixed in solid form. He notes Dr. Black called it "fixed air" because it loses its air-like quality and assumes a solid condition in these materials. It can be released from marble using muriatic acid.
Chapter 21
What two combustion-related properties does Faraday demonstrate for carbonic acid?
Faraday shows that carbonic acid is neither combustible nor does it support combustion. When he tests it with a taper, the flame is extinguished, just as with the air from the chimney over a burning candle. This distinguishes it from oxygen, which supports combustion.
Chapter 21
How does Faraday show carbonic acid dissolves in water, and how is it detected?
Faraday uses an apparatus with marble and acid below and cold water above, letting gas bubble through the water overnight. Drawing off the water, he finds it tastes slightly acid, showing it is impregnated with carbonic acid. Adding lime-water turns the solution turbid and white, which is the test proving carbonic acid's presence.
Chapter 21
How heavy is carbonic acid compared with air, and what experiments show this?
Faraday's table gives a pint of carbonic acid as 16⅓ grains and a cubic foot as 1⁹⁄₁₀ ounces, heavier than air at 10⁷⁄₁₀ grains per pint. He pours the gas into a glass and finds a taper extinguished, lowers a bucket into a "well" of carbonic acid, and shows a balance sinking when the gas is poured in.
Chapter 21
Section 234 cards
By weight, what proportions combine to form carbonic acid, and what does it form with lime?
The author states that 6 parts of carbon by weight combined with 16 parts of oxygen by weight give 22 parts of carbonic acid. Those 22 parts of carbonic acid, combined with 28 parts of lime, produce common carbonate of lime. He notes an oyster-shell would show the same proportions: every 50 parts give 6 of carbon, 16 of oxygen, and 28 of lime.
Chapter 23
How does Faraday demonstrate that carbonic acid contains oxygen?
He burns potassium in carbonic acid. The potassium takes oxygen from the carbonic acid as it burns, and when the result is put into water, a quantity of carbon is left behind as a black substance. Faraday admits his demonstration was rough, but says a careful day-long experiment would yield the full amount of charcoal, proving carbonic acid consists of carbon and oxygen.
Chapter 23
What happens to oxygen's bulk when carbon dissolves into it, and what is left if pure carbon burns?
The author notes that when carbon burns in oxygen, the oxygen does not change in bulk by the solution of the carbon in it; the volume is the same at the end as at the start, only it has become carbonic acid. He also states that a perfectly cleansed and purified piece of carbon leaves no ash or residue whatever when burned.
Chapter 23
How does Faraday show carbon is present in wood and coal-gas?
Burning wood in a bottle with lime-water turns the lime-water cloudy, showing carbonic acid formed from the wood's carbon. Partly burning wood and blowing it out leaves carbon behind. For coal-gas, he mixes it with a body that burns the hydrogen but not the carbon, leaving a dense black smoke — though a candle flame itself does not visibly show carbon.
Chapter 23
Section 243 cards
How does carbon's combustion differ from that of iron or lead?
The author explains that carbon burns as a solid but its product passes off as a gas, leaving the remaining carbon clear with no ash. Iron and lead burn into solid products, so the unburned portion underneath is shielded from air and cannot be consumed. Lead pyrophorus burns brilliantly when divided but not in a mass, because air cannot reach it.
Chapter 24
Why does exhaled breath extinguish a candle in Faraday's apparatus?
The author's lungs remove oxygen from the air, so air passed from his mouth into the tube contains no oxygen to supply combustion. The candle burns briefly until the bad air reaches it, then goes out for want of oxygen, not from blowing. He notes one inspiration completely spoils a jar of fresh air.
Chapter 24
What practical lesson does Faraday draw from the breath experiments?
The author argues that because a single breathing spoils air so thoroughly, it is improper to let the poorer classes breathe air over and over again for want of proper ventilation. He concludes that a sufficient supply of fresh air, achieved through adequate ventilation, is essential to health.
Chapter 24
Section 254 cards
What does Faraday's lime-water experiment show about expired air?
Drawing external air through lime-water produces no effect, but air forced from the lungs through lime-water several times turns it white and milky. Faraday concludes that expired air is spoiled by carbonic acid, which he demonstrates by its contact with lime-water.
Chapter 25
How does Faraday compare respiration in the lungs to a burning candle?
The author argues that food acts as fuel: air and food meet in the lungs separated only by a thin surface, and the air's oxygen combines with carbon from the food to form carbonic acid and evolve heat, just as a candle combines with parts of the air, forms carbonic acid, and gives off heat.
Chapter 25
How does Faraday describe the composition of sugar?
Sugar is a compound of carbon, hydrogen, and oxygen. Faraday's table gives 72 parts carbon, 11 hydrogen, and 88 oxygen. Because the oxygen and hydrogen are in exactly the proportions that form water, he says sugar may be regarded as 72 parts carbon and 99 parts water, and it is the carbon that combines with oxygen in respiration.
Chapter 25
What daily carbon quantities does Faraday give for respiration?
A man converts about seven ounces of carbon into carbonic acid in twenty-four hours, a milch cow seventy ounces, and a horse seventy-nine ounces, solely by respiration. Faraday says respiration in London alone forms about 5,000,000 pounds, or 548 tons, of carbonic acid daily, which passes into the air and supports plants.
Chapter 25
Section 264 cards
How do animals and plants depend on each other for carbon and oxygen?
The author explains that fish respire using oxygen dissolved in water and produce carbonic acid, while plants absorb carbon from the atmosphere in the form of carbonic acid and thrive on it. He notes that pure air would kill plants, and that what is disease to animals is health to plants, tying all Nature together so one part conduces to the good of another.
Chapter 26
Why does carbon in ink and candles wait rather than burn at once?
The author contrasts lead, which starts burning as soon as air reaches it, with carbon, which waits days, weeks, months, or years. He cites the carbonaceous ink of Herculaneum manuscripts, unchanged by the atmosphere for 1,800 years or more. Carbon, appointed as fuel, waits for action, while lead and finely divided iron start at once.
Chapter 26
How does gun-cotton differ from gunpowder when heated?
Faraday demonstrates that both gun-cotton and gunpowder wait to ignite but start under different conditions. Touching gun-cotton with a heated wire makes it go off, yet even the hottest part of the wire is not hot enough to fire the gunpowder. This shows substances differ in the degree of heat needed to make them act.
Chapter 26
How does Faraday compare respiration to combustion in the lungs?
Faraday argues the analogy between respiration and combustion is beautiful and striking. In the lungs, as soon as air enters, it unites with carbon, producing carbonic acid of respiration even at the lowest temperature the body can bear short of freezing. Unlike gun-cotton waiting for heat, respiration waits no time. He closes wishing his audience might be fit to compare to a candle.
Chapter 26
Section 274 cards
Which metals does Faraday list as the platiniferous metals found with platinum?
Faraday names palladium, rhodium, iridium, osmium, and ruthenium as the platiniferous metals almost always found associated with platinum. He groups them into two sets: platinum, iridium, and osmium in one; ruthenium, rhodium, and palladium in the other. Three have a chemical equivalent of 98½ and the others about half that number.
Chapter 27
How do the specific gravities of the two platiniferous groups compare?
Faraday states the first group has extreme specific gravity: osmium is 21.4, the heaviest body in nature, while platinum and iridium are both 21.15. The second group is only about half as heavy, at 11.3, 12.1, and 11.8. He notes the curious likeness between metals of such different weights, such as palladium and iridium.
Chapter 27
What process did Faraday describe for obtaining platinum in the old way?
The ore was digested in nitro-muriatic acid, dissolving the platinum while leaving other bodies behind. Adding muriate of ammonia threw down a yellow precipitate, which was washed and heated to give platinum sponge. Because this sponge could not be fused in available furnaces, the divided particles were washed, pressed, heated, and hammered until they cohered into a dense mass that could be rolled and extended.
Chapter 27
What experiment does Faraday use to demonstrate the welding of platinum?
Faraday bends platinum wire so the ends cross, heats the junction with a blowpipe, and taps it with a hammer to unite the pieces. He notes platinum resists acids and oxidation, so no flux is needed. When he pulls the wire apart, it breaks where the pincers cut it, not at the weld, showing the junction is complete. He presents this as the principle of the old manufacture.
Chapter 27
Section 284 cards
What three points does Deville's platinum purification process depend on?
The author states Deville's process depends on three points: intense heat, blowpipe action, and the volatility of certain metals. He notes it is proposed to use the volatility of metals such as gold and palladium to drive them off and leave other material behind, counting on the volatility of metals usually considered fixed rather than volatile.
Chapter 28
Why did the Russian Government stop issuing platinum coin?
The author explains that with three precious metals coined, their market values ran counter to one another. The Government's fixed price for platinum coin made it worthwhile to buy platinum elsewhere, coin it, and circulate it in Russia at a profit. The composition was 97.0 platinum, 1.2 iridium, 0.5 rhodium, 0.25 palladium, plus copper and iron—bad platinum that scales.
Chapter 28
Why is iron a problem in treating platinum ore, and how does Deville remove it?
The author says iron is one of the most annoying substances present because it is not volatile; while it adheres to the platinum, the platinum will not flow readily, and high temperature cannot drive it off. Deville mixes ore with its own weight of sulphuret of lead and about fifty parts metallic lead; the sulphur takes up iron, copper, and other impurities to form a slag.
Chapter 28
What does Faraday demonstrate about heating platinum with the voltaic battery?
Faraday shows that when the electric current is compressed into thin conducting wires offering resistance, it evolves heat to a large extent. The platinum wire glows intensely and can melt; the melted wire forms little spheres strung on an axis. He also melts platinum in a carbon crucible at one battery pole, producing a brilliantly fused globule, and wears spectacles because the spark can injure the eyes.
Chapter 28
Section 294 cards
What happens when lead is heated on platinum foil, and why?
The platinum is destroyed: a hole is made in it. Faraday explains that platinum has a strong affinity for metals such as lead and tin, so the two fuse together at once when heated. The heat of the spirit-lamp alone would not harm the platinum, nor would other chemical means; it is the presence of the lead that causes the damage.
Chapter 29
How does Deville remove lead from platiniferous lead after melting and mixing?
After melting the substances and stirring them well to get a complete mixture, Deville throws air onto the surface to burn off sulphur from the remaining sulphuret of lead. He then heats the platiniferous lead and throws air on the surface so the lead oxidises; the litharge flows out fused into a receiving vessel, and the platinum remains behind.
Chapter 29
What heat source and vessel material does Deville use to melt platinum?
Deville obtains his heat by combining oxygen with hydrogen or carburetted fuel, using a blowpipe with two pipes, one to coal-gas and one to oxygen; this flame melts platinum foil like wax. For vessels he uses a kind of chalk found around Paris (calcaire grossière), which endures extreme heat; the lime suffers no sensible deterioration except mechanical wear from the gas current.
Chapter 29
What does Faraday show about lime in the oxy-hydrogen flame?
Faraday puts a piece of lime from the chalk into the flame and obtains the lime-light, the most intense heat from chemical action. Despite this, there is no sensible deterioration of the lime except mechanical force of the gases sweeping away loosely aggregated particles, sometimes called 'vapour of lime.' He notes almost any other substance would melt at once.
Chapter 29
Section 304 cards
How does Faraday make a candle melt platinum wire?
He uses platinum wire drawn by Wollaston's process to about one three-thousandth of an inch in diameter, enclosed in silver and then freed with nitric acid. He reports fusing this fine wire in a common candle, though heat radiates away so fast that fusion requires the most careful arrangement.
Chapter 30
Why does the blowpipe melt antimony that a plain candle flame cannot?
The candle lacks a continuous source of heat, and heat radiates away too quickly. The blowpipe sends a current of hot air, made hot by combustion, forcibly against the object, so particle after particle impinges on the antimony. Faraday shows the antimony then burns on its own combustion if air keeps being supplied.
Chapter 30
How does fused iron behave differently from antimony in the blowpipe?
The iron becomes red-hot and flows like mercury, covered with a coat of melted oxide. Faraday notes he cannot raise any vapour from it; instead it burns in a fixed condition, giving beautiful sparks as it is driven off. Antimony, by contrast, throws off abundance of fumes.
Chapter 30
What furnace does Deville use to fuse large amounts of platinum?
Deville uses a furnace of lime above and below, since lime withstands heat without changing shape and conducts heat badly, preventing loss. Blowpipes through apertures send oxygen with coal-gas, water-gas, or hydrogen onto the metal. Faraday says this furnace fuses forty or fifty pounds of platinum at once, and no workman has been injured.
Chapter 30
Section 313 cards
What did Faraday demonstrate about gold and silver using the blowpipe and battery?
Faraday showed that gold and silver can be volatilized by intense heat, whether from a voltaic battery or a blowpipe. He drove off gold vapour onto Paris limestone, leaving a purple patch of condensed gold, and boiled silver to produce green-coloured fumes. He argued the volatility is the same regardless of which agent is used.
Chapter 31
According to Deville, which two metals resist removal when purifying platinum, and why?
Deville proposed using intense heat to drive off extraneous substances from platinum except iridium and rhodium. Faraday notes that these two metals make platinum more resistant to acid attack. Alloys are compounded up to 25 per cent of rhodium and iridium, which increases platinum's chemical inaction as well as its malleability and other physical properties.
Chapter 31
What did Faraday say about his failing faculties at the end of the lecture?
Faraday admitted that gradual loss of memory and other faculties was painfully evident to him, requiring continued remembrance of his audience's kindness each time he appeared. He said he had desired to retire before his faculties became impaired, but his affection for the place and its attendees made it hard to know when the proper time had arrived.
Chapter 31
Section 324 cards
What does the air-burner's iron-wire gauze accomplish in Faraday's footnote?
The air-burner is a cylindrical metal chimney topped with coarse iron-wire gauze, set over an argand burner so gas mixes with enough air to burn carbon and hydrogen together, preventing soot. The flame cannot pass through the gauze and burns steadily and nearly invisibly above it.
Chapter 32
How did Davy isolate potassium, and why does the metal react with water?
Sir Humphry Davy discovered potassium, the metallic basis of potash, in 1807, separating it from potash using a powerful voltaic battery. Its great affinity for oxygen causes it to decompose water, releasing hydrogen that ignites from the heat produced.
Chapter 32
What happens when marble is treated with muriatic acid?
Marble is a compound of carbonic acid and lime. Muriatic acid is the stronger of the two acids, so it takes the place of the carbonic acid, which escapes as a gas, while the residue forms muriate of lime, or chloride of calcium.
Chapter 32
What is water-gas, and how is it produced?
Water-gas is formed by passing vapour of water over red-hot charcoal or coke. It is a mixture of hydrogen and carbonic oxide, each of which is an inflammable gas.
Chapter 32
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Text used: Project Gutenberg eBook #14474 (Public domain in the United States). Generated from the full text; cards paraphrase the source.
Version: Public domain edition. Retrieved 2026-10-29. Cards reviewed 2026-10-29.
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