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<^r**
LIQUID AIR
AND THIS
LIQUEFACTION OF GASES
THEORY, HISTORY, BIOGRAPHY
PRACTICAL APPLICATIONS
MANUFACTURE
BY
T. O'CONOR SLOANE, PH.D.
SECOND EDITION.
NEW YORK
NORMAN W. HENLEY & CO.
132 Nassau Street
1900
COPYRIGHTED 1899
BY
NORMAN W. HENLEY & Co.
MACGOWAN & SLIPPER
NEW YORK, N. Y., U. S A.
PREFACE.
In Gulliver's veracious account of his travels we
read of the work done in the famous Academy of
Logado. In one department fifty men were at work
under the superintendence of the universal artist,
as one of the illustrious investigators was called.
These men were engaged in various occupations.
" Some were condensing air into a dry tangible sub-
stance by extracting the niter, and letting the aque-
ous or fluid particles percolate." So says the great
Dean, selecting the solidification of air as one of the
impossibilities worthy of embodiment in his sarcastic
romance.
During the present generation the triumphs in
natural science have been most wonderful. The
prosaic narration of what has been done sounds like
the romancing of a Cyrano de Bergerac. We read
of the hardest metals, such as iron and nickel, car-
ried off in the gaseous state by carbon monoxide ;
the surgeon unconcernedly has the interior of his
living patient's body photographed ; the triumphs of
chemical synthesis culminate in the production on
the scale of manufacturing industry of a hydrocarbon
from coal and water ; Marconi follows a yacht race
and telegraphs its phases to the distant shore over
miles of water, without a wire ; and to-day air is
liquefied by the gallon, hydrogen and helium suc-
cumb to intense cold, becoming mobile liquids, and
PREFACE.
the last miracles of science may figure among her
greatest.
The present work aims to tell the history of the
liquefaction of gases, wherein the physicist has ex.
ceeded the fictitious achievements told of in Gulli-
ver. The subject, extending over a century, is full
of interest from the biographical as well as scientific
standpoint, and it is hoped that the presentation of it
with such scope will be acceptable to the reader.
For assistance in the compilation the author's
thanks are due to many. His requests met with
quick response from such men as L. P. Cailletet,
Henri Dufour, Charles E. Tripler and James Dewar.
And a personal friendship brought about by this book
has fully justified the labor of writing it— the friend-
ship of that wonderfully endowed scientist Raoul
Pictet, one of the fathers of liquid air, poet, musi-
cian, physicist, chemist and mathematician — a verit-
able Admirable Crichton.
The work is but begun, the future possibilities are
great, and it is impossible to foresee the impending
developments in the liquefaction of gases.
TABLE OF CONTENTS.
CHAPTER I. — PHYSICS. Pages 9-36
What is liquid air?— The three states of matter : Solid, liquid and gaseous-
Relations of pressure and heat to state assumed by matter — The critical
state and its phenomena — Natterer's tube — Physical units — Space, mass
and time — Force and energy — Conservation of force an abandoned doc-
trine— Conservation of energy — Work a synonym for development of
energy — Waste of energy and entropy — Possibility of utilizing the lower
forms of energy of the universe.
CHAPTER II.— HEAT. Pages 37-58
Heat and its measurement— Thermometers— The zero point— The Celsius or
Centigrade thermometer scale— Fahrenheit's thermometer scale— The abso-
lute zero — Its basis — Coefficient of expansion of gases — Determination of
temperatures in the liquefaction of gases — Different liquids used in filling
thermometers — The air thermometer —The hydrogen thermometer — De-
tails of its construction — Electrolytic hydrogen — The hydrogen or air
thermometer formula — The thermo-electric thermometer — Onnes' instru-
ment and details of its construction — Its calibration — The electric resist-
ance thermometer— Calorimetric determination of temperatures.
CHAPTER III.— HEAT AND GASES. Pages 59-84
The perfect gas— The ultra-perfect gas— Energy expended in heating a gas-
Specific heat at constant pressure and at constant volume — Atomic heats
and variations of same from equality with each other — Adiabatic and iso-
thermic expansion of gases— Carnot's cycle— The perfect heat engine-
Available and unavailable energy— Unavailable energy rendered available
by liquid air— patent heat of melting, of vaporization, of expansion— Boil-
ing a cooling process — Expansion a cooling process — The spheroidal state
— The Crookes layer — Experiments and illustrations — Utilization of the
spheroidal state in low temperature work and in liquid air investigations.
CHAPTER IV. — PHYSICS AND CHEMISTRY OP AIR.
Pages 85-91
The atmosphere as an ocean— What air is— Its constituents— Relations of air
to living beings — The chemist's and physicist's view of air — Its constancy
of composition — Carbon dioxide — Oxygen — Nitrogen, argon and other con-
TABLE OF CONTENTS.
CHAPTER V. — THE ROYAL INSTITUTION OP ENGLAND.
Pages 92-99
The Royal Institution — Its origin and objects — Count Rumford — Sir Humphry
Davy — The Pneumatic Institute — Davy's experiments in inhaling poison-
ous gases— His engagement as director of the Royal Institution— His
views on the utility of liquefying gases.
CHAPTER VI. — MICHAEL FARADAY. Pages 101-115
Michael Faraday— His early life — Early devotion to science— His introduction
to Humphry Davy— Attendance at scientific lectures — Engagement at the
Royal Institution — Injuries from explosion in the laboratory— European
tour with Davy — Rivalry of scientific men — Davy and Faraday as rivals—
The liquefaction of chlorine— Davy's share in the experiment— Davy's
opposition to Faraday's election as fellow of the Royal Society— Dr. Paris
and the liquefaction of chlorine— Faraday's descriptions of his liquefac-
tions—Explosions— Northmore's priority published by Faraday — Notes on
Faraday's liquefaction of gases — His exhibit'on of Thilorier's apparatus —
His later work in liquefying gases— Discovery of the magnetism of oxygen
gas — His death — Bent tubes as used by Faraday — Experiments with use of
bent tubes— The Davy-Faraday Laboratory.
CHAPTER VII. — EARLY EXPERIMENTERS AND THEIR
METHODS. Pages 116-151
Perkins' claim to have liquefied air — Its absurdity— Northmore's liquefaction
of chlorine — Rumford's experiments as commented on by Faraday — Bab-
bage's experiment in a drill hole in limestone rock — Monge and Clouet's
alleged liquefaction of sulphurous oxide— Faraday's liquefaction of chlo-
rine— Stromeyer's liquefaction of arseniureted hydrogen — Faraday's bent
tubes for liquefaction of gases — Manometer for use with them— Experi-
ment in a straight sealed tube on the liquefaction of chlorine — Davy's sug-
gested method— Cagniard de la Tour— His bent tube experiments— D. Col-
ladon— His apparatus as still preserved— ThilorLr- His discovery of solid
carbon dioxide— A fatal explosion — The improved Thilorier apparatus —
Johann Natterer's apparatus— His experiments — Loir and Drion's solidifi-
cation of carbon dioxide — Thomas Andrews, of Belfast.
CHAPTER VIII.— RAOUL PICTET. Pages 153-171
The life of Raoul Pictet— His education— His ice machines— Disputed priority
—Honors awarded— His apparatus for liquefying gases— Description of its
operation — Temperatures of the cycles of operation — His dispatch of De-
cember 22, 1877, to the French Academy — Regnault's statement — Hydrogen
—His dispatch of January n, 1878, to the French Academy- Olszewski's
comments on the hydrogen experiment — Pictet's arrangement of pumps —
His desire to produce liquid oxygen in quantity— Comments on his work —
The liquide Pictet.
CHAPTER IX.— LOUIS-PAUL CAILLETET. Pages 173-202
The life of L--P- Cailletet— His education — Honors received— His modification
TABLE OF CONTENTS.
of Colladon's apparatus — Accidental liquefaction of acetylene by release —
Description of his apparatus— How the apparatus was filled — The full appa-
ratus with hydraulic press — liquefactions of nitrogen oxide — Of carbon
monoxide and oxygen mixed — Liquefactions of the same separately— His
letter of December 2, 1877, to the French Academy — liquefaction of nitro-
gen—Of hydrogen— Rival claims of Cailletet and Pictet— Mercury stopper
method— Manometers— Original methods of testing— Eiffel tower mano-
meter—Carbon dioxide experiments— Mercury pump— High pressure gas
reservoir— Ethyl ene as a refrigerant -Closed cycle method— Accelerated
evaporation— Electric conductivity at low temperatures— Comparison of
thermometric methods— La Tour's experiment repeated.
CHAPTER X.— SIGMUND VON WROBLEWSKI AND KARL
OLSZEWSKI. Pages 203-229
Wroblewski's life— Banishment from his native country— Early scientific
work — His association with Olszewski — Study of Cailletet's methods— Their
apparatus— Defective position of the hydrogen thermometer — Liquefac-
tions of oxygen, carbon monoxide and nitrogen — Ethylene data — Solidifi-
cation of carbon disulphide and alcohol— Determination of the critical
pressure and temperature of oxygen— Liquefaction of hydrogen— Use of a
thermo-electric thermometer — Electric resistance of metals at low tempera-
tures— Two liquids from air — Olszewski's individual work — Apparatus for
producing liquid oxygen in quantity — Comparison of platinum resistance
and of hydrogen thermometers — Determination of hydrogen constants.
CHAPTER XL— JAMES DEWAR. Pages 231-285
Dewar's life and education — His associates — Controversies with Cnilletet as to
priority — Early liquefaction apparatus — Solid nitrous oxide as a refriger-
ant—Royal Institution apparatus — Cooling cycles employed — Laboratory
apparatus —Vacuum vessels— Air as a heat conveyer — Experiments with
incandescent lamps— Reflection of ether waves from vacuum vessel— Keep-
ing power of vacuum vessels— The Dewar vacuum— Its extraordinary per-
fection— Analogy with population of earth— Experiment in slow diffusion
of mercury vapor— Incidental production of vacuum vessels — Elasticity and
strength of metals at low temperatures— Apparatus used — Elongation of
metals when stressed at low temperatures —Determination of specific and
latent heats of liquefied gases — Gas-jet experiments— LOW temperatures
thus obtained — Freezing air — Large jet apparatus —Analysis by liquefaction
—Liquefaction of fluorine — Liquefaction of hydrogen and helium — Experi-
ments to show the intense cold of liquid hydrogen.
CHAPTER XII.— CHARLES E. TRIPLER. Pages 287-296
The life of Charles E. Tripler — His early experiments with gas motors —
Mechanical difficulties encountered— His electrical experiments —Chemistry
—His work in fine art — Exhibition of his paintings— Return to the investi-
gation of compressed gases — Liquefaction of air— He endeavors to utilize
the low grade heat of the universe — Simplicity of his apparatus— The plant
— The compressor— General plan of operations— Capacity of his plant-
How he transports liquid air— His lectures— Raoul Pictet in Charles E.
Tripler 's laboratory.
TABLE OF CONTENTS.
CHAPTER XIII. — THE JOULE-THOMSOX EFFECT.
Pages 297-306
First attempts at liquefying gas— Joule and Thomson and their discovery —
Coal a cheap chemical— Substitution of mechanical for chemical energy
Sir William Siemens' regeneration of cold— Self-intensive refrigeration-
Negative Joule-Thomson effect — Mathematics of the theory — Conditions of
pressure for economical application.
CHAPTER XIV. — THE LINDE APPARATUS.
Pages 307-319
Linde's apparatus — The simplest form of apparatus— Its operation — Its stor-
ing of air at atmospheric pressure— Avoidance of atomization and waste —
Subdivision of pressure-drop— laboratory apparatus— A feature of ineffi-
ciency in it — Its power of liquefaction— Continuous oxygen-producing appa-
ratus-Date of Linde's first successful use of his apparatus.
CHAPTER XV. — THE HAMPSON APPARATUS.
Pages 320-324
Hampson's apparatus— Its general features of construction— The jet and
regulating device— Thermal and mechanical advantages— Data of its opera-
tion—Use of cylinders of compressed gas instead of pumps— Application of
preliminary cooling to the air or gas to be liquefied.
•^CHAPTER XVI. — EXPERIMENTS WITH LIQUID AIR.
Pages 325-337
Experiments with liquid air— Formation of frost on bulbs— Filtering liquid
air — Dewar's bulbs— Liquid air in water — Tin made brittle as glass— India
rubber made brittle -Descending cloud of vapor— A tumbler made of frozen
whisky—Alcohol icicle— Mercury frozen— Frozen mercury hammer-
Liquid air as ammunition — Liquid air as basis of an explosive- Burning
electric light carbon in liquid air — Burning steel pen in liquid air -Carbon
dioxide solidified— Atmospheric air liquefied— Magnetism of oxygen.
CHAPTER XVII. — SOME OF THE APPLICATIONS OF Low
TEMPERATURES. Pages 338-356
Frigotherapy — The frigorific well— Pictet's experiment — Effects of the first
trial of the system — Medical uses of liquid air— Critical point as test of pur-
ity of chemicals —Purification of chemicals by low temperature crystalliza-
tion—Low temperature distillation - Regulation of chemical reactions by
cold— Liquid air explosives— The principle of their action— Liquid air in
electric power transmission— Liquid air as a reservoir of energy.
TO
RAOUL PICTET
•'
LIQUID AIR
AND THE
LIQUEFACTION OF GASES
CHAPTER I.
PHYSICS.
j»
What is liquid air ? — The three states of matter : Solid,
liquid, and gaseous — Relations of pressure and heat to
state assumed by matter — The critical state and its phe-
nomena— Natterer'stube — Physical iinits — Space, mass,
and time — Force and energy — Conservation of force an
abandoned doctrine — Conservation of energy — Work a
synonym for development of energy — Waste of energy
and entropy — Possibility of utilizing the lower forms of
energy of the universe.
A question has often been asked latterly ; it is,
" What is liquid air?" The subject has been so
much discussed, and so much has been made of it,
that it is hard to believe that there is not some ,
occult mystery attending it. Liquid air is simply
air which is so cold that it assumes the liquid state.
The fact that the question has been so often asked
suggests the need for a thorough answer ; for back
of it there lies a great region of physics and chemis-
try, a summary exploration of which in the light of
10 LIQUID AIR AND THE
the knowledge of to-day cannot but be interesting.
In it are concerned the great doctrine of the con-
servation of energy, the laws of heat, the three
states of matter, and the chemistry of air, and it is
not expecting too much of the reader of to-day to
hope that the theory of the subject presented within
the compass of an hour's reading will interest him.
The account of the liquefaction of gases includes
a period of about one hundred years, and with it isN
bound up the history of the Royal Institution of
London. In its laboratory Faraday worked with
bent tubes, liquefying gases and blowing the tubes
to pieces and nearly blinding himself in his efforts.
This was half a century ago and more. And now
within its walls, with elaborate machinery based upon
Pictet's circuits of 1877, James Dewar, the successor
of Faraday, liquefies hydrogen and helium and ends
the century's work.
In Switzerland and France, toward the end of
1877, the beginning of the end appeared when oxygen
was liquefied. Pictet and Cailletet were the rivals,
separated only a few days in their liquefaction of
this gas, discovered by Priestly and Lavoisier almost
exactly one hundred years before the date of its re-
duction to the liquid state.
America was not idle. Tripler working away
privately, with no institution or association to back
him, has surpassed the dreams of the most enthusi-
astic visionaries and has made liquid air by the barrel,
and has sent it all over a wide range of country in
tin cans.
The long record should not be read until the
answer to the query cited above has been given ; the
LIQUEFACTION OF GASES. . I I
reader should know accurately what liquid air is,
what constitutes a gas, what the relations of heat and
pressure to state of matter are, and how heat is
treated by the modern scientist.
Matter is generally stated to exist in three forms
or states — the solid, liquid and gaseous. An attempt
has been made to assert the existence of a fourth
state — the ultra-gaseous or radiant state. There is a
certain objection, however, to this. The first three /
states are broadly differentiated. As a rule, there is
little question of the form or state being solid, liquid
or gaseous, but the ultra-gaseous state is only recog-
nizable by rather refined tests and may perhaps be
better considered as the extreme carrying out of the
gaseous condition. .1
Water is the most convenient substance to cite to
illustrate the three states. In ice we have solid
water. The masses are of fixed contour, and, even if
ice is subject to a species of flow, the masses of ice
definitely hold their shape. The molecules of solid
water are in constant vibration back and forth over
the same path, under any conditions of temperature
we are familiar with. At the absolute zero this
motion would cease. The paths are inconceivably
short. We cannot and probably never will acquire any
direct knowledge or sight of these vibrations. All
we know is that ice at mundane temperatures is hot.
It will be seen that, dropped into liquid air, it makes
it boil as if the ice were a red hot poker thrust into
it. By the kinetic theory of heat all hot bodies are
held to have their molecules in constant vibration.
Molecular attraction holds the particles of the ice
firmly together in spite of this vibration.
12 LIQUID AIR AND THE
If we apply heat, we diminish this attraction,
we increase the repulsive forces, and the ice reaches
a temperature where the two opposing forces about
balance each other, the attractive ones slightly pre-
ponderating. Now there is no longer a powerful
set of forces in operation binding the molecules
together. They begin to slide about on each other,
their vibrations continue with energy, but the paths
vary. A molecule bounces back and forth like a billiard
ball, recoiling to right or left from its neighbor, so that
sooner or later it travels through the entire mass and
never ceases its travels. As the molecules slide
V about without true friction the ice loses all tendency
to preserve its shape and falls to pieces, literally
speaking. In other words, the ice melts, and we have
water — a representative^ the liquid state Of matter.
Let us apply more heat. Our water is already
shapeless. We have to keep it in a containing vessel.
Even a drop of water hanging from the window shuttef
on a rainy day is held in a little sack of water-film.
Later on we shall see what an important bearing the
liquid film has in the manipulation of liquid air. So
we put our water in a kettle and heat it. Soon" a
white cloud issues from the spout, and we may say
that we see the steam. If we make such an assertion,
it is an erroneous one, as the white cloud is really
composed of little balls of liquid water, each held in
its own little sack of water-film. As the kettle boils/
harder, we find that the white cloud does not begin
its existence until it is a few inches from the mouth
of the spout, and a space apparently void of all
matter intervenes between spout and white cloud.
This space is filled with the substance we are in
LIQUEFACTION OF GASES. 13
J
search of; it is occupied by a column of gaseous
water or steam rushing out of the spout and as in-
visible as air itself.
By applying heat to our water, we have made the
molecules vibrate through paths many times longer
than the old paths; a cubic inch of water gives us
approximately a cubic foot of steam. The molecules
travel about through the mass with greater rapidity
than ever. The mass loses all pretensions to shape
or cohesion. A vessel will not hold it unless it is
closed everywhere. The third state of matter is y
formed— the water exists as a gas.
By refinement of observation and experiment most
interesting and captivating views are formed concern-
ing these states of matter. Their individual prop-
erties are not so sharply cut off and defined as might
be supposed. A body is said to be solid when it is
practically unchanging in the shape imparted to it.
But many solids flow under pressure. The suffering
" continuous deformation under the action of a con-
tinuous force " is not a certain criterion of a liquid,
but it is good enough to define it or identify it by.
A barrel of asphalt opened and thrown on its side
in the street seems to be filled with a black solid, yet
by the end of the day it will have flowed and
changed shape. A stick of sealing wax supported
at its ends slowly and continuously bends. Some
authorities consider these as examples of liquids.
A soft jelly pressed by a spoon yields consider-
ably, but, when the pressure ceases, springs back into
its original shape. Jelly, therefore, is treated as a
solid.
All this seems to cast confusion on the subject.
14 LIQUID AIR AND THE
But nothing very critical hinges on the sharp sepa-
ration of solid, liquid and gas. It would perhaps be
better to assume a continuity of state between solids
and liquids, and to consider asphalt, sealing wax and
the like as being on the border line. If sealing wax
is to be considered a liquid, then lead and most other
metals could be considered such; for metals, as a rule,
are more or less malleable and ductile, and the quali-
ties of malleability and ductility depend upon the
flow of the material composing them.
We are confronted with the old property of nature
expressed in the adage, Natura non facit saltum,
Nature does not jump. The air we breathe is in the
gaseous condition. The water we drink is in the
liquid condition. The glass which holds the water
is in the solid condition. Yet we can indicate many
cases where an intermediate state exists and where a
substance cannot well be termed one thing or the
other. Even air is not a perfect gas, and hydrogen
is an ultra-perfect gas.
For want of correct understanding of such things
as these, confusion in ideas results and an obscurity
bordering upon complication is introduced into our
conception of the laws and system of nature. Thus
moist air is generally considered heavier than dry
air, presumably because a wet cloth is heavier than
a dry one. Popularly, people would say that the air
is damp and heavy. Now air is wet because of the
mixture with it of another gas, gaseous water or
literally steam. Water from rain, from the ground
and from the immense evaporating surface of the
leaves of the vegetable world assumes the gaseous
form and mixes with the air. The specific gravity
LIQUEFACTION OF GASES. I 5
of water in the gaseous condition is less than that of
air. It is about two-thirds as heavy only. Wet air,
therefore, is lighter than dry air. A balloon would
rise better on a dry day than on a wet day, not only
because there would be no moisture with which to
dampen the cordage and cloth, and thereby increase
the weight, but because the dry air is a better float-
ing medium than wet air, because it is heavier.
Wet air is not air soaked like a sponge with water.
It is simply a mixture of dry air with gaseous water.
The truth is here far simpler than fiction.
The sequence followed by a substance in passing
from state to state is not always the same, as a solid
on heating is often vaporized or gasified directly
without passing into the liquid state at all. This
occurs in slow vaporization very often. Thus ice in
the open air below the freezing temperature wastes
away by volatilization and is gasified slowly, with-
out liquefying, and contributes water vapor to the
air, although far below the solidifying temperature.
Iodine volatilizes in the same way, and those who
have used camphor or naphthaline for preserving
clothes from moths have observed the same mysteri-
ous diminishing of the lumps of preservative used.
In druggists' windows the shrinkage of camphor
there exposed is sometimes quite striking. Now it
is less often exposed than formerly, as naphthaline
has largely supplanted it in the trade.
Carbon dioxide, the gas which escapes from soda
water and other effervescent beverages, when sub-
jected to cold and pressure, liquefies. When the
pressure is released and it is allowed to escape into
the open air, it solidifies and produces a true carbon
l6 LIQUID AIR AND THE
dioxide snow. This snow exhibits surprising per-
manency, disappearing quite slowly in the open air-
In disappearing it evaporates and produces gas
directly without passing through the intermediate
liquid state.
Such direct transition from a solid into a gaseous
state is termed often sublimation ; an expression, per-
haps, too limiting, covers the extreme case where a
solid on application of heat sublimes vigorously before
melting. It is to the effect that the substance boils at
a lower temperature than that at which it liquefies—
that the temperature of boiling is lower than that of
liquefaction. The idea of a solid boiling seems rather
odd.
It is not only the change of temperature which
brings about change of state. Change of pressure V
affects it greatly. The greater the pressure, the
higher is the temperature at which a liquid becomes
a gas. A gas just hot enough to hold that form may,
under some conditions, be converted into a liquid \ J
by applying pressure, without any change in tempera-
ture being required to effect the change of state.
This, too, is very natural. For a liquid, under ordin-
ary conditions, being of smaller volume than the. same
molecules gasified, is naturally brought to the liquid
condition by mechanical reduction of volume as well
as by thermal reduction.
Pressure will not always do it, and by combining
the effects of great heat and great pressure, conditions
foreign to the ordinary status of matter are brought
into existence which complicate the problem. Heat
is the great and all-controlling agent. Heat is what
establishes the critical state, and pressure is quite a
LIQUEFACTION OF GASES. I/
secondary matter. For every gas there is a critical
temperature and a critical pressure, but the latter is
quite a subsidiary thing, and is not critical in the full
sense that the temperature is.
Pressure tends to liquefy a solid, it the latter grows
smaller on liquefaction. So that it is quite conceivable
that a point might be reached where pressure would
help to convert a liquid into a gas. As such a phe-
nomenon, uncomplicated by other factors (page 24),
has never been observed, it is better to set it aside
and consider pressure as invariably on the side of
cold in liquefying gases.
A gas must be pictured to the imagination as a
very active thing. In a room full of air the molecules
are moving about rapidly, colliding with each other,
and bounding about like billiard balls. We know
that, if we turn on the gas without lighting it, in a
very few minutes the odor of gas will be perceived
in all parts of the room. This can only be so because
in those few minutes the gas has penetrated every
corner. Its molecules have traveled about until
some of them are everywhere present, and the
activity of their operations may be judged by the
amount of gas and the size of the room. An ordinary
burner delivers one cubic foot of gas in about ten
minutes, and in that time a room of over a thousand
times that volume would be pervaded with it. Hence
it will be seen how active the molecules of a gas
are.
If there were no wind, if the air were absolutely
motionless, its molecules would be as active as ever
in their own spheres. The air which on one day
would be in America would be scattered the next
18 LIQUID AIR AND THE
day far and Wide, and its molecules would find their
way sooner or later all over the world.
The same is true in a lesser degree of liquids.
The water of a tideless, currentless lake is in mole-
cular motion. The water which beats against the
coast of America is in constant process of change,
and its molecules are changing and moving about all
the time. Sooner or later some of them will be in
the waves which break upon the Irish cliffs and
English beaches, nearly three thousand miles away.
They would travel thus were there no oceanic cur-
rents and no waves.
This molecular travel is termed diffusion.
We have seen that the motions of the molecules
are increased in vigor by heat, that, if heat is with
drawn, they decrease in intensity. The obvious
question arises, What would happen if there were no
heat? The molecular motions would cease, and
molecular death would ensue.
The passage of a substance from the solid to the
liquid state or from the liquid to the gaseous state
involves generally a change in dimension or size, and
in the case of many substances the liquid state is the
one of smallest size. This is the case with water. In
round numbers, a pint of water gives nearly a pint
and two ounces of ice, if it freezes, and if converted
into steam, gives nearly two hundred gallons. We
are most concerned with the liquid and gaseous
states, and under ordinary circumstances there is a
very great reduction of volume incident to the pass-
age of a substance from the gaseous to the liquid
state.
It follows that, to produce liquefaction of a gas,
LIQUEFACTION OF GASES. \Q
the first thing we should naturally try to do would
be to reduce it in volume, and the simplest way to
do this would be by pressure. Early experimenters
adopted this plan. Natterer attained pressures of
many thousand pounds to the square inch, yet gases
compressed to a small fraction of their volume staid
gases and refused to yield.
At last Andrews, of Belfast, made his classic dis-
coveries, and the existence of a critical state was es-
tablished. This state is very easy to understand. It
depends on the fact that for every gas there is a
temperature called its critical temperature, and a
. corresponding pressure called the critical pressure.
When hotter than this temperature, no compression,
however great, will liquefy it. Below this tempera-
ture, a compression easy of attainment is enough to
effect the change to the liquid state.
The critical pressure is a term which is often mis-
understood. It may be said that the pressure is
never critical in the full sense in which temperature
becomes critical. There is no pressure which can be
defined as so low that liquefaction would be impossi-
ble in it. There is a theoretical point of cold never
yet attained, which is termed the absolute zero. At
this point heat ceases, the molecules no longer
vibrate, and absolute cold exists. If a body were
reduced to the absolute zero, where the motions of
the molecules cease, pressure would be without
effect upon it, as its only power is to shorten the
paths of vibration of the molecules. The term criti-
cal pressure is used to describe the pressure required
to liquefy a gas when it is at the critical temperature.
When a gas is at the critical temperature and at
20 LIQUID AIR AND THE
the critical pressure also, the least increase of
pressure or decrease of temperature will convert it
into a liquid. When in this condition, ready to be a
gas or a liquid, it is said to be in the critical state.
It will be seen how very well the term critical
state applies when a substance is at the critical
pressure and temperature, the least change will so
profoundly modify its state.
A law relating to the critical state is known as
La Tour's law, and expresses very succinctly the
phenomenon of the critical temperature. It is the
following :
There is for every vaporizable liquid a certain
temperature and pressure at which it may be con-
verted into the aeriform state in the same space occu-
pied by the liquid.
It will be evident how strikingly this puts the fact
that, above a certain temperature, a gas can be
squeezed down to the volume of its mass as a liquid
without liquefying. If a gas rigorously followed
Mariotte's law and changed in volume in inverse
proportion to the pressure exerted upon it, and if
pressure sufficient to reduce it to the absolute
volume, as it may be termed, or the volume it should
have at the absolute zero, were exerted upon it, it is
hard to say what would become of it.
The condition of a substance in the neighborhood
of the critical state is sometimes termed the inter-
mediate state. The expressions are almost synony-
mous— the first is the more abstract, the latter the
more concrete expression.
The reduction from the gaseous to the liquid state
is usually a reduction of volume. A cubic foot of
LIQUEFACTION OF GASES. 21
steam gives about a cubic inch of water ; eight hun-
dred cubic inches of ordinary air give about a cubic
inch of liquid air. But owing to the phenomenon of
the critical temperature, or, what is the same thing, to
La Tour's law, this is not always true. The existence
of a gas of no greater volume than the liquid it could
be converted into is a sort of scientific riddle. It
has its counterpart in the inexplicably great power
of expansion by heat possessed by some liquefied
gases without departure from the liquid state.
The passage of a substance from the liquid to the
gaseous state is marked by a change of appearance
A liquid has always a defined limit. It lies in the
containing vessel and its upper surface forms a visi-
ble boundary. If the vessel is of large diameter, the
surface is level and flat, except along the edges,
where it curves up or down a little. If the diameter
is small, it curves throughout its whole extent, form-
ing a little cup or a little hill, as the case may be.
The upper curved surface of a liquid is termed the
meniscus. Mercury in a glass tube forms a convex
meniscus; water, a concave one. For different
liquids in contact with solids the meniscus varies, a
characteristic one obtaining for each condition.
A very interesting suggestion is due to Jamin.
It is that when oxygen and carbon dioxide are com-
pressed together, a point may be reached when the
carbon dioxide will liquefy but will be lighter than
the compressed gas, so that we should have the
curious phenomenon of a fluid floating upon a gas.
Prof. Ramsay seems to think that he has observed
this phenomenon. The meniscus in this case lies
at the bottom of the liquid and above the gas.
22 LIQUID AIR AND THE
For years the disappearance of the meniscus was
regarded as marking the change or transition from
the liquid to the gaseous state. This view seemed
satisfactory. But science is not restful. Doubts
began to be cast upon the coincidence of this disap-
pearance with the true transition.
Thus in 1892 Zambiasi attacked the problem by
experimenting with ether in a sealed tube and repro-
duced the intermediate and critical state phenomena
therewith. Cagniard de la Tour's and Cailletet's
observations were studied with the more manageable
ether. Zambiasi came to the conclusion that the
appearance and disappearance of the meniscus, while
occurring at a constant temperature for a given tube,
occurs at different temperatures in different tubes,
the temperature being determined by the relative
proportion of liquid to gas in the tubes.
In 1893 there were published a number of papers
by Ramsay, Galitzine and others on the subject of
the critical state and the uncertainty of the optical
method, by simple inspection, of determining the
transition from liquid to gaseous state. Quite an
acrimonious discussion is contained in successive
communications between the opposition scientists.
The subject is left rather unsettled ; the disappear-
ance of the meniscus with some has lost its old time
definite status, and the case is left pretty nearly in
statu quo.
But the disappearance of the meniscus is not the
only phenomenon of change of state. A peculiar
flickering appearance is noted as indicative of it, to-
gether with the formation of striag, and so character-
istic is this feature that it is used by Pictet in some
LIQUEFACTION OF GASES.
of his most recent work as an indicator of gasefac-
tion.
If a tube is partly filled with a liquid, is sealed and
heated, the first indication of a change of state to be
looked for is the disappearance of the meniscus. As
it vanishes, the flickering striae appear and a sort of
unrest pervades the tube, and quickly the critical
state is passed and the liquid has become a
gas.
The phenomenon is conveniently shown
in a sealed tube half filled with ether, as
shown in the cut. It is mounted within a
larger tube filled with paraffin wax. The
latter is opaque and solid when cold, but
on heating melts and becomes transpa-
rent. On heating the wax, the liquid in
the inner tube goes through the critical
state, the phases can be watched, and the
phenomena described above can be seen.
If it is to be shown to an audience, the
image of the tube is projected upon a
screen by the magic lantern, and the phe-
nomena are produced so as to be visible
by a roomful of spectators. The sealed
tube is termed Natterer's tube.
Hannay and Hogarth, in 1880, in experi- Natterer's
ments on the critical state of matter, found
that several salts, such as potassium iodide and bro-
mide, would dissolve or volatilize in gaseous alcohol
at a temperature of 375° C. (707° F.), the whole
being contained in a strong sealed tube.
P. Villard (1898) extended the scope of this in-
vestigation and got very interesting results with
24 LIQUID AIR AND THE
solids and liquids. As a liquid, bromine may be
cited. This was placed in a tube with oxygen gas,
and the pressure was gradually increased. Normally
increase of pressure would be supposed to tend to
keep the bromine liquid. But, on the contrary, at
two hundred atmospheres, the bromine began to
take the gaseous form and to dissolve in the com-
pressed oxygen. The action of the dark brown
liquid was exactly that of a substance entering into
solution. The gaseous mixture took a darker color
at three hundred atmospheres than that of a solution
of bromine in water. Villard recalls Cailletet's ob-
servation that liquid carbon dioxide dissolves in
air. We may also call to mind the liquide Pictet
(page 1 70) in this connection.
Bromine is a brown liquid, and is one of the ele-
ments ; its near neighbor, iodine, is a solid. The
latter was found to dissolve in small proportions in
oxygen. Formene was another gas which was ex-
perimented with. It dissolved ethyl chloride, car-
bon disulphide, alcohol, camphor, paraffin and
iodine. In some cases the gas-solution phenomena
were almost reproductions of the critical state phe-
nomena, including the obliteration of the meniscus.
A very interesting suggestion was made by Vil-
lard ; it was that gaseous solution might take the
place of distillation as a laboratory operation.
As the doctrine of the conservation of energy is
intimately involved in the liquefaction of air and of
all gases, something may be said of the relations of
force and energy. This may more appropriately be
done as it will bring forward a treatment of the sub-
ject which may commend itself to some interested
LIQUEFACTION OF GASES. 25
in physics. This treatment of the subject is based
on the substitution of two units for three. Usually,
force, work and energy are the interrelated units ap-
pealed to in treatises on mechanics. The far more
desirable way is to follow out the theory of dimen-
sions and to take two of these units only as the
foundation stones of the science. These two are
force and energy. Work, instead of being awarded
an important place, should be treated only as an
adjunct and convenient expression of the concrete
and accidental. This sounds, perhaps, heterodox.
It is really orthodox, and is a move in the direction
of avoiding confusion.
As music is built up out of a few notes, as the
twenty-odd letters of modern alphabets in a sense
are the basic units of the written languages, so we
have certain fundamental elements in natural science.
These may, for our purposes, be stated as distance or
linear space, mass and time. These are familiar to
all. The accepted units are the centimeter (0*39
inch), gramme (15*43 grains) and the second. Then
there are two derived units, less familiar in their
scientific status, and less generally understood,
than the others cited above. These are force and
energy.
Distance is linear space, space measured along a
line, space ol one dimension. A foot, an inch, a
centimeter, are units of distance. An attempt was
made to get an absolute unit by taking one ten-
millionth part of the quadrant of the earth as a unit.
This is what the French meter was supposed to be,
but the measurement was inexact ; so the unit is as
truly inexact as was the old time barleycorn, except
26 LIQUID AIR AND THE
in degree. Its exactness was many. times greater, as
it approximated at least to a fixed standard, and the
length of a barleycorn is as unfixed a standard as
could well be imagined, although our system of
measures is based on it. Three barleycorns make
one inch, and the exceedingly exact standard yard
measures carefully preserved by the British and
American governments had their origin in the
length of a corn of barley. The most recent and
scientific unit of length is the wave length of a given
monochromatic light. But for everyday purposes
the foot is very generally used in this country.
Time is the measure of duration and is the function
having a truly international unit, the second. This
is an astronomical unit, and might be used as a basis
of all others. The proposal to do so has been made,
but has never been carried out.
Mass indicates the quantity of matter in a body.
It is a somewhat unfortunate unit, as it is constantly
confused with weight. Apiece of iron has a definite
mass, but it weighs one amount at the equator and
another amount at the poles. On the surface of the
moon it would weigh far less than on the surface of
the earth. From one point of view the proper unit
of mass would be equal to a pound, or a gramme, or
whatever may be taken as the unit of weight divided
by the velocity a body acquires in falling through a
vacuum for one second . As this last quantity varies
at different parts of the earth, it would seem that
the unit of mass should in some way be fixed, and
that the unit of weight should vary. Accordingly,
the quantity of matter in one gramme is taken as the
unit of mass. Weight varies, for a pound of sugar
LIQUEFACTION OF GASES. 2/
at the poles is slightly greater in mass than a pound
at the equator. This is very scientific, but does not
square with the relative sweetening power of the two
pounds.
We have just spoken incidentally of velocity.
This is a unit which indicates the distance passed
over in a second. As two unitary quantities, time
and distance, are involved, it is compound.
We are now ready to see what force and energy
are. They are the hardest of all to grasp. Had
Faraday and a host of others grasped their signifi-
cance, the erroneous doctrine of the conservation of
" force " would never have been invented.
Force may be variously defined. Newton's defini-
tion of it as given by Daniell is "a measurable action
upon a body, under which the state of rest of that
body, or its state of uniform motion in a straight
line, suffers change." But force may be exerted
without producing any such change, so that the de-
finition, like many others, is not satisfactory. A copy-
ing press applies force to the book it squeezes as
long as the screw is left turned down, but it imparts
no change of state ot motion or of rest to the book. A
spring held by a catch of any kind so as to be in a
state of tension exerts force against the restraining
piece, but there is no question of change of state of
motion or of rest. The definition of force as that
which exerts a pressure or a pulling stress upon
anything, or between any two or more masses, is,
for ordinary purposes, an exact enough definition,
though not a very elegant one.
The total forces exerted in the universe may vary
constantly in amount. There is no such thing as the
28 LIQUID AIR AND THE
conservation of force, conservation meaning, in such
a connection, constancy or invariability of quantity.
Force may be called into existence and annihilated at
will. It varies ad libitum just as motion does. A
man may run or walk or stand still. He thereby
creates or annihilates motion. He may do the same
for the force he exerts by his own control.
Not many years ago a work was published on the
subject of the Conservation of Force. It was made
up of extracts from the writings of various scientists
which treated of the supposedly true doctrine of
the conservation of force. Among other writers
Faraday was quoted, and it is curious to see how he
could not reconcile the contradictions of the sup-
posed law. He accepted it on the weight of
authority of others, his acceptance giving a lesson in
humility which some doctrinaires of the present
day might profitably study.
All the while the doctrine was an utter falsity and
is now discarded absolutely. It is one of the monu-
mental errors of the scientific world. It shows that
students of science have their own errors to contend
with and guard against. We can reasonably believe,
however, that we are not fast bound at present in any
such error, at least in the field of physics.
Faraday, who has been cited above, was one of the
loveliest figures in modern science and his appearance
here is not the only one he makes in the pages of
this book, as he appears as one who paved the way
for the liquefaction of air and for that of the so-
called permanent gases. He it is who gave one of
the first blows to this name.
There is one survival of the erroneous doctrine
LIQUEFACTION OF GASES. 2Q
which, although it only affects the nomenclature, is
interesting to notice. It is the term " living force,"
which cannot be said to have quite disappeared from
the language. It was long used as the expression
for mechanical energy. The French, who are more
conservative than we, adhere to it far more tena-
ciously, and its equivalent is found in many recent
scientific papers in that language. The term is a
metaphorical presentation of the idea of force in
action, and force in action is nothing more or less
than energy. If the acton is positive, it is the
exertion of energy ; if the action is negative, it is the
development and consequent absorption of energy.
But the best method of avoiding confusion in
modern science is to concentrate the nomenclature
and to avoid useless multiplication of terms. So the
term living force, picturesque as it is, is very pro-
perty abandoned for the more concise term energy.
Energy is a unit which expresses the action of a
force along a distance. If a man pushes against a
car, and all remains stationary, he exerts, properly
speaking, no mechanical energy, but only force. But
if the car moves, and he follows, pushing it before
him, his force is exerted along a distance, and the
compound force-distance unit thus indicated is called
energy. Two actions are involved. The man ex-
pends energy and gets rid of it. It disappears. But
the car receives energy, and in the overcoming of its
inertial and f rictional resistances an amount of energy
is received by it precisely equal to that which has
disappeared. This energy is largely converted into
heat.
Suppose an athlete holds a dumbbell by his side
30 LIQUID AIR AND THE
and raises it to arm's length. The dumbbell weigh-
ing ten pounds and the lift being four feet, he would
have expended on it energy represented by the pro-
duct of force and distance. The force may be
popularly expressed in this case as ten pounds, the dis.
tance is four feet ; the energy expended is forty foot-
pounds. The energy which he spent in lifting the
dumbbell has disappeared, and in its place has been
created the energy now inherent in the lifted mass.
By virtue of its position the dumbbell has an ability
in recovering its old position to exert energy in its
own turn. If the bell drops the four feet, it will, in
doing so, lose its favorable position and exert energy.
The exerted energy will disappear and cease to exist,
but in its place a precisely similar and equal quantity
of energy will be developed.
Suppose now that the dumbbell is allowed to fall
the four feet through a vacuum. At the end of its
fall it will be moving quite rapidly and will be able
to strike quite a severe blow. This blow it can in-
flict by virtue of the energy inherent in it. As this
is derived from a fall of four feet, it will be measured
by distance and force as before, by forty foot-pounds.
If it strikes its blow and comes to rest four feet from
its starting point, its energy will disappear, and in
some form or other forty foot-pounds of new energy
will be created.
The reader will observe that the dumbbell held
motionless four feet above its level of rest has the
power, when called upon, of exerting in its descent
the forty foot-pounds of energy which the athlete
exerted on it. It possesses the power of exerting
energy, which power is termed potential energy.
LIQUEFACTION OF GASES. 31
Reaching the end of its four-foot fall, it then is
charged with energy real and positive, by virtue of
which it can inflict a blow. This is the energy of
motion or kinetic energy.
Illustrations could be produced in any desired
quantity. It would be found that whenever energy
disappeared, an equal quantity of other energy
appeared. This law holds good always without any
exception, and is universally accepted as fixed and
invariable. It is most generally expressed by say-
ing that the total energy of the universe is always
the same in amount.
It will be noticed that the term "work" has not
been used in this brief exposition. Usually, it is one
of the first things cited in such cases, and energy is
defined as the power of doing work. But it is
much better to keep the fact clearly before us that
energy is the important and more fundamental unit,
and that work is simply another term for develop-
ment of energy. To " do work " is to expend
energy. Our athlete, in raising the dumbbell, ex-
pends his own energy, develops new energy, and the
latter is the doing of work. The particular energy
exerted by the athlete ceases to exist, and is re-
placed by an exactly equal amount of energy devel-
oped in the dumbbell by its change of position. The
dumbbell, it would generally be said, has had work
done upon it, the lifting of it constituting work ; it
is far more logical to term this lifting the develop-
ment of energy in the object acted on.
It would seem somewhat presumptuous to at-
tempt to do away with the term work, and the word
is so convenient, and is in such universal use among
32 LIQUID AIR AND THE
physicists, that it cannot be dropped. It should,
however, be treated rather as a convenience than as
a real physical unit, and it should always be under-
stood to be a shorthand term and synonym for de-
velopment of energy. If work is performed, it is
development of energy that is performed, and the
object which does the work expends energy in de-
veloping new energy.
There is a very simple experiment, which anyone
can try, which supplies an excellent illustration of
the conversions of energy. An india rubber band is
held by the two hands across the mouth, so as just
to lie between the lips. It is now stretched.
The energy of the experimenter is spent on
stretching the band; some other equivalent of
energy must be developed to take its place. As
the band stretches, the lips can feel it grow
warmer. The mechanical energy expended in
stretching it is converted into the kinetic energy of
heat. It is allowed to resume its original length.
In doing so, it exerts energy. It has only the kinetic
energy of its heat to call upon. Accordingly, it
grows cool as it resumes its original length, and the
lips feel the cooling effect. It illustrates the law of
the conservation of energy excellently, and is parti-
cularly interesting to the reader, as it applies very
strikingly to the expansion and contraction of gases.
We can now appreciate the conception of a reser-
voir of energy. The pound weight, held at four feet
elevation, exerts no energy, but does exert force. It
is a reservoir of energy in potential form. The
same weight, moving with the velocity acquired by
a fall of four feet, is a reservoir of energy in
LIQUEFACTION OF GASES. 33
kinetic form. Brought to rest after its fall, the
kinetic energy it was charged with disappears and
it is no longer a source or reservoir of energy.
When energy is expended by any mechanism, the
new energy developed to replace the old in the
world's scheme, and to keep the amount of the
world's energy invariable, is apt to take largely the
form of heat energy. A railroad train has expended
on it the energy of the locomotive. Suppose it runs a
mile upon a dead level. At the end of the mile it
occupies a position not one whit more advantageous
than when it started, as far as energy of position is
concerned. Yet the fire in the fire-box of the engine
has fiercely burned over the mile run, and the en-
ergy of the sun of bygone ages, stored up for geo-
logic epochs in the inert coal, has been expended.
What energy has been developed to take its place
and keep up the balance ?
It is energy of heat. The wheels have pounded
over the rails, heating themselves and the rails, their
journals and the journal-boxes have been heated, and
even the energy expended on overcoming the air
resistance has heated it a little, and the sides of the
cars have been heated a little also. This heat is
absolutely useless, or even pernicious. We cannot
move a train along a level roadbed, we cannot drive
a ship across the level plain of the ocean, without
expending energy which we can never recover. It
goes into the storehouse of nature, never to be re-
covered by man until another great step in advance
is made. The liquefaction of air has in it a germ,
dimly recognizable, which may enable us to utilize
the low forms of energy with which nature is
34 LIQUID AIR AND THE
charged. The ocean path, and the steamer which
traverses it, at the end of the Atlantic trip may have
received one hundred and forty thousand horse power
days of energy. Now it is all lost to man. Man's
ingenuity perpetrates no more wasteful and unsatis-
factory acts than the transfer of himself and his
possessions across the ocean or over continents.
The thirty thousand horse power engines of the
transatlantic liner are no more a triumph of human
ingenuity than in their enormous wastefulness of
practically one hundred per cent, they are a conces-
sion to his inability to utilize the energy of the
universe.
This brings us face to face with the doctrine of
entropy. We have seen that the low degrees of
heating produced by the friction of machinery, and
which represent its wasteful resistance, are lost for-
ever to us. The potential chemical energy repre-
sented by the separation of carbon and oxygen is the
energy of carbon or coal which can be burned under
a boiler when it unites with the oxygen of the air.
This is one of the world's energies which can be util-
ized by man, and these energies are called available
energy or entropy. The world's coal is being burned
up, its forests are being destroyed, machinery is add.
ing to the irreclaimable energy of the world, and, by
the doctrine of the conservation of energy, is destroy-
ing that same quantity of available energy ; hence
the entropy of the universe is becoming smaller day
by day.
Clerk Maxwell saw the possibilities of the utiliza-
tion of the unavailable energies of the universe. It
is provoking to know that our great ocean of air
LIQUEFACTION OF GASES. 35
is pulsating with molecular energy which we do not
utilize. Yet we do utilize it in a sense in compressed
air motors, we call upon it in liquid air work, and
Clerk Maxwell's dream of the utilization of the lost
energies of the universe may yet come true by the
application of liquid air and liquefied gases to motors.
A popular paradox, which has been much dis-
cussed, may be used to give an example of the doing
of work at the expense of the low grade heat of the
air and of other matter. A steel spring is placed in
tension or is wound up. It is then dissolved in acid.
The question is, What becomes of the energy which
seems to be present in the spring, and ready for
utilization ? One theory is that there is present in it
no energy which in any way is due to its being
wound up. When first wound, the energy expended
in the operation develops new low-grade heat energy,
and the spring is slightly heated. Then it loses the
heat in a few seconds, and there is no longer any
more energy in it wound than unwound. Therefore,
it dissolves in acid without having any special
energy to account for.
Now, the question may be asked, How can the
spring, if it has no energy, drive a clock? It does
this, not at the cost of any mechanical energy due to
its tension, but utilizes the low-grade heat energy
of which we have been speaking. As it drives the
clock it gets cool, and the energy required to drive
the clock is represented by this cooling. As air
circulates around it, it recovers immediately any
loss of temperature, so that no loss of heat is practi-
cally discernible. But the clock is driven primarily
by the heat of the air, by heat such as is usually
36 LIQUID AIR AND THE
treated as unavailable. The India rubber band ex*
periment described on page 32 is an exact illustra-
tion of the point involved.
Elsewhere *,he possibility of using liquid air as a
substance for the storage of power is alluded to. If
this were done, an engine could be driven by it exactly
as by steam, except that the heat would be drawn
from the atmosphere instead of from a burning fur-
nace of coal, and there would be a utilization of low
heat energy.
LIQUEFACTION OF GASES. 37
CHAPTER II.
HEAT.
Heat and its measurement — Thermometers — The zero point —
The Celsius or Centigrade thermometer scale — Fahren-
heit's thermometer scale — The absolute zero — Its basis —
Coefficient of expansion of gases — Determination of
temperatures in the liquefaction of gases — Different
liquids used in filling thermometers — The air thermome-
ter— The hydrogen thermometer — Details of its con-
struction— Electrolytic hydrogen — The hydrogen or air
thermometer formula — The thermo-electric thermometer
— Onnes ' instrument and details of its construction — Its
calibration — The electric resistance thermometer — Calori-
metric determination of temperatures.
Heat has been referred to. While all have a gen-
eral idea of heat, the basis of the different thermome-
ter scales may be spoken of, and the absolute zero
defined more fully.
Various thermometer scales have been proposed,
and three are in general use. Thermometers
generally indicate the temperature by the move-
ments of an indicator over a graduated scale.
Mercury and colored alcohol are the substances
whose expansion by heat is utilized for ordinary
thermometers, and the upper surface of the column
of mercury or alcohol forms the indicator. The
scales had to be divided on some system or other.
The first thing to be settled was where to place the
zero point at which to begin the division. Fahren-
38 LIQUID AIR AND THE
heit placed it well below the freezing point of
water. Reaumur and Celsius placed it at the point
where ice melts, which is the freezing point of water
also. A name for this point is required, and the
name zero, of Italian origin, from the same Arabic
root as our word cipher, is given to it. Zero seems
to apply more to thermometric scales than to others,
simply because we are more familiar with this class
of scales than with hydrometers and other scale-
bearing instruments.
At the zeros of the above thermometric scales
an active molecular motion exists; there is a
quantity of heat present in all things, at and far
below the zeros ; ice is hot, ice water is hot, frozen
mercury is hot. This seems illogical; nothingness
on the thermometer scale should indicate nothingness
of heat. As thermometer scales are graduated now,
their zero points are placed in a locus of very con-
siderable heat. They can only be called points of
relative cold ; we think them cold because of our
physiological peculiarities. Bacteria do not seem
to think that ice is cold ; at least they live through
freezing unimpaired in vitality.
Two easily produced temperatures are used for
establishing thermometer scales. One is the boiling
point of water, the other the melting point of ice.
By comparatively simple apparatus these tempera-
tures can be reproduced at will, without need of the
application of any difficult correction. For the gra-
duation of ordinary thermometers no correction is
applied, although the barometer reading should be
taken into consideration.
The standard scientific thermometer is the Celsius
LIQUEFACTION OF GASES. 39
or Centigrade instrument. In this the temperature of
melting ice is taken as zero, that of boiling water, or,
more accurately, of steam at atmospheric pressure,
as one hundred, and the space between and above
and below these points is uniformly divided off on
that basis.
One account says that Fahrenheit attempted to get
absolute cold, that he made a freezing mixture with
ice water and salt, or sal ammoniac, and took its
temperature as being perfect cold. Then he took
the temperature of the human body as another
datum point, and tried to have the freezing point of
water one-third way between his zero and the human
body temperature. Of the three devisers of ther-
mometric scales, he was the only one who made an
attempt to get a genuine zero. In the early days of
the eighteenth century, when Fahrenheit was doing
his work, the kinetic theory of heat, which is what
we are here describing, had not been evolved. It
was in 1724 that his low temperature experiment was
published.
Another explanation of Fahrenheit's thermometer
is that he took as his zero a temperature observed
at Dantzig, Prussia, which he found that he could
always reproduce by salt and ice. He computed
that at that temperature, which he believed to be the
absolute zero, as he interpreted it, his thermometer
contained 11,124 parts °f mercury, which expanded
to 11,156 parts in melting snow. This gave him 32
parts expansion, or 32 degrees. In boiling water he
found his mercury had increased to 1 1,336 parts. This
gave him (11,336 — 11,124=212)212 parts or 212 de-
grees between his zero and the boiling point.
40 LIQUID AIR AND THE-
Absolute cold has been defined. It is the temper-
ature at which all heat energy ceases — when the
molecules would cease to vibrate, when molecular
death would occur. This point is the starting point
of the theoretically correct themometer scale — its
zero. Were it not too late, the thermometer scales of
the world should be based on this point as a starting
point.
This point is termed the absolute zero. It lies at
273° C. below the Centigrade zero ( — 459*4° F.)
A good temperature for a living room is 20° C.
(68° F.) It would on the absolute thermometer be
273+20=293° C. (527-4° F.) Instead of complaining
that the mercury has gone up to 99° in the shade,
we might correctly call it 558° in the shade and feel
that we had better ground for complaint. The
absolute zero has had a definite place assigned it,
based on the properties of the form of matter which
is acted on by heat with perfect freedom. It is the
form of matter in which the molecules are free to
move under the influence of heat unhampered by
any individual attraction, in other words, the gaseous
form of matter.
Imagine a quantity of gas which we will suppose
to have, at the freezing point, a volume of 273 cubic
inches. If we heat it i degree Centigrade, it will
become 274 cubic inches. Another degree rise of
temperature will make it 275 cubic inches, and so on.
If we cool it i degree Centigrade below the freez-
ing point, it will become. 272 cubic inches, and so on
all the way down. The paths of vibration of the
molecules thus grow smaller and smaller with each
reduction in temperature, until we are led to the con-
LIQUEFACTION OF GASES. 41
elusion that, when the temperature has been lowered
273 degrees, the gas, losing i cubic inch at each
degree reduction, will have lost its entire volume,
or will have been reduced as near to a volume of
nothingness as it can get. Now, the idea of its
having a volume of nothingness or of a gas losing
its entire volume being absurd, we substitute the
theory that, at 273 degrees below freezing, the
paths of vibration of the molecules will become
infinitely short, that their length will become
nothing, and that the molecules will rest.
The absolute zero is based on these considerations.
The proposition is stated and proved above in a very
crude way, but it gives a simpler presentation of the
subject than is given in the ordinary statement of the
subject. The law of the expansion of gases by heat
may be thus more scientifically stated.
If we start with a volume of gas at any tempera-
ture and apply heat, it will increase in volume. For
equal increments of heat it will increase identical
amounts, or for equal increments it will increase
equal portions of the original volume. Confining
ourselves now to the Centigrade scale, we find that
for increments of temperature of i degree, the
volume of a gas will increase by ^--g- of what its
volume would be at the temperature of melting ice
or zero Centigrade. This is termed the coefficient
of expansion of gases. The same occurs for re-
ductions of temperature. Therefore, at 273° below
zero no more reduction in volume will be possible.
At this point the motions of the molecules must stop
— it is absolute zero.
The determination of the low temperatures em-
42 LIQUID AIR AND THE
ployed in experiments on the liquefaction of gases is
naturally attended with difficulty. The mercurial
thermometer Jiad to be discarded because the metal
solidified at a comparatively high temperature when
referred to the degree of cold attained in the experi-
ments. Even in Faraday's experiments the mercurial
thermometer was discarded in favor of the alcohol
thermometer. The degrees on the instrument he
employed, which was a Fahrenheit thermometer, were
graduated below 32° F. into degrees respectively
equal in length to those between 32° F. and 212° F.
on its scale. He got down to — 1 10° C. ( — 166° F.)
Not reaching the critical temperature of oxygen, he
naturally failed in liquefying it. What Wroblewski
and Olszewski term "a dazzling demonstration"
(eine gl'anzende Bestatigung) is given by an experi-
ment of Natterer, who shows that the incredible
pressure of 3,000 atmospheres alone is insufficient
to liquefy oxygen. When it is realized that the
pressure in a modern cannon at its maximum is
about two-thirds of this amount, it can be seen what
the scope of Natterer's experiment was.
Natterer used a thermometer filled with phos-
phorous chloride, as he orally informed Wroblewski
or Olszewski (Wicdemanns Annalen, 1883), and
Cailletet, in his work on low temperatures, used a
carbon bisulphide thermometer. Wroblewski and
Olszewski used a hydrogen thermometer constructed
on the model of Joly's air thermometer (Poggendorff s
Annalen, 1874).
Wroblewski and Olszewski found a slight discrep-
ancy between" the readings of a carbon bisulphide
and a hydrogen thermometer. The carbon bisulphide
LIQUEFACTION OF GASES. 43
instrument read about 2 degrees Centigrade lower
than did the hydrogen thermometer. This reading
was but a few degrees above the solidification point
of carbon bisulphide, and under such conditions,
namely, an approach to its solidification temperature,
an irregularity in expansion and contraction is always
to be looked for in a liquid. The carbon bisulphide
thermometer scale is graduated on the basis of
higher temperatures — the coefficient of expansion
is much greater near the solidification point than it
is higher up the scale.
The same observers note that when the carbon
bisulphide freezes in the thermometer, the tube breaks
into several pieces. They found that a couple of
minutes' evaporation of ethylene in a vacuum was suf-
ficient to freeze bisulphide of carbon. They put its
freezing point at about — ii6°C.( — 177° F.) Itmelts,
they state, at about — 110° C. ( — 166 F.) Common 95
per cent, alcohol thickened at — 129° C. ( — 200*2° F.)
and froze solid at about — 1 30'$° C. (—203° F.) Methyl
alcohol (wood alcohol) was easier to freeze than
ordinary alcohol. Phosphorous chloride froze at
about —i 1 1*8° C. (—169° F.) These substances, it is
claimed, were never frozen before this period
(Wiedemanri s Annalen, 1883).
The figures show that these liquids are not avail-
able for low temperature thermometers, and are
cited here for the purpose of showing that fact.
The ordinary mercury and spirit thermometers,
familiar to all, and their modifications, the carbon
bisulphide and other themometers of liquid contents,
then, are useless for very high or very low tempera-
tures, their liquid contents volatilizing or freezing
44
LIQUID AIR AND THE
Celsius ^Absolute
r Scale
250-
200-
150—
50—
--0-I
-60—
-100
-150—
-450
!00
350
—300
-260
—200
-150
— 100
-50
Gas Thermometer
of Varying Vol-
ume.
solid at high and low temperatures
respectively. Air was substituted
for the liquids, and thermometers
operating by its expansion when
heated were devised. The cut
shows the general features of con-
struction of one of these. The bulb
contains air at E. Mercury, D, lies
in the tube, cutting off the end from
the bulb. As the air expands, it
forces the mercury up ; as it con-
tracts, the mercury descends. This
is a thermometer of changing vol-
ume. It is not so satisfactory as
the air thermometer of constant
volume.
The cut also shows the relation
of the Centigrade and absolute
thermometer scales. On the left is
engraved the Centigrade or Celsius
scale, with its zero marked o at the
point of melting ice, its 100° mark
at the point of boiling water, and
— 273° at the absolute zero. On
the right is the absolute scale, on
which ice melts at 273° and water
boils at 373°.
There is a third thermometer
scale which may be mentioned
here, although it is rarely used in
scientific work; it is called the
Reaumur. The zero is the same as
the Centigrade zero, and the boil-
LIQUEFACTION OF GASES. 45
ing point is made to read 80°. This is the basis for
its expansion up and down. At the absolute zero its
reading is — 218*4°.
If, as the temperature changes, a confined gas is
kept at a constant volume, its pressure will vary ; it
will rise as the temperature rises and will fall as it
falls. If we provide a means for measuring the
presure of the confined gas, we can determine there-
from its temperature.
The word gas has been used instead of air, for
other gases can be used with equal accuracy. For
the extraordinarily low temperatures encountered in
gas liquefaction investigations an air thermometer is
useless, because the air liquefies. Just as mercury
gave place to alcohol in liquid thermometers for low
temperature work, so did air give place to hydrogen
in gas thermometers.
The constant volume hydrogen thermometer as a
standard temperature-determining instrument for
low temperature work is of simple construction,
based on the phenomena of change of pressure under
change of temperature in a gas kept at constant
volume. This is the converse of the expansion and
contraction of matter when heated. It is practi-
cally only applicable to matter in the gaseous
state.
If a thermometer of the ordinary construction is
heated until the tube is filled to the top by the ex-
panding mercury or alcohol, a little more heat will
crack the glass, and the contents will escape. The
expansion of liquids when heated generates enor-
mous pressures. But if the thermometer were filled
with air or hydrogen or other gas, it could be
46
LIQUID AIR AND THE
heated very hot, probably to the melting point of
the glass, before it would give way.
In the mercurial, alcoholic or other thermometer
with liquid contents, the heat is measured by the ex-
pansion of the liquid, which is purposely so placed
as to be perfectly
free to expand. In
the air, hydrogen or
other gas-filled ther-
mometer of the type
we describe, the gas
is kept at constant
volume, and the
pressure it exerts is
measured. A dia-
grammatic repre-
sentation of the con-
struction is given,
which can be readily
followed by the
reader.
A bulb, A, is filled
with perfectly dry
pure hydrogen.
From its top a capil-
lary tube, d, rises
and connects with
a mercury tube, 5.
The connection is
preferably so made that the top of the mercury
tube shall be perfectly flat. The capillary tube, d,
enters a little to one side of the flat top of the tube,
S. In its center a point, e, of glass, ivory, steel, or
Details of Hydrogen Thermometer.
LIQUEFACTION OF GASES. 47
some material unattacked by mercury, is attached,
which points downward.
The bottom of the mercury tube is reduced in
diameter, is open, and an india rubber tube has its
end thrust over it. The other end of the india
rubber tube is connected to the bottom of another
glass tube, R, termed the manometer tube. When
the apparatus is set up, this tube can be moved ver-
tically up and down. A clip moving up and down
a vertical rod on a firm stand and attached to the
tube enables this to be done. The tubes, R and S,
contain mercury.
If the tube, R, is raised or lowered to the proper
point, the mercury in 5 can be brought to precisely
the level of the point. This is indication by a point,
a very delicate means of fixing the level of mercury.
It is used in barometers in adjusting the level of the
mercury in the cistern, and is taken as being sensi-
tive to one-thousandth of an inch. The mercury as
it rises reflects, mirror-like, the point. When the
latter touches the mercury, the point and its re-
flection form a continuous line. If the mercury is
raised too much, a dimple forms on its surface. The
appearance is unmistakable.
By the manipulation of the observer sliding the
manometer up and down the rod, the mercury is
brought into accurate contact with the point, e. This
is done for every reading of a temperature. This
being the case, it is obvious that the heights of the
upper surface of the mercury in R will vary accord-
ing to the pressure of the gas in A. As this is
greater, the surface of the mercury in R will be
higher ; as the pressure is less, the level in R will
48
LIQUID AIR AND THE
be lower ; the readings being taken only when the
mercury in 5 has been brought to its exact level by
raising or lowering the manometer tube, R. The
greater pressures corre-
spond to greater heat of
the contents of the bulb, Ay
the lesser pressures to lower
heat. By measuring the
difference of level of the
surfaces of mercury, the
data for calculating the
heat are given.
The height is best read by
a cathetometer. This is a
telescope with cross- wires
across its tube, in the focal
plane, and mounted to be
moved up and down a
vertical rod on another
stand, without ever depart-
ing from a perfectly hori-
zontal position. A vertical
scale of great accuracy of
division is mounted near
the manometer tube. The
telescope is focused from
a distance upon the appa-
ratus. The mercury is ad-
justed by moving the mano-
meter tube until the mer-
cury touches the point, e.
The telescope is slid up
Hydrogen Thermometer, and down until the image
LIQUEFACTION OF GASES. 49
of the surface of the mercury in the manometer
lube, R, exactly coincides with the cross- wire as seen
in the telescope. The telescope is now swung in a
horizontal arc if necessary, until it takes the vertical
scale into the field. The reading of the scale gives
the height of the mercury. The same is done for
the mercury in the tube, 5 ; the difference gives the
pressure of the hydrogen in units of a column of
mercury.
As the point, c, is supposed never to change posi-
tion, the scale may be adjusted so that its zero is at
the level of the point. For a series of readings one
reading of the point level would in any case suffice.
The general mounting and disposition of parts of
a constant volume gas thermometer are shown in the
cut. A is the gas bulb, d the capillary tube, 5 the
mercury tube, R the manometer, T T the frame,
and B the vertical scale. Clamps are arranged to
slide up and down the side rods of the frame so as to
adjust the levels of the mercury vessel and mano-
meter tube.
Prof. H. Kamerlingh-Onnes, of Ley den, prepares
hydrogen for his hydrogen thermometer by electro-
lysis as described in the most general terms on
page 148. A very carefully constructed apparatus is
used for the purpose. The interior of the hydrogen
bulb and tubes are most elaborately cleaned with
chemical solutions and distilled water and dried be-
fore the introduction of the hydrogen, and various
modifications have been introduced by him.
At the risk of trenching upon the determination to
avoid the introduction of much mathematics into
this volume, the very simple calculation used in re-
50 LIQUID AIR AND THE
ducing the hydrogen thermometer readings to the
standard is given. The reader may be assured that
it is not as complicated as it appears.
To obtain the formula for the thermometer, the
bulb is immersed in melting ice or snow, and the
manometer is adjusted so that the level of the
mercury in 5 just reaches the point, e. (See cut on
page 46.) The readings of the heights of the two
mercury columns are now taken.
The calculation is based upon equating two ex-
pressions for the weight of hydrogen contained
under the conditions of the two readings in the bulb.
Let S0 be the specific gravity of the gas in the bulb,
let V0 be the volume of the bulb, and v§ the volume
of the capillary tube ; let H' be the height of mer-
cury column, measured from the fixed level of the
point, c, to the level of the upper surface of the mer-
cury in the manometer tube increased by the height
of the barometric column. S0 is taken at o° C. and 760
mm. barometer. The weight then will be expressed by
H'
o
/ 760-
Next the bulb is placed in the substance whose
temperature is to be determined. Let k be the
coefficient of expansion of hydrogen (0*00367), a that
of glass, / the temperature to be found, and H the
new difference of levels of mercury columns increased
by the height of the barometric column. The weight
of hydrogen, the same as before, is
LIQUEFACTION OF GASES. 5 1
And equating we have :
/ \ H'
S0 I V0 4- z/0J = S0 i v o
\ / 760 \ \-\-kt i 760
Solving these with respect to /, we find that —
\+at \ H
+^o
I 4- k t / 760
V0 (k H'—a H)- VQ k (H— HO
This seems rather a complicated formula, but the
use of the hydrogen thermometer is amply justified
by the sensitiveness of the instrument, its great
accuracy and great range. It can be used from the
temperature of liquefied gases up to that of the
melting point of glass.
If two dissimilar substances have their ends con-
nected so as to make a circuit, and if both are con.
ductors of electricity, a current of electricity will
pass through them as long ^ as one of the contact
points of the dissimilar substances is hotter or colder
than the other. The effect is termed thermo-electric
and the junction is termed a thermo-electric junction.
The current with a single pair of junctions will be
due to a very slight potential difference. The
greater the difference of temperature, the greater will
the potential difference be. If means are provided
for measuring the potential difference, and if the
temperature of one of the junctions is known, then
the amount of the potential difference will give data
for calculating the temperature of the other junction.
The thermo-electric junction has been much used
in low temperature work. The conductors may be
varied . a good deal. A standard type is German
silver — copper. The former metal is an alloy of
LIQUID AIR AND THE
Kamerlingh-Onnes '
Thermo-electric
Thermometer.
copper, nickel ana zinc. Other
couples are German silver — cop-
per sulphide (Becquerel's); Ger-
man silver — zinc-antimony alloy
(Noe's); iron — bismuth-antimony
alloy (Clamond's).
The ordinary practical unit of
potential difference in electric
work is the volt. In the thermo-
electric junction the difference is
so slight that it is usually meas-
ured by micro-volts, or mil-
lionths of a volt. The measure-
ment of the potential difference
is effected by means of a sensi-
tive galvanometer. It is unne-
cessary to give the details of this
operation.
As an example of the thermo-
electric couple, as applied to the
determination of low tempera-
tures as encountered in the lique-
faction of gases, an illustration
of the couple used in the cryo-
genic laboratory of the Univer-
sity of Leyden is given. This
laboratory, specially fitted with
elaborate apparatus of the Pictet
type, has won considerable fame,
and, under the charge of Prof.
H. Kamerlingh-Onnes, much
excellent work has been done
there. In a journal recently
LIQUEFACTION OF GASES. 53
started in Berlin, and which is devoted to the topic of
compressed and liquefied gases (Zeitschrift fuer com-
primirte und fluessige Gase), is given a description of
the principal apparatus in the laboratory, which
may be advantageously studied by those specially
interested in the liquefaction of gases.
The cut gives the section of the thermo-electric
couple. It is formed of a straight German silver
wire soldered at its lower end to a thin copper wire.
The latter is coiled into a helix.
The cut shows in the center the German silver
wire as a straight black line. It lies within a glass
tube. Around the outside of the latter is wound a
thin silk-covered copper wire. The ends of the
two are inserted into a block of copper and soldered.
The silk insulation serves to keep the copper wire
from touching itself in its successive turns. Another
way of arranging it is to melt and wind a thin glass
filament around the tube and wind the wire in the
grooves it forms.
Outside of the inner tube and of its winding of
copper wire is a second glass tube. By india rub-
ber tubing the junctions are completed as shown.
The copper block at the bottom is turned off to a
shoulder, so as to fit inside the outer glass tube. A
thin tinned sleeve of copper is soldered to it, and
this sleeve goes outside the lower end of the outer
glass tube. The joint is made good with melted
sulphur. By the side branch the apparatus is filled
with dry air, two apparatus being joined by a rubber
tube for the purpose.
By immersing the copper block in anything colder
or hotter than the wires themselves are, a tempera-
54 LIQUID AIR AND THE
ture difference is established. One of the junctions
of two dissimilar metals is at a temperature different
from that of the rest of the wires and of the other
junction. If the ends of the wires are connected in
circuit with a galvanometer, it will be deflected by
the current due to the thermo-electric effect.
Such an instrument is calibrated by comparison
with an air or hydrogen thermometer, and indicates
changes of heat with great delicacy. A moment's
reflection will show that where two dissimilar
metallic or other conductors are joined, so as to
form a circuit, there will be two junctions of dis-
similar conductors; the circuit must include two
thermo-electric junctions. The general law is that
the electromotive force developed by a thermo-
electnc couple varies with the excess or depression
of temperature of one junction over that of the other
junction, which must lie in the rest of the circuit.
This law holds measurably true for excessive varia-
tions. For a German silver — copper couple, the
potential difference is about one hundred-thousandth
(0*0000 1 ) of one volt per degree Centigrade, or five-
ninths of this amount per degree Fahrenheit.
Many substances possess the property of opening a
path through the luminiferous ether for electricity.
A constant discharge at very low potential can occur
through such a path. The discharge of electricity
is called a current, the substance whose presence
opens the path is termed a conductor. Copper
wire is one of the best conductors known, and is
very familiar in such application. House work
for telephones, electric lights and electric bells is
generally, almost universally, done with copper
LIQUEFACTION OF GASES. 55
wire. It is rapidly being introduced on main tele-
graph and long distance telephone lines.
Electric conductors, like water pipes, may be good
or bad conductors. A smooth-lined water pipe will
carry or conduct more water than one with rough
interior. Some metals will conduct electricity
better than others. A metal of poor conducting
power is said to have great or high resistance.
Iron is of rather high resistance, platinum is of ra-
ther high resistance, copper and silver are of low
resistance.
The same conductor varies in resistance with its
temperature. Generally, the hotter it is, the higher
is its resistance, and the colder it is, the lower is its
resistance. It is believed that at the absolute zero
of temperature, the resistance of copper or of iron
would be abolished almost entirely or even entirely.
Then the thinnest wire could conduct the horse
power of Niagara to any distance without loss.
Based on the above facts, the platinum wire
resistance thermometer is constructed, and while
it is also an instrument adapted for high tempera-
tures, it has been used with the best results in the
investigation of the low temperatures encountered
in the investigations of liquid air and liquefied gases.
Olszewski in an article in the Philosophical Maga-
zine for 1895, claims that his associate, Witowski,
was the first to successfully use the platinum resist-
ance thermometer for the determination of liquefied
gas temperatures. In its usual form it is very
simple, such simplicity being possible because liquid
air and the liquefied gases in which it is used are
excellent insulators. As the wire is to be surrounded
LIQUID AIR AND THE
by them, the fact that it can be immersed uninsulated
without short-circuiting conduces to simplicity of
construction and to sensitiveness.
The principle of construction can be seen in the
cut, in Avhich is given a representation of an appa-
ratus used by Prof. Dewar to show the decrease of
resistance of a wire when the temperature is lowered.
The tube is a vacuum tube containing liquefied oxy-
gen or liquid air. In it is im-
mersed a coil of fine platinum
wire, held in shape by a sheet of
mica with notched edges, around
which it is wound. Two heavy
platinum wires serve as connect-
ors. These are so large in dia-
meter, and so short, that their
resistance may be regarded as
quite negligible. The wire with
the mica sheet, and its mounting
is the thermometer.
Another form of construction
provides for a more thorough
exposure of the platinum wire
to the changes of temperature
by separating it as far as possi-
ble from contact with other mat-
ter than the liquefied gas. Out
of very thin mica or ebonite a frame is made whose
cross-section is a sort of hexagonal star. Around
this the platinum wire is wound. This arrange-
ment provides a coil of wire in contact with a non-
conducting substance only at a comparatively small
number of points, six for each complete turn of the
Principle of the
Electric Resistance
Thermometer.
LIQUEFACTION OF GASES. 57
coil. It is a disposition of the wire which secures a
considerable length in a small space, and which
leaves the wire free to be in most intimate contact
with the material surrounding it. The temperature
of the wire changes with the greatest quickness, and
the thermometer is of the most sensitive type yet
devised. It is due to Prof. Olszewski.
The platinum wire he employed was 0*025 milli-
meter, or about one-thousandth of an inch in diame-
ter. The successive turns of the wire were one-half
to one millimeter, or one-fiftieth to one twenty-fifth
of an inch distant from each other.
Witowski's electric resistance henr.ometer was
constructed with a view 'o keeping the platinum
wire out of contact with the liquid it was to be im-
mersed in. The wire was wound upon a copper
cylinder with mica insulation. It was inclosed in a
copper foil cylinder, and was hermetically sealed
therein.
Callendar and Griffiths studied the subject of pla-
tinum res:'stance thermometers in the Cavendish
Laboratory, at the University of Cambridge, Eng-
land. They reached the conclusion that the instru-
ment is accurate to one-thousandth of a degree
change of temperature. This fact, together with its
great sensitiveness, makes it an ideal instrument for
use with non-conducting liquids such as liquid air.
The thermometers are used bypassing an almost
infinitesimally small current through them and
accurately measuring the resistance. It varies in
degree with the temperature, and the instrument
may be standardized by the hydrogen thermometer.
Finally, there is one more way of determining
58 LIQUID AIR AND THE
what may be termed extreme temperatures, which
was tested by Cailletet in some of his recent work,
which showed that it was reliable for liquefied gas
temperatures. A piece of metal of known weight
and specific heat is immersed in the liquid whose
temperature is to be determined. After it has
attained the temperature, in five minutes, more or
less, it is removed and transferred to a calorimeter or
apparatus for determining the quantity of heat in it.
The simplest calorimeter is a vessel of water, and for
rough work this can be used. The piece of metal
is quickly thrown into a vessel of water of known
weight and temperature. The change of tempera-
ture of the water brought about by the introduction
of the piece of metal, by a simple calculation gives
the temperature of the piece of metal.
For scientific work some of the more accurate
forms of calorimeter are used, which it is unnecessary
to describe here. The calorimeter method has been
very rarely used, and is only mentioned here on
account of Cailletet's paper of 1888.
LIQUEFACTION OF GASES. 59
CHAPTER III.
HEAT AND GASES.
The perfect gas — The ultra-perfect gas — Energy expended in
heating a gas — Specific heat at constant pressure and at
constant volume — Atomic heats and variations*of same
from equality with each other — Adiabatic and isothermic
expansion of gases — Carnot's cycle — The perfect heat
engine — Available and unavailable energy — Unavailable
energy rendered available by liquid air — Latent heat of
melting, of vaporization, of expansion — Boiling a cooling
process — Expansion a cooling process — The spheroidal
state — The Crookes layer — Experiments and illustra-
tions— Utilization of the spheroidal state in low tem-
perature work and in liquid air investigations.
The perfect gas has certain defined characteristics,
or it may more properly be said, should have them ;
for a perfect gas is a rarity, and some of the repre-
sentative methods of liquefying air are supposed
to be based on the fact that air is not a perfect
gas.
If a gas is compressed, energy is expended upon it
and an equal amount of energy is developed in the
gas. This appears largely and principally as heat.
Were air a perfect gas, it would all appear as heat.
But in the case of air at 19 atmospheres, about ^3-
of the energy spent in compressing it fails to show
itself as heat energy.
Following this out, a perfect gas expanding against
pressure and developing energy should lose heat
6o
LIQUID AIR AND THE
exactly equal to the energy it expends in the ex-
pansion. But here, too, there is a loss of heat
energy. The expanded air is a little cooler than it
ought to be, because the act of expansion requires
energy to be spent upon the molecules in some not
well understood way. Hence there is a greater
cooling than would be indicated by the energy ex-
pended.
Hydrogen is a gas that acts in the opposite way.
It requires more energy to compress it than would
Joule's Experiment.
be indicated by the heat developed, and in its ex-
pansion it does not get as cool as it ought to.
Hence it is a more than perfect gas — an ultra-per-
fect gas.
There is no perfect gas known. None has ever
been found capable of standing the tests which a
perfect gas should respond to.
One test to which a perfect gas should respond is
the following : Two gas receptacles are connected
by a tube. One is charged with gas under pressure,
the other has a vacuum produced within it. A cock
LIQUEFACTION OF GASES. 6l
upon the pipe connecting them is closed so as to
maintain the condition described. The two con-
nected vessels are immersed in water and all is left
standing until the gas receptacles, the gas in one of
them and the water surrounding them, are of even
temperature. Now the gas cock is opened.
The compressed gas streams out of the one recep-
tacle into the other. As it expands it exerts mechan-
ical energy. This must be supplied from some
source, and heat energy is called upon. The ex-
panding gas grows cooler. The gas in the other
vessel is compressed. Energy is developed and must
show itself ; it appears as heat. The gas in the second
vessel is heated.
If the gas were a perfect gas, the heating would
exactly balance the cooling, and the temperature of
the water would be unchanged. Joule tried the ex-
periment, and thought that the temperature of the
water was unchanged. There was so little altera-
tion that it completely escaped recognition ; a ther-
mometer with bulb immersed in the water was
apparently unaffected. But there was a difference.
If air was used, the temperature would fall, and the
same is to be said for most other gases.
These differences are so slight that it is only by
delicate tests that they can be detected. The scien-
tific incredulity of Joule and Thomson led them to
try a simple experiment, which may be described
here.
A tube is provided with an air-tight piston. A
diaphragm extends across its center. This dia-
phragm is made of a porous material which will only
permit the passage of air with some difficulty. If
62 LIQUID AIR AND THE
the piston is forced in, the air is compressed and
heated. It escapes through the pores in the piston
and expands as it escapes. Now, as the expansion
of the air exactly undoes the compression, there
should be an exact balance of energy expended on
the air on the piston side and energy expended by
the air on the free side. Hence, the escaping air
should be of the temperature of the atmosphere.
But it is found to be lower. Air is an imperfect
gas. If hydrogen be substituted for air, the temper-
ature is higher. Therefore, hydrogen is an ultra-
perfect gas.
Our ancestors had their own way of looking at
gases. They at-
tempted to classi-
•£+ c fy them into per-
manent and non-
Joule's and Thomson's Experiment, permanent gases,
for they believed
that there were some gases which could not by any
degree of cold or pressure be liquefied or solidified.
These they called permanent gases. Then there was
adopted a rather crude division of gases and vapors.
The latter were easily reducible to the liquid form,
the former were not. This was profoundly unscien-
tific and inexact. It left it largely a matter of fancy
when a gas should be called a vapor. It led to con-
fusion of ideas, and such expressions as vapor den-
sity, tension of aqueous vapor, and the like have
done much to obscure the student's view of the
status of things. But it is uncertain when the terms
which have more or less had this effect will have
better ones substituted for them. Perhaps it
LIQUEFACTION OF GASES. 63
may be that it will be hard to find better expres-
sions.
The best definition of a vapor is, perhaps, the
following : A gas which, by the least increase of
pressure or reduction of temperature, would be re-
duced, in part, to a liquid. The term vapor, thus
defined, is subjective. If a liquid is introduced into
a vacuum, it evaporates in whole or in part. If
enough is introduced, an excess of liquid may be left,
and will lie on the bottom of the vacuum chamber.
The gas filling the chamber is then a typical example
of a vapor as thus defined.
In the upper part of a barometer tube there is
present volatilized mercury, mercury gas or vapor,
in exceedingly small amount. This varies in amount
with every change of temperature and of barometric
pressure. In the outer chamber of Dewar's bulbs
for holding liquid air a globule of mercury is seen.
This fills the vacuous space with mercury gas or
vapor. These are examples of vapor as defined
above.
In the present work an endeavor will be made to
adhere to the term gas, to the exclusion, as far as
possible, of the term " vapor." As we have little to
do with chemistry, the subject of gases will be com.
paratively simple, as they will be dealt with as
physical concepts. Thus, although air is a mixture
of two principal gases, oxygen and nitrogen, with
smaller amounts of others, such as argon, gaseous
water, and carbonic acid gas, it will be spoken of as
a gas when only its physical relations are under con-
sideration.
Another definition of vapor is, a gas at any tern-
64 LIQUID AIR AND THE
perature below its critical one. It is a gas which by
pressure alone can be reduced to the liquid state.
However little one may fancy the term vapor,
owing to the varied definitions given for it, there are
some cases when its use is almost obligatory. Water
vapor is one of these. If we speak of water gas, it is
taken to indicate a combustible gas, containing free
hydrogen, but no water, which is produced by
passing steam through incandescent coal or other
carbonaceous material. Therefore, as the chemist
calls carbon monoxide, incorrectly, carbonic oxide,
simply to avoid confusion incident to the attempt to
supersede a long standing error in terminology, we
may, and almost must, adhere to the term water
vapor.
A gas may be heated so that it will expend energy
on account of the heating. This takes place if it is
allowed to expand. Hence the heat required to
raise the temperature of a gas free to expand
involves two offices to be performed. A substance,
which is the gas in question, is to be heated. This
requires one portion of the heat. Then energy has to
be supplied to the gas to enable it in turn to expend
energy on its own expansion. This requires a second
portion.
If the gas is confined so as to be incapable of
expansion, the temperature can be more readily
raised. The gas is inert and merely represents a
mass to be heated. Less heat is required than in the
case where the gas expands.
If it took a quantity of heat energy represented
by I to heat a given weight of unexpanding gas a
given amount, to heat the same weight of gas the
LIQUEFACTION OF GASES. 65
same amount, when the gas is free to expand under
its effect, would require a quantity of heat energy
represented by 14058.
The quantity of heat required to heat identical
weights of different solids, liquids or gases under
identical conditions varies. The relative quantities
required are termed the specific heats of the sub-
stances in question. The two kinds of specific heats
of gases which have just been described are termed
specific heat under constant volume and specific
heat under constant pressure.
The same two kinds of specific heats exist for
solids and liquids. The expansive force exerted by
the latter when heated is so enormous that there is
no practical way of accurately determining the spe-
cific heat at constant volume of most liquids or solids,
because neither can be kept at a constant volume
except in a very few instances.
Specific heat is, as has been said, the relative quan-
tities of heat required to produce an identical change
in temperature in equal quantities of different sub-
stances. The laws of specific heat vary in the cases
of matter in the solid, liquid or gaseous state, and
also vary with the temperature. In liquids and
solids there is no approach to regularity. Water is
taken as the standard, and the specific heat of liquids
is stated by weight. Water has a very high specific
heat. Mercury, for instance, has but approximately
one-thirtieth the specific heat of water. A pound
of water at a high temperature would have as much
heating power in its cooling as would thirty pounds
of mercury.
When we come to elements, we at once find a law
66 LIQUID AIR AND THE
which is approximately followed. If we multiply
the atomic weight of an elementary substance, such
as gold, silver, lead, etc., by its specific heat, we get
a number which is almost constant for all of the solid
elements. This indicates that the heat required to
heat an atom of a substance a given amount is ap-
proximately the same, of whatever element the
atom may be.
The atomic weights of elements represent the
relative weights of single atoms of the bodies in
question or of equal numbers of atoms. It follows
that if we take the ordinary specific heats, which are
referred to equal weights of the substances, and
multiply them by the atomic weights of the respec-
tive elements, the product will give the specific
heat referred to, the heating of weights correspond-
ing to the weights of the atoms.
These products are termed the atomic heats, and
they vary but slightly among themselves. They are
so nearly the same that a law was enunciated by
Dulong and Petit to the effect that the atomic specific
heats of the elements are identical.
Like many other enunciated laws, it does not hold
true. The products given by the required multipli-
cations vary from 5*39 to 6*87, and it is not easy to
reconcile one's self to the idea that the differences are
due to experimental error. The law is best accepted
as being, like many other natural laws, only approxi-
mately true, and as being a useful instrument in
determining certain chemical constants.
There are two expressions in constant use in
thermodynamics which should be explained in this
book, as they occur in discussions of the problems of
LIQUEFACTION OF GASES. 67
expansion and contraction of gases. Once explained,
the explanation may be easily remembered as being
descriptions of near relatives of the two specific
heats which have been described. The two specific
heats were specific heat at constant volume and
specific heat at constant pressure. The two expres.
sions to be explained are adiabatic and isothermic
expansion or contraction.
Suppose that a gas is placed in a condition which
permits it to expand. The molecules repel each
other, they beat back and forth constantly, striving to
augment the length of the paths they move over, so
if the conditions permit expansion, the gas expands.
In expanding it will exert energy, and the energy
has to be supplied from some source. If none is
supplied from an external source, the gas will fall in
temperature, the energy will be drawn from the in-
herent heat of the gas itself. Imagine the almost
theoretic case when the gas expands thus absolutely
at the expense of its own heat. No heat has been
added to it, the expansion^ adiabatic.
The condition rarely exists in practice, except in
approximation, because as we work with gases under
confinement, there is a surrounding vessel of more or
less heat-conducting material, the gases pass through
pipes and valves, and are in constant contact with
objects at various temperatures. But one case exists
in which a gas is compressed without the use of any
restraining or impelling mechanism, without piston
and cylinder, and where the expansion is so rapid
and of such short duration that the adiabatic condi-
tion is almost exactly obtained. It occurs in the
sound wave.
68 LIQUID AIR AND THE
When a sound is made in a gas, waves start from
the center of sound disturbance, and travel through
space at the rate of about a thousand feet a second.
In a second there may be anywhere from nine or ten
waves up to twenty or more thousand such waves
within the range of human audition. Each wave is
composed, not of up and down motions, as in a wave
on the sea, but of a forward impluse of the particles,
followed by a springing back. On the forward im-
pulse the air is compressed ; on the reverse impulse,
expanded. The action is very brief in duration and
very slight, but the expansion and compression arc
practically adiabatic.
The air is surrounded by no containing vessel,
and is condensed against its own inertia, so that
every disturbing condition is absent, such as metal
or glass to be heated, and the shortness of the pe-
riod contributes to the perfection of action. The
phenomena of the propagation of sound in air are
used to deduce the factor i-*4O5 * (page 65). The de-
termination is based upon the assumption that air
in the sound wave expands adiabatically.
Now suppose that the gas expanded just as before,
except that we added heat to it, so that as it expand-
ed it kept exactly the initial temperature. If it was
air expanding in a cylinder, we might have a fire
heating the cylinder. The air would absorb heat as
it expanded without rising in temperature. Although
the expression is not generally applied to such a
case, the heat would be as truly latent heat as is the
heat of liquefaction or of vaporization. We might
start with I cubic foot of air at a temperature of
1 00° and end with 2 cubic feet of air at the same
LIQUEFACTION OF GASES. 69
temperature. Our fire would do the work of pre-
venting an adiabatic fall of temperature.
Such expansion is called isothermic expansion.
Opposed to expansion is contraction. There is an
adiabatic contraction in which a gas yielding to ex-
ternal energy diminishes in volume without impart-
ing to anything the heat given it by the energy ex-
pended on it. It grows hotter. If the action is
theoretically perfect, if it gives off absolutely none
of the heat energy into which the mechanical energy
exerted upon it has been converted, the contraction
is adiabatic.
But the vessel in which the air is compressed may
be cooled artificially, so as to keep the air at precisely
the same temperature. A stream of water may cir-
culate through a water jacket surrounding the
vessel. The water may be assumed to absorb the
heat. The contraction is isothermic if the cooling is
so complete that no rise in temperature takes place.
The primitive idea of a steam engine, if we except
Hero's reaction engine, is represented by a piston
and cylinder. A little water is placed in the cylinder
and under the piston and is boiled. The steam forces
the piston upward. At the end of the stroke, the
steam is cooled and condensed to water and the pis-
ton descends.
Now, to avoid complication, imagine the steam re-
placed by air. The air is heated. It expands, and
heat is constantly applied till the stroke is partly
completed, so as to keep the air at the same temper-
ature. This much of its expansion is isothermic.
Next it is left to itself, and without receiving any
more heat, expands until the end of the stroke is
70 LIQUID AIR AND THE
reached. This is adiabatic expansion. It now re-
turns or performs the return stroke, the first portion
by isothermic contraction, the air being cooled and
kept cool, and completes the return stroke by
its own contraction, with ensuing rise of tempera-
ture, or by adiabatic contraction. We will assume
it to return to exactly the temperature it started at
before it was heated at all.
The course of operations started with the air at a
given volume and temperature, it went through a
cycle of changes, and returned to its original volume
and temperature, thus completing the cycle. To
carry it out, conditions impossible of realization
would have to be obtained. No engine could be
built which would give the cycle perfectly.
An engine operating thus by expansion and con-
traction of a gas is a reversible engine. The steam
engine is a typical example. The gas engine is an-
other.
The cycle is termed Carnot's cycle, and the suppo-
sititious engine that would carry it out is called
Carnot's engine. Such a cycle represents the most
economical conditions under which power can be
generated by heat. But the engine will never be
built.
By following out the theory of Carnot's cycle, we
reach the following law, the famous second law of
thermo-dynamics :
In a reversible heat engine, the efficiency is re-
presented by a fraction whose numerator is the
range of temperature included in the operation of
the engine, and whose denominator is the highest
temperature included therein. These temperatures
LIQUEFACTION OF GASES. ?I
must be expressed in the absolute scale of temper-
ature.
The law is all-important ; directly or indirectly, it
crops up constantly in the mechanics of the liquefac-
tion of gases and of heat.
It has been stated thus :
Heat cannot of itself pass from a colder body to a
hotter one, nor can it be made so to pass by any in-
animate material mechanism, and no mechanism can
be driven by a simple cooling of any material object
below the temperature of surrounding objects.
(Daniell.)
Another way of putting it is :
If the absolute temperature of a uniformly hot
substance be divided into any number of equal parts,
the effect of each of those parts in causing work
to be performed is equal. (Rankine.)
If we indicate absolute temperature by 6), and let
6)1 and ®2 indicate two temperatures, ©' being the
higher, the second law states that in a reversible
heat engine —
6)i — ©2
Efficiency =
feH
Mechanical energy can be expended and can de-
velop heat energy, but heat energy can never de-
velop in the mechanical form but a portion of its own
quantity of energy. More and more mechanical
energy is being converted into heat energy, and
only a small portion can ever be recovered. Every-
thing in the world tends to get to the same temper-
ature ; equalization of temperature is constantly
taking place. In the existence of coal and air we
72 LIQUID AIR AND THE
have a form of potential energy, a potential high
temperature. But even this potential high temper-
ature is disappearing as coal is burned up. The
available energy of the world gets less and less.
The total energy is invariable.
The second law of thermo-dynamics leads us to
the same conclusions as does the doctrine of the con-
servation of energy, although in this lowering of the
scale of the world's energies, and the rendering them
unavailable by man, there seems to be involved a
contradiction of conservation of energy. But en-
ergy is intact in amount ; in lowering its pitch, as
we may express it, it ceases to be utilizable by man.
Liquid air, once produced, enables us to utilize
heat which otherwise would be unavailable. The
trouble is that to produce liquid air we have hitherto
been obliged to expend a great deal more available
energy than we can utilize of normally unavailable
energy by its gasification.
Matter, as it exists in three states, solid, liquid and
gaseous, is subject to two changes of state. Melting
is one of these changes, when it changes from the
solid to the liquid state ; vaporization is another,
when it changes from the liquid to the gaseous
state.
Energy has to be used to bring about such changes
of state, and no insignificant amounts, but very large
amounts, relatively speaking, must be expended to
effect the changes. Such energy is usually applied in
the form of heat. If we wish to apply energy to a
lump of ice and change it to the liquid state, we place
it in a vessel upon a hot stove. If we wish to apply
energy to the water so produced and change it to
LIQUEFACTION OF GASES. 73
the gaseous state, we keep it on the stove, and pres-
ently it boils.
By measuring the heat applied, it is found that
a great deal is required to change the solid into a
liquid and the liquid into a gas. This is not all.
If we put a lump of ice into water, the water
always takes the same temperature and keeps it until
the last bit of ice is melted, provided that time is
given for the water to assume the given tempera-
ture. We may apply heat to the water. If it were
plain water, or if it were water with some unliquefi-
able solid floating in it, such as a lump of cork or a
block of wood, every addition of heat would show
itself in a rise of the thermometer. But as long as
the ice is floating about in. it the water will be prac-
tically unchanged in temperature, and will come
back to the original temperature from any slight
departure therefrom, as soon as taken from the fire,
so that the ice has time to act upon it. Suppose we
have put a pound of ice into the vessel. To melt it
will require as much heat as would raise a pound of
water nearly to the boiling point.
Imagine a pound of ice just ready to melt put into
one vessel and a pound of water into another. If
both were equally hot, their temperature would be
o° C. (32° F.) Now imagine exactly the same
amount of heat applied to both until the ice was
completely melted. We started with a pound of ice
at o° C. We should find at the end of the process that
we had a pound of water at exactly the same tern,
perature in the place of the ice. Meanwhile what
would have happened to the water in the other ves-
sel ? It would have become so hot that the hand
74 LIQUID AIR AND THE
could not endure the heat. It would have taken a
temperature of 80° C. (176° F.)
We have seen that our forefathers were not so
fond of the term energy as we are. The ideas of the
scientific world were not so well formulated as now,
and the inevitable result followed that there was
more complexity grafted upon the natural order of
things than was necessary. They found that a
quantity of heat was required to melt ice, and that it
melted it without raising the temperature. The tern-
perature would only begin to rise after the ice was
melted. So they said the heat lies hidden ; as it did
not show itself on the thermometer scale, it must be
concealed from us. They called it Latent Heat,
which means hidden heat.
A similar, but more pronounced, disappearance of
heat takes place when water is made into gas, when
we boil it in a kettle or boiler. The heat required to
convert a pound of water into steam at atmospheric
pressure would raise the temperature of ten pounds
of water 54° C. (97*2° F.) Suppose that the water
we proposed to boil off had the temperature of
46° C. (115° F.) when we started. This would be
a heat which the hand could comfortably bear.
Then it is obvious that after enough heat had been
applied it would reach the temperature of 100° C.
(212° F.) A thing heated is supposed to grow
hotter, and our water would act as it ought to do.
But once the temperature of 100° C. (212° F.) was
reached, the water would no longer grow hot. It
would stay at the temperature named, it would
begin to boil, and would gradually grow less and
less in volume, and without the heat increasing, each
LIQUEFACTION OF GASES. 75
particle would require ten times the heat expended
on its preliminary heating to be converted into
steam or gaseous water. The temperature of the
steam, however, would be 100° C. (212° F.)
These are examples of the two most prominent
latent heats, the latent heat of fusion and of vapori-
zation. The term is so convenient that it will be
used for a long time to come. The better term
would be the energy of melting or of fusion and the
energy of vaporization.
When a gas expands, it practically always expends
energy and grows cold. Therefore, in the expansion
of a gas under ordinary conditions, a loss of heat
occurs, so that a third kind of latent heat may be
assumed to exist, the latent heat of expansion against
pressure. This, however, is an expression not much
used, and it is in the relation of specific heats at con-
stant volume and at constant pressure that the con-
ception finds its nearest expression.
We use ice to cool our drinking water, and per-
haps never give a thought to the phenomena mani-
fested. Yet it is very impressive to see how a small
lump of ice can cool a large pitcher of water. In
melting, it can reduce four times its own weight of
water from the temperature of a living room to that
of freezing, and as long as a particle of ice is left, the
water will remain cold. A lump of ice, weighing
one hundred pounds, lasts for a long time in a refri-
gerator. It absorbs as much heat in melting as
would heat a -ton of water through several degrees
of the thermometric scale.
If circumstances are such as to produce vaporiza-
tion at ordinary temperatures, the substance vapor-
76 LIQUID AIR AND THE
ized must absorb heat energy. A cloth wet with
alcohol dries rapidly, because alcohol vaporizes or
is converted into gas at ordinary temperatures.
Heat is absorbed, and the cloth becomes very cold.
In the tropics drinking water is kept in porous
vessels. It exudes to the -surface and evaporates
therefrom. Heat is absorbed in the process, and the
water gets cool. A workman employed in steel
works cannot endure the heat of the ' furnaces and
metal until he perspires heavily, and then he is com-
fortable. Irrespective of the physiological aspect
of the case, the heavy perspiration by the heat
energy absorbed in its evaporation keeps the skin
from scorching. If he ceases from any cause to per-
spire profusely, he has to stop work until the sudo-
rific glands begin to work once more.
Evaporation, which is slow boiling, here effects a
cooling of the water and of the perspiring work-
man.
The term " boiling " is so firmly rooted in the mind
as an expression of heat that it is a little hard to
think of it as indicating cold. Repeatedly we read
of experimenters with liquefied gases using a vacuum
so as to make a gas boil and thereby produce cold.
One might think that anything which would make a
gas boil would be heat.
If what has been said about latent heat has been
read and understood, it will be seen that boiling is a
cooling process. If we wet the finger and hold -it in
a draught it becomes cold, because the water evapor-
ates or boils off. This is a practical proof. But if it
were possible to heat water so that it would not boil,
the temperature of a pound of water would rise close
LIQUEFACTION OF GASES. //
to a red heat if enough heat were applied to it to boil
it away under ordinary conditions. In other words,
boiling keeps water relatively cool ; it cannot get
hotter under atmospheric pressure than 100° C.
(212° F.)
The way in which water is made to boil is usually
by applying heat to it. A very familiar old experi-
ment may be cited where cold is applied, producing
a vacuum, and the simple vacuum causes strong
ebullition. A round-bottom flask is half filled with
water, and it is brought to the boil and kept so until
the upper half of the flask is full of steam. It is re-
moved from the source of heat, allowed to come to
rest, and is then tightly corked and inverted. Cold
water is poured over it. This condenses the steam,
and forms a partial vacuum. The water which was
quiescent now boils with great energy, because of
the reduction of pressure, and its own temperature
falls. If a thermometer had its bulb immersed in
the water, a reduction of temperature would be in-
dicated.
It is obvious that this application of a vacuum is a
means of lowering temperature. It lowers it by
causing water to boil, so that we find the boiling of
water a synonym for cooling or reduction of tem-
perature.
Substitute liquid ethylene, liquid air, or other
liquefied gas for water and apply a vacuum. The
liquid will boil with increased energy and vigor, and
its temperature will fall. A boiling gas is a cooled
gas and is used as a cooling or refrigerating agent.
No one ever thinks of boiling a gas by imparting
artificial heat to it. It is done either by exposing it
78 LIQUID AIR AND THE
to the atmosphere or by exhausting the vessel in
which it is contained. The exhaustion makes it boil
harder than ever. Exposure to the temperature of
a boiling gas is exposure to cold. The more intense
the boiling is, the greater is the cold. This expresses
the condition of things obtaining in the work we are
t® describe.
If we speak of a thing being exposed to the tem-
perature of boiling oxygen, at atmospheric pressure,
it is very cold ; if to the temperature of oxygen
boiling under exhaustion, it is still colder. If we
speak of a gas being made to boil, it means that we
apply exhaustion, and that its boiling is a synonym
for its growing colder. The student of this subject
must therefore associate boiling with coldness, and
get rid of its old association with heat. He must
realize that boiling is a cooling operation, that if it
did not boil, the water in a tea-kettle would get
several times hotter than it can in fact.
The spheroidal state of matter forms so important
a subject, in connection with the liquefaction of
gases, that it should be well understood by the
reader. It is to our vision a very peculiar condition
into which liquids sometimes enter. In reality it is
their normal condition, and the reason it seems to us
peculiar is because the conditions for breaking it up
are so very generally present.
In a liquid there is a slight force of attraction be-
tween the molecules. Hence the interior molecules
are drawn to one another and are subjected to equal
pulling stresses in all directions. On the outside
or on the surface of a liquid, the molecules are
pulled right and left and inward. Hence the outside
LIQUEFACTION OF GASES. 79
is in a state of strain and constantly wants to become
of as small area as possible. By an elementary pro-
position of geometry we can prove that of all solids
of equal volume, the sphere has the smallest super-
ficial area. Hence, if a mass of liquid is perfectly free
from all external influences, the outer surface, under
the effects of the lateral pulling that goes on among
the molecules, will shrink to the smallest possible
area by drawing the liquid into the shape of a sphere.
A liquid so situated that it is drawn by its own
surface film into a shape approximating a sphere is
said to be in the spheroidal state. The surface film
composed of molecules acts exactly like a thin mem-
brane of india rubber.
When a liquid touches no solid or liquid, it
takes the spheroidal shape. The free portion of a
drop of water, dependent from a rod, is drawn by its
enveloping film into a spheroidal shape. If another
rod touches it, the spheroidal shape where they
meet is destroyed. When a solid is wet by a liquid,
it is because the molecules of the liquid have a
greater attraction for the solid than they have for
themselves. Hence the skin-like action of the outer
layer of molecules is destroyed when a solid which
the fluid can wet is brought into contact with them.
Mercury wets very few substances. When thrown
upon a non-metallic surface, or upon a metallic sur-
face of iron or of some metal which it cannot wet, it
forms, as it is scattered about, a quantity of minute
globules. Each seems to be a minute ball rolling
about freely. Yet they are perfectly liquid. The
surface tension, or the elastic pulling of their surface
layer of molecules, draws them into an approxi-
80 LIQUID AIR AND THE
mately spherical form. If mercury is dropped
upon silver, the spheroidal tendency is no longer
discernible, because it makes a true contact with the
silver, which destroys the spheroidal state.
If a liquid is placed upon a surface very much
hotter than itself, it slowly evaporates, and the pro-
ducts of its evaporation form a sort of cushion
upon which it lies out of contact with the hot sub-
stance. The formation of this cushion of vapor or
gas is interesting. It forms what is known as a
Crookes layer. It is named from Prof. William
Crookes, of England, who discovered the character-
istic phenomena of gases at high rarefactions.
When gases exist in the condition in question,
which condition is sometimes called the radiant
state, they are in so rarefied a state that their mole-
cules, in their vibrations, rarely collide. A billiard
ball pursues normally a straight course from cushion
to cushion, unless it collides with another ball.
This is what the molecules of a gas do. They keep
a straight path until deflected from it by collision
with other molecules. If a silver dish is heated
quite hot, and a drop of water is placed in it, the drop
becomes warm and evolves steam. The molecules
of steam from its under surface, under the influence
of the hot vessel, become hot and beat back and
forth from drop to vessel. This distance is so small,
and the paths of vibration of the molecules are so
long on account of the heating, that very few col-
lisions occur. The molecules simply repeat their
paths up and down from drop to dish, and thus
form a cushion which prevents the water from
touching the dish. The water is drawn into an
LIQUEFACTION OF GASES. 8 1
approximately spherical shape, and the spheroidal
state appears.
The cushion formed by the non-colliding mole-
cules is termed a Crookes layer. Because the mole-
cules do not collide there is no tendency to drive
the steam out laterally. There is probably a very
small proportion which escapes at the sides. The
diagram gives the ideal
section of a drop of
water resting on a
Crookes layer. The real
layer is exceedingly thin. Theory rf Sp^roida, state
The distance between
water and vessel may be termed infinitesimally
small.
A very homely simile would be afforded by a
moving crowd. A man might elbow his way
through it, and thereby thrust people to the right
and left. But if the crowd was sparse enough, he
would go right through it without pushing anyone
laterally. In the Crookes layer the crowd of mole-
cules is so sparse that the molecules do not hit
and elbow each other. Therefore, there can be no
side pressure, and the cushion of steam, in the
experiment cited, stays under and supports the
water.
It might be said that ordinary steam would form
a cushion or layer between the water and hot metal.
But it would not, because the weight of the water
would squeeze it out and the water would touch the
hot metal and would boil violently. But it is
obvious that in a Crookes layer, where the particles
of molecules do not collide, there is no possibility of
82 LIQUID AIR AND THE
their being squeezed out sideways, as there can be
no side push upon them.
The experiment, as usually shown at lectures, is
thus performed : A thick metal cup, preferably of
silver, although brass is almost as good, is heated
nearly or quite to redness. Water is now poured
into it. Instead of bursting into violent ebullition, it
lies in a shape like a flattened sphere, moving about
constantly, but not boiling. The cup is allowed to
cool, the water keeping the spheroidal state, but
losing heat slowly. After a while the cup gets so
cool that the water can touch the metal, which is still
hot. Violent boiling begins and gets more and more
violent, with a curious crescendo effect, until the water
is reduced considerably in amount, when perhaps
the small residue resumes the spheroidal condition
for a few seconds more.
An excellent cup for the experiment can be made
by hollowing out a thickish disk of brass. A round-
ended cylinder of wood may be placed vertically
upon it, the brass resting over a hole somewhat
smaller than itself, bored in a block of wood. A
blow with a hammer on the wooden cylinder will
cup the brass sufficiently to make it hold water. It
may be heated over a candle or alcohol lamp, and
the water may be poured in from a spoon. A silver
coin makes a still better cup. A long wire handle
with one end thrust into a cork and the other bent
into a ring will answer to hold it.
The demonstration, to show that the drop does
not touch the metal, is illustrated in the cut. A drop
of water rests on a Crookes layer over a hot flat
silver plate. It may be projected by a magic lantern
LIQUEFACTION OF GASES. 83
on the screen or may be looked at directly. In
either case it is seen that light passes between drop
and plate.
The importance of the spheroidal state in relation
to the liquefaction of gases cannot be overestimated.
It alone has rendered possible the achievement of the
extraordinary results of the last few years. Except
for the spheroidal state, it would be a matter of the
greatest difficulty to manipulate liquid gases, and
the perils of liquid air would be beyond estimate.
Demonstration of Existence of Crookes Layer in
Spheroidal State.
But owing to the existence of the spheroidal state,
and to its ready assumption by liquid gases, we are
able to handle them much as we should water,
although it is literally the same as if we kept water
in red hot vessels. The experiments just described
show how easy it is to do this. It is still easier to
keep liquid air in vessels at atmospheric temperatures
because the atmospheric temperature keeps our
vessels, in a sense, almost red hot for liquid air.
They are maintained at fhe temperature producing
84 LIQUID AIR AND THE
the spheroidal state without the need of any artifi-
cial source of heat.
A familiar experiment in the solidification of gases
is the production of carbon dioxide snow. This
intensely cold solid can be handled with impunity,
it can be taken into the mouth, but does no harm,
unless it is pressed against the skin, when it pro-
duces a bad blister from the intense cold. It is pre-
vented from touching the skin by a Crookes layer,
although it is hard to believe that a Crookes layer
could support a solid of fixed shape on its cushion,
but such must be the case. The support of the drop
of water is easy to comprehend, because the drop
flattens down until it is of the same shape as the
body it rests on, and, adapting itself to the shape, is
practically at even distance from it as concerns its
lower surface, so that all the molecules have practi-
cally the same length of path. But to imagine an
irregular lump of carbon dioxide snow so supported
is not so easy, although we know that it occurs.
Yet a common experience is that many intensely
cold objects can be handled without hurting the
skin, and in many cases it is due to the spheroidal
state, or at least to the formation of a Crookes layer.
LIQUEFACTION OF GASES. 85
CHAPTER IV.
PHYSICS AND CHEMISTRY OF AIR.
The atmosphere as an ocean — What air is — Its constituents —
Relations of air to living beings — The chemist's and
physicist's view of air — Its constancy of composition —
Carbon dioxide — Oxygen — Nitrogen, argon and other
constituents.
The physics of the atmosphere is very simple.
The members of the animal world are often said to
walk about on the bottom of an ocean of air, like
crustaceans in the ocean of water. As fish swim
about in the water of the actual ocean, so may birds
and flying insects be noted as tenants of the atmo-
sphere itself. There are, however, very great and
fundamental differences ; the analogy is a very in-
complete one.
The fish and crustaceans live surrounded by a
medium whose specific gravity is not far different
from their own. A fish not only swims in water,
but floats in it. By muscular contraction of his air
bladder, he can increase his specific gravity so as to
sink toward the bottom, or he can increase its size
and rise toward the surface. Neither, bird nor in-
sect floats in equilibrium in the air. They are sus-
tained by mechanical energy, derived partly from
their own muscular system and partly, perhaps, by
the internal energy of the air, due to variations in
velocity of air currents. A crab has but the slightest
86 LIQUID AIR AND THE
hold upon the bottom of the water over which he
crawls. Almost all his weight is buoyed up by the
water. When he crawls on the shore, his legs have
probably over eight hundred times as much weight
in the concrete to deal with as when he is in the
water.
Thus, our atmosphere has a far different relation
to us than 13 held by the true ocean of liquid matter
that spreads over so large a proportion of the
earth's surface to its tenants. Its chemical constitu-
tion also is fundamentally different.
Water is a chemical compound, containing in
chemical combination two elements, oxygen and
hydrogen. The composition of its molecule is ex-
pressed by saying that it contains two atoms of
hydrogen and one of oxygen. If water is decom-
posed, it resolves itself into two volumes of hydrogen
to one volume of oxygen. A cubic inch of water
will give about one and a half cubic feet of the gases
named.
The. atmosphere, the survivor of countless geolo-
gic ages, left after terrestrial changes of every kind,
which has been warmed by centuries of sunlight,
and which has been the theater of electric disturb-
ances of the most violent kind, and which has been
acted on by the tremendous vegetation of the car-
boniferous era, remains a simple mixture of gases, as
far as its essential constituents are concerned. The
constituents are not chemically combined, but are as
free from any alliance with each other as the clay of
the Mississippi and Missouri is from any fixed com-
bination with the water that carries it in suspension
toward the Gulf of Mexico.
LIQUEFACTION OF GASES. 8/
For many years the composition of air has been
given in text books as approximately consisting of one
volume of oxygen and four volumes of nitrogen.
This has proved an error. A chance discovery that
nitrogen prepared irom chemical sources had a dif-
ferent specific gravity from that prepared from the
atmosphere was brilliantly utilized by the discoverers,
Lord Rayleigh and Prof. Ramsay. They were en-
gaged in physical research, and having lighted upon
this very extraordinary fact, explained it by the dis-
covery that a third element, argon, exists in air. It
was a contribution from physics to chemistry. A
chemist would not have had the audacity from
purely chemical considerations to believe or suggest
that an undiscovered element lay hidden in our
atmosphere, and that we had breathed an unidenti-
fied gas, and had analyzed our air without finding it
or suspecting its existence. The discovery was so
revolutionary that it formed another step on the road
to scientific credulity which we are traveling.
Science has done so much that we are prepared to
believe anything which may be attributed to her.
Since 1894 other elements have been found in the
air, and we find all our text books further invalidated
in their descriptions of the very air we breathe.
Air is not a chemical combination, because its con-
stituents have so little affinity for each other, and
nitrogen has long been cited as an element of gene-
rally feeble affinities, and rather of the inert type.
But it has to yield the palm to argon in this regard.
The latter seems to be able to combine with nothing
whatever.
Physiologically, our active relations with the air
88 LIQUID AIR AND THE
concern only its oxygen, leaving aside impurities.
We use the oxygen in our bodies to maintain life.
The human system burns up the food it eats, and
exerts energy of various kinds. The nitrogen and
other elements act as diluents only. The animal sys-
tem can do nothing with either of them.
An infinitesimal amount of nitrogen in chemical
combination may have very grave effects. A frac-
tion of a grain of strychnine, which has as an essen-
tial constituent a very small fraction of a grain of
nitrogen, will kill a man. Without the nitrogen it
would no longer be strychnine, and would be innocu-
ous; so that in the case of this poisonous alkaloid, we
find a small fraction of a grain of nitrogen an essen-
tial in a deadly composition.
Yet, in the case of the air, because of its nitrogen
being in the free state, we breathe in and out of our
lungs tons and tons of nitrogen, and it has no effect
upon us whatever. It is only a diluent of the oxy-
gen which we live upon.
A cubic foot of air weighs about 536 grains. It is
generally taken as the basis of specific gravity of
gases,, which is a misfortune, because it is only a
mixture, and has nothing essentially fixed in its com-
position. Yet it is rather remarkable that air
always contains exactly the same proportions of its
important constituents, and, therefore, always has
the same specific gravity. There is nothing com-
parable to it in nature, if we regard it as what it
essentially is — a fortuitous yet absolutely uniform
and identical mixture of independent and uncom-
bined gases.
The physicist can speak of air differently from
LIQUEFACTION OF GASES. 89
the chemist. For the first named it is an almost
perfect gas, and he can speak of it as a typical gas.
The chemist cannot do this. To him it is a mixture
of gases, and he cannot term air a gas.
Air supports combustion and life, on account of
the oxygen which it contains. If the quantity of
the oxygen in a volume of air is increased, it will sup-
port combustion with much more vigor than in the
ordinary state. This increase may be effected by
adding oxygen or removing nitrogen, or mechanical
pressure may do it. In either case combustion be-
comes more intense. In constructing foundations
under water or under the water-level in soil, the
engineer uses an inverted case, like a gigantic box.
From it water is excluded by air pumped in it at
high pressure, which may rise to fifty pounds pres-
sure to the square inch. These structures are termed
caissons, and in them where air is used, compressed
up to three atmospheres excess of pressure, there is
in one foot of the compressed air four times as much
oxygen as under ordinary conditions. A piece of
lighted paper, when blown out in such an atmosphere,
will relight instantly. This mode of increasing the
oxygen increases, also, the nitrogen. The com-
bustion is not nearly as vivid as with artificially en-
riched air.
One would suppose that some difference in the
composition of air would be possible under the con-
ditions prevailing on the earth. It is being constantly
drawn upon by animal life. Animals, in breathing
it, rob it of a portion of its oxygen, and add carbon
dioxide gas to it ; the plant world adds to its oxygen
and removes its carbon dioxide. Yet so constant
90 LIQUID AIR AND THE
are the mixing and disturbance to which it is
exposed, that it proves the same when subjected to
analysis, no matter where collected — practically the
same, for there are slight variations which can be
detected in the percentage of its impurities.
The principal one of these last named substances
is carbonic acid gas or carbon dioxide gas. By the
rules of chemical terminology, this gas should be
called carbonic oxide, but a concession to long usage
is made in its case, and the older names are adhered
to. It is a product of animal respiration, and is a
chemical compound, each molecule containing one
atom of carbon and two of oxygen. It is about fifty
per cent, heavier than air, but, by the law of diffusion,
tends to mix itself with perfect evenness with the
lighter air. It is a product of all combustion, our
chimneys delivering quantities of it. An ocean
steamer pours out from her funnels nearly a ton a
minute. Dissolved in water, it gives it a slight flavor,
and is an antidote to flatness of taste of the fluid. It
makes soda water and aerated beverages in general
sparkle and effervesce. It has played an important
role in the liquefaction of gases. It has itself been
one of the earliest ones experimented on with any
degree of success, and has been liquefied on the com-
paratively large scale for many years. It has been
a good object for experimenters to practice on in
order to enable them to liquefy other gases which
less readily succumb to pressure and cold.
Its history is not without its tragic side. There
are many caves and wells in which it accumulates.
To enter and remain in one of these means a speedy
death by asphyxiation. Casks or vats in breweries
LIQUEFACTION OF GASES. QI
get filled with it in the fermentation process, and
many instances of death to workmen, who incau-
tiously descended into them, are told of. In its lique-
faction at least one fatal explosion has occurred, as
we shall see Jater.
The liquid carbon dioxide possesses one very
striking peculiarity. It cools so rapidly when re-
leased from confinement that it renders latent so
much heat as to produce large quantities of carbon
dioxide snow. Other liquids solidify in part when
allowed to evaporate rapidly, but none does it with
such facility as carbon dioxide.
When air is liquefied, a cloudy appearance is al-
ways presented, which is removed by filtering it
through filter paper. This cloudiness is attributed
to solid carbon dioxide disseminated like pulverized
chalk through the liquid.
92 LIQUID AIR AND THE
CHAPTER V.
THE ROYAL INSTITUTION OF ENGLAND.
The Royal Institution — Its origin and objects — Count Ruin-
ford — Sir Humphry Davy — The Pneumatic Institute —
Davy's experiments in inhaling poisonous gases — His
engagement as director of the Royal Institution — His
views on the utility of liquefying gases.
The Royal Institution of England has been iden-
tified for more than three-quarters of a century with
the liquefaction of gases. Davy, Faraday and Devvar
have associated this line of research firmly with it.
The recent investigations of Dewar and his associ-
ates have been performed in part in the laboratory
where Faraday worked so patiently with his bent
tubes and did work which appears of such extra-
ordinary merit, when his limited appliances are con-
sidered.
The Royal Institution was founded in 1799. ^n
1796, Sir Thomas Bernard, the Rt. Rev. Shute Bar-
rington, LL.D., William Wilberforce and Mr. Elliott
founded the " Society for Bettering the Condition of
the Poor." One of its principal objects was the
establishment of an institution to teach the applica-
tion of science to the advancement of the arts of
life.
A select committee was appointed in 1799 to con-
f er with Count Rumford on the matter, subscriptions
LIQUEFACTION OF GASES.
93
were received, and the Royal Institution was estab-
lished.
Count Rumford, who took such an interest in its
organization, was an American, Benjamin Thompson
by name, born in 1753, in Woburo, Mass. His life
94
LIQUID AIR AND THE
was a curious medley of diplomatic and army ser-
vice and scientific study. He pretty thoroughly
expatriated himself, his politics during the Ameri-
can revolution being on the Tory or Royalist side.
Yet Harvard College and the American Academy
of Sciences were remembered in his will. He
married the widow of Lavoisier, the famous French
chemist, whose almost prophetic words on the lique
LIQUEFACTION OF GASES. 95
faction oi gases are proudly quoted by the French
Academy of Sciences.
From an official copy of the charter and by-laws
of the Royal Institution of Great Britain, dated
1835, we learn something of the early history of the
foundation of the society.
It was legally established under a charter dated
1800, in the days oi George the Third, and in 1810
its powers and functions were enlarged and con-
firmed by act of Parliament. It was a somewhat
high priced society, as such things go. The entering
member had to pay five guineas admission fee, and
the annual dues were also five guineas. • The enter-
ing member had to pay five guineas in addition to
the above, to be devoted to the library or to some of
the collections.
Mr. John Fuller was one of the great benefactors
of the Institution. He established two professor-
ships on foundations of £3,333 6s. 8d. each, which
sums constitute two-thirds of £10,000, for which
the Institution was his debtor.
The Fullerian Professorship of Chemistry is the
one of most interest in connection with our subject.
Its first incumbent was Michael Faraday. The
chair was established in 1833, ten years after Fara-
day's first work on the liquefaction of gases. Fara-
day's appointment in the same year is chronicled in
the pamphlet of 1835, just alluded to. The donor
did not long survive his f undation of the chair. In
the Philosophical Magazine for 1834, we find re-
corded a meeting of the Royal Institution, held on
April 1 8 of that year, on account of the death of
Mr. Fuller, who had done so much for the Institution.
g6 LIQUID AIR AND THE
Prof. James Dewar now occupies this chair.
Count Rumford had heard of the young scientist,
Humphry Davy, and he engaged him a few years
after the founding of the Institution, when only twenty-
two years old, to be director. At first Count Rumford
distrusted Davy and felt that he had been engaged
precipitately. There were certain peculiarities about
him which caused him to produce an unpleasant im-
pression. But it very soon transpired that Davy
was a most capable chemist, although it was im-
possible to foresee the renown he was destined to
win for his country and for the Royal Institution. It
is said that Count Rumford wished to find some one
to give fame to the Institution. It soon appeared
that he had made a most happy choice, and Davy
gave it the most liberal meed of fame by his re-
searches and discoveries.
Humphry Davy was born in Penzance, Cornwall,
Eng., December 17, 1778. He early in life showed
a great fondness for science. A Dr. Beddoes had
established at Clifton, near Bristol, a sort of hospital
for the investigation of the treatment of disease by
the application of gases in general. It was entitled
the Pneumatic Institution. Davy was engaged to be
the superintendent and accepted, although he was
but nineteen years old.
As we now look back upon Davy's early engage-
ment, it is impossible to avoid feeling that the scheme
in which he was embarked savored of strong peculi-
arity, to say no more. Yet he inspired it with rays
from the lamp of true science, and thereby brought
the genuineness of his character more strongly than
ever to the front.
LIQUEFACTION OF GASES. 97
He was engaged to test the action of gases as
remedial agents. He came very near proving their
efficacy as a means of bringing about the death of
subjects submitted to them. This was in his own
person. He experimented by personally inhaling a
number of different gases, a class of experiments
which showed, in the state of science as it existed at
that early day, the most intrepid courage. He
experimented extensively with nitrous oxide or
laughing gas. To test the combined effect of nitrous
oxide and alcohol, he stupefied himself by drinking
wine, and tried, as soon as he could collect himself,
the effects of deep inhalations of nitrous oxide.
What he called nitrous gas was then tried, with
rather disastrous results. We know now that, whether
it was the lower or higher oxide, the ultimate effect
of its reaction with the moisture of the mouth and
mucous membrane would be to produce nitric acid
within the system. This is exactly what his de-
scriptions of the effects suggest. He burned his
tongue and palate with it, it affected his teeth, and
inflamed the mucous membrane. Then, not satisfied
with this most disagreeable and dangerous experi-
ment, he essayed what he called carbureted hydrogen.
This time he nearly died. He first, by expiration,
got all the air possible out of his lungs and then in-
haled what we know now to be a poison, or a mix-
ture of poisons, as it probably contained carbon
monoxide and carbon dioxide with hydrocarbons.
The description of his sufferings and almost death
is impressive, when read in the light of our present
knowledge.
He tried carbon dioxide, but here Nature asserted
98 LIQUID AIR AND THE
herself, and he could not get the pure gas into his
lungs. Not to be beaten by the spasmodic closing
of the epiglottis, he diluted the gas with air and tried
it that way.
At twenty-two years of age we find him engaged
by Count Rumford for the Royal Institution, inde-
fatigably working in chemistry and physics, dis-
covering the metals of the alkalis, producing the
electric light, and after he had been but a few years
in its service, doing one of the greatest services to
science that ever fell to the lot of man to do — the
engaging of Michael Faraday as his assistant in the
Institution.
It is said that Davy's researches into the action of
nitrous oxide or laughing gas on the human system
were what led to his appointment to the Royal In-
stitution.
Davy was very far-sighted in his views. He saw
great possibilities in the liquefaction of gases.
He said that it offered a way of impregnat-
ing water with gas without mechanical means.
Soda water has since his time been made thus.
He said that great cold can be produced by
liquid gases allowed to evaporate, and suggested
the use of this faculty for preserving food. This
outlines one of the cold storage processes, and it is
hoped that liquid air may serve precisely the pur-
pose outlined nearly eighty years ago by the great
English philosopher.
Davy also had a great faith in the possibilities of
liquefied gases as agents for generation of power.
One of his papers {Philosophical Transactions, vol.
xxiii., page 199) is devoted to this topic, and he gives
LIQUEFACTION OF GASES. 99
figures to show what great power could be obtained
from liquid carbon dioxide and the other gases
which had been liquefied, and we find that, early in
the life of the Royal Institution, Brunei tried the
experiment of running an engine with liquefied
carbon dioxide.
In connection with the subject of the liquefaction
of gases, three names bring the Royal Institution
prominently into notice : Davy, Faraday and Dewar.
The first did comparatively little, but his sugges-
tions were striking and suggestive.
The Royal Institution has struggled along for
about a century, its centennial is at hand as this book
goes to press, and the fine work done by Dewar and
his associates in liquefying gases fitly marks the clos-
ing years of its first century of existence. Faraday's
connection with it did more than was due merely to
his far-reaching researches in chemistry and physics.
The Institution has never been richly endowed, and
for twenty-six years Faraday is said to have kept it
alive by his lectures. He kept its accounts, and
noted every expenditure down to the last farthing.
The Institution gave him a fixed income of £100,
and eventually the Fullerian professorship, appoint-
ing him for life, with the privilege of giving no
lectures. The salary was then placed at ;£ioo.
In the same year the Institution was in trouble,
and a committee reported on salaries, advising that
no reduction should be made in Faraday's salary,
" £100 per annum, house, coals and candles," which
can only be taken as a compliment to the young
scientist.
LIQUEFACTION OF GASES. IOI
CHAPTER VI.
MICHAEL FARADAY.
Michael Faraday — His early life — Early devotion to science—
His introduction to Humphry Davy — Attendance at
scientific lectures — Engagement at the Royal Institution
— Injuries from explosions in the laboratory — European
tour with Davy — Rivalry of scientific men — Davy and
Faraday as rivals — The liquefaction of chlorine — Davy's
share in the experiment — Davy's opposition to Faraday's
election as fellow of the Royal Society — Dr. Paris and
the liquefaction of chlorine — Faraday's descriptions of
his liquefactions — Explosions — Northmore 's priority
published by Faraday — Notes on Faraday's liquefaction of
various gases — Exhibition of Thilorier's apparatus — I^ater
work in liquefying gases — Disco very of the magnetism of
oxygen gas — His death — Bent tubes as used by Faraday
— Experiments with use of bent tubes — The Davy-Fara-
day laboratory.
Michael Faraday was born on September 22, 1791,
at Newington, Surrey, England. His family was
poor, with no pretensions to being in any but a low
social level as society is organized and differentiated
in England. His mother, who lived until 1838, was
very proud of her son and his honors, although
quite insufficiently educated to at all enter into his
life's work. She was an excellent and extremely
neat housekeeper. Faraday's education comprised
little more than the rudiments of reading, writing
and arithmetic. In 1804 he went as an errand boy to
102 LIQUID AIR AND THE
a bookseller, George Ribeau. Part of his work was
the delivery of newspapers. Each copy circulated
among a number of readers, for Ribeau ient the
papers instead of selling them, and Faraday had to
circulate in succession from house to house with
the same copies.
In 1805 he began his apprenticeship as book-
binder and stationer, and at once began reading
everything scientific that came in his way. He made
simple experiments in chemistry, built an electric
machine and other apparatus, and began to attend
scientific lectures. In 1812 he heard four lectures
by Sir Humphry Davy, and the same year he took
an engagement as a journeyman bookbinder. The
position was very disagreeable to him.
Before he had completed his seven years apprentice-
ship he took the step which shaped his whole life.
He wrote to Sir Humphry Davy, asking for a posi-
tion and sending elaborate notes of Davy's lectures
which he had taken. He received a reply which he
termed " immediate, kind and favorable," and early
in March, 1813, he was engaged as assistant in the
laboratory of the Royal Institution.
The histories of the early years of great men's
lives are often of interest, and few exceed in this re-
gard those of Faraday. Books were not so plentiful
then as now, and Faraday used the opportunities
which his trade of bookbinder and stationer put in
his way to read scientific works. A series of letters
by him written to his great friend Abbott show the
tendency of his thoughts to chemistry, and incident-
ally show how indefinite were the theories on which
the chemistry of that time was based ; but Faraday's
LIQUEFACTION OF GASES. 103
observations are often far in advance of the age.
He speaks of the odor given off by metals when
rubbed. Exactly this subject of odors, a very myste-
rious one, too, has been the topic of recent investi-
gation. He objects to the names muriate of sodium
and chlorate of sodium for common salt, and says
that it should be called chloride of sodium, and
sodium chloride is its name to-day. Another
tendency of his mind was toward electricity. He
gives the account of his making batteries, on the
now old fashioned "pile" system, placing disks of
zinc and copper, one upon the other, with paper
moistened with acid between the alternate pairs.
With these he decomposed water and acids and tells
the results in the letters which have been preserved.
These letters, many of them written when he was
but twenty years old, are wonderful examples of
his intellectual powers. Here was a bookbinder's
apprentice, but twenty years old, self-educated,
speculating on subjects which constituted the most
recondite branches of science and speculating rightly.
The instances given above are but a few out of many
which could be cited to show the precocity of his
genius.
He kept a note book in which he entered the
names and abstracts of articles in books and journals
which had interested him. Sir Humphry Davy
appears in it, for in this note book is the entry :
" Galvanism. — Mr. Davy has announced to the
Royal Society a great discovery in chemistry — the
fixed alkalis have been decomposed by the galvanic
battery." This he credits to the Chemical Observer.
The greatest achievement of Sir Humphry Davy's
104 LIQUID AIR AND THE
long career is noted by the humble apprentice, who
was destined to succeed the older master and to
equal or exceed him in renown.
An interesting illustration of Faraday's thorough-
ness occurred when he was but nineteen years old.
He had attended some lectures given by Mr. Tatum
on natural philosophy. They were given at his
residence, 53 Dorset Street, Fleet Street. To enable
him to do justice to the illustration of these lectures
he actually learned perspective, doing all the draw-
ings in a quarto treatise on this subject.
In this early work we recognize a threefold bent
of his mind, always discernible in his long life's work.
Chemistry was the branch of science which first claim-
ed his attention and electricity was the work which he
took up later in life. Chemistry and electricity, it will
be remembered, were the two principal studies of his
youthful days. The third subject which interested
him was lecturing, and early in life we find him a
lecturer in the Royal Institution, and for year after
year he lectured there, and held a higher position
than perhaps has ever been awarded an English speak-
ing scientific lecturer. He also wrote upon the sub-
ject of lecturing and on the methods which should be
followed in addressing audiences. He comes to the
same conclusion which has so often been reached
since — that a popular lecture will not be a good
scientific one and that the converse also holds. From
passages often quite long which refer to lecturing,
the conclusion is drawn that he gave a great deal of
thought to the subject and desired to achieve success
in it.
On March i, 1813, Faraday was engaged as assist-
LIQUEFACTION OF GASES. 1 05
ant at the Royal Institution, at the salary of 25
shillings a week and the use of two living rooms
at the top of the building. At once he began his
initiation into serious work by assisting Davy in in-
vestigations into the properties of chloride of nitro-
gen, one of the worst explosives known to man.
He chronicles explosion after explosion with it, his
hand is torn open, his eyelid is cut ; Sir H., as he
calls Davy, has his hand bruised. They <try to
distill it, and it explodes, and Davy gets the worst of
it, his face being cut in several places. They know
the danger they are in, and wear glass masks, and
Faraday at last says that " It is, as I before said, im-
proper to consider it at any time as secure.'*
The dangers of science are appropriate to our
subject. The liquefaction and compression of gases
have given rise to many explosions, and to one of the
worst explosions that has ever happened to an ex-
perimenter. We shall see later how Faraday and
others suffered in experiments in these fields.
On October 13 of the same year, Sir Humphry
Davy started on a tour over the Continent, on which
Faraday was to accompany him. At the last moment
Davy's valet refused to go, and Faraday agreed to do
certain things which more properly would have
fallen to the lot of that functionary. This arrange-
ment, it was understood, was only to last until Paris
was reached. In reality Davy completed the tour
without any valet, and Faraday shrewdly concluded
that finally he preferred to do without one.
In the early days of science there was a much
greater spirit of rivalry among scientific men than at
the present time. Seventy or eighty years ago there
IC6 LIQUID AIR AND THE
was a comparatively small body of scientific facts in
the possession of man. The initial steps toward the
acquirement of this knowledge had been made, and
the acquirement and recording of facts proceeded
more and more rapidly every year, until at present
we have been presented with amazing developments*
one after another, which in their rapid succession
have almost robbed us of the capability of being
surprised.
In reading the quaint story of the life of the book-
binder's apprentice Faraday, and of his experiences
with Sir Humphry Davy during their continental
tour, it is easy to perceive a sort of overriding ten-
dency on the part of the older philosopher whose
assistant he was. Faraday, too, had something to
complain of from Lady Davy, but he seems to have
held his own with her. Faraday's complaint was
that he was requested to do certain things on the
tour which he had not uadertaken to do and against
doing which he protested. At intervals after this
journey, which took place in 1813-14, while he was
twenty-two and twenty-three years old, some notes
of discord can be heard, and the culmination seems
to have been definitely reached in 1823. We have
little to do with the unpleasantness between Faraday
and Sir Humphry Davy ; so we may briefly dispose
of it now.
In 1823 Faraday did his first work on the lique-
faction of gases. He liquefied chlorine and published
the result, eventually disclaiming priority in favor
of another investigator, Northmorc, whose work is
recorded later in this book.
On May i, 1823, he was proposed lor a fellow of
LIQUEFACTION OF GASES. 1 0/
the Royal Society, of which Sir Humphry Davy was
president. Faraday had succeeded by following
Davy's suggestions in liquefying chlorine. Davy
had not told him that liquefaction of chlorine was to
be anticipated in carrying out his suggestions, and it
was liquefied and identified as chlorine in Davy's
absence. The work was therefore Faraday's own.
Yet Sir Humphry Davy seems to have been jealous
that part of the credit should attach to his junior
associate. At any rate, it is definitely certain that
Davy opposed Faraday's election as a fellow of tho
Royal Society, and actually asked him to withdraw
the paper of nomination. Faraday said that, as the
paper had been posted by his proposers, he could not
take it down, and, on a further request, said that he
knew that his proposers would not take it down.
Then Davy said that he, as president, would take it
down.
One of Faraday's proposers afterward told him
that Davy spent an hour arguing that Faraday
should not be elected. The certificate of his pro-
posers had to be read at ten meetings. On the final
ballot there was only one black ball. It is to be
hoped that it was not thrown in by Sir Humphry
Davy. After this Faraday and Davy got on more
smoothly in all their relations. The culmination of
their troubles seemed to mark the end of disturb-
ance.
Thus Faraday's connection with the liquefaction of
gases is concerned with one of the more important
episodes of his life.
A gossipy life of Sir Humphry Davy has been
written by Dr. John Ayrton Paris, who was an
IO8 LIQUID AIR AND THE
intimate friend of the philosopher, and who seems to
have had a fancy for natural science. He was the
first person to witness the liquefaction of chlorine by
Faraday. The passage from his life of Davy in
which he describes it is well worth transcribing, if
only for the picture it gives us of the scientific life of
those days. Dr. Paris had been invited to dinner
with Sir Humphry Davy to meet the Rev. Uriah
Tonkin. Sir Humphry had just set Faraday to
work heating chlorine hydrate in a closed tube.
We can see in our minds the brilliant company
assembled at Sir Humphry's for dinner, while, not
far away, Faraday, alone in the laboratory, was
heating his chemical in a sealed tube, in imminent
danger of blowing his eyes out. We can see Davy's
biographer, dressed for dinner, standing by the side
of the ex-bookbinder in his laboratory garb, watch-
ing and commenting on the operations of the master-
hand. We can do no better than let Paris himself
tell the story of Faraday's liquefaction of the gas
chlorine :
" I had been invited to dine with Sir Humphry
Davy on Wednesday, the 5th of March, 1823, for the
purpose of meeting the Rev. Uriah Tonkin, the heir
of his early friend and benefactor of that name. On
quitting my house for that purpose, I perceived that
I had time to spare, and I accordingly called on my
way at the Royal Institution. Upon descending
into the laboratory, I found Mr. Faraday engaged in
experiments on chlorine and its hydrate in closed
tubes. It appeared to me that the tube in which he
was operating upon this substance contained some
oily matter, and I rallied him upon the carelessness
LIQUEFACTION OF GASES. log
of employing- soiled vessels. Mr. Faraday, upon in-
specting the tube, acknowledged the justice of my
remark, and expressed his surprise at the circum-
stance; in consequence of which he immediately
proceeded to file off the sealed end, when, to our
great astonishment, the contents suddenly exploded
and the oily matter vanished.
" Mr. Faraday was completely at a loss to explain
the occurrence, and proceeded to repeat the experi-
ment with a view to its elucidation. I was unable,
however, to remain and witness the result.
" Upon mentioning the circumstance to Sir Hum-
phry Davy after dinner, he appeared much sur-
prised ; and, after a few moments of apparent ab-
straction, he said, * I shall inquire about this experi-
ment to-morrow.'
11 Early on the next morning I received from Mr.
Faraday the following laconic note :
" ' DEAR SIR: The oil you. noticed yesterday turns
out to be liquid chlorine.
" ' Yours faithfully,
MICHAEL FARADAY/ "
It is seldom that we find such an interesting side-
light thrown upon the pages of early scientific his-
tory. It is a contribution to the everyday life of the
old London world for which we cannot be too grate-
ful to Dr. Paris. It reads like a bit out of Pepys'
Diary. The unprejudiced reader of the present day
will envy Dr. Paris his interview with Faraday, and
few will feel that the meeting with the Rev. Uriah
Tonkin should excite the same feeling to as great a
degree.
110 LIQUID AIR AND THE
In Faraday's letters we find several references to
his work on the liquefaction of gases. In 1823 he
had received from Davy the suggestion mentioned
above to heat hydrate of chlorine in a sealed glass
tube. This he did, and the fluid separated into two
layers, and Faraday identified the lower layer as
true liquid chlorine. He, to confirm this, com.
pressed some chlorine gas in a tube, sealed it, cooled
it, and again obtained liquid chlorine. The latter
gas was dried before compression, so as to make the
experiment absolutely conclusive.
He was troubled by his tubes bursting. His eyes
were once burnt, another time were cut. He speaks
of them as being filled with broken glass, the explo-
sion being so violent as to. drive pieces of glass
through the window panes, " like pistol-shot," he
writes.
This was in 1823. He found, on investigation,
that neither he nor Sir Humphry Davy had priority
in condensing gases into liquids, and so he published
the article spoken of elsewhere (page n 8) telling of
Northmore's work.
In a letter written in 1836 he refers to Monge and
Clouet's liquefaction of sulphur dioxide probably
before 1800. This gas Faraday prepared by treat-
ing mercury with concentrated sulphuric acid, and
found no difficulty in liquefying it. He attached
credence to Monge and Clouet's very doubtful rec-
ord, because he found the liquefaction of sulphurous
oxide such an easy experiment to perform.
Sulphureted hydrogen he made in a sealed tube
by first pouring into it some hydrochloric acid.
Over this he placed a piece of platinum foil, and on
LIQUEFACTION OF GASES. Ill
this placed iron sulphide. The tube was then sealed,
the acid was brought into contact with the sulphide
of iron, and the tube was left for some days for the
acid to act upon the sulphide. If necessary, the
filled end of the tube was heated while the other end
was cooled. He obtained a very limpid, clear fluid,
whose specific gravity he puts at about 0*90.
When he came to experiment with carbon dioxide
gas, he was badly troubled by explosions. He pre-
pared it from ammonium carbonate and concen-
trated sulphuric acid. He credits it with requiring
36 atmospheres at o° C. (32° F.) for liquefaction.
Euchlorine, as it was then called, he made by
acting on potassium chlorate with sulphuric acid.
After twenty-four hours' standing he heated the mix-
ture to nearly 38° C. (100° F.), cooling the other end
of the tube to — 16° C. (3° F.) and condensing a dark
yellow fluid.
Nitrous oxide or laughing gas was prepared by
heating ammonium nitrate. This he heated first to
partial decomposition, in order to get it as dry as
possible. The procedure was rather superfluous, as
in the decomposition water is inevitably produced,
no matter how dry the salt is. Again he was
troubled with explosions, for he got the pressure up
to 50 atmospheres at 7-2° C. (45° F.)
Cyanogen he produced by heating dry mercury
cyanide in one end of the sealed tube, and the cya-
nogen was condensed as a liquid in the other end.
Ammoniacal gas was absorbed by silver chloride.
He found that 100 grains of silver chloride would
absorb 130 cubic inches of the gas. This highly
charged .salt of silver, heated in the sealed tube,
112 LIQUID AIR AND THE
evolved ammonia in abundance, and he liquefied it
without trouble.
Hydrochloric acid was made from ammonium
chloride and sulphuric acid, and liquefied.
This was the work done in 1823. In another place
will be found a full description of the bent tubes
used by Faraday to liquefy gases. These tubes are
still useful in demonstrations and for tests on the
small scale, although their use is not free from
danger.
It is reported by Prof. James Dewar, of the Royal
Institution, that it appears from old papers or
records that in 1838 Faraday exhibited at the Royal
Institution Thilorier's apparatus for the liquefaction
of carbon dioxide, lent him by Mr. Graham. This
was a few years only after its first construction by
the French scientist. The date of the lecture in
which it was exhibited by Faraday was May 18,
1838. The exact date is recorded in the Philosophical
Magazine, vol. xii., 1838, page 536.
With the exception of this incident, we have to
pass over a long period, some twenty-odd years,
before we find Faraday again seriously occupied
with the liquefaction of gases. When past his fiftieth
year he returned to the subject. He had then done
much of his life's work, he had formulated theories
of electricity, especially in relation to magnetism,
and was in the midst of the electric studies of his
life, which lasted until 1855. His work in electricity
underlies all the amazing developments of the last
two decades, and the action of the magnetic circuit
and the production of definite voltages from dynamo-
electric generators were never brought to an intelli-
LIQUEFACTION OF GASES. 11$
gible condition except by the use of lines of force,
and these were a device of Faraday's, which enabled
him to picture in his mind the action of a magnetic
field of force upon a conductor swept through it.
To return to the liquefaction of gases, it was in
1845 that he began anew to try to liquefy various
gases, and the results are embodied in a paper pre-
sented to the Royal Society and published in ab-
stract in the Abstracts of the Papers communicated
to the Royal Society of London under date of
January 16, 1^45. Some additional remarks on the
same subject are given in the same volume under
date of February 20.
He combined mechanical compression with cool-
ing, using two air pumps, working in succession, one
after the other, reminding us of Pictet's pumps, de-
scribed on page 165. The first one had a cylinder one
inch in diameter. The next pump, whose cylinder
was one-half inch in diameter, took the compressed
gas from the first one and gave a second com-
pression. The gases were pumped into green
bottle-glass tubes, one-sixth to one-quarter inch in*
external diameter. This seems a very small tube to
employ,, but the diameter is so stated in the abstract.
The tubes were sealed at the upper end, which was,
in some cases, bent downward so that it could be in-
serted into a cooling mixture. The pressure could
be raised to fifty atmospheres. He sometimes used
tubes closed with brass stopcocks.
The cold was produced by what he calls Thilorier's
mixture of solid carbon dioxide and ether. This
gave a temperature directly of —767° C. (—106° F.)
To increase the cold he placed the mixture under an
II~4 LIQUID AIR AND THE
air pump and exhausted down to one twenty-sixth of
an atmosphere. This gave him a temperature of
-110° C. (—166° F.) His bath of carbon dioxide
and ether, under these conditions, lasted only fifteen
minutes.
He found that several gases condensed to liquids
at the atmospheric temperature under this degree of
refrigeration. Sometimes he preserved them by
sealing up the tubes, and they remained liquid at
ordinary temperatures. Others troubled him by
their chemical action on the cement employed in
connecting his apparatus. Some he succeeded in so-
lidifying. These were sulphur dioxide, sulphureted
hydrogen, nitrous oxide, hydriodic acid, hydro-
bromic acid and ammoniacal gas. He suggests the
great availability of liquid nitrous oxide as a refrig-
erating agent.
It is interesting to note that he tried hydrogen
and oxygen at 27 atmospheres, and failed to liquefy
them. He also failed with nitrogen and nitric oxide
at 50 atmospheres, carbon monoxide at 40 atmo-
spheres, and coal gas at 32 atmospheres.
His work was greatly facilitated by the adoption
of low temperatures. In his use of a volatile freez-
ing mixture in a vacuum combined with mechanical
pressure applied to the gas, we recognize the ele-
ments of the work of most of his successors in the
work of liquefying gases.
Faraday did some of the greatest work of his life
in the realm of electricity, and here we have to
chronicle a discovery which is the basis of some
very striking liquid air experiments. He found that
not only iron and a few other metals are attracted by
LIQUEFACTION OF GASES. 115
the magnet, but he found that the gas oxygen is
highly magnetic, the discovery of this fact coming
after Baucalari's discovery of the same. Baucalari
was professor at Genoa. Faraday's date was 1847.
What strange exultation would have possessed his
soul could he have seen liquid oxygen adhering in
quantity to the pole-pieces of a magnet, and lying in
a vessel over its poles and drawn by the attraction
as if it were a veritable metal, although it is as far
removed chemically from the metals as possible.
After a long life, one of the most touching and in-
teresting in the history of science, Faraday felt his
powers gradually failing. His life had few episodes
outside of his scientific discoveries. Sir Humphry
Davy, at last, did him justice ; the disagreeable in-
cident of 1823 was the last of its kind.
At the age of seventy-five, on August 25, 1867, he
died. He had spent all his scientific life in the
Royal Institution, and left it as a veritable legacy
the story of his work on the liquefaction of gases, so
ably prosecuted in the same building by Prof. Dewar.
Davy and Faraday are now commemorated by the
Davy-Faraday Research Laboratory, in connection
with the Royal Institution, founded by Dr. Ludwig
Mond, which was opened in 1896.
Il6 LIQUID AIR AND THE
CHAPTER VII.
EARLY EXPERIMENTERS AND THEIR METHODS.
Perkins' claim to have liquefied air — Its absurdity — North-
more 's liquefaction of chlorine — Rumford's experiments
as commented on by Faraday — Babbage's experiment in a
drill hole in limestone rock — Monge and Clouet's alleged
liquefaction of sulphurous oxide — Faraday's liquefaction
of chlorine — Stromeyer's liquefaction of arseniureted
hydrogen — Faraday's bent tubes for liquefaction of gases
— Manometer for use with them — Experiment in a straight
sealed tube in the liquefaction of chlorine — Davy 's sug-
gested method — Cagniard de la Tour — His bent tube
experiments — D. Colladon — His apparatus as still pre-
served— Thilorier — His discovery of solid carbon dioxide
— A fatal explosion — The improved Thilorier apparatus —
Johann Natterer's apparatus — His experiments — Loir and
Drion's solidification of carbon dioxide — Thomas An-
drews, of Belfast.
The first hint of the liquefaction ofc air is given in
the Annals of Philosophy, new series, vol. vi., page 66,
1823. It is merely a short note giving the title of a
paper by Mr. Perkins. The paper was to be read at
a meeting of the Royal Society, in 1823, but it was
mislaid, and the Royal Society were spared the
reading of it.
Mr. Perkins says that he exposed air to a pressure
as high as i,ico atmospheres, which is nearly eight
tons to the square inch, or over half the pressure
produced in a modern cannon. He says that the air
LIQUEFACTION OF GASES. 117
upon compression disappeared, and left in its place
a small quantity of liquid, permanent when the pres-
sure was removed, tasteless, and without action on
the skin. Faraday says (Quarterly Journal, xvi.,
page 240) "it resembled water," but thinks that it
may be some unknown product of compressed air.
The present generation, to whom liquid air in
quantity has become a plaything, recognize in Mr.
Perkins' work a very simple state of things. The air
disappeared because it all leaked out, and the water
vapor present was condensed by the high pressure
and was left in the apparatus. Had Faraday been
given a sample of Perkins' "liquid air," he would at
once have identified it as water.
In 'i 805 and 1806 papers by Thomas Northmore
appeared in Nicholson s Journal, xii., page 368 ; xiii.,
page 233. Northmore was experimenting to see what
effect pressure had upon a mixture of gases. He
had a compression pump, mercury gauge and re-
ceivers, and pumped his gases directly into the re-
ceivers. He tried a metal receiver, but found it
unsatisfactory and adopted a glass one.
Very fine illustrations of some of his screw con-
nections, of his valve and of his siphon gauge, are
given in the Journal. They show so little and such
unimportant parts that it is rather surprising why
smch care was taken in so beautifully reproducing
them.
He had all sorts of difficulties. His stopcocks
troubled him, as they leaked. The metal parts of
his pump corroded under the effect of the gases he
experimented with, and his receivers exploded
several times.
Il8 LIQUID AIR AND THE
He condensed chlorine gas, then called oxy-
genated muriatic acid, describing the experiment as
follows :
" Upon the compression of nearly two pints of oxy-
genated muriatic acid in a receiver two and a quarter
cubic inches capacity, it speedily became converted
into a yellow fluid."
He then comments upon its pungent odor and its
great volatility.
He thinks that he liquefied sulphurous acid, but
his pump piston became immovable very soon, on ac-
count of the action of the gas. He says that he ob-
tained " a thick slimy fluid, of a dark yellow color."
This, he claims, confirms Monge and Clouet's ex-
periment, as given in Accum's " Chemistry," vol. i.,
page 3 1 9.
Faraday, whose mind was pre-eminently illumined
and guided by the lamp of truth, contributed
to the Quarterly Journal of Science, Literature and
the Arts, vol. xvi., page 229 et seq., a paper on
the history of the condensation of gases. He
states that when he liquefied chlorine gas a
little earlier in the year 1823, he was unaware
that " any of the class of bodies called gases had been
reduced to the fluid form." He started an investi-
gation into the history of the subject. He found
that Count Rumford, in 1797, had exploded gun-
powder in closed vessels and had claimed to confine
the gases produced within the space previously oc-
cupied by the powder. This may, with all due re-
spect to the distinguished inventor, be doubted.
Faraday speaks of the hissing sound observed when
the products of combustion in Rumford's experi-
LIQUEFACTION OF GASES. 119
ment were allowed to escape, and concludes that
this may have been due to liquefied carbon dioxide.
The accepting a hissing sound as proof of liquefac-
tion reminds us of Pictet's claim for the liquefaction
and solidification of hydrogen, when so much was
inferred from the noise due to the escaping of the
stream and to its impinging on the floor.
Faraday does not make any point of the fact
that carbon dioxide snow or solid carbon dioxide
should have been produced. That this is formed
when the liquid in question is permitted to evapor-
ate under atmospheric pressure was unknown at the
time the paper was written.
A most curious experiment on the decomposition
of marble under pressure was made by Mr. Babbage
in 1813. He wished to ascertain whether pressure
would prevent chemical decomposition. The idea,
in- our days of high grade explosives, and when the
recent explosions of liquid acetylene have done so
much to bring a safe illuminant into evil repute,
seems curious. But Mr. Babbage, with his inquiring
mind, had a hole thirty inches deep and two inches
wide drilled in the limestone rock at Chudley Rocks,
Devonshire. A quantity of strong hydrochloric
acid was poured into the hole, and a conical wooden
plug, previously soaked in tallow, was driven into
the mouth of the hole and the experimenters stood
off and waited. They might be waiting yet, as far
as the experiment went, for nothing occurred, the
rock was not split and the plug was not expelled.
Faraday thinks that liquid carbon dioxide may have
been formed and lain quietly in the hole. He over-
looks an important point — that the water of the
120 LIQUID AIR AND THE
hydrochloric acid would assist in lowering- the
pressure by its solvent action on the carbon dioxide.
Mr. Babbage's conclusions are not given.
Faraday, in his paper on the historv of the lique-
faction of gases, says it is asserted that sulphurous
acid gas had been liquefied by Monge and Clouet>
but that he had not succeeded in finding any account
of their process. Their work dates back to the end
of the eighteenth century. Anyone who wishes to
investigate the subject will find it clouded by un-
certainty. On page 234 of the Quarterly Journal
of Science, Literature and the Arts, vol. xvi.,
will be found references to seven authorities, and
there seems to be no certainty obtainable from any
of them. Faraday reaches the conclusion that the
degrees of pressure and of cold required to liquefy
sulphurous oxide are so slight that there is little
doubt that Monge and Clouet did actually accomplish
the experiment. The original authority cited for
their work is Fourcroy, vol. ii., page 74. He states
that the gas is liquefiable at " 28° of cold." This tern-
perature refers probably to the Centigrade scale,
and reduces to — 18'4° F.
The early experimenters had found that by expos-
ing chlorine gas, produced by the usual methods, to
cold, a solid substance was produced which was sup-
posed to be solid chlorine. About 1810 this was
examined by Sir Humphry Davy, who found it to
be a compound of water and chlorine. Faraday
analyzed it, and found it to contain approximately
" 277 chlorine, 72-3 water, or i proportional of chlo-
rine and 10 of water.*'
Modern analysis but slightly changes Faraday's
LIQUEFACTION OF GASES. 121
figures, to chlorine 28 per cent., water 72 per cent,
giving as a formula C1.OH5. The old investigators
had not produced dry chlorine, and the substance
which they cooled contained so much water that
chlorine hydrate was produced by the refrigeration.
Sir Humphry Davy suggested that exposing the
chlorine hydrate to heat under pressure would prob-
ably lead to some interesting results.
Without detailing Faraday's exact words, it may
be enough to refer the reader to the Philosophical
Transactions of the Royal Society of London, 1823, vol.
xiii., page 160 et seq. — a most sumptuous publication
wherein the work is described in full detail by Para-
day. A subsequent note by Davy says that he
thought one of three things might result from the
experiment, and among them was the liquefaction of
chlorine.
This was the origin of the last and most bitter dis-
pute between Faraday and Davy. More is said of it
on pages i« 6 and 107. After this the two lived on ex-
cellent terms. It must also be said that it was a very
one-sided dispute, as far as any acrimony was con-
cerned, Faraday showing not the least spirit of con-
tention.
The assertion by Davy of what ideas were present
in his mind when he suggested the experiment to
his assistant was calculated to deprive Faraday of the
entire glory of being the first to successfully liquefy
chlorine. But the historical investigations of Fara-
day showed him that nearly twenty years -earlier
Northmore had made liquid chlorine, so that the
bone of contention was pretty well disposed of.
Other less important liquefactions are that of
122 . LIQUID AIR AND THE
arseniureted hydrogen, claimed for Prof. Stromeyer,
of Gottingen, in 1805, but very much doubted by
Faraday {Quarterly Journal, xvi., page 236) ; and that
of hydrochloric acid, claimed for Mr. Northmore, in
1805 (ibid., page 236; Nicholson's Journal, xii., page
368, idii., page 232).
The arseniureted hydrogen experiment, however,
has a great subjective interest, as it illustrates the
danger inherent in the work or the early chemists.
This gas is so frightfully poisonous that its dis-
coverer is said to have been killed by inhaling a
single bubble. Yet we read of Stromeyer producing
it in quantity, by digesting an alloy of 15 parts tin
and i ot arsenic in strong muriatic acid, collecting
it over the pueumatic trough, and exposing it to the
temperature produced by mixing snow and calcium
chloride, in which, as a test of its coldness, several
pounds or quicksilver had been frozen in the course
01 a few minutes. This was certainly a most.power-
ful freezing mixture. Yet Faraday doubts if the gas
was really liquefied, as he himself had tried it at nearly
— 1 8° C. (o° F.) at a pressure of three atmospheres.
Had any accident happened during these experi-
ments, had a retort burst or the high pressure ap-
paratus exploded, the intrepid experimenters would
have had a narrow escape with their lives, if they
had not instantly succumbed to the poisonous gas.
As for hydrochloric acid gas, whose liquefaction
had been claimed by Northmore in 1805, Faraday
concludes that as 40 atmospheres pressure are re-
quired to liquefy it at an ordinary temperature, and
as Northmore employed no cooling mixture, the
supposed condensation did not take place.
LIQUEFACTION OF GASES. 123
For liquefying gases on the small scale when they
can be evolved by heat, and at not too high pressures,
the bent glass tubes devised by Faraday for this use
may be employed. There are many shapes given by
him, two of which are more directly in the line of
our subject. One is applicable where no liquid is
given off in the process of producing the gas, for it
must be produced in the tube. Another is used
where some liquid, such as water, is evolved during
the gas evolution process.
The simple bent tube is shown in the cut. The
tube as made is sealed at one end and bent in the
middle. The gas-evolving material is placed in the
closed end, and the other end, which has been left open
for the introduction of
the material, is closed
after the introduction
by melting the glass
with a blow-pipe or Faraday's Simple Bent Tube.
Bunsen burner flame.
In the construction of the tube care must be taken
to maintain a good thickness of the glass where it is
drawn out for closing. Often in drawing a tube
down the glass becomes too thin for strength.
If the gas is one which liquefies by pressure alone,
all that is necessary is to hold the tube in the
position shown and heat the full end. As the gas is
evolved it produces pressure in the tube, and if the
pressure becomes great enough, and if the tempera-
ture of the empty end of the tube is cool enough, it
liquefies and collects there in the liquid state.
But often cold is required in addition to pressure,
and this is secured by inserting the empty end of the
124
LIQUID AIR AND THE
tube into a freezing mixture. Powdered ice and salt
or powdered ice and calcium chloride are typical
mixtures.
The other shape of tube is shown in the next cut.
The tube was held inverted, as shown in the upper
figure, and the substances were inserted, as shown,
into one or both bends, b and c. A long-stemmed fun-
nel was used to pour the liquids through, if liquids
were used. The ends, a and dy were then sealed,
and, by turning the tube over, everything collected
in one end, a. The tube was placed
with the empty end, d, in a freezing
mixture. The end, a, was heated,
if necessary. The liquefied gas
collected in the further end, and
any liquid that distilled over was
caught in the intermediafe bend.
To determine the pressure pro-
duced in the tube, a small tube
closed at one end, o, and with a
short bit of mercury, ?/, in its bore,
was placed in the experimental
tube before closing it. As the pres-
sure rose, the mercury was forced
toward the end of the small tube
containing it. This it did because
the air confined between the mer-
cury and the top of the tube is compressed. If the
distance from the mercury to the closed end of the
tube is diminished to one-half its original length, and
if the tube is of exactly even bore, it indicates a
pressure of about fifteen pounds to the square inch
in excess of the atmospheric pressure.
Faraday's Bent
Tubes and
Manometer.
LIQUEFACTION OF GASES. 12$
Faraday directs the manometers to be made of
drawn-out tubing which is of greater diameter at the
open than at the end which was to be closed. He
directs that they be from eight to twelve inches long.
They wore calibrated and graduated by placing in
them a drop of mercury. By careful manipulation
this was moved from end to end of the tube and its
length was marked off, step by step, for the whole
length of the tube. This left the tube divided into
lengths varying among themselves, but, as each cor-
responded to the volume of the same drop of mer-
curv, each length would give an equal volume. By
having the tube larger at the base than at the top
the readings for high compression became more deli-
cate. The mercury was left in the tube to act as an
index ; the upper end of the tube was sealed after
the graduation was ended.
In graduating the wide parts a larger quantity of
mercury is prescribed for the operation, but the ori-
ginal divisions on the upper part of the tube gave
the basis for its entire division.
In Faraday's " Chemical Manipulation," American
edition, 1831, page 608, quite elaborate directions are
given for making these gauges. It will be evident
that -considerable accuracy is attainable with them.
By such a tube he states that it is easy to read off to
above one hundred atmospheres.
In use he says that the compression tube should
be bent in two places, giving three straight divisions,
something like a letter N, and the little manometer
is to be inserted in one of the divisions.
Seventy-five years ago Faraday, with such appa-
ratus, liquefied chlorine, cyanogen, ammoniacal gas,.
126 LIQUID AIR AND THE
carbonic acid gas and some others, as described in
this and the two preceding- chapters.
The greatest care is to be recommended in carry-
ing out these experiments. The tubes are very
prone to explode, and if they do, the explosion is
very violent. A tube will sometimes be in part re.
duced to sand like grains of glass. There were
many such explosions in the early days of chemistry,
and the experimenters wore glass masks.
A very pretty experiment, which can be done in a
straight closed tube, occurs in the liquefaction of
chlorine from the hydrate. Chlorine hydrate, a
compound of chlorine and water (C1.OH5), is made
by saturating water with chlorine gas and surround-
ing the vessel containing it with ice. A somewhat
strongly green-colored crystalline substance sepa-
rates, which is chlorine hydrate. A more intense
cold is needed to separate the crystals well.
A quantity of the crystals is placed in a tube
closed at the bottom and the upper end is sealed.
On heating the hydrate it melts. A purse-like drop
of chlorine forms near the surface of the liquid and
hangs therefrom down into the liquid, constantly in-
creasing in size until it falls to the bottom and the
fluid is divided into two layers. At the bottom is
liquid chlorine, above it is water. By slight addi-
tional heat, if the other end of the tube is in a freez-
ing mixture, chlorine can be distilled over, and will
collect as a liquid in the cool end of the tube. The
double bent tube may be used in this latter experi-
ment.
Sir Humphry Davy, in 1823, suggested a modifica-
tion of Faraday's process. He would fill the tube
LIQUEFACTION OF GASES. 12?
with the gas to be liquefied. Then a little water,
ether or alcohol is introduced, and the tube is sealed
up. By heating the alcohol or other fluid, it gives
off its vapor, and the pressure in the tube can there-
by be brought up to any desired point within the
limits fixed by the strength of the tube. In his own
words, gas " is in one leg of a bent sealed tube, con-
fined by mercury." The idea undoubtedly was to
use such a tube as shown on page 124, and to place
mercury in the intermediate bend, so as to shut off
the water from the gas.
The idea is rather ingenious, but we cannot ascer-
tain that it led to any results. Gas has practically
always been compressed either by the pressure pro-
duced by its own evolution or by a pump or press,
and Davy's suggestion has not been utilized to any
extent.
Faraday thought so highly of the use of tubes in
chemistry that a long chapter in his " Chemical
Manipulation " is devoted to what he terms tube
chemistry. It is illustrated with cuts representing
many kinds of tubes, and the use of sealed tubes as
here described for the liquefaction of gases forms
only one of many applications which he describes.
To orientate ourselves we must note that the book
in question appeared long before Faraday did his
final work on the liquefaction of gases. In 1845 he
used the two condensing pumps, one working into
the other, for compressing gases, and condensed
them in tubes made of green glass, and sometimes
fitted with brass cocks at the ends. Thus he de-
parted, in 1845, from the simplicity of manipulation
which distinguished his work of 1823. The book
128 LIQUID AIR AND THE
whose American edition is dated 1831 is an expo-
nent of his earlier and simpler methods.
Faraday has been used as a starting point in the
history of the liquefaction of gases, because he not
only is the first who did really thorough work on
the subject, but because his investigations into the
literature of the subject have greatly facilitated the
fixing of the date of the work of the older investi-
gators.
The earliest ideas about the possibility of lique-
fying gases were based very largely on the efficacy
of pressure. The influence of pressure on lique-
faction was not kno\vn, and various experimenters
investigated it. M. le Baron Cagniard de la Tour
attacked the subject, but in an inverted order. He
demonstrated that liquids could be converted into
gases of volume little more than twice their own.
Had the scope of his work been properly appreciated,
much trouble might have been spared more recent
investigators. We know now that temperature is
the essential thing in .liquefying gas, and that pres-
sure is altogether subsidiary to and dependent on it.
There is no more impressive contrast to the work
of the early investigators who devoted all their ener-
gies to the production of pressure for liquefying
gases than the experiment described later (page 336;,
when the exterior surface of the simple tube of
liquid air, exposed to exhaustion, drips with liquid
air condensed from the atmosphere at atmospheric
pressure by the intense cold.
It was just before Faraday liquefied chlorine that
the baron did his work and established La Tour's
law, that a liquid can be converted into a gas
LIQUEFACTION OF GASES. 129
which shall not exceed in volume the liquid itself,
At least, his investigations gave the proof of this fact
so nearly that the law is thus stated under his
name.
La Tour worked with sealed tubes, as did Fara-
day, partly filling tubes with various liquids and ap-
plying heat. He made a portion of the tube itself
act as a manometer or pressure indicator.
Before beginning his more accurate work on the
small scale with glass tubes, he tried an experiment
on the large scale which reminds one of Otto Van
Guericke's methods. The wonder is that he did not
have an explosion.
His original papers were published in the Annales
de Chimie et de Physique in 1822, and afford a good
example of early methods of work.
He first took the end of a cannon and filled one-
third of its interior volume with alcohol. In it he
placed what he calls a ball of silex, and closed the
gun hermetically. On shaking it, the ball was
checked in its motion by the liquid. He applied
heat gradually, and eventually reached a point when
the ball bounced about without obstruction, as heard
from the outside. Water was tried, but did not
work so well. Petroleum naphtha (?) and ether acted
like alcohol.
He unhesitatingly took it as proved that he had
gasified alcohol, ether and petroleum naphtha in a
space but three times their original volume. The
fact that water did not give the same evidence
operated in strong confirmation of his conclusions.
The next point was to obtain ocular evidence of
the gasification of a liquid in such a limited space.
130
LIQUID AIR AND THE
Accordingly he sealed up in glass tubes ether, alco-
hol and his petroleum naphtha, and, providing the
tubes with long glass tails melted to them for han-
dles, he heated them. As the heat rose the liquids
expanded, sometimes to twice their original volume,
and became very mobile, and suddenly disappeared
as they became converted into gas.
The baron had this doubling of vol-
ume firmly fixed in his mind, for he filled
his tubes about two-fifths full and suc-
ceeded in his "experiment. Then he
tried, with success, a tube nearly one-
half filled, and another he filled a little
over one-half with the liquid. This tube
burst. He was careful also not to have
any air mixed with the vapor of the
liquids in his tubes.
His apparatus as shown in the cut
was of the simplest description. Mer-
cury was introduced before the tube
was sealed. It settled in the bend, c.
The liquid was poured into the large
tube or bulb, and after expulsion of
air, if desired, by boiling, the bulb was
sealed. The other end, a, was also
sealed. Now, the mercury lying in the
bend had air above it in the small tube,
and if the air changed in volume, the
mercury, by rising or falling, would
indicate the extent of such change.
The liquids in the bulb were heated. As the pres-
sure rose, the mercury was forced up the small tube,
and the •diminution of volume of the air gave the
De la Tour's
Apparatus.
LIQUEFACTION OF GASES. 131
pressure. The air tube was so small in reference to
the other that the mercury in rising made but little
difference in the volume of the bulb.
The liquids, it will be observed, could not increase
but two or three fold in volume. Any space in the
right hand division of- the tube not filled with the
liquid contained its vapor. As the heat increased
the liquid disappeared, being completely gasified,
and eventually all the gas from one volume of liquid
was contained in the space to the right of the mer-
cury, in volume but two or three times the original
volume.
The apparatus has various levels indicated in the
original cut which the baron used in his description
of his several experiments. Our illustration is a
close reproduction of the original cut from the An-
nales, and, like Faraday's bent tubes, is an interesting
example of early methods. The levels r, /, b, b ',
etc., indicate the levels assumed by the mercury as
the conditions of volume of liquid, of gas, and the
pressure in the tube varied.
He gives the details of several experiments. The
details of a single one will be sufficient to give an
idea of his methods of work.
In one experiment he filled the part of the tube
marked b, c, d, e, in the cut on page 1 30 with mercury.
The space above the mercury in the wide part of the
tube was partly filled with ether. When all was in
place, the ends, a and/, were sealed by melting the
glass with a blowpipe. Heat was applied and the ether
expanded and became gas, forcing the mercury up to
the mark, g. The narrow portion of the tube con-
tained the compressed air, and from its reduction in
132 LIQUID AIR AND THE
volume he calculated the pressure to which the gasi-
fied ether was subjected.
The tube of larger diameter was four and a quarter
millimeters (about one-fifth of an inch), the smaller
tube was one millimeter (about one twenty-fifth of an
inch) in diameter. Care was taken to have this nar-
rower tube of even diameter. Other marks of level,
e'* b'> S '» are given by the baron to indicate how the
experiment was performed with alcohol.
The experiments with different liquids are de-
scribed, and some of his calculations show to advan-
tage the work of a careful observer employing sim-
ple apparatus.
One tube was two-fifths filled with alcohol sp. gn
O'844- The liquid expanded to double its volume and
then, at a temperature of 2587° C. (4977° F.), sud-
denly disappeared. The pressure was about 119
atmospheres. Ether became gaseous at a tempera-
ture of 200° C. (392° F.) with a pressure of 37-5
atmospheres, the gas occupying twice the volume
of the liquid.
Water became gaseous in four times its bulk at a
temperature of about 412° C. (773*6° F.), or that of
melting zinc. A little sodium carbonate had to be
added to the water to prevent it from attacking the
glass of the tube. Before he adopted this expedient
his tubes broke when he used pure water in them.
Many years later we find Cailletet repeating this
last experiment with pure water in a metallic tube.
As the vapors cooled, a cloudy appearance was ob-
served, and the liquid, when the temperature fell
sufficiently, suddenly reappeared.
La Tour was very near to obtaining the evidences
LIQUEFACTION OF GASES. 133
of the intermediate state observed by Thomas An-
drews (page 147). As it was, he found that under the
conditions a very wide departure from the law of re-
lation of volumes of gases to their pressures existed,
and he should be credited with a certain amount of
important preparatory work in the liquefaction of
gases, attacking the problem from the other end-
effecting the gasification of liquids with very slight
change of volume.
In Colladon's work, Geneva figures for the first
time in the field we are treading. Later Pictet made
the city by the lake famous by his liquefactions of
gases.
Daniel Colladon, of Geneva, was the assistant of
the great Ampere, and no apology is needed for in-
serting an incident in his life, as told by Raoul Pictet
in his work " Etude Critique du Materialisme et du
Spiritualisme." The last word is not to be rendered
as our word " spiritualism ;" in the French language
it refers to the operations of the mind and soul, not
to the fraudulent manifestations of so-called medi-
ums.
Ampere had studied out his theory of magnetism,
and had ordered apparatus to be made for its de-
monstration. A distinguished audience assembled
for the lecture, and at the last moment the appa-
ratus arrived from the ranker.
Those who are familiar with the Ampere theory
of magnetism know how it is demonstrated by wire
bent into helices, which are poised like compass
needles and are subject to the movements of a com-
pass needle when an electric current is passed
through them. When the current passes, the solen-
134 LIQUID AIR AND THE
oids point north and south, the ends are attracted
or expelled by one or the other pole of a magnet.
Ampere began his lecture and gave his demon-
stration on the blackboard. He was, in Prof.
Pictet's words, " superb, eloquent in the power of
his conviction." All present were delighted. Then
the apparatus was taken in hand, and the practical
proof of the theory was to be given.
The solenoids were mounted and connected to the
electric terminals so that the current passed. They
refused to move.
Ampere tried again, but in vain. The audience
began to grow impatient. In the midst of the grow-
ing inquietude the suffering scientist did his best,
but could get no result.
Ampere left the hall with Colladon. No one else
was with them. They followed the Boulevard
St. Michel toward the Seine, the tears running
down Ampere's cheeks. He went to the house of an
intimate friend, and tried to distract himself with a
game of checkers — an old distraction with him.
Colladon now took the matter up, and began to
reorganize the apparatus. He altered the method of
suspension, substituting mercury cups for the solid
contacts. He connected the electric terminals so
that the currents passed, and all worked perfectly.
It was eleven o'clock at night when he succeeded.
He ran to where Ampere was trying to forget
his sorn)ws in checkers, and called out to the great
scientist, gloomily studying his game, " It works, it
goes, it moves !"
Ampere seized his hat, and the two rushed off to
the laboratory, where it was so late that the porter
LIQUEFACTION OF GASES. 135
wanted to exclude them from the laboratory. The
scientist saw the experiments successfully performed
as midnight crept over Paris.
The lecture was repeated to a wildly enthusiastic
audience with the beautiful experimental demonstra-
tions which have done so much to immortalize the
name of Ampere.
As the audience left the hall, the Marquis de
Laplace waited at the door until Colladon, the last
to leave, was crossing the threshold. Laplace barred
the way, extending his arms, and looked him in the
face, and said :
" Young man, you did not give it the least little
touch? "
Three or four years later, in 1828, Colladon, then
corresponding member of the Academy of Science,
performed many experiments in attempting to liquefy
gases. His apparatus was almost exactly that of
Cailletet, without the release cock, which was at the
base of the success of the later experimenter.
The dimensions of the apparatus, in the metric
system, are quoted on the cut, which is an exact
reproduction of one given by Prof. Pictet in his arti-
cle on his work in the liquefaction of gases.
Two shapes of the capillary tube are shown, for
it was of importance to be able to introduce the end
into a freezing mixture. The bending down of the
end makes this more convenient than with a straight
tube.
The tube within the steel reservoir was nearly an
inch in external diameter. As it was exposed to the
same pressure inside and outside, it could be made
of thin glass. The thick walled capillary tube
136
LIQUID AIR AND THE
D. Colladon's Apparatus of 1828.
which rose from
it was from 0*06
to 0*08 inch inter-
nal diameter. The
steel reservoir
was about one
and three-quarter
inches in internal
diameter and
about five and a
half inches high.
A steel reser-
voir, B, held mer-
cury. By a tube,
C, connection
could be made
with its interior.
An extension, A
A, was bolted
firmly to it. A
glass gas tube,
T T, open at the
bottom, with a
long capillary
tube, / /, rising
from its upper
end, was mounted
and inclosed in
the mercury cis-
tern as shown.
The end of the
capillary tube
was closed. A
LIQUEFACTION OF GASES. 137
limited amount of mercury only was required, as
water could be used above it in the reservoir, B.
The capillary tube nearly fitted the long tube
through which it passed, and the joint between metal
and glass was made secure by gum lac.
Colladon worked at — 30° C. ( — 22° F.) and 400
atmospheres pressure, without result.
The principal parts of his apparatus are still in ex-
istence, carefully preserved in the offices of the So-
ciete genevoise pour la construction des instruments
de physique, in Geneva, Switzerland. An accurate
sectional view of the same, reproduced here, is given
in the Annales de Chimte et de Physique, fifth series,
vol. xiii., plate facing page 288.
Thilorier applied the pressure produced in the
generation of a gas to its own liquefaction. His
pattern in this was Faraday, and he has been fol-
lowed by Pictet and some others. He worked upon
carbon dioxide gas, the gas familiar to all as the one
which -escapes from effervescing liquids. A pair of
cast iron vessels were employed. In one the gas was
generated, in the other it was received after genera-
tion, and the pressure alone was relied on to produce
the liquefaction. He had no idea of applying refrig-
eration.
Producing liquid carbon dioxide on the large scale,
he found, on releasing it from pressure, that the now
familiar solid carbon dioxide was produced in snow-
like masses. This gives an admirable example of
the cold of a boiling liquid. The liquefied gas boils
so energetically that it renders a quantity of heat
" latent," or uses up heat energy, and the chilling of
it is so great that some of it becomes a solid.
138 LIQUID AIR AND THE
When Thilorier first observed this, he attributed
it to the moisture of the air, and thought that the
white solid was snow. A committee of the French
Academy of Science examined it and found that it
was carbon dioxide gas solidified.
The original Thilorier apparatus for liquefying car-
bon dioxide was made of cast iron, as has just been
stated. In 1835 one of them blew up at the Ecole
de Pharmacie, Paris, and tore off both legs of the un-
fortunate operator, M. Hervy. The use of the cast
iron apparatus was proscribed on account of this ac-
cident. Mareska and Donny then modified the appa-
ratus by constructing it without employing cast iron
for generator or receiver.
In Liebig's chemical letters is given an account of
this accident, which, as expressed in the words of the
great German chemist and writer, is worth quoting
in full:
" A melancholy accident occurred at Paris which
proved the extreme danger of the preparation of
liquid carbonic acid by the action of sulphuric acid
on bicarbonate of soda, which is accompanied by a
strong disengagement of heat. Just before the com-
mencement of the lecture in the laboratory of the
Polytechnic School, a cast iron cylinder two feet and
a half long and one foot in diameter, in which car-
bonic acid had been developed for experiment
before the class, burst, and its fragments were scat-
tered about with the most tremendous force ; it cut
off both the legs of the assistant, and the injury was
followed by his death. We can scarcely think with-
out shuddering of the dreadful calamity which the
explosion of this vessel, formed of the strongest cast
LIQUEFACTION OF GASES.
139
iron and shaped like a cannon, would have occa-
sioned in a hall filled with spectators, and yet the
apparatus had been often used for the same experi-
ments, which naturally banished all idea of danger."
(Liebig's " Familiar Letters on Chemistry," London,
1851 ; letter x0, pages 130, 131.)
The Thilorier improved apparatus is shown in the
Thilorier's Apparatus for liquefying Carbon Dioxide.
illustration. The right hand vessel, carried by trun-
nions, is of lead, inclosed in copper, with iron hoops
or bands. It is connected by a tube with screw
joints and connections as shown to a cylindrical re-
ceiver of similar construction. The tube connecting
the two is of copper and has two stopcocks. The
size of the apparatus as made may be gauged from
140 LIQUID AIR AND THE
the fact that the generator was of 6 to 7 liters capa-
city, or nearly 2 gallons.
To use the apparatus, the two vessels were first
disconnected. Eighteen hundred grammes of sodium
hydrogen carbonate (common baking soda), with four
liters of water, were placed in the generator. A cyl-
indrical vessel containing one thousand grammes of
sulphuric acid was placed in it. In some construc-
tions this vessel had a wire-like projection from the
bottom designed to keep it in position, as shown in
the cut.
The generator, which is the left hand vessel in the
cut, was closed, the top being screwed on and the
cock closed. By rocking and inclining it, the acid
was discharged with some degree of control upon
the sodium carbonate solution and upon the undis-
solved salt, and the gas was produced.
The generator and receiver (the right hand vessel)
were now connected by the copper tube, the cocks
were opened, and the gas rushed over into the re-
ceiver. A minute of time was allowed for the es-
tablishment of equilibrium, the faucets were closed,
and the vessels were again disconnected.
The residual gas in the generator was blown off,
the top was removed, and the whole operation as
described was repeated. Five to seven repetitions
were required to produce four liters, or a little over
a gallon, of liquid carbon dioxide.
It is calculated that, with the apparatus charged as
described, there was room in the generator for about
one liter or a quart of gas. At the temperature of
40° C. (104° F.) the pressure would rise to one hun-
dred atmospheres.
LIQUEFACTION OF GASES. 141
Thilorier did some good work on liquid carbon
dioxide. As far back as 1835 we find a paper of his
in the Annales de CJiimie et de Physique on the
properties of the liquefied gas. The extraordinarily
high expansion of the liquid is spoken of, and the
figures as he determined them are given. He finds
it insoluble in water and in fatty oils. He gives a
freezing mixture based on its employment, suggest-
ing a mixture of liquid carbon dioxide and ether.
He found that this gave a frigorific agent of
great power. By placing liquid carbon dioxide in a
vessel provided with an outlet in the form of a blow-
pipe jet, he was able to produce local cooling effects.
A jet of vapor would rush out, and would have great
chilling powers. The arrangement he terms a cha-
lumeau de froid — a cold blast blowpipe. He hopes
for still better effects from a mixture of carbon
disulphide and liquid carbon dioxide.
It is interesting, forty to fifty years later, to find the
idea of producing cold by a jet from a liquefied gas
again brought forward. Cailletet proposed to utilize
the latent heat of liquid ethylene in this manner.
The subject will be found treated on page 198 of this
work, and Dewar used an escaping jet of liquefied
hydrogen to freeze air and oxygen into solid white,
icelike masses, as described on page 269.
Eleven years after Thilorier had devised his dan-
gerous apparatus, a new one was produced by an
Austrian scientist, which apparatus was compara-
tively safe. In a pump was the compressor, and a rel-
atively small receiver, artificially cooled, took the
place of Thilorier's large vessel. It was in 1845 that
the apparatus was produced, and subsequent changes
142 LIQUID AIR AND THE
materially improved it. Johann Natterer, of Vienna,
was its originator.
The apparatus consisted of a vertical compression
pump actuated by a crank with flywheel. The pump
was mounted in an inverted position and delivered
the gases which it compressed upward from its
highest point, which in its inverted position was
really the bottom of the pump barrel. It was sur-
mounted by a wrought iron reservoir of about one
liter capacity which was strong enough to withstand
a pressure of 600 atmospheres.
The liquid gas reservoir, slightly pear shaped, was
surrounded with a basin of copper, designed to hold
a cooling mixture. The pump had a solid piston. At
the point where the pump barrel connected with the
reservoir was a valve which opened upward. The gas
to be liquefied was conducted to the lower end of the
pump barrel, where a tube entered it far enough from
the end to be above the solid piston as it reached its
lowest point of descent.
An important modification was introduced by
Bianchi. He surrounded the pump barrel with a
jacket of metal, and let the liquid which drained from
the refrigerating basin flow down and fill this jacket,
whence it could be drawn from time to time by an
outlet cock. Thus the pump barrel was cooled and
a better working insured as regards the lubrication.
The compression of a gas produces heat, and this
dries up most lubricants. The gas also was thus
delivered at a lower temperature to the reservoir,
which in itself was an advantage. Those who have
used compression pumps are familiar with the
heating effect, which can be observed even in a
LIQUEFACTION OF GASES. 143
bicycle tire pump when inflating a pneumatic tire.
A second jacket surrounded the piston rod, which
jacket received the melted material flowing from the
refrigerating basin, so as to cool the piston rod
directly.
The liquid gas reservoir could be unscrewed from
the pump and carried about. The valve at its
base closed and prevented any escape of gas. At
its top the reservoir was provided with a cock by
which the gas could be drawn off.
The gas is made in a generator, and may be first
introduced into india rubber bags, which supply it
to the apparatus, as shown in the cut. The drying
apparatus, shown in the cut, is a Wolf's bottle (three-
necked bottle) charged with a drying agent. The
drying agent may be sulphuric acid, chloride of
calcium, or some other of the regular materials used
by chemists to remove water from gases.
The apparatus, which is a sort of classic, shows
every sign of being designed to insure perfection
rather from a mechanical than scientific standpoint.
Simply for lecture demonstrations it is rather effect-
ual, and is considered safe — something which can-
not be said of some of its predecessors. The early
experimenters, from Northmore down, have been
troubled by explosions which culminated in the kill-
ing of a man, as already alluded to in the description
of Thilorier's apparatus.
In the cut the entire apparatus is shown mounted
and ready for work, and a sectional view on a larger
scale shows the interior of the pump, gas reservoir
and connections. A is the liquid gas reservoir, with
its escape valve, r, x, for drawing off the liquid, and
144
LIQUID AIR AND THE
its self-acting base valve, S, through which the gas
enters. It will be seen that, to draw off liquefied
gas, the reservoir must be inverted. B is the cool-
Natterer's Apparatus for Liquefying Carbon Dioxide.
ing basin ; ;«, //, <?, the drainage pipes and cock ; Cy
the cylinder or pump barrel cooling jacket ; and be-
low is seen the small jacket for cooling the piston
LIQUEFACTION OF GASES. 14$
rod. The piston rod, t, with pitman, E, works in
the slides, P, Q, in the massive metal frame. The
gas from the bag, R, dried in its passage through
the bottle, V, enters by the pipe, H.
It is Natterer -who is celebrated for his liquefac-
tion of nitrous oxide gas on the large scale, and who
mixed the liquid with bisulphide of carbon for the
production of an intense yet manageable refrigerat-
ing agent for scientific uses.
For determination of low temperatures Natterer
used a thermometer filled with phosphorus chloride.
This he told orally to Prof. Wroblewski or Ols-
zewski (Wiedemanris Annalen, 1883).
The old apparatus was quite troublesome to use.
It required one to one and a half hours' intermittent
pumping to complete the operation. The piston rod
had a way of heating, and this interfered with its
lubrication ; so that the operator had to stop from
time to time to oil it, and this gave it a chance to
cool.
When the receiver was two-thirds full 450 grammes
of liquid carbon dioxide could be taken from it.
In the Leipzig Journal fuer praktische Chemie for
1845 is to be found a description of the early form
of Natterer's apparatus, unimproved by the auxiliary
cooling jackets shown in the more modern apparatus
illustrated by us. The article is by Prof. Pleischl,
and is quite quaintly expressed, or at least reads so
in the light of over half a century's developments.
Prof. Pleischl notes the danger incident to the use
of Thilorier's apparatus, and speaks of the death of
Hervy, who was killed by its explosion some years
previously. He says that his talented young student
146 LIQUID AIR AND THE
Johann Natterer had succeeded in liquefying carbon
dioxide with an air pump, and that led to the con-
struction of what is known as Natterer's apparatus.
The great safety of the new pumping system is quite
enthusiastically commented on, and more notes of a
public exhibition given on March u are embodied,
at which exhibition carbon dioxide snow produced
by Natterer's process was shown to a delighted audi-
ence. It was mixed with ether and used to freeze
mercury, among other experiments.
Natterer made great efforts to liquefy the more
permanent gases, but without success, and seems to
have greatly regretted that better fortune did not
attend his work. He carried his pressures up to
nearly 4,000 atmospheres, or double the pressure pro-
duced in a cannon by the exploding powder. Some
of his work is described in the Wiener Berichte, vols.
v., vi. and xii. A rather complicated screw pressure
apparatus is described and illustrated, by means of
which he performed his high pressure experiments
and determined quantities of data of the compression
of gases under pressure. In vol. xii. of the Berichte
he expresses his regret at not succeeding in lique-
fying gases.
Had he given the same attention to cooling his
gases that he did to compressing them, he might
have had a different tale to tell. The realization of
all that the critical temperature means has given the
liquefaction of gases its new aspect, and has led to
the recent triumphs.
Far too little attention is given to Natterer's ex-
cellent work. He subjected gases under perfect
control and visibility to most enormous pressures,
LIQUEFACTION OF GASES. 147
and certainly to that extent helped to prove the doc-
trine of the critical temperature.
In 1888 Amagat, carrying pressures up to 3,000
atmospheres, got some discrepancies in his
compression figures as compared with
those of Natterer.
The work done by Thomas Andrews,
of Belfast, in 1861 to 1870, as determining
the existence of a critical state, is classic,
and his simple apparatus is shown in the
cut. A small glass tube contains the gas ;
a short column of mercury closes the tube
below the gas ; the upper end of the tube
is sealed. The tube passes through a brass
block, E, which is held by screw bolts on
the end of a copper tube, R. A perforated
block with screw thread cut in the per-
foration closes the lower end, and a steel
screw, Sy passes through the hole and
closes it. All is packed so as to secure
absolute tightness. The copper tube is
filled with water. On screwing in the steel
screw, the water is forced up against the
mercury in the glass tube, g, and the mer-
cury, in its turn, is forced up and the gas
is reduced in volume, the object of the
mercury being to cut off the water so that Andrews'
there shall be no action of the water on Apparatus
the gas. forCom-
t* • ,1 • ^i.i. pressing
I o use mercury in this way, the tube, g, Gases.
has to be of small caliber, or else the mer-
cury would drop out. But another reason obtains.
The steel screw is small, and the tube must be of
148 LIQUID AIR AND THE
the volume, or not much in excess of the volume, of
the portion of the screw which can be screwed in
and out.
By screwing in the screw the pressure could be
raised to 500 atmospheres. Sometimes the tube was
bent downward, so that its end could be placed in a
freezing mixture, as shown in Colladon's apparatus,
page 136.
Other varieties of the apparatus are shown in his
paper published in the Transactions of the Royal
Society of England for 1869.
In his early work he had used the compression
produced by the electrolysis of water. If two ter-
minals of an electric circuit of about two volts or
more difference of potential are placed in a vessel
of acidulated water, or of a solution of various chem-
icals, such as sodium hydrate or potassium hydrate,
gaseous oxygen will be liberated from one terminal
and gaseous hydrogen from the other.
The illustration shows a simple arrangement for
carrying out the experiment. In the background is
seen the battery. In the foreground is the decom-
position vessel, with two spiral terminals or elec-
trodes immersed in it. Only the spiral ends of the
electrodes are bare. The other parts are covered by a
tube of india rubber. The bare ends are inclosed in
inverted test tubes, themselves filled with the solu-
tion. When the battery is connected as shown,
bubbles rise from the wire's, and hydrogen and oxy-
gen gases collect in the test tubes.
Now, if such electrodes with some solution were
introduced into a hermetically sealed and very
strong vessel, the two gases would be evolved and
LIQUEFACTION OF GASES.
149
enormous pressures could be generated by the quiet
effects of the electric current. This is what Andrews
did in his early work. With such apparatus he re-
duced oxygen gas to one three-hundredth of its
volume.
In his later work, using apparatus on the principle
Electric Decomposition of Water.
described above, and using strong capillary glass
tubes for the compress'ed gas, supplementing high
pressure by cold of — 106° C.(— 159° F.), he reduced
air to one six-hundred and sixty-fifth part of its vol-
ume. He got no result with any of what he called
the six non-condensible gases.
150 LIQUID AIR AND THE
These were hydrogen, oxygen, nitrogen, carbonic
oxide, nitrogen dioxide and marsh gas.
One of Andrews' principal papers, utilized above,
is published in the Transactions of the Royal Society,
as quoted, with very elegant cuts of the apparatus.
It appears in a translation in the Annalcs de Chimie ct
de Physique of 1870.
Clerk Maxwell was much interested in Andrews'
work. One of his letters alluding to Andrews' ex-
periments, and addressed to the scientist, and be-
stowing his encomiums on his explorations into the
realm of gases, is given in Tait and Brown's memoir
on the life of Andrews.
The date of Andrews' work is generally put about
1862, one of his principal papers being published
twelve years after his researches were made.
We have now reached a period whose history de-
mands a somewhat different treatment. Up to the last
date mentioned certain gases had resisted all attempts
at liquefaction. Those which had been liquefied had
been the subject of experiments on the small scale,
and the efforts of investigators had been directed to
the attaining of purely theoretical results. Two in-
vestigators now appear who profoundly modified
the views of the scientific world. Pictet and Cail-
letet demolished the old division of permanent gases,
and in doing so had a close race for priority. The
French scientist Cailletet was awarded the priority by
a few days only. But the work of the two men was
so different in its scope and results that they should
be considered hardly as rivals. Cailletet, by acci-
dent, produced mists in a small glass tube. These
mists were due to the momentary liquefaction or
LIQUEFACTION OF GASES. 151
reduction to the vesicular state of the gases con-
tained. Pictet, on the other hand, directed his
efforts from the first to producing a tangible quan-
tity of liquefied gas. He was the first to secure this
result ; he was the first to produce a jet of liquid
oxygen ; he established the system of cascade or
closed cycle refrigeration that has been the guiding
principle for some twenty years of laborious investi-
gation. Basing his work on Pictet's cycles, Dewar
filled the Royal Institution laboratory with machin-
ery and produced liquid gases by the gallon. Wro-
blewski and Olszewski combined Colladon's and
Cailletet's methods with Pictet's cycles for the at-
tainment of their results.
It should be felt that Pictet and Cailletet are to
be placed side by side, and that no question of prior-
ity should be appealed to as existing between them.
LIQUEFACTION OF GASES. 153
CHAPTER VIII.
RAOUL PICTET.
The life of Raoul Pictet — His education — His ice machines —
Disputed priority — Honors awarded — His apparatus for
liquefying gases — Description of its operation — Tempera-
tures of the cycles of operation — His dispatch of Decem-
ber 22, 1877, to the French Academy — Regnault's state-
ment— Hydrogen — His dispatch of January n, 1878, to
the French Academy — Olszewski's comments on the
hydrogen experiment — Pictet 's arrangement of pumps —
His desire to produce liquid oxygen in quantity — Com-
ments on his work — The liquide Pictet.
Raoul Pictet was born in Geneva, Switzerland, on
August 4, 1846. He finished his studies in the
Academy of Geneva when eighteen years old, and
published some memoirs on binocular vision and on
the resistance of the air. He went to Paris, and, al-
though a foreigner, was received as a student at the
ficole Polytechnique in that city. He also took courses
in the College of France, and in the Sorbonne.
There the young student became the friend of the
greatest French scientists, Wurtz, J. B. Dumas, Reg-
nault, Quatrefages and others. He received recog-
nition from a most distant quarter, when the Saint
Petersburg Academy of Sciences crowned his in-
vestigations of binocular vision and offered to pub-
lish all of his researches in full.
Three years were devoted in great part to the
LIQUID AIR AND THE
study of thermodynamics. He made during the in-
terval several long tours, and then returned to
Geneva.
At the age of twenty-five he entered the service of
the Viceroy of Egypt. He was charged with estab-
lishing a course of instruction in experimental phy-
sics at the Ecole Superieure, in Cairo. While thus
occupied he gave a good example of his aptitude for
languages, acquiring Arabic in a few months' study.
Three years were passed in Egypt, and his life
there gave rise to various interesting memoirs. The
atmospheric phenomena of the desert, solar action,
dust, whirlwinds and eddies, the temperature and
floods of the Nile, were among the subjects studied
and written on. He organized hunting expeditions
into the interior, enriching with the spoils the
museums of Cairo and of Naples.
The poisonous reptiles of the Nile regions, one of
whose ancestors may be assumed to have, inflicted
the death wound on Cleopatra, attracted his atten
tion, with a view to combating their venom in the
human system. He collected snakes, and studied
their poison in its action on the animal system. At
one time he had four hundred specimens of Nile
snakes in captivity. The natives of the region, it
is said, still speak of the Geneva scientist who strove
to diminish the deaths due to serpents' bites.
In 1877 Geneva claimed her son, and he accepted
there a chair of physics and mathematics in the
University of Geneva. He had for some years made
ice machines, and had invented a process for freezing
large areas of ice for skating, being a skater of no
mean order himself. London, Manchester and other
LIQUEFACTION OF GASES. . 155
places saw skating rinks constructed on the Pictet
system.
On his establishing- himself once more in his native
city, he was well prepared to begin his work on the
liquefaction of gases. His work is detailed else-
where. His friend Prof. Dufour, of the University
of Lausanne, describes a visit made by special invi-
tation to the buildings of the Societe genevois pour
la construction des instruments de physique. The
visitors were a number of professors and scientists
from Lausanne, the date was December 29, 1877,
and Pictet showed them the liquefaction of oxygen.
It will be seen that his early work in the produc-
tion of low temperatures was in the practical line,
and, therefore, on the large scale. This it was
which gave his liquefaction of gases such value. He
was not content to produce an infinitesimal amount
of liquid. The desire to produce tangible quantities
was ever present in his mind. As regards the
method, it was based on practically successful pro-
cesses. The engineer's mind appeared in the work-
ing of his cumulative cold-producing circuits, and he
established a system which has done service for over
twenty years of investigation in England, Holland,
Poland and Germany.
As will be seen by those who follow the dates
given in this book, there was a close coincidence be-
tween the dates of Pictet's and of Cailletet's liquefac-
tions of oxygen. This was the origin of hot disputes
waged by the political dailies, for in Europe all sorts
of pretenses are seized upon for political effect.
The methods followed and apparatus employed by
the two scientists were so radically different that at
156 LIQUID AIR AND THE
last Cailletet protested, the war ceased, and an inti-
mate friendship was formed between the rivals that
was never broken. Regnault interested himself in
the work he had so long followed, and informed the
Academy of France that Pictet's system of cumula-
tive cold-producing circuits, to his knowledge, dated
back five years, and that the experiments might have
been performed five years earlier had events favored
the work.
The dispute was ended, and Pictet received the
decoration of the Legion of Honor. France, as
always, was generous to the foreign rival for scien-
tific honors.
The mechanical theory of heat was, about this
time, investigated by him in union with M. Gustave
Cellerier for eighteen months. The study was so
intense that Pictet nearly broke down in health on
the completion of the work.
In 1878 he received from the International Expo-
sition at Paris the gold medal, and in the same year
the Royal Institution of England gave him the
Davy medal.
In 1880 he went to Berlin, and there established a
low temperature laboratory. The study of frigo-
therapy was taken up, and the purification of chemi-
cals by intense cold was worked upon.
The cities of Antwerp and of Rome have recently
honored him by diploma and medal of honor. In
1895, the Societe Industrielle du Nord de la France
gave him its grand medal of honor at Lille.
His life has been written from the standpoint
of a dear friend by Prof. Henri Dufour, of the
University of Lausanne, Switzerland. To him the
LIQUEFACTION OF GASES. 157
«
author of this book is indebted for copious notes on
the life of Pictet, and interesting accounts of the
personal traits of the distinguished scientist, who
knows how to charm children by feats of legerde-
main as well as to-interest and delight the world of
scientists by his achievements in physics and in the
realm of low temperature.
He has entered the field of intellectual and moral
philosophy in his treatise entitled Etude Critique du
Materialisms et du Spiritualism* par la Physique Ex-
perimentale. This is a large octavo, and investigates
the relation of material energy and mental opera-
tions most interestingly, and is a scientific protest
against doctrines leading to the depression or de-
spair which sometimes seems to obtain a foothold
among scientific students.
Pictet's apparatus by which he succeeded in lique-
fying oxygen is described in the Comptes Rendus,
vol. Ixxxv., page 1214. The illustration we give is
substantially identical with the one given in the
Comptes Rendus, except that it is completed by the in-
troduction of the gas burner for heating the oxygen
retort, and that a manometer or pressure gauge and
outlet cock are shown at R, N.
The Pictet apparatus, as shown, deserves especial
attention because it is the original of a type which
only now encounters in self-intensive processes a
really efficient rival. It was far in advance of its
time. Apparatus of its type was added to the Col-
ladon apparatus by Wroblewski and Olszewski for
their work. Dewar employed it in his Royal Insti-
tution researches, and the extensive apparatus in the
Leyden University cryogenic laboratory is based
158
LIQUID AIR AND THE
upon its lines. This apparatus was the first to pro-
duce a stream of liquid oxygen, and it cannot be
awarded too high a place in the history of low tem-
perature experimentation and research.
L is a wrought iron retort calculated in the origi-
nal Pictet apparatus to resist 500 atmospheres pres-
sure. Subsequently, it is said to have been made
Raoul Pictet 's Apparatus for Liquefying Gases.
stronger, so as to be able to withstand three times
this pressure. A weighed amount of potassium
chlorate was introduced by the opening, P, which
was then closed. On heating it by the lamp, O, the
quantity of oxygen to give any desired pressure was
produced, such quantity being determined by the
weight of potassium chlorate employed.
LIQUEFACTION OF GASES. 159
The tube, M, was thus filled with oxygen at a pres-
sure regulated by the weight of potassium chlorate.
Pressure was thus produced, which is one element
of the process of liquefaction. The next step is the
cooling of the compressed gas.
The condenser jacket, C, contains liquid sulphur
dioxide. This tends to evaporate and to produce
thereby great refrigeration. From the upper end of
the jacket, C, a pipe goes to the pumps, A and B.
These pump out gaseous sulphur dioxide. The
liquid sulphurous oxide in C boils, therefore, with
greater rapidity than ever, and produces greater
cold. The gas goes through the pumps and is com-
pressed by them in the condenser jacket, D. The
outlet of this condenser jacket, D, is a narrow pipe, d,
which, being of small diameter, produces the requi-
site pressure to condense the sulphur dioxide to a
liquid. Through the condenser jacket, D, a pipe
runs, and cold water passing through this pipe cools
the sulphur dioxide as it comes heated by compres-
sion from the pumps, A and B.
The upper system of pumps and cooling arrange-
ments is almost in exact duplication of what has just
been described, except that liquid carbon dioxide
takes the place of liquid sulphur dioxide, and the
liquid sulphur dioxide under exhaustion takes the
place of the cold water.
The condenser jacket, //, contains liquid or solid
carbon dioxide, which constantly evaporates. The
pumps, E and F, pump gaseous carbon dioxide out
of the upper end of H and condense it in the tube,
K, where it is cooled by the boiling sulphur dioxide.
The small pipe, k, creates the requisite back pressure
160 LIQUID AIR AND THE
for the liquefaction, and a constant circulation is
thus maintained, and the boiling carbon dioxide
keeps the tube, M, inclosed in the condenser jacket,
H, at a very low temperature.
The following figures are given in the Comptes
Rendus as the data of the first successful attempts at
liquefying oxygen :
The sulphur dioxide liquefied in D at a pressure of
two and three-quarters atmospheres, and produced
by its evaporation in the jacket, C, a temperature of
— 25° C. ( — 13° F.) The carbon dioxide liquefied
in Cat a pressure of five atmospheres and a tempera-
ture of —65° C. (—85° F.) The tube, M, by the
evaporation of the cold carbon dioxide, was kept
at a temperature of — 140° C. ( — 220° F.)
In the improved apparatus, the tube, M, was made
of copper, and the liquefied gas was withdrawn at N;
but in the apparatus of 1877, as shown in the Comptes
Rendus, the tube in question was unprovided with a
faucet, and its lower end was within the condenser
jacket, H. The tube was one meter or a little over
a yard long.
In the original experiments, which now may be
considered historic, the pumps were worked for sev-
eral hours circulating the sulphur dioxide and car-
bon dioxide. A 15 horse power engine was employed
to drive them. Meanwhile oxygen was being evolved,
and the pressure was brought up to 320 atmospheres.
Then the cock at P was suddenly opened, and the
sudden expansion of the tremendously compressed
and very cold oxygen absorbed so much heat ener-
gy, rendering the heat latent, that the temperature
fell still further, the oxygen was liquefied in part,
LIQUEFACTION OF GASES. l6l
and the tube, J/, was filled to one-third of its length
with the liquid. The tube being of i centimeter (0*4
inch) internal diameter, it will be seen that this was
a considerable quantity of oxygen — about 22 cubic
centimeters or i£ cubic inches of the liquid.
On inclining the tube by raising the lower end, the
liquid rushed out of the orifice at P(" et jaillisse par
1'orifice en inclinant 1'appareir). It will be remem-
bered that in the original apparatus there was no
way of opening the lower end of the tube, which
was closed and within the condenser jacket, H.
Pictet's dispatch announcing the success of his
experiment, on which so much time, thought and ex-
pense had been lavished, was received by the French
Academy of Sciences on December 22, 1877, at 8 P.
M. It was as follows :
" Oxygene liquefie aujourd'hui sous 320 atmo-
spheres et 140° de froid par acide sulphureux et
carbonique accoup!6s.
"Signe,
" RAOUL PICTET."
(TRANSLATION.)
" Oxygen liquefied to-day under 320 atmospheres
and 140° of cold by suphurous and carbonic acid
working together.
" Signed,
" RAOUL PICTET."
The terms sulphurous acid and carbonic acid are
synonyms for sulphur dioxide and carbon dioxide.
The substitution of the open copper tube M for the
closed one and the use of the manometer, R, and cock,
N, are later modifications. The temperature of the
oxygen generating retort, L, is now put at 485° C.
1 62
LIQUID AIR AND THE
LIQUEFACTION OF GASES. 163
(905° F.) The manometer in the course of the conden-
sation rose gradually until it indicated a pressure in L
and M of 500 atmospheres. The gas began to liquefy
and the pressure fell to about 320 atmospheres. On
opening N, the oxygen rushed out under the great
force of the pressure with violence, looking like a
dazzling white pencil. The escape lasted for 3 or 4
seconds ; the manometer showing some 400 atmo-
spheres, which rose again and again fell when lique-
faction occurred.
The large cut shows the general disposition of
Pictet's apparatus as installed in Geneva.
Fand //"are two boxes packed with non-conducting
material, and in each of these are two concentric
tubes constituting a condenser of the Liebig type.
In F is the oxygen liquefaction tube surrounded
with another tube through which the carbon dioxide,
solid, liquefied and partly gaseous, circulates. This
corresponds to M and Hoi the diagram on page 158.
In H is the carbon dioxide tube, where the gas
from the outside tube in F is cooled by boiling sul-
phurous oxide, which is in a tube inclosing and
concentric with the carbon dioxide tube. These are
K and C of the diagram.
G is a gasholder filled with carbon dioxide gas.
K is a reservoir of liquid sulphurous oxide. P are
the pumps, and B is the oxygen retort.
A moment's inspection of the cut, after study of the
cut on page 158, will suffice to give a full understand-
ing of the operation of the apparatus.
It was no easy matter to obtain the small quantity
of liquid gas that greeted Pictet's vision on the
twenty-second of December, 1877 — the first sight of
164 LIQUID AIR AND THE
liquid oxygen in quantity that ever was granted to
man. Regnault told the French Academy that he
had assisted Pictet and De la Rive five years before
the date of the liquefaction in experiments on lique-
fying gases, and the work of five long years reached
only then its culmination.
Pictet examined with a polariscope the escaping
jet of liquid oxygen as it rushed violently out of his
tube, and thought that he obtained evidences of the
presence of solid particles in the stream.
Pictet did not rest here. The few cubic inches of
liquid oxygen which he had produced acted as an
incentive to go further, and he endeavored to liquefy
hydrogen.
The details of the experiment are given in the
Comptes Rendus, vol. Ixxxvi. They are contained in a
dispatch from Geneva, followed by a letter.
He wished to make his hydrogen by heating
a solid substance in a retort, so as to preserve
the general system of his oxygen method. Accord-
ingly, he employed a mixture of potassium formiate
and potassium hydrate. This mixture, he says, gives
pure hydrogen, free from water or carbon dioxide,
and leaves a non-volatile residue.
On applying heat to his retort, the pressure ran up
to 650 atmospheres and then remained stationary.
The temperature of the gas tube was about — 140°
C. ( — 220° F.) Enough gas was generated to meas-
ure 252 liters at o° C. (32° F.) The cock was opened
and what is described as a steel blue jet escaped with
a sharp hissing sound. A length of 12 cm. (about 5
inches) of the jet was opaque. The jet struck the
floor with a sound like hail. The hissing sound
LIQUEFACTION OF GASES. 165
changed its character until it resembled the noise
produced when metallic sodium is thrown upon
water. The pressure ran down to 370 atmospheres
and the delivery became intermittent, the tube or
cock being choked. For over fifteen minutes the
delivery by the jet occurred in intermittent dis-
charges.
The liquefaction of hydrogen has been felt to be
open to doubt. The fact that the temperature as
given is entirely insufficient, at any pressure, to
cause liquefaction does not at all invalidate the expe-
riment. The release from high pressure of the gas,
bringing about its expansion, rendered heat practi-
cally latent and caused intense chilling of the gas,
already at very low temperature, and might produce
liquefaction of the hydrogen. The experiments of
Cailletet confirm strongly this view of Pictet's expe-
riment. But we know that no hydrogen was lique-
fied in volume in the tube before it was opened.
Ten years later Olsze wski tried to throw some doubt
on the method followed in the hydrogen experiment
of Pictet. He published in \\^Q Philosophical Magazine
for February, 1895, a long article giving a full ac-
count of his work of bygone years, in which he, with
Wroblewski, produced liquefied gases. This article
is a statement of Prof. Olszewski's part in liquefying
gases and air. In the course of the article he criti-
cises Pictet's hydrogen experiment, saying that
hydrogen made as Pictet made it would be contam-
inated with water and carbon dioxide.
As a piston works in a pump cylinder, what is
termed clearance occurs. This is the failure of the
piston to expel everything from the cylinder. It is
1 66 LIQUID AIR AND THE
mechanically impossible to do this with steel or iron
parts, as the piston cannot well be so accurately
made as to just touch the cylinder on its completion
of a stroke. Even if it could, the valve passages
would be left.
As all gases are elastic by nature, it follows that,
when a pump is caused to operate upon a gas, the
clearance of the piston is a great obstacle to its
operation. As the piston of a pump cannot abso-
lutely touch the cylinder end at each stroke, some
gas must always remain in the cylinder, and during
certain conditions of tension and compression, when
the suction is of high degree, and the delivery is
against a high pressure, the piston may work back
and forth without any result whatever. The gas re-
maining in the cylinder ends may be enough in
amount to prevent any movement of the suction or
inlet valve, or to admit other gas if it were opened,
and not enough, on the other hand, to open the outlet
valve, or, if it were opened, to go through it.
This difficulty, inherent in all ordinary piston air
pumps, Pictet avoided by coupling his pumps two in
a set. Thus, when one pump was aspirating from the
cooler jacket or other source of gas, it was deliver-
ing, not against a high pressure, but into the suction
pipe of the other pump. The other pump took this
partly compressed gas through its suction pipe as
delivered by the first and gave it its second compres-
sion.
By this arrangement the difficulties were suppressed
and the four pumps working in sets of two each
operated perfectly. They were driven by band
wheels at from 80 to 100 revolutions per minute.
LIQUEFACTION OF GASES. 1 67
The temperature was determined by a formula
which is deduced from the mechanical theory of
heat applied to change of state. The formula can
be found in the paper of Prof. Pictet as given in the
Annales de CJiimie et de Physique, Paris, fifth series,
vol. xiii., or in the Archives des Sciences Physiques et
Naturellcs, Geneva, January 15, 1878.
It is most interesting in this paper, which is the
definite and authoritative presentation of the experi-
menter's views to find the following passage. It must
be remembered that the oxygen had been liquefied
in an opaque tube, that it was withdrawn therefrom
by the cock under enormous pressure, and that the
sight of the jet, which lasted only three or four
seconds, was the nearest approach to really seeing
liquid oxygen which the definite experiment afford-
ed. We quote the passage :
" We must try to render this liquid oxygen visible
by condensing it in transparent apparatus. The pro-
blem is very complex, bristling with practical diffi-
culties. We must avoid the condensed ice (givre,
hoar frost) which instantly forms on cold surfaces,
and impairs visibility; we must have tight joints with
fragile material," etc.
Had Pictet foreseen the importance of the spher-
oidal state in its relations to the handling of liquefied
gases, and could he have divined how greatly it
would facilitate all operations with them, he would
have seen the difficulty disappear in great part. But
no human being could have imagined how greatly
the maintenance of the spheroidal state was to affect
the question.
The same desire to get oxygen in quantity is here
l68 LIQUID AIR AND THE
discernible which formed the inspiration for Wrob-
lewski, Olszewski and Dewar. A scientist might be
satisfied with Cailletet's mist or with Pictet's jet, but
they were not. The desire to see oxygen and the
other gases liquefied in volume has proved itself no
mere idle dream, but a real, earnest and scientific
longing. The effort and desire to satisfy this long-
ing has led to the achievements commemorated in
this volume.
The oxygen in five of Pictet's early experiments
was evolved from a mixture of 700 grammes potas-
sium chlorate and 300 grammes potassium chloride.
This mixture may be taken as a typical one.
The hydrogen mixture used in his experiment of
January 10, 1878, consisted of potassium formiate,
1261 grammes; potassium hydrate, 500 grammes.
The importance and value of Pictet's early work
cannot be overestimated. His double cycle with
continuous liquefaction of the gases in the two re-
frigerating cycles has been the instrument of the
greatest successes in the hands of subsequent work-
ers. All who worked upon this line in those early
days overestimated the importance of pressure, but
the keynote of Pictet's work was a very advanced
refrigerating apparatus. The critical temperature
is the great element in attaining success in liquefac-
tions. It would have been but a small change to
have compressed by mechanical means the gas to be
liquefied. Had he done so, the effect would have
been twofold.
He would have had more gas to be acted on. As
his experiments were conducted, he had a very
limited supply of gas, and on opening the cock of
LIQUEFACTION OF GASES. 169
his apparatus it rushed out violently, and a fleeting
glance of a second or two at the liquefied gas was all
that it was in his power to obtain. But had he gone
a single step further, and connected a third pair of
pumps to the inner tube, M, of the gas condenser,
there is every probability that he would have suc-
ceeded in his long-cherished wish much better. To
him might have been granted the success claimed
by Olszewski, of pouring for the first time liquefied
oxygen or air from one vessel into another. But the
work of Natterer and Andrews had its effect, and
high pressure was striven for, and static air and
oxygen remained for several years an unfulfilled
hope and expectation.
Pictet, in the year 1885, devotes a paper to a new
refrigerant, which has been named from him the
liquide Pictet. It is still used by him for the pro-
duction of low temperatures. The paper will be
found in the Comptcs Rcndus, vol. c. He suggests
that, for the production of low temperatures, a mix-
ture of two or more volatile liquids may be em-
ployed. It has been aptly said that in mixing
metals so as to produce new alloys the metallurgist
is able to produce so many new metals. Each alloy
may be taken as equivalent to a new metal. The pro-
perties of an alloy are not the average of the proper-
ties of its constituents. In specific gravity, electrical
conductivity, thermal and other properties no aver-
age can be traced in many instances.
Pictet found that tHe case was the same with mix-
tures of liquefied gases, and in the paper in question
discusses at some length the use of such liquids,
which at relatively low temperatures separate into
I/O LIQUID AIR AND THE
their components. He gives a table of the boiling-
points of different mixtures of carbon dioxide and
sulphurous oxide, using molecular mixtures, or mix-
tures in which the proportions of the constituents
stand in molecular proportion to each other.
He succeeded in producing liquids which boil any-
where from— 71° C. (—96° F.) to —7-5° C. (—18-5 F.)
But this range of selection open to the physicist is
not the only advantage. There is a sort of recupera-
tive or self-intensive action involved which makes the
liquide Pictet peculiarly available.
At low pressures its evaporative power is aug-
mented by its disposition to dissociate molecularly,
or to separate into the two gases, carbon dioxide and
sulphurous oxide. At high pressures a sort of chem-
ical affinity of low order seems to come into play, and
the two gases liquefy much more easily than they do
when unmixed. It is easy to see how this phenome-
non lightens the work of the pump used to condense
them. On the exhaust side the action is aided by
the dissociation tendency of the liquids evinced in
their gasification. This lightens the work of the
pump, as it does not have to draw so hard to cause
rapid evaporation. This evaporation is the refrige-
rating action.
At high pressures the chemical affinity also helps
the work of the pump ; for, less power being required
to liquefy them than otherwise, the pump has not got
to develop the same pressure as it would otherwise.
Hence its work is lightened on the pressure side also.
This peculiarity is brought out by a comparison
of the liquide Pictet (formula CSO4) with sulphur-
ous oxide. At high temperatures the vapor ten-
LIQUEFACTION OF GASES. I /I
sion of the liquide Pictet is higher than that of the
sulphurous oxide. But on increasing the pressure
and lowering the temperature the vapor tension in-
creases in a less rapid ratio with the liquide Pictet than
with the sulphurous oxide, and at a low enough
point the sulphurous oxide shows the higher tension.
In graphic terms the curves of tension and tempera-
ture relations cross each other.
All of Pictet's work cannot be given within the
limits of this book. This chapter gives the summary
of his original liquefaction of gases. But his prac-
tical mind sought fields for the utilization of his dis-
coveries, and in subsequent chapters will be found
described his application of low temperatures to
treatment of disease and to the purification and pro-
duction of chemical and technical products.
LIQUEFACTION OF GASES.
CHAPTER IX.
LOUIS-PAUL CAILLETET.
The life of I,. -P. Cailletet — His education — Honors received —
His modification of Colladon's apparatus — Accidental
liquefaction of acetylene by release — Description of his
apparatus — How the apparatus was filled — The full ap-
paratus with hydraulic press — Liquefactions of nitrogen
oxide — Of carbon monoxide and oxygen mixed — Lique-
factions of the same separately — His letter of December 2,
1877, to the French Academy — Liquefaction of nitrogen
— Of hydrogen — Rival claims of Cailletet and Pictet —
Mercury stopper method — Manometers — Original meth-
ods of testing — Eiffel Tower manometer — Carbon dioxide
experiments — Mercury pump — High pressure gas reser-
voir— Ethylene as a refrigerant — Closed cycle method —
Accelerated evaporation — Electric conductivity at low
temperatures — Comparison of thermometric methods — La
Tour's experiment repeated.
Louis-Paul Cailletet was born in Chatillon-sur-
Seine, in the Cote d'Or, France, on September 21,
1842. He studied at the Lycee Henri IV. and then
entered the Ecole des Mines, Paris. On finishing his
course he returned to Chatillon-sur-Seine and soon
was placed in charge of his father's iron works at
that place.
He made many researches into the working of
blast furnaces, the problems of combustion and of
metallurgy. The occlusion of gases and the causes
of explosion of iron while in the process of forging
174 LIQUID AIR AND THE
were also investigated, and a number of his papers
were published in different scientific journals.
His investigations in the field of the compression
and liquefaction of gases began about 1876, and
reached their culmination in his liquefaction of oxy-
gen and other " permanent gases " in 1877 and 1878.
But he did not desert the subject, and for years after
numerous papers by him in the Comptes Rendus attest
his interest in it and his indefatigable powers of
work.
Honors were given him for his work, of which we
do not give the full list. It must suffice to say that
he was elected a correspondant of the French
Academy of Sciences December 17, 1877. On April
28, 1884, he received the prix Lacarze from the
French Academy of Sciences, for the liquefaction of
gases, the report coming from the following dis-
tinguished committee: Profs. Chevreul, Fremy,
Wurtz, Cahours, Friedel, Berthelot, Dumas, Pasteur
and Debray ; and on May 26, 1884, he was elected
membre libre of the Academy.
He had done much work upon the other subjects
when he took up the action of gases under compres-
sion. At first he had no idea of liquefying the per-
manent gases, but he was a keen observer, and this
led to his success.
Looking back at the work of his predecessors, he
found that they had settled upon one type of com-
pression apparatus, which rendered possible the sub-
jection of a considerable body of gas to an enormous
pressure, and that in a transparent tube.
He had adopted Colladon's well known compres-
sion apparatus (page 1 36) for the purpose of his inves-
LIQUEFACTION OF GASES. 1/5
tigations, but he connected to the hydraulic press by
which it was operated a valve for sudden release of
the compressed gas from pressure.
He builded better than he knew. His release
method introduced a factor which produced intense
cold in the gas, which cold brought about its lique-
faction. The importance of the critical temperature
may have been perfectly well known in 1877, but it
was not so fully appreciated as now. Cailletet,
almost by accident, came upon a method which
enabled him to liquefy gases, simply because it low-
ered their temperature below the critical point.
But when Cailletet first lowered the temperature in
this way he did it without the least idea of liquefying
a gas. The liquefaction was accidental, and was not
even recognized as being what it was.
The authoritative statements of each step of Cail-
letet's work, published as soon as each step was com-
pleted, are given in the Comptes Rendus of the French
Academy. He follows the custom of some other
scientists by giving in another publication the re'sume'
of his entire work up to the time when it was prac-
tically complete. A paper by him, with illustrations
of his apparatus, is published in the Annales de
Chimie et de Physique •, 1878, which does this for his
first work on the liquefaction of gases.
Pictet follows a like course, publishing specific
papers in the Comptes Rendus, and following them
with a general illustrated description in other publi-
cations.
The work of Cailletet on the liquefaction of gases
begins with his work on acetylene. From the some-
what concise statements in the Comptes Rendus we
1/6 LIQUID AIR AND THE
may trace his work as originally published. But it
will be better to invert the natural order a little and
first present the more general view of his operations
with the description of his apparatus, and then give
a brief recapitulation of the more important Comptes
Rendus articles.
Cailletet's original liquefactions seem to have been
less satisfactory than Pictet's, as the proof depended
on the production of a mist or fog of the liquefied
gas. He compressed the gas which he was working
on, cooled it, and then suddenly released it from pres-
sure. The quick expansion absorbed heat, the tem-
perature fell and he got the mist, which he describes
by the word brouillard. We find here an indirect
appeal to the critical temperature. He refrigerated
the gas to such an extent by the sudden expansion
that it fell far below the critical temperature.
The experiments were easily performed, and could
be repeated over and over again upon the same por-
tion of gas during the same day, so as to acquire force
by reiterated success. The apparatus and its use
were both simple, relatively speaking, and as demon-
strations the experiments were accepted by scien-
tists of absolutely the highest standing as satisfac-
tory.
The compression apparatus will be recognized as
a development of Colladon's and of Andrews' appa-
ratus, which is illustrated and described elsewhere
(pages 136 and 147). The cut shows the essential por-
tion of Cailletet's apparatus as given by him in his
article in the Annales de Chimie et de Physique of
1878, in which journal he describes his work in
more detail, or, at least, in more popular style than
LIQUEFACTION OF GASES.
1/7
in the Comptcs Rendus. In the latter publication,
under various dates, are published the somewhat
condensed statements of the results of his work, but
in the Annales a general view of the course of ex-
perimentation which led up to his final liquefactions
of 1877 is given.
Referring to the cut, B represents a heavy steel
cistern into which a glass vessel, 7", dips, whose upper
end forms a tube, T P. This is
sealed at the top, P, and contains
the perfectly dry and pure gas.
It is sealed with an absolutely
tight joint where it passes
through the metal piece, A. A
gland, E, screws down against
the flange on the bottom of A,
squeezing it against the packing
shown under A. M is an open
glass vessel which contains a
cooling mixture if such is desired
to be used, and a glass shade, C,
covers the upper part simply as
a matter of security. The darkly
shaded part within B and T re-
presents mercury ; the lighter
shaded portion in B is water. A
cock serves to draw to draw off
the refrigerating agent from M.
U is a pipe joined by the coup-
ling, R E, to the mercury vessel,
which supports the shade, C, and refrigerant ves-
sel, M.
When the apparatus is first set up, the level of the
Cailletet's Liquefac-
tion Apparatus.
is the platform
1/8 LIQUID AIR AND THE
mercury in T is much lower than is shown in the
cut. It would be considerably below 7", or not far
from the bottom of the gas tube.
By a pump or hydraulic press water is forced into
B. This forces the mercury up into the tube, P Tt
until the gas is greatly compressed. The upper
portion of the gas tube, it will be seen from the con-
struction, is the only part which is subjected to a
bursting pressure, and it is so small in diameter that
it can be made very strong without being of inordi-
nate thickness.
The gas was compressed by a hydraulic press, as
shown in the cut, page i So. A valve in the compress-
ing press or pump was suddenly opened by the han-
dle, <9, and the gas was so cooled by its own expansion
that a mist formed, which was composed of particles
of the liquefied gas. The liquefaction consisted in
the production of this mist.
In his original work Cailletet used a very power-
ful screw press worked by handles on a large fly-
wheel. In the illustration of the entire apparatus the
disproportion between the great compressing press
and the little glass tube holding its minute quantity
of gas is impressive.
The filling of the gas tube with dry gas was thus
effected. The upper end of the tube was left open.
A drop of mercury was placed in the large gas tube
or bulb, the tube being held horizontally, and a tube
from the gas evolution apparatus was slipped over
the other end. A current of gas to be experimented
on, purified by proper chemicals, was passed through
the tube, and while it was still passing the upper end,
P, was sealed tight with the blowpipe or blast-lamp.
LIQUEFACTION OF GASES.
This was done with the tube in an approximately
horizontal position. Next the tube was returned
into the vertical position with the sealed end upper-
most. The drop of mercury ran down into the bent-
up lower end, and the gas was thus hermetically
sealed in the tube. It was then lowered into the
reservoir of mercury, J3. The connections were made
and all was ready for the experiment.
The gas tube, it will be observed, differed from
Colladon's in its bent-up lower end. This feature
enabled the globule of mercury to act as a valve and
seal the gas up in the tube before the latter was in-
serted in the cistern.
It is impressive to contrast the diminutive size of
the liquefaction apparatus with that of the hydraulic
press. The whole mechanism, whose size can be
judged from the figure of the operative, is devoted
to producing liquefaction phenomena in a glass tube
of a fraction of an inch in internal diameter. The
old error was perpetrated of overestimating the
importance of pressure and underestimating the
influence of reduction of temperature.
The first cloud he ever produced with a gas in his
apparatus was with acetylene on sudden release
from pressure, and it was unintentionally produced.
He was experimenting with the gas, subjecting it to
pressure not sufficient to liquefy it. He opened his
release cock, and, as the gas expanded suddenly, he
saw a mist or cloud form within the gas tube.
The first stroke of the piston of an air pump in ex-
hausting a glass receiver produces such a cloud
within the receiver, owing to the precipitation of
moisture in the air by the cold due to rarefaction of
i8o
LIQUID AIR AND THK
00
n
o
1
<u
3
cr1
O
LIQUEFACTION OF GASES. l8l
the air in the receiver. The appearance is very
familiar to all who have used the old-fashioned air
pump. It was, therefore, quite natural for Cailletet
to conclude that the acetylene with which he was
working- was impure. He wished to avoid the pres-
ence of impurities. So he procured some absolutely
pure acetylene gas from Berthelot's laboratory, filled
his tube with it, and on compression and sudden re-
lease got the same cloud as before. He tried nitro-
gen dioxide and again the cloud appeared.
He now recognized fully what was occurring, and
saw a very simple and effective way of showing the
liquefaction of gases. He tried his famous experi-
ment of December 2, 1877, in which he used oxygen
gas and got the same appearance of a mist with it.
The large illustration shows the full apparatus
used by Cailletet. A is a steel cylinder with plunger
actuated by a screw, Ft and held in brackets, B B.
Jf is a wheel by which the screw is turned. The
cylinder is filled with water by the glass funnel, G.
To relieve the pressure when it might be desirable,
a special valve operated by a wheel, (9, was provided,
and it was this valve which constituted the distin-
guishing feature of Cailletet's process and apparatus.
At 5 is a cross-connection to bring into connection
the hydraulic cylinder, A, the liquefaction apparatus
of page 1 77, and the gauges. Two of these are shown.
One, designated by TV, is a Thomasset manometer ;
N' is a Cailletet glass bulb manometer, such as
spoken of on page 187.
The liquefaction apparatus, mt stands upon a shelf
of iron,;}, with set screws, d d, to secure the mercury
reservoir, a.
1 82 LIQUID AIR AND THE
The value of his work depended on the sudden
release of the gas from pressure. As this was
effected by opening a valve on the compressing ap-
paratus, it caused the mercury to suddenly fall in
the gas tube, but there was no loss of gas. The
same sample of gas could be experimented with
over and over again.
The sudden release, Cailletet calculates by Pois-
son's formula, should give a lowering of tempera-
ture of 200° C. (360° F.) This release constitutes
the advance in his work over all his predecessors.
As a physical demonstration, it gives a very elegant
method of cooling a gas below its critical tempera-
ture. It is so direct an attack upon the molecules,
and is so quick, as to effect the refrigeration without
need of jacketing the tube. The expansion is almost
perfectly adiabatic.
The pressure applied to the gas was determined
by various manometers. One of his own devising,
which we describe from papers in the Comptes Rendus,
was employed, as well as another one by Thomasset.
Both were connected to his compressing press. For
lower pressures he could use an open end manome-
ter of his own construction. This, however, was
more adapted for standardizing purposes ; his glass
compression manometer was the instrument best
adapted for use on his gas liquefying appara-
tus.
In the Comptes Rendus of October 29, 1877, page
851, he describes his work with acetylene. At 18° C.
(64-4° F.), and a pressure of 83 atmospheres, he got
drops of liquid acetylene. Then, on suddenly releas-
ing it from pressure, a fog or cloud of acetylene
LIQUEFACTION OF GASES. 183
formed. He reports the liquid as colorless, mobile
and of a high refracting power.
A letter from him is given in the Comptes Rendus
for November, 1877, Pa§"e 1017, in which he says that
he has liquefied nitrogen dioxide, using a tempera-
ture of — n° C. (i2'2° F.)and a pressure of 104 atmo-
spheres. At 1 8° C. (64-4° F.) it resisted a compres-
sion due to 270 atmospheres. Formene was tried,
and on release gave a mist.
Next, in the same volume, he says he got a mist
with a mixture of carbon monoxide and oxygen, and
we find in the same volume, page 1217, his letter
to the French Academy of Sciences, announcing the
liquefaction of oxygen and carbon monoxide. It is
dated December 2, 1877, and is given below. The
very modest tone of the letter, and the feeling of
the writer that his mist of condensed gas was hard-
ly a sufficient liquefaction, are very evident, and
inspire the readers of the letter with additional con-
fidence in Cailletet's work.
The letter is historic, as it is used to determine the
question of priority between the French and the
Swiss scientists, Cailletet and Pictet.
We give a translation of the letter :
" I hasten to tell you, you first, and without losing
a moment, that I have liquefied to-day both carbon
monoxide and oxygen.
" I am, perhaps, wrong in saying liquefied, for at
the temperature obtained by the evaporation of sul-
phurous acid, say — 29° and 200 atmospheres, I do
not see the liquid, but a mist so dense that I can
infer the presence of a vapor very near to its point
of liquefaction.
1 84 LIQUID AIR AND THE
" I write to-day to M. Deleuil to ask of him some
nitrogen protoxide, with the aid of which I will be
able, doubtless, to see carbon monoxide and oxygen
flow.
" P. S. — I have just performed an experiment
which gives my mind great peace. I have com-
pressed some hydrogen to 300 atmospheres, and,
after cooling to — 28°, I have released it suddenly.
There was no trace of mist in the tube. My gases
(CO and O) are then on the point of liquefying, this
mist not being produced except with the vapors near
liquefaction. The (provisions) prophecies of M.
Berthelot are completely realized.
" Louis CAILLETET.
"December 2, 1877."
The control experiment with hydrogen, with its
negative results, gives great conclusiveness to the
experiments in which a positive result was obtained.
The letter had been deposited, sealed, with the
Academy of Sciences at Paris on December 3, 1877.
He next turned his attention to nitrogen, com-
pressed it to 200 atmospheres at 13° C. (55*4° F.),and
on releasing it from pressure it condensed very per-
fectly, " like a pulverized liquid," giving u droplets
of appreciable size," which gradually disappeared
from the walls toward the center of the tube, form-
ing finally a vertical column around the axis of the
tube. The duration of the phenomena was about three
seconds. On December 30, 1877, the experiment
was repeated many times before several members of
the Academy.
The next day he tried to liquefy hydrogen in pres-
ence of MM. Berthelot, Sainte-Claire Deville and
LIQUEFACTION OF GASES. 185
Mascart, obtaining evidences of the liquefaction of
the gas, and repeating the experiment a great many
times. He compressed it to 280 atmospheres, and,
on sudden release, it formed an exceedingly fine and
subtile mist which suddenly disappeared.
Air purified from carbon dioxide and from water
produced the mist without difficulty.
Berthelot, in commenting on the liquefaction of
hydrogen, says :
" The extreme tenuity of the liquefied particles
which form this mist of hydrogen, a sort of dissem-
inated glimmer (lueur\ as well as their more rapid
return to the gaseous state, are in perfect accord
with the comparative properties of hydrogen and of
the other gases.'* (Comptes Rcndus, vol. Ixxxv.)
The rival claims of Pictet and Cailletet are com-
pared by Sainte-Claire Deville, who says that Caille-
tet's experiments were repeated in the Ecole Normale
on December 16, and succeeded perfectly. This
was the day of his election as a correspondent of the
French Academy of Science. The priority of dis-
covery is awarded to Cailletet.
When we see later how much store Olszewski
sets by his claim to have been the first to produce
liquefied oxygen in quantity sufficient to be poured
from one vessel to another, when we read between
the lines of Cailletet's letter that he would have
liked to produce a real visible bulk of liquid
oxygen, we can appreciate Pictet's work at its full
value, and feel that the two deserved at least equal
honor.
The two worked quite independently and without
knowledge of the scope of each other's work. It
1 86 LIQUID AIR AND THE
seems a pity that they could not have been associated
as were Wroblewski and Olszewski five years later.
It is the great chemist Dumas who, in the Transac-
tions of the Academy of Science, calls attention to
their ignorance of each other's work. It is pleasing
to know that later in life they contracted an inti-
mate friendship with each other.
Cailletet seemed to think that, as he had liquefied
the constituents of air, the liquefaction of air itself
was of little importance.
On trying air at 200 atmospheres, and on cooling
the upper part of the tube with nitrous oxide,
threads of liquid appeared on the walls of the tube.
They were very agitated, and, on running down until
they struck the mercury, they recoiled or drew
back.
He felt that a control experiment was needed to
determine if a liquid near its point of condensation
would act in this way. Ether was selected on account
of its high volatility. He poured it down a tube and
found that it gave the same effect as he had seen in
his compression apparatus.
Inspired by confidence from this control test, he
increased the degree of compression in his apparatus
until the mercury rose into the small tube within
the refrigerating vessel, the pressure rising to 225
atmospheres and the liquid threads or streamlets in-
creasing in number.
Continuing the compression until 310 atmospheres
pressure was attained, the mercury reached the level
of the nitrous oxide, when it froze, stopping up the
tube. The refrigerating apparatus was at once re-
moved, when it was seen that the surface of the
LIQUEFACTION OF GASES. l8/
frozen mercury was covered with hoar frost, which
he thought was solid air.
This closing the tube with a stopper (bouchori) of
frozen mercury appears to him a method of very
useful application in some of these investigations.
Cailletet showed much ingenuity in his methods,
and the construction of his manometer for indicating
high pressures and its standardization give a good
sample of his work.
He first determined that glass yielded to pressure
and returned perfectly to its original shape. He
then constructed a manometer or pressure indicator
by making what was practically a mercurial ther-
mometer. The bulb was hermetically sealed in a
steel reservoir full of water. On pressure being ap-
plied to the water, the bulb was squeezed and the
mercury rose. The steel reservoir could be connected
by a pipe to any fluid whose pressure was to be
tested, as, for instance, to the water or mercury in
his liquefaction apparatus. The manometer was kept
at a uniform temperature by melting ice. The height
to which the mercury rose gave the pressure.
The methods he adopted for testing its accuracy
are striking. He fitted it with an index like a maxi-
mum thermometer and lowered it to known depths
in the sea, in the harbor of Toulon, so that the water
produced the known pressure for its calibration. He
complains of the bad seas encountered. Another
way was to lower it into an artesian well. In these
cases he introduced maximum and minimum ther-
mometers with it in order to secure corrections for
temperature.
He also constructed an open end mercurial mano-
1 88 LIQUID AIR AND THE
meter, which was a long tube running up a cliff,
and by maintaining mercury in it at different heights
he produced a range of pressures from zero up to
34 atmospheres. This he used as a standard for test-
ing the accuracy of his small manometers.
This was in the early period of his labors. It was
not likely that such a practical and hard working
scientific investigator could fail to see years later the
chance which the Eiffel Tower, nearly a thousand
feet high, offered for the construction of an open
tube manometer. He interested M. Eiffel in the
work. A soft steel tube was erected which ran up
the framework of the tower. It was 4% mm. (nearly
£ inch) in internal diameter. Every 3 meters (nearly
10 feet) a projecting pipe with stopcock was placed,
and to each of these a glass tube, in length slightly
in excess of the 3 meters, was placed. Thus read-
ings could be taken all the way up the tube. As
each glass tube became filled, and the readings com-
prised within its length were completed, the stop-
cock was closed and more mercury was pumped in
at the bottom.
The mercury came in from below. The steel tube
dipped into a cistern, and a pump by hydraulic pres-
sure forced the mercury into the cistern and up into
the tube.
With this apparatus some 400 atmospheres of
pressure could be reached.
Some rather curious corrections had to be applied.
For a range of temperature of 30° C. (54° F.) the
tower and steel tube expanded -^-^ of their length
or height. This was a very minor matter. But
the mercury for the same range expanded ^. The
LIQUEFACTION OF GASES. 189
heat expansion of the mercury, therefore, had to be
corrected. The compressibility of the mercury and
the diminished pressure of the air due to the great
height were sufficient in extent to require correction
also.
He tried manometers, as we have seen, by lower-
ing them into water of great depths. The mano-
meters operated by mercury rising in a glass tube.
In the artesian w.ell or in the harbor of Toulon the
manometer was inaccessible, and an index was
needed to show how far the mercury had risen in
the tube.
This he secured by gilding the interior of the
glass tube. As the mercury rose, it amalgamated
with the gold and removed it from the glass. The
portion of the glass tube stripped of gold showed
how much of the tube had been filled with mercury.
The arrangement operated like a maximum ther-
mometer.
It cannot but impress the reader of the old time
original papers on scientific work which have
marked the steps of our progress that there is much
good matter in them which has been forgotten. An
original memoir ten years old is apt to be forgotten
or to be treated as something which has been sup-
planted by more modern writings. But this view of
the case is wrong and unjust, for the history and
development of science is a most interesting study,
and in these days, when the inductive method of
teaching is so extensively employed, the old original
papers by the great ones of the scientific world
should receive much more attention than is generally
awarded them. This book has been written from
190 LIQUID AIR AND THE
this standpoint. The bibliography of liquid air and
liquefied gases testifies to the amount of material
there is to be drawn upon.
Cailletet's work on his manometers shows a very
good and conclusive method of measuring high pres-
sures. His operations indicate an original cast of
thought. After his great work on the liquefaction
of oxygen by the use of his happily utilized pressure
release he continued his work on gases. In 1880 he
investigated the phenomena brought about by com-
pressing a mixture of carbon dioxide and air. He
found that the carbon dioxide was first liquefied and
then disappeared as the pressure rose, which he in-
terpreted as the solution of a liquid in a gas. It
reminds us of the solution of a solid in a gas shown
when a solution of a solid in a liquid is heated to a
point above the critical one for the solution in ques-
tion. Thus, if potassium iodide or chlorophyl is dis-
solved in alcohol, and the solution is heated in a sealed
tube to 350° C. (662° F.), the whole disappears, and
the solid is, so to say, dissolved or diffused in the gas-
eous alcohol. The observation is due to Hannay
and Hogarth, page 23.
Cailletet noted the same thing with the liquid car-
bon dioxide and the gaseous air. He wished to have
some test to determine when his carbon dioxide
parted from the liquid state, and he sought a coloring
agent for it. He thought that, if he colored it, the
change from liquid to gaseous would be discernible.
After some trials of different agents, he found a
coloring matter which would dissolve in and color
liquid carbon dioxide. It was the blue oil of gal-
banum.
LIQUEFACTION OF GASES. igi
Galbanum is a resin imported from the Levant,
used in medicine, and of somewhat uncertain origin.
Those who are interested in the archasology of sci-
ence will find it mentioned in Exodus xxx. 34. The
old name for it was chelbenah.
This ancient member of the pharmacopoeia gave
Cailletet the coloring matter he sought for. Liquid
carbon dioxide dissolved it, and was colored blue
thereby. On gasification the blue oil was deposited
on the sides of the tube and on the surface of the
mercury.
He investigated the peculiar striations which
occur around the critical point, and concluded from
the action of the coloring matter that they were
liquid carbon dioxide. The disappearance of the
meniscus was determined to be due not to liquefac-
tion of the entire contents of the tube, but to gasifica-
tion. The general phenomena presented by a mix-
ture of carbon dioxide and air when highly com-
pressed were studied, and the results are given in
the Comptes Rcndus, vol. xc.
Years later he returns to this question of coloring
liquid carbon dioxide in order to determine the point
of its gasification when heated in a sealed tube under
pressure. He expresses some discontent with oil of
galbanum and tries iodine. He sublimes this in his
gas tube, so that portions of the glass collect a subli-
mate. He liquefies carbon dioxide in this tube, when
it becomes colored by the iodine. On heating to dis-
appearance of the meniscus, he finds that the gas or
liquid in the lower part of the tube is blue, while that
above is colorless, although iodine is there to color it.
A test with the spectroscope shows that the car-
IQ2 LIQUID AIR AND THE
bon dioxide colored with iodine gives the spectrum
of iodine in solution, not of gaseous iodine. So the
conclusion is reached that the disappearance of the
meniscus is not necessarily synchronous with the
attainment of the critical temperature.
To further examine the question, he tries an analo-
gous experiment with two liquids, immiscible under
ordinary conditions. Amylic alcohol and common
alcohol, each with some water, lie one above another
without mixing. He places the two in a sealed tube
and applies heat. The line of separation between
them begins to disappear, vanishes, and striations,
such as seen with liquid and gaseous carbon dioxide
heated to the critical temperature, appear.
He gives a new definition of the critical tempera-
ture, as follows : The temperature at which a liquid
and a gas above it are capable of mutually dissolving
each other in all proportions.
His condensing pump, without harmful clearance
or lost space (sans espace nuisible), excited considera-
ble attention. If a condensing pump has much clear-
ance, if the piston or plunger does not go against the
end of the cylinder as it expels the gas, as the pres-
sure against which the pump works rises sufficiently
high, no gas will be expelled, and the pump will do
no work. This point is spoken of where Pictet's ex-
periments are treated of, on page 166, and his way of
getting over the difficulty, the coupling of two
pumps, was spoken of.
Cailletet constructed a single acting plunger pump.
It was placed with its cylinder vertical. The gas
was forced out of its upper end. To avoid clearance
he placed a quantity of mercury over the piston. As
LIQUEFACTION OF GA.SES. 193
it rose, the mercury was forced into the clearance
space, so as to completely fill it and thus suppress its
injurious action.
It is evident that it is impossible to construct a
pump without any clearance as they are ordinarily
built. But the liquid piston obviates the trouble,
and at each stroke every particle of gas is expelled,
whatever may be the pressure against which it
works.
Before Cailletet's pump was devised, Regnault had
experimented with a mercury pump on somewhat
the same principle. The Cailletet pump has, how-
ever, been accepted as a most valuable contribution
to compressed gas work, and has been adopted by
the Leyden University in its cryogenic laboratory.
It has done much service in the hands of other
investigators.
The cut gives a section of the barrel of the
pump. B B is the barrel with plunger, A. The dark
portion over the plunger is mercury. At a, b are
packing rings of leather. R is the inlet valve,
which is worked by a cam and lever system auto-
matically. The neck, O, through which the gas
enters, can be connected by a rubber tube to the
source of supply. 5 is an ebonite valve through
which the gas is forced by the plunger into the bon-
net which surmounts the barrel. The tube, T T, de-
livers the compressed gas. A flexible copper pipe
is connected to the tube, T Tt and leads to the
vessel in which the gas is to be condensed.
The operation of the pump is obvious. The
plunger begins to rise, and the valve, R, closes.
The plunger then drives the gas before it through
194
LIQUID AIR AND THE
the valve, 5, and as it reaches the upper part of the
cylinder, the mercury rising into the narrow tube
below 5 expels the last traces of gas. As the
plunger descends, an almost
perfect vacuum forms above
the mercury until the valve,
-ft, is passed and opens, so
that the gas to be com-
pressed can enter. On the
return stroke, this quantity
is driven out through the
valve, S.
If any mercury enters the
bonnet or space above the
valve, 5, it cannot reach the
gas reservoir, because the
outlet tube, 7", takes the gas
from the top of the space.
The pump was operated
with a fly-wheel and crank
motion, much like Natter-
er's pump. Sometimes a
screw valve was placed on
the summit of the bonnet
to make possible the expul-
sion of all air from the
pump.
The base of the barrel
screwed into a socket or
Cailletet's Mercury Plunger base piece, which held some
Air Pump. ! .
glycerine or mercury, to
insure the tightness of the packings, a and b.
The presence of mercury made the lubrication
LIQUEFACTION OF GASES.
'95
problem somewhat
and grease coming
formed almost solid
letet adopted
vaseline and
glycerine as lu-
bricants.
With this
pump a man,
without over-
exertion, readi-
ly liquefied
400 to 500
grammes of
carbon dioxide
in an hour.
Recognizing
the danger of
the larger cyl-
inders used for
holding lique-
fied gases,
Cailletet re-
placed them by
a group of nine
copper tubes,
arranged in a
cy 1 indri cal
group, and all
connected by
small copper
tubes, a a, to one
outlet coupling, O.
troublesome, as ordinary oils
in contact with the mercury
compounds. Eventually Cail-
Cailletet 's High Pressure Reservoir
for Liquefied Gases.
central delivery cock, K, and
The group was mounted on
196 LIQUID AIR AND THE
trunnions, B, in a frame, as shown in the cut. The
tubes had a capacity of about four liters.
The mercury pump without lost space (sans
espace nuisible\ as invented by Cailletet after Reg-
nault had experimented with one, is of special
interest, and has been very often used in liquefied
gas investigations. One of the most celebrated high
pressure gas laboratories, that of the University of
Leyden, uses it in a modified construction. The
mercury no longer lies on the plunger, but is beneath
its end. A U-shaped tube constitutes the pump bar-
rel. In one limb the plunger works downward.
The bend of the tube is filled with mercury, and the
outlet for gas as compressed is at the top of the
other limb.
All through the history of investigations on this
subject we find at intervals Cailletet's pump men-
tioned ; so it has survived a long time as things go in
this age of progress. The new demand is for a pump
that will continuously and powerfully compress a
gas. Formerly it was a single sample of gas at a
time which was to be compressed. This was effected
by a screw or other device, as explained and de-
scribed in many places in this book. But when Pic-
tet, in 1877, established his double cycle liquefaction
of gas, he instituted a method calling for a pump
with constant delivery at high pressure, and his
method has been utilized in some shape or form by
most subsequent investigators until within the last
few years. It is by no means abandoned yet, and
Cailletet's pump is still, in improved form, doing ser-
vice at the cryogenic laboratory of the University
of Leyden.
LIQUEFACTION OF GASES. 197
Cai'lletet and Hauteville, in 1882, approached the
difficult task of determining the specific gravity of
liquid oxygen in the following way :
One volume of oxygen was mixed with seven vol-
umes of carbon dioxide. The mixture was submit-
ted to pressure while maintained at a temperature
exceeding the critical temperature of the relatively
easily liquefied carbon dioxide. Then, after the com-
pression was effected, the temperature of the mixture
was lowered and the two gases liquefied together
without separation. Numerous experiments with
other gases had shown that there was no reason to
expect any shrinking, except in very slight degree,
upon mixing two such liquids. The specific gravity
of liquid carbon dioxide was easily determinable and
was accurately known. The mixture of liquid oxy-
gen and carbon dioxide was perfectly manageable,
and its specific gravity was determined with ease,
and by simple alligation the following results were
obtained. At the melting point of ice, o° C. (32° F.)
and at — 23° C. ( — 9*4° F.), it was for various pres-
sures expressed in atmospheres :
Pressure. o° C. (32° F.) —23° C. (—9-4° F.)
200 0*58 sp. gr. 0^84 sp. gr.
275 0*65 " 0*88 "
300 070 " 0-89 "
As a control, a similar experiment with nitrous
oxide, substituted for carbon dioxide, gave at 300
atmospheres and at — 23° C. (—9*4° F.) a specific
gravity of 0*94.
Another of Cailletet's classic discoveries is the use
of liquid ethylene as a cooling agcn-t. According to
1Q8 LIQUID AIR AND THE
him, it liquefies at the following pressures and tem-
peratures :
45 atmospheres at i° C. (33-8° F.)
50 « 4° C. (39-2° F.)
56 " 8° C. (46-4° F.)
60 " . "10° C. (50° F.)
Its critical temperature is about 13° C. (55*4° F.),
while that of its predecessor in the refrigerating line,
carbon dioxide, is 31° C. (87'8° F.) Using a carbon
bisulphide thermometer, he reached a temperature
of — 105° C. ( — 157° F.) in liquid ethylene, while in
liquid nitrous oxide he only reached — 88° C.
(-126-4° F.)
He made the ethylene by the old method of heat-
ing together alcohol and concentrated sulphuric acid.
The latter, with its high affinity for water, takes the
elements of water from the alcohol, and gaseous ethy-
lene is evolved. This gas he liquefied by the use of
his mercurial pump just described. He found it far
from manageable by his appliances, and first em-
ployed it as a refrigerant in the form of a jet, remind-
ing us of Thilorier's chalumeau de froid, or cold jet
blowpipe, spoken of in a preceding part of this book
(page 141).
In its release from confinement it goes into the
gaseous state, not solidifying into snow, like carbon
dioxide.
The classic interest of this discovery lies in the
great use that subsequent investigators have made
of liquid ethylene as a refrigerant. Notably is this
the case with the work done in the Royal Institution
by Dewar. One of the most striking features of his
LIQUEFACTION OF GASES. 199
work was the number of cylinders of liquid ethylene
which he prepared for his liquefactions. Such was
the comment made by Prof. George Barker on his
visit to the Royal Institution. The quantity of
liquid ethylene was as remarkable in its way as the
liquefaction of air itself, and the manufacture of this
ethylene was one of the principal sources of expense
incurred in the Dewar liquefactions.
The ease of liquefaction of ethylene, its reasonably
high critical temperature and the high degree of cold
produced by its evaporation, make it a particularly
valuable and manageable agent. The difficulties
Cailletet experienced have disappeared with the im-
proved appliances of fifteen years later.
Ethylene is a very old acquaintance and a com-
pound that, in giving its luminosity to coal gas, has
played an important role in technology.
An objection to ethylene, as a refrigerating agent,
is its cost. It is no great matter to make a few cubic
feet of the gas from alcohol and sulphuric acid;
but when it comes to condensing the gas to a liquid
with many hundredfold reduction of volume, the
cost becomes very great. A 5 or 10 gallon cylinder
of the liquid represents immense expenditure of
alcohol. Cailletet's very inartificial way of. using
ethylene as a cold jet blowpipe and letting the gas
go completely to waste complicated the difficult gas
liquefactions by the introduction of a very serious
factor of expense.
In a subsequent paper we see that he appreciated
this state of affairs and tried to work with less waste
and to introduce a rational economy into his pro-
cess.
200 LIQUID AIR AND THE
In 1883 Cailletet speaks of a continuous liquefy-
ing apparatus, but declines to describe it. Hitherto
he had operated with small quantities of liquid ethy-
lene at a time, by the use of his mercury condens-
ing pump, and had applied the ethylene as a jet, but
now he uses a closed cycle. The ethylene circulates
through a steel cylinder, being released from com-
pression as it enters, so as to take the gaseous form,
and reducing the temperature greatly on the latent
heat principle. Through the steel cylinder a tube
passes, so that the two represent a condenser of the
type of the well-known Liebig's condenser, similar
to Pictet's apparatus. The pump draws out the gas
from the cylinder and compresses it to the liquid
state, so that it is ready to expand again as it enters
the cylinder. He got an almost complete vacuum
in the cylinder of his condenser, and a very low
temperature resulted.
The arrangement is practically that of Pictet of
1877. Cailletet in 1883, and Dewar in 1890, and at
later periods, bear testimony to the good quality of
Pictet's early work in the arrangement of apparatus
they adopted, and which was based on Pictet's appa-
ratus, illustrated in this book.
Cailletet hoped to get oxygen in large quantities by
the use of this new apparatus, evidently appreciating
the defect inherent in the Colladon apparatus, which
quite excluded the idea of operating on large quan-
tities of gases, and which produced them in a neces-
sarily non-continuous process. It will be remembered
that it was the Colladon apparatus which Cailletet
had adopted in his work of 1877.
A very ingenious method of producing low tern-
LIQUEFACTION OF GASES. 2OI
peratures was studied by Cailletet, and his paper on
the subject was published in 1885. He effected the
evaporation of a liquefied gas with accompanying re-
duction of temperature by passing a stream of a cold
gas through it. He placed a tube with ethylene
within a vessel of dry air, and by blowing cooled
and dry air or hydrogen through it accelerated its
evaporation until its temperature fell to — 136° C.
( — 212-8° F.) By such a process he produced cold
sufficient to liquefy oxygen, the latter being com-
pressed to the requisite extent.
Working with M. Bonty, in the same year, he
made quite an elaborate series of experiments on the
electrical conductivity at low temperatures of a num-
ber of metals — copper, mercury, silver, aluminum,
tin, magnesium, iron and platinum. He suggests the
availability of copper wire as a means for determin-
ing low temperatures, by its decrease of electrical
resistance as the temperature falls. This suggestion
is interesting, in view of subsequent developments.
A passage from the paper on the subject will be of
interest :
" It seemed probable that this resistance would
become extremely small, and consequently the con-
ductivity very great, at temperatures below — 200°,
although our first experiments did not permit us to
form a definite idea of that which would occur under
such conditions." (Comptes Rendus, vol. c., page
1189.)
This is in strict accord with the facts as ascertained
by other experimenters at later periods.
In 1888 we have from him a comparison of five me-
thods of determining low temperatures. They were
202 LIQUID AIR AND THE
the following: i. A thermo-couple of iron and cop-
per. 2. A platinum wire resistance. 3. A thermo-
couple of pure platinum and of an alloy of platinum
and rhodium. 4. An ingot of platinum used in con-
junction with a calorimeter. 5. The hydrogen ther-
mometer. Boiling water, melting ice and boiling
methyl chloride, at atmospheric pressure, supplied
the three fixed points for his scale, and he obtained
very closely according figures with all of these
methods. The temperatures of boiling ethylene and
of boiling nitrous oxide were determined as tests of.
accordance of results.
Cagniard de la Tour had long ago tried to
determine the point at which the meniscus of
water disappeared when it was heated in a
sealed tube. Pure water attacked the glass tube
so actively that he could not produce the disappear-
ance. Cailletet took up the question and tried the
experiment in a metal tube, with pure water, apply-
ing a mathematical calculation to determine the
desired point. The older observer had added
chemicals to the water to diminish their action on
the glass. Cailletet discerned in the presence of the
chemicals a source of error and recognized the im-
portance of performing the experiment with pure
water. The description will be found in the Comptcs
Rendus, vol. cxii.
LIQUEFACTION OF GASES. 203
CHAPTER X.
SIGMUND VON WROBLEWSKI AND KARL OLSZEWSKI.
Wroblewski's life — Banishment from his native country —
Early scientific work — His association with Olszewski —
Study of Cailletet's methods — Their apparatus — Defective
position of the hydrogen thermometer — Liquefactions of
oxygen, carbon monoxide and nitrogen — Ethylene data
— Solidification of carbon bisulphide and alcohol — Deter-
mination of the critical pressure and temperature of oxy-
gen— Liquefaction of hydrogen — Use of a thermoelectric
thermometer — Electric resistance of metals at low tem-
peratures— Two liquids from air — Olszewski 's individual
work — Apparatus for producing liquid oxygen in quan-
tity— Comparison of platinum resistance and of hydro-
gen thermometers — Determination of hydrogen constants.
As a serious investigator in the realm of the lique-
faction of gases, no one can be cited who surpassed
the Polish scientist Sigmund von Wroblewski (pro-
nounced Vroblevski). He was born in Grodno,
Poland, in 1845. Grodno is a province which went
to Russia in the partition of Poland and figures in the
final partition of 1815 as part of Russia. The king-
dom of Poland, as arranged by the Congress of
Vienna at the same time, remained as a separate
kingdom and intact, although its monarch was the
Czar of Russia. Then there was a long series of po-
litical disturbances and bloodshed, culminating in the
disturbances of 1861-64, and Russia succeeded by
204 LIQUID AIR AND THE
the most arbitrary enactments and severe measures
in suppressing the insurrections and in assimilating
the so-called kingdom of Poland.
Wroblewski took part in the uprising as a Polish
patriot, and was sent to Siberia in 1863, where he
spent four years. His friends had influence, and
managed to obtain his release from exile, to the ex-
tent of being allowed to live in an obscure Russian
town. Eventually he was released from surveillance
and went to Germany, visiting Heidelberg and
Bonn, meeting Kirchoff and Clausius. He had a
cosmical theory which was not received by either
the physicists of Heidelberg or of Bonn with any en-
couragement. At the University of Berlin he con-
sulted Prof. Helmholtz, who started him to work
on physical investigation touching his new theory,
and he completed two years of work under the
many-sided and brilliant German. He published
papers bearing on gases which received the honor of
attracting the attention of Clerk Maxwell. His prin-
cipal work on high pressure and low temperature
applied to gases dates from his knowledge of the
work of Cailletet on the same subject. He spent
some time at the ficole Normale, in Paris, and saw
and studied Cailletet's work. He had as associate
Karl Olszewski (pronounced Olshevski), in the
writing of the initial of whose Christian name a cer-
tain amount of confusion obtains, as it is sometimes
written K, for Karl, and sometimes C, for Charles.
The association between the two in their early work
of 1883, and thereabout, is very intimate. In Wiede-
vianns Annalen, 1883, is published an article which
gives the lull account of their first important work
LIQUEFACTION OF GASES. 2O$
in the liquefaction of gases. The authorship is given
a dual form. The title reads in translation, " On the
liquefaction of oxygen, nitrogen, and carbon monox-
ide, by Sigmund v. Wroblewski and Karl Olszewski."
The article, it is impossible to believe, was written
by anyone but Wroblewski, but when in its course
anything is to be attributed to a single investigator,
the expression " einer von uns" (" one of us") is
always used.
Wroblewski died in 1888. As early as 1884 he
predicted that liquid air would be the refrigerant of
the future. His emotions, had he lived to see what
has been done in the liquefaction of air, can only be
imagined. The principal reason for his belief in the
capabilities of liquid air was that it did not have to
be prepared like carbon dioxide, sulphur dioxide,
ethyl chloride, or ethylene, that the atmosphere gave
an inexhaustible supply of matter adapted for the
function of refrigeration and for use in a cooling
cycle.
Wroblewski, in the early days of the liquefaction
of gases, in 1885, pointed out the method of the
future. In the light of what has been since then
accomplished, a translation of his remarks from
the Wiener Sitzungsberichte reads almost like a pro-
phecy :
" The essential step forward which should be
made with regard to the extension of the method is
to change it so that we* may be prepared to pour
oxygen as we pour ethylene to-day. It is my convic-
tion that the thing will only be successfully carried
out when we return to Pictet's method, and by
cycles of various liquefied gases make a cascade of
206 LIQUID AIR AND THE
temperatures whose last step will produce the stream
of liquefied oxygen."
It is precisely by carrying out such a line of work
that Dewar won fame for himself and the Royal In-
stitution.
The carefully prepared article in Wiedemanris An-
nalcn is an example in its way of how a scientific
paper should be written. There is in its aspect and
tenor such sincerity and so careful an avoidance of
anything like self-assertion that it is at once convinc-
ing and impressive.
These investigators were subsequently attached to
the University of Cracow, and much of their work
dates from that city. The results are published in
various languages. There is no need to study Polish
to read them.
" One of us," Wroblewski, while in Paris studied
Cailletet's apparatus and methods, and had an ap-
paratus made by a Paris mechanic, E. Ducretet, for
the prosecution of researches on liquefied gases. The
point is made that it is superior to the Cailletet ap-
paratus of that early date because it could be used
with five or six times as much gas as could be used
in Cailletet's apparatus.
The apparatus may be considered in two divisions
— one the condensing apparatus by which the gas to
be experimented on was subjected to pressure, the
other the refrigerating apparatus for cooling it be-
low the critical temperature.
We reproduce the cuts of the apparatus from
Wiedemanris Annalen. It will be seen that the gas
compression apparatus is practically a copy of Cail-
letet's apparatus, so that the apparatus goes back to
LIQUEFACTION OF GASES.
207
k-
the days of Colladon. In the gas refrigerating por-
tion will be found a reminder of Pictet's circuits, not
as yet fully
utilized by the
Polish scien-
tists.
The gas tube,
f, is designed to
hold about 200
cubic centime-
ters of gas. It
has an upturned
capillary tube
at its bottom.
A very thick-
walled capilla-
ry tube extends
from its top and
bends down-
ward. The cyl-
inder, a, which
contains the
gas tube, is of
heavy cast iron.
Very exact di-
mensions are
given in the
paper in Wiede-
manrfs A nnalcn
already cited.
The general di-
mensions are Wroblewski and Olszewski's Gas
Stated as 58 Compression Vessel.
208 LIQUID AIR AND THE
centimeters (23-2 inches) deep and 8'5 centimeters
(3*4 inches) wide, c and o is a bronze piece which
forms a tight connection between the gas tube, /,
and the upper tube, e, f, g, e. A very strong steel
tube runs through the orifice in the piece, d. To
get it in place the horizontal portion of the piece in
question was sawed through horizontally in the line,
e, e, and bored downward from g and /. The steel
tube was inserted in place, a groove along the line,
e, e, receiving it. The piece which was sawed off
was replaced and brazed in its former place, so as
to surround the steel tube.
At the end, h, the steel tube expands, and the
glass gas tube, t, is cemented into it. At k the
bronze steel-lined piece has a conical end. m is a
glass tube cemented in place, and all is secured by a
coned piece, /, with screws, n, as shown, the screws
uniting all parts to a^n airtight joint.
At /a tube is connected which leads to a force
pump.
The next illustration shows how the apparatus was
set up for the liquefying of gases in the downwardly
extending tube from the compressing apparatus.
This cut is also an exact reproduction of the cut
given in Wiedemanns Annalen.
We have, as before, the vessel, i, with its steel con-
taining vessel, by only the top of which is shown.
The capillary tube, q, was 0-9 centimeter (0-36 inch)
external diameter and a little over 0*2 centimeter
(0-08 inch) internal diameter. The glass vessel, /',
was filled with the gas to be experimented with.
A jar, y, has calcium chloride at its bottom to keep
the air within it perfectly dry. A second vessel, s,
LIQUEFACTION OF GASES.
209
is set into it airtight with an india rubber stopper.
The vessel, j, is provided with an india rubber stop-
per of its own, perforated for three tubes. One is
Wroblewski and Olszewski's Apparatus for
Liquefying Gases.
the end; q, of the gas tube, i, the other the stem of the
hydrogen thermometer, t. The third receives a T
shaped tube, u. Liquid ethylene is contained in the
2IO LIQUID AIR AND THE
cylinder, x, where it is kept cool with ice and salt.
The liquid ethylene is withdrawn at a, through a
thin tube, w. This tube is coiled into a cooler, b'y
charged with liquid and solid carbon dioxide. This
brings it down to a very low temperature.
As needed it is drawn into the vessel, s. An air
pump connected to the T tube, u, by the tube, v,
produces an almost full vacuum in the vessel, s. The
upper end of the T tube is provided with an india
rubber cork through which the tube, w, passes air-
tight, the liquid ethylene dropping from c.
The gas to be experimented on was introduced into
the tube, *', mercury was contained in the vessel, b,
and the pressure was increased to any desired extent
by pumping water into b. The end of the gas tube,
which was sealed and bent down, was cooled by ad-
mission of the cooled ethylene into the vessel, s, and
this vessel was pumped out by an air pump, so that it
was kept down to a pressure of but 2i millimeters of
mercury, which is a small fraction of an atmosphere.
The ethylene, when first admitted to the vessel, st
boiled tumultuously, but soon quieted down and
kept slowly boiling, thereby producing a very low
temperature.
Each experiment required 200 to 300 grammes of
ethylene and about 400 grammes of solid carbon
dioxide. Very little ethylene was lost.
The apparatus worked well. The only trouble
chronicled was due to the mercury freezing in the
capillary tube, which brought about an explosion
which did no great injury.
The temperatures were taken by the hydrogen
thermometer, /, whose bulb, it will be observed, is
LIQUEFACTION OF GASES. 211
placed in the refrigerating vessel, not in the gas ex-
perimented with. Thus the temperature recorded
is that of the environment of the sample, not that of
the sample itself, which is a defect worthy of com.
ment.
While on the subject of thermometers, it may be
noted that there occurs in the Wiedemann's Annalen
article an interesting statement to the effect that
Natterer told "one of us," orally, that he filled his
low temperature thermometer with phosphorus
chloride. This gives us a glance at the work of a
preceding generation and is mentioned elsewhere
in this book.
The results obtained with this apparatus were very
good. Oxygen liquefied at — 130° C. ( — 202° F.)
and at a pressure of a little over 20 atmospheres. It
was a colorless fluid, the slight blue tint not showing,
presumably because of its slight amount. It had a
flatter meniscus than that of carbon dioxide. On
reducing the pressure to a relatively small degree
it foamed, evaporated from the surface, and on
further reduction, boiled throughout its entire mass.
The work of these investigators at about this
period is the subject of other papers in the Comptes
Rendus and elsewhere.
In the Comptes Rendus, vol. xcvi., is given the dis-
patch announcing Wroblewski's liquefaction of oxy-
gen. It was received by M. Debray, secretary of the
Academy of Sciences, on April 9, 1883, from Cracow.
It reads as follows :
" Oxygene liquefie, completement liquide, incolore
comme 1'acide carbonique. Vous recevrez une note
dans quelques jours."
212 LIQUID AIR AND THE
"Oxygen liquefied, completely liquid, colorless
like carbonic acid. You will receive a note in a few
days."
The " note " which follows is given in the same
volume of the Comptes Rcndus and alludes to Cail-
letet's ethylene paper (ibid., vol. xciv., page 1224).
The authors say that Cailletet did not fully satisfy
himself. Wroblewski and Olszewski, with apparatus
made by " one of us " (" un denous "), who was in this
case Wroblewski, and using a quantity of oxygen,
effected the liquefaction. They found liquid oxygen
colorless and transparent, very mobile, and giving a
sharp meniscus.
With boiling ethylene in approximate vacuum
they got a temperature of — 136° C. ( — 212*8° F.) by
the hydrogen thermometer. They found that at the
atmospheric pressure ethylene boils at — 102° to
—103° C. (—151-6° to 153-4° F.), and not at —105° C.
( — 157° F.) The following data for oxygen were
determined on April 9 :
At temperature of — 131*6° C. ( — 204-9° F.) begins
to liquefy at 25*5 atmospheres.
At temperature of — 133-4° C. ( — 208-1° F.) begins
to liquefy at 24-8 atmospheres.
At temperature of — 135*8° C. ( — 212-4° F.) begins
to liquefy at 22*5 atmospheres.
They took advantage of their ethylene apparatus
to try some other experiments in the direction of
freezing carbon bisulphide and alcohol.
Carbon bisulphide froze at about — 116° C.
( — 176-8° F.), alcohol became thick like sirup at
about — 129° C. ( — 200-2° F.), and froze a degree
lower, —130° C. (—202° F.)
LIQUEFACTION OF GASES. 213
On April 16, 1883, another dispatch was received
by the secretary of the Academy of Sciences, telling
of the same investigators' liquefaction of nitrogen :
" Azote refroidi, liquefiee par detente. Menisque
visible, liquide incolore."
"Nitrogen cooled, liquefied by release. Visible
meniscus, colorless liquid."
The note which gives the details of the liquefac-
tion of nitrogen says that they exposed nitrogen at
— 136° C. ( — 212*8° F.) to a pressure of 150 atmo-
spheres. On sudden release there was a tumultuous
ebullition (" -aufbrausen ") like that of carbon dioxide
in a Natterer's glass tube of carbon dioxide (page 23)
when it is plunged into water which is a little
warmer than the critical temperature of carbon
dioxide. Then they tried a partial release from
pressure, lowering it to 50 atmospheres, when the
nitrogen liquefied completely with a meniscus. It
remained a few seconds only. It was colorless and
transparent.
On April 21, 1883, the following dispatch was
received by the Academy from the same investi-
gators :
" Oxyde de carbone liquefie dans les me'mes con-
ditions que 1'azote. Menisque visible. Liquide in-
colore."
" Carbon monoxide liquefied under the same con-
ditions as nitrogen. Meniscus visible. Colorless
liquid."
Hydrogen they failed to liquefy. It was cooled
to — 136° C. ( — 212-8 °F.), compressed to 150 atmo-
spheres, then was suddenly released, but not even a
mist appeared. Boiling oxygen is recommended as
214 LIQUID AIR AND THE
a cooling agent, but the impetuousness with which it
boiled was a great obstacle to its use. Even at one
atmosphere of pressure it proved uncontrollable.
The duration of its ebullition was very short, and
this proved an objection. Eight years later, in 1891,
Olszewski overcame this trouble by bubbling hydro-
gen through it gradually. Cailletet's production of
cold by bubbling a gas through a volatile liquid, as
described on page 201, may be noted also. By a
thermo-electric couple its temperature was deter-
mined. It is given as — 186° C. (—302-8° F.)
Nitrogen was compressed and cooled with boiling
oxygen without result, but on sudden release from
pressure it formed snow-like crystals of remarkable
size.
In 1883 Wroblewski and Olszewski attacked the
problem of determining the specific gravity of pure
oxygen. They introduced a known quantity of
oxygen into their apparatus and liquefied it as com-
pletely as possible. This gave them an approxima-
tion, if they neglected to take into account the un-
liquefied gas which lay above the liquid. To deter-
mine what value this unliquefied portion had, a con-
trol experiment was done with liquid carbon diox-
ide whose specific gravity wras known, the experi-
menters using Andreeff s determination (Liebigs An-
nalen, vol. ex., page i). The calculations are too com-
plicated to be here reproduced. The result ob-
tained for oxygen at about — 130° C. ( — 202° F.) and
the pressure of liquefaction was 0*899.
Wroblewski, still longing to produce liquid oxy-
gen in quantity, says, in December, 1883, tnat it is
merely a question of appliances to produce liquid
LIQUEFACTION OF GASES. 21$
oxygen, but acknowledges that he has never suc-
ceeded in producing oxygen in the condition of a
static liquid. Any attempt to use the refrigerating
effect of oxygen, he said, involves its use at the in-
stant of production or cessation of pressure. Such
danger of explosion attended attempts in this direc-
tion that masks were worn.
A valuable suggestion would seem to be the one
made in 1884, when Wroblewski suggests the use of
liquid marsh gas as a refrigerant. In its properties
it is adapted to fill the gap which exists between
liquid ethylene and liquid oxygen. The honor of
being the first in the field with this suggestion
was afterward claimed by Cailletet. Dewar, how-
ever, was able to show that he had suggested the use
of liquid marsh gas as far back as 1883, which ante-
dates Wroblewski, and Cailletet's date goes back
to 1881.
After this period the two scientists appear as in-
dividual workers. The path started on the lines of
Cailletet's and Pictet's work led to direct experimen-
tal determinations, but these appear in later work.
The early apparatus, just described, did not lend itself
to thoroughly reliable temperature observations. In-
direct methods of dealing with problems had to be
used, and in some cases data were reached on almost
purely theoretical grounds. This was done to some
extent quite recently, and the hydrogen data were
determined with fair approximation partly from a
theoretical basis.
Much ingenuity appears in the methods of attack-
ing the problems which presented themselves in
the course of their experimentation. As an example
2l6 LIQUID AIR AND THE
may be cited the determination of the critical tem-
perature and pressure of oxygen {Comptes Rendus,
vol. xcvii.)
Oxygen gas was liquefied in the downwardly bent
tube, q, of the apparatus, page 209, by the aid of
boiling ethylene contained in the vessel, j, as already
described. As the oxygen liquefied its level rose in
the tube, q, and eventually reached a point above
the level of the liquid ethylene in s. Now it is evi-
dent that, as the liquid oxygen reaches a point in the
gas tube above the ethylene, the temperature of its
upper layers is higher, and the more it rises, the
higher is this temperature. As the temperature in-
creases, the pressure necessarily rises.
At last a point is reached when evidences of the
critical state begin to show themselves. The menis-
cus flattens, the line of demarkation between liquid
and gas becomes indistinct and at last entirely dis-
appears. The only way to trace the position of any
separating level is by the difference of refractive
power of the different layers in the tube. The de-
scription as given by Wroblewski exactly describes
the phenomena observed in a Natterer's tube (page
23).
If the pressure is lowered, the temperature of
the oxygen falls, liquefaction ensues, and the men-
iscus again forms. Working in conjunction with
Olszewski, the investigator found that this phenome-
non of the critical state occurred always at about
the pressure of 50 atmospheres.
The pressure of oxygen under these conditions is
so high and its temperature so low that it appeared
desirable to exercise some sort of a check upon this
LIQUEFACTION OF GASES. 2I/
experiment. The same tube was charged with liquid
carbon dioxide overlaid by the gas, in exact ana-
logue with the conditions of the oxygen experiment.
The boiling ethylene was replaced by melting ice, and
warm water at 50° C. (122° F.) surrounded the upper
part of the tube. Hence, within the length of the gas
tube the temperature had a range of 50° C.
Pressure was applied, and at 35 atmospheres traces
of liquid carbon dioxide appeared in the bottom of
the tube, which was the cold part. The gas kept on
liquefying until the liquid rose above the level of the
melting ice and began to reach the warm portion of
the gas tube. The pressure increased as the lique-
fied carbon dioxide attained in its upper layers a
higher temperature.
As the pressure approached 76 atmospheres the
meniscus became flat, then indistinct, and eventually
disappeared. The critical state was reached. On
lowering the pressure, the liquid diminished in
amount, the level fell, and the upper layer reached a
cooler part of the tube. The meniscus at once showed
itself again. The appearance and disappearance of
the meniscus evidently took place at a point of the
tube where the critical temperature existed. The
pressure in the apparatus when the phenomena
described took place was the critical pressure.
The attempt was made now to ascertain the criti-
cal temperature of oxygen — a far more difficult factor
to determine. A small quantity of oxygen was lique-
fied in the apparatus, so that it was below the level of
the liquid ethylene. The latter was boiling under
exhaustion so as to give a very low degree of
temperature. The exhaustion was stopped and the
2l8 LIQUID AIR AND THE
temperature of the ethylene began to rise. The
meniscus was watched.
Two things were occurring in the tube. The tem-
perature was rising and the pressure increasing as
the ethylene became warmer. Sooner or later the
balancing point, the critical state, would be reached
and the disappearance of the meniscus gave the indi-
cation. This was watched for, the temperature of
the ethylene being constantly observed.
The observations were extremely difficult, and
Wroblewski gives the figure of — 113° C. ( — 171*4°
F.) in his own words, " as the first approximation to
the critical temperature of oxygen." The tempera-
ture we now know was too high by nearly 6° C.
Cailletet had brought before the French Academy
of Sciences his liquefaction of hydrogen (page 184).
He had on release from pressure obtained a mist or
fog, which he claimed was due to liquid hydrogen.
Naturally some doubt was felt about it.
Wroblewski had tried it, and in an early number
of the Comptes Rendus — early as regards its date —
referring to the history of the liquefaction of oxygen
and of the " permanent gases," says that he tried
Cailletet's experiment and failed.
On January 4, 1884, the following dispatch from
Wroblewski was received by the French Academy
of Sciences:
" Hydrogene refroidi par oxygene bouillant s'est
liquefie par detente."
" Hydrogen cooled by boiling oxygen has been
liquefied by release."
Debray commented on the dispatch and says that
this experiment confirms Cailletet's experiment.
LIQUEFACTION OF GASES. 219
In the Comptes Rendus of February, 1884, Wro
blewski tells of his liquefaction of hydrogen. He
compressed hydrogen to 100 atmospheres in a
glass tube whose general dimensions were from 0*2
cm. to 0*4 cm. (0*08 inch to 0*16 inch) in internal
diameter and 2 cm. (0*8 inch) external diameter. It
was arranged for very sudden release of pressure.
The tube was surrounded with boiling oxygen in
order to reduce the temperature of the hydrogen.
On sudden release of pressure the hydrogen gave
the mist as in Cailletet's experiment of 1882.
To determine the temperature a thermocouple was
used, which was connected to a galvanometer which
could show a potential difference of roiiWir volt,
which corresponded to half a degree on the ther-
mometric scale. It was standardized by comparison
with a hydrogen thermometer.
It was known that the electric resistance of metals
falls with the reduction of temperature. As early as
1885 Wroblewski had tried silk-covered copper
wire, cooled to a temperature of — 200° C. ( — 328°
F.), and found that its resistance was less than one-
hundredth of what it was at the temperature of
boiling water. He says that oxygen and nitrogen,
in the liquid state, are among the most perfect insu-
lators known. He says that the electric resistance
of copper, at a temperature approaching that of boil-
ing nitrogen, tends to become zero — the conduc-
tivity approaches perfection.
This view has been very prominently brought for-
ward again by Dewar and others, and Elihu Thom-
son goes so far as to believe that in liquid gases a
useful reducer of electric resistance for power dis-
220 LIQUID AIR AND THE
tribution may be found. It is certainly very capti-
vating to think of a thin copper wire in a pipe filled
with liquid air carrying the energy of Niagara Falls
over hundreds of miles of country.
An experiment which excited much comment, and
which now, in these days of wholesale liquefaction
of air, is almost lost sight of, was described by Wro-
blewski, who, in 1885, *n liquefying air, produced
from it two liquids superimposed and which re-
mained separate for some minutes. He managed to
withdraw, by a metallic tube, samples from each layer
for analysis — rather a delicate operation, it would
seem. On analysis, the lower layer, after gasifica-
tion, gave a little over one-fifth of its volume of oxy-
gen (21-28 per cent, to 21-5 per cent, oxygen). The
upper liquid gave a little over seventeen-hundredths
of its volume of oxygen after gasification (17*3 per
cent, of nitrogen).
Wroblewski had used various thermometers for
determining the low temperatures which he obtained
in his experiments, the hydrogen-filled thermometer
seeming eventually to give him most satisfaction.
Cailletet had used various thermometers, finally tend-
ing to the hydrogen one. Pictet had adopted a very
indirect method of calculating temperatures, and the
thermo-couple had also been employed, as we have
just seen.
In 1885 Wroblewski published a paper embodying
his experiments on the relations existing between
temperatures as determined by the hydrogen ther-
mometer and a thermo-electric couple of copper and
German silver.
After this year but little appears under the name of
LIQUEFACTION OF GASES. 221*
this distinguished investigator. He seemed to pos-
sess the rare faculty of not disputing with any of his
confreres. The disputes as to priority in the lique-
faction of gases are very numerous and extend over
the greater part of a century. Wroblewski was for-
tunate in not being involved in any of them, as far as
his own statements are concerned at least.
Wroblewski and Olszewski worked together for a
number of years, but the latter scientist continued
the same line of work alone up to a recent period.
In the Philosophical Magazine, March, 1895, he pub-
lished a re'sumi* of his work, incidentally giving vent
to a certain amount of feeling and attacking Dewar
and Pictet.
In 1885 Olszewski made what may be called an
approximate liquefaction of hydrogen. He mixed
two volumes of hydrogen with one volume of oxy-
gen and liquefied the mixture successfully. The
mixture was colorless. On release from pressure it
lost most of its hydrogen. The residual liquid lasted
for some time at the atmospheric pressure.
He is much interested in showing that he pro-
duced oxygen in quantity large enough to pour from
one vessel into another. In October, 1890, he
produced 100 cubic centimeters before an au-
dience, and in July of the succeeding year, also
before an audience, he produced 200 cubic centi-
meters. He lays great stress on this achieve-
ment.
His apparatus, by which he produced oxygen in
what were large quantities for the period, was very
simple. Its essential feature was the use of a steel
cylinder of small capacity in which the oxygen was
222 LIQUID AIR AND THE
liquefied. This took the place of the glass tube in
which the gases were liquefied in the original Wro-
blewski and Olszewski experiments.
In 1883 and the subsequent years the two asso-
ciated investigators had liquefied gases in glass
tubes. The almost capillary tube of their early ex-
periments was changed sometimes for a larger one.
Thus the following are given as the dimensions of a
tube in which many liquefactions were carried out:
The tube was 30 centimeters (about 12 inches) long
and 14 to 1 8 millimeters (0-56 to 072 inch) in in-
ternal diameter. The walls were 3 to 4 millimeters
(0-12 to 0-16 inch) thick.
All the "permanent" gases then known, from
which argon, helium and the companions of argon
must be excluded, for they were not yet discovered,
had been liquefied in this apparatus, as already
described, and nitrogen, carbonic oxide, nitric oxide
and marsh gas had been solidified.
It will be observed, especially if the cut of the 1883
apparatus (page 209) be inspected, that no means
were provided for drawing off the small amount of
liquefied gas which might be produced in the glass
tube. If an attempt had been made to substitute a
large glass bulb for the tube, it would never have
stood the strains due to changes of temperature and
high pressure. By the repetition of numberless
liquefactions, the conditions necessary to produce
them became so accurately known that it was no
longer necessary to see the liquefaction to know
that it was produced. The necessity for a trans-
parent vessel had ceased.
Olszewski accordingly substituted for the glass
LIQUEFACTION OF GASES. 223
tube a small steel reservoir. This would stand the
pressure without danger of explosion, and was so
good a conductor of heat that the most sudden
changes of temperature had not the least effect upon
it in the direction of causing it to break.
This apparatus was described in 1890 in the Bulle-
tin internationale de I Academic de Cracovie. While
Olszewski, in the Philosophical Magazine article, seems
to indicate that his work has not been fully enough
appreciated, he makes very evident one reason. He
gives the list of his original papers. So many of
them appeared in the Cracow Bulletin, whose title is
given above, that they were deprived of the circu-
lation which was their due and which would have
been secured by a wider publication in the German,
French and English scientific annals.
But Olszewski's steel reservoir, like Pictet's lique-
faction tube, was provided with a cock by which its
contents could be withdrawn, and this certainly was
an advance over a sealed glass tube. The proba-
bilities are that in 1 883 the possibility of handling
liquid gases at atmospheric pressure like so much
water was undreamed of.
The mechanically bad feature of Pictet's old ap-
paratus was present in this one, which comes some
thirteen years later. The liquid was drawn from a
reservoir in which it was confined under enormous
pressure. The outrush of the almost uncontrollable
fluid must have given some trouble to the experi-
menter.
We give the diagram of the steel reservoir appa-
ratus with which oxygen was liquefied in quantities
sufficient to pour from one vessel into another.
224
LIQUID AIR AND THE
A is a cylinder of oxygen gas compressed to 100
atmospheres. It is connected by a tube to the steel
reservoir, B. From the lower end of the steel reser-
voir a tube with stopcock, b, descends. A gauge, a,
indicates the pressure of the oxygen. It is obvious
that any considerable diminution of pressure would
indicate liquefaction.
Olszewski's Liquefaction Apparatus of 1890.
The reservoir, B, is contained in a double-walled
vessel, C, hermetically closed at the top. From it
one tube, g, runs to an exhausting pump. This tube
has a cock, g% and vacuum gauge, v. Another tube,
/, runs to an ethylene cylinder, D. This tube has a
stopcock, ey and is bent into a coil between C and D.
LIQUEFACTION OF GASES. 22$
The coil is contained in a vessel, E, which is charged
with a mixture of ether and solid carbon dioxide.
A tube, o, leads from this vessel, which is absolutely
tight, to an exhausting pump. D contains liquid
ethylene, which is kept cold by ice and salt mixture
in the outer vessel, F.
The oxygen under high pressure filled the steel
vessel, B, which was quite small, of but a few ounces
capacity. Here it was subjected to the refrigeration
due to the liquir1 ethylene, cooled by exhausted carbon
dioxide and ether, and also subjected to exhaustion,
so as to have its temperature greatly reduced by
boiling. The intense cold, which was below the
critical temperature of oxygen, rapidly liquefied it
under pressure, and soon the vessel, B, filled with
the liquid. It could then be drawn off by opening
the cock, b.
By opening and shutting the cocks the apparatus
could be manipulated very readily, and the pressure
gauge, a, and vacuum gauge, v, gave certain indica-
tions of the progress of operations. If the apparatus
is analyzed and reduced to its elements, it will be seen
to be a simplification of Pictet's apparatus of 1877,
simplified by the suppression of pump circuits and
by the use of compressed gases. I": will be seen to
be much the same as Dewar's apparatus of 1883
(page 236), and the latter expresses himself as of the
opinion that the substitution of the steel reservoir for
the glass tube which he employed was not a very
important change.
To keep this delivery under some control, the out-
let tube from the steel oxygen vessel had lateral
openings. This prevented the stream of liquid from
226 LIQUID AIR AND THE
rushing- out against the bottom of the vessel and
driving out the contents as fast as received.
It is impossible within the limits of this work to
give the entire work of any investigator. Olszewski
determined many constants, by many methods, and
the general abstract of his work, with table of con-
stants determined and bibliography or list of his pa-
pers, may be found in the Philosophical Magazine for
1895.
For determining low temperatures he used as a
matter of preference the hydrogen thermometer, and
used it to standardize a platinum resistance thermo-
meter when the temperature fell too low for the
hydrogen instrum nt. But he distrusts all except
the hydrogen thermometer, except under limited and
defined conditions. Extrapolation he naturally sus-
pects, and, on account of variations in specific heat
as lower temperatures are reached, he has little con-
fidence in calorimeter methods.
During his investigations he was troubled with
bursting tubes. His work, like that of other investi-
gators, was not of the safest order.
James Clerk Maxwell, one of the most illustrious
physicists and mathematicians of England, had
doubted the possibility of liquefying hydrogen.
Faraday had not felt so. He believed that it might
yet be accomplished, and expresses himself in rather
uncertain phrase concerning it. Olszewski had no
hopes of liquefying it in volume or as " static hydro-
gen." The lesson of Cailletet's production of cold
by release from pressure seems to have been lost to
the world, only to be successfully applied within the
last five years by Tripler, Linde, Hampson and
LIQUEFACTION OF GASES. 22/
Dewar. But without attempting to liquefy it in
large volume, Olszewski tried to determine the con-
stants of liquid hydrogen. Now, his temperatures
ran so low that he was forced to use a platinum
resistance thermometer, which he compared with a
hydrogen thermometer, with the following result :
Electrical resistance of
Temperature by hydrogen platinum resistance
thermometer. thermometer.
o° C. (32° F.) 1000 ohms.
_-;8-2° C. (—108-8° F.) 800 "
—182-5° C. (—296-5° F.) 523 «
—208-5° C. (—343*3° F.) 453 "
This shows the decrease in electrical resistance due
to reduction of temperature- which is utilized as a
thermometric factor. But more is shown. The fall
in electrical resistance per degree fall in tempera-
ture grows greater as the temperature descends.
Thus:
Ohms.
Between o° and — 78-2° C. the fall per degree is 2 -557
« —78-2° "— 182-5° C. " " " " 2-655
"—182-5° "— 208-5° C. " " " "2-692
The last figure was adopted for the extrapolation,
or carrying out the scale beyond the limits of the
experiment.
He found for hydrogen a critical temperature of
—234-5° C. ( — 390-1° F.) and a boiling point at atmo-
spheric pressure of — 243-5° C- ( — 406-3° F.) The
lowest static temperature Olszewski claims to have
attained is —225° C. (—373° F.) The hydrogen tem-
peratures were of exceedingly brief duration.
The method adopted for reaching this figure de-
228 LIQUID AIR AND THE
pended on the observation that if a gas is exposed to
high pressure and is then cooled to a temperature
not far from the critical temperature, a slow reduc-
tion of pressure will bring about liquefaction of the
gas. The appearance of a mist indicated the lique-
faction. The result of numerous experiments with
hydrogen showed that this mist appeared always
at exactly the same pressure if the experimenter
started with a high enough pressure.
Thus he varied the initial pressure all the way
from 80 to 140 atmospheres by 10 atmospheres at a
time, cooled the compressed gas to — 211° C.
( — 347*8° F.) and suffered the gas to expand, watching
the change in pressure as it did so, and watching for
the mist. This mist always showed itself at 20 atmo-
spheres of pressure, whether the initial pressure was
high or low, provided it did not range below 80 at-
mospheres.
If the initial pressure did fall below this point then
the pressure at which liquefaction took place also fell,
and, starting from initial pressure of 50, 60 and 70
atmospheres, the mist appeared at pressures of 14, 16
and 1 8 atmospheres respectively. All constancy was
lost.
Therefore, Olszewski accepted 20 atmospheres as
the critical pressure of hydrogen, and thence de-
duced the conclusion that hydrogen liquefying at
20 atmospheres had the critical temperature. As
he could always produce the slight evidences of
liquefaction at this pressure in the small glass tube,
he believed that he could always produce liquid hy-
drogen at the critical temperature by establishing
the conditions described.
LIQUEFACTION OF GASES. 22Q
The only trouble was that such a minute quantity
of hydrogen was liquefied in his glass tube that it
was impossible to determine its temperature. He,
therefore, resorted to his steel vessel apparatus (page
224), established the proper conditions of initial pres-
sure and temperature, slowly reduced the pressure
to 20 atmospheres, and took the temperature of the
hydrogen in the steel vessel.
He saw no liquefaction, for the steel vessel hid its
contents. He established the conditions which had
always produced the mist in the transparent glass
tube, and he relied upon the large size of the steel
vessel to give enough liquid hydrogen to affect the
electric resistance thermometer which he employed.
Dewar, after producing liquid hydrogen in quan-
tity so that it could be poured from vessel to vessel,
and so that its temperature could be accurately de-
termined, comments unfavorably on Olszewski do-
ing his work in an opaque vessel. Although, too,
Olszewski's assumptions seem rather forced, and led
him to too high a critical pressure figure, his results
are surprisingly good, and compare well with Wro-
blewski's calculated ones and Dewar's presumably
more accurate ones.
LIQUEFACTION OF GASES. 231
CHAPTER XL
JAMES DEWAR.
Dewar's life and education — His associates — Controversies
with Cailletet as to priority — Early liquefaction appa-
ratus— Solid nitrous oxide as a refrigerant — Royal Insti-
tution apparatus — Cooling cycles employed — Laboratory
apparatus — Vacuum vessels — Air as a neat conveyer —
Experiments with incandescent lamps— Reflection of ether
waves from vacuum vessel — Keeping power of vacuum
vessels — The Dewar vacuum — Its extraordinary perfec-
tion— Analogy with population of earth — Experiment in
slow diffusion of mercury vapor — Incidental production
of vacuum vessels — Elasticity and strength of metals at
low temperatures — Apparatus used — Elongation of metals
when stressed at low temperatures — Determination of
specific and latent heats of liquefied gases — Gas jet ex-
periments— Low temperatures thus obtained — Freezing
air — Large jet apparatus — Analysis by liquefaction —
Liquefaction of fluorine — Liquefaction of hydrogen and
helium — Experiments to show the intense cold.
James Dewar was born in 1842, in Kincardine-on-
Forth. He was educated at the Dollar Academy,
and subsequently at the University of Edinburgh.
He acted as assistant in chemistry to Sir Lyon
Playfair in the University of Edinburgh, where the
former was Professor of Chemistry. He also stu-
died in Ghent under Auguste Kekulie. He has had
many honors accorded him. For sixteen years he
has been Jacksonian Professor in the University of
232 LIQUID AIR AND THE
Cambridge. He is Fullerian Professor of Chemistry
in the Royal Institution of England, thus being
Faraday's successor.
The list of papers by Prof. Dewar and his col-
leagues relating to investigations at low tempera-
tures is a long one, extending from 1874 down to the
present time, and including nearly eighty titles.
His colleagues in this work comprise Professors G.
D. Liveing, J. A. Fleming and Moissan, Most of
the papers are by Dewar alone.
Dewar had been interested in calorimetry for a
long time, and had used a vacuum vessel as an insu-
lator in calorimetrical experiments in 1874, at the
University of Edinburgh. This date was brought
out in a claim of Cailletet, who thought that he
antedated Dewar in this device. Had it not been
for the old Edinburgh experiments, the French
scientist would probably have carried his point.
An early reference of Dewar's involved him in a
second controversy with Cailletet. At the 1883
meeting of the British Association for the Advance-
ment of Science he had pointed out the advantages
of a liquid of low critical pressure, such as liquefied
marsh gas, for the production of intense cold. The
critical temperature of this gas he put at less than
— 1 00° C. ( — 148° F.), with a corresponding pressure
of only 39 atmospheres. He then stated that he
hoped soon to approach the absolute zero by the use
of this refrigerant.
Dewar set considerable store by this utterance, as
he had hoped to prove by it his priority in the use
of liquid marsh gas for the production of cold, which
priority was claimed by Cailletet.
LIQUEFACTION OF GASES. 233
In 1885 he and Cailletet had a discussion or inter-
change of communications on the subject of the
priority in the use of liquefied marsh gas, Dewar re-
ferring to his British Association remarks as pub-
lished in Nature in 1883, and Cailletet referring
to a sealed communication deposited by him with
the French Academy of Sciences, dated 1881.
As a portion of his duties at the Royal Institution,
Dewar had to lecture on chemistry and physics, and
naturally felt called upon to show liquid oxygen to
his audiences. The work of Cailletet, Pictet, Wro-
blewski and Olszewski was still fresh and in pro-
gress. Accordingly, Dewar had arranged a lique-
faction apparatus on the lines followed by the last
named investigators for exhibiting liquid oxygen to
his audiences. These lines, it will be remembered,
involved originally a combination of Cailletet's and
Pictet's apparatus. As their work progressed, Cail-
letet's apparatus became less a feature of it, but
Pictet's system of successful cooling cycles was
preserved.
This feature is prominent in Dewar's early appa-
ratus, and has always been retained up to the present
time. Pictet set the example, which was followed
in Cracow, Leyden and London, only now to be
abandoned by Tripler, Linde and Hampson, who
have dispensed entirely with outside refrigerants
and have made air and gases supply the cold for
their own liquefaction.
Dewar's early apparatus of 1883 was designed sim-
ply to liquefy oxygen in a glass tube for lecture pur-
poses. The apparatus was arranged for projection
of the gas tube by the magic lantern. It is of interest
234
LIQUID AIR AND THE
Courtesy of Xc Clvre't Magazine.
Prof. Dewar in the Laboratory of the Royal Institution.
LIQUEFACTION OF GASES. 235
as being the predecessor of the expensive apparatus
since that period installed in the laboratories of the
Royal Institution. It will be seen that it differed very
little from Olszewski's apparatus of 1890, except that
the receiver for the liquefied oxygen was a glass tube
and that no means were provided for withdrawing
the liquefied gas. In any case, far too little was
produced at a time to make it possible to pour it
from vessel to vessel except on the most limited
scale, if at all.
Prof. Dewar has been far from communicative on
the subject of the liquefaction apparatus and meth-
ods employed at the Royal Institution. They are
based on the Pictet system of successive cycles of
cooling agents, one agent cooling the next, so as to
secure several steps down the thermometric scale, the
last being utilized for the gas to be liquefied. It is
only very recently that a step forward has been made
and the self-intensive method adopted, and in the case
of his hydrogen liquefactions superadded to the Pic-
tet cycles.
Now that the work has been done and air has
been liquefied in large quantities by the expensive
methods adopted and devised for the Royal Institu-
tion work, it is with a feeling of sadness that we
realize that the great quantities of liquefied ethylene
which excited so much admiration were not needed,
and that, by the simple methods of Tripler, barrels of
liquid air could have been made at relatively nomi-
nal expense.
Referring to the cut, C is an iron oxygen reservoir
within which is the oxygen gas compressed to 150
atmospheres. A is the regulating stopcock by which
LIQUID AIR AND THE
it is allowed to flow out of the reservoir as desired.
The glass tube in which the gas is liquefied is in-
dicated by F, and the gas from breaches it through
a fine copper tube, 7. Z?is a manometer to show .the
Dewar's Karly Oxygen Liquefaction Apparatus of 1883.
pressure of the gas, and J is an air pump gauge to
indicate the vacuum under which the refrigerant
boils. H is the point of attachment of an air pump
lor producing this vacuum.
LIQUEFACTION OF GASES. 237
The gas liquefaction tube, F9 is surrounded by an-
other tube, G, also of glass, in which is liquid ethy-
lene, liquid nitrous oxide or solid carbon dioxide.
These boil in the approximate vacuum produced by
the air pump. It will be observed that a third
vessel, K, surrounds G and F, and that the exhaus-
tion takes place from its bottom. Its top is hermeti-
cally sealed, and holes at E permit the cold gas from
G to flow down the annular space between G and K
to keep the temperature low.
When the pressure in the vessel, G, containing
ethylene, is reduced to 25 millimeters of mercury,
the temperature falls so low that oxygen liquefies
when the manometer shows a pressure of 20 to
30 atmospheres. If liquid nitrous oxide or solid
carbon dioxide is used in G, then the pressure of
the oxygen must be brought up to 80 to 100
atmospheres to compensate for the lower tem-
perature. Or the lower temperature produced
by the last two refrigerants may be supplemented by
sudden release of pressure. The cock, B, is adapted
to effect this application of Cailletet's principle.
An ingenious suggestion is made by Dewar that
solid nitrous oxide should be used instead of liquid
nitrous oxide in order to prevent troublesome ebul-
lition.
He tried the specific gravity by evaporating a
measured volume of the liquid and determining its
amount, and performed a number of experiments,
naturally very much restricted in number and im-
pressiveness by the exceedingly small quantity of
liquid available and by its inclosure in a glass tube.
Lately, however, more has been said of the Dewar
238 LIQUID AIR AND THE
processes of liquefaction, and details of a laboratory
apparatus of his for liquefying air and other gases
have been made public. In England so much
interest has been excited by the work of Linde and
of Hampson, and the construction and theory of
their apparatus have been so freely disclosed, that it
seems time for the processes of the Royal Institu-
tion laboratory to be made more public than they
ever have been. Details, however, are still wanting.
It follows, therefore, that there is no possibility of
exactly describing the liquefaction apparatus in
question. If, however, Pictet's apparatus be taken
as representing the type of a double cycle refrige-
rating apparatus, the following give the data of its
operation for the Dewar liquefactions of five years
ago.
The cooling agent of the first cycle was liquid
nitrous oxide. This was compressed to about 90 at-
mospheres and was evaporated in a condenser jacket
so as to give a temperature of — 90° C. ( — 130° F.)
Through the inner condenser chamber liquid ethy-
lene passed. This was under a pressure of over 120.
atmospheres, and was cooled by the evaporating
nitrous oxide which surrounded it. The liquid
ethylene, brought down to nearly — 90° C. ( — 130° F.),
was passed into the jacket of a second condenser in
which it was evaporated. The intensely cold liquid,
cooled still more by its own evaporation, brought
about a temperature of — 145° C. ( — 229° F.)
A tube passed through the condenser jacket in
which the ethylene evaporated, and through the tube
oxygen, compressed to 50 atmospheres, flowed. It
liquefied rapidly, and was drawn off as required. In
LIQUEFACTION OF GASES.
239
drawing it off at this pressure, nine-tenths of it was
lost. It was another illustration of the difficulty of
coping with the mechanical troubles of too high
pressure. We have had occasion more than once to
allude to this trouble, and Dewar's statement that he
lost the greater part of his liquefied gas emphasizes
what we have said about this feature of Pictet's,
Olszewski's and Dewar's early apparatus. A jet of
Courtesy otMeOlure's Magazine.
Machinery for Operating Liquefaction Apparatus,
Royal Institution.
liquid at 50 atmospheres is almost uncontrollable,
and the action of a regulating cock is apt to
involve some wasteful atomizing action upon the
liquid.
It was with this apparatus that oxygen and
other gases were liquefied by Dewar in quantities
almost unhoped for up to his time, and with it liquid
air was prepared for the lectures which did so much
240 LIQUID AIR AND THE
to excite public attention on the subject of the lique-
faction of gases.
The apparatus was very large and heavy, and it
involved the making of great quantities of ethylene
by decomposing alcohol with concentrated sul-
phuric acid. This cost a great deal. Faraday's old
laboratory became the scene of operations which
recalled a machine shop rather than a scientific
workshop.
Prof. George F. Barker, of the University of
Pennsylvania, in visiting the scene of Dewar's work,
found almost as much to admire in the dozen cylin-
ders of liquid ethylene as in the air and gas lique-
factions which it accomplished. Commenting on
the strange uses to which Faraday's laboratory was
put, Prof. Dewar told his friend that Faraday would
have been the most delighted man in the whole
kingdom had he been alive to see what was in course
of accomplishment. The work was nothing but the
following out of the path that Faraday pointed out,
and in which he went as far as the knowledge of his
time permitted.
There is no difficulty in assenting to Prof. Dewar's
views thus expressed.
Simpler apparatus was constructed later, and we
illustrate Prof. Dewar's small apparatus for effecting
liquefactions without the use of pumps, reliance
being placed on the use of cylinders of compressed
gases.
In the general view of the apparatus two com-
pressed gas cylinders are seen. The one to the right
contains compressed and liquid carbon dioxide, the
one on the left contains compressed and gaseous
LIQUEFACTION OF GASES.
24I
air or oxygen. The small cylinder above and
in a central position contains the liquefaction appa-
Dewar's Small Gas Liquefaction
Apparatus.
ratus. It forms a very compact piece of apparatus.
The next cut shows the condensing and liquefying
portion of the apparatus in section.
242
LIQUID AIR AND THE
The carbon dioxide gasifies as it escapes from
the cylinder and enters the apparatus, passing in by
the inlet, B. It follows
a coil of pipe which
winds around the in-
terior of the cylinder
in parallel with a sec-
ond similar pipe. This
second pipe communi-
cates by the inlet, A,
with the cylinder of
compressed air or oxy.
gen. In the sectional
cut the carbon dioxide
pipe is represented by
the black circles, the
air or oxygen pipe by
the open ones. The
carbon dioxide after
passing through this
coil escapes into the
inner chamber of the
apparatus and is regu-
lated by a valve ope-
rated by the hand
wheel above C.
The air or oxygen,
Section of Dewar's Small Gas after £oing through
Liquefaction Apparatus. the outer coil, and get-
ting a preliminary
cooling from the carbon dioxide coil, enters the coil
in the inner chamber indicated by the triple set of
small open circles. Here it circulates around
LIQUEFACTION OF GASES. 243
through a great length of pipe and is further cooled
by the expanding carbon dioxide, then goes through
a third coil, intermediate between the outer coil and
the inner chamber, and escapes, regulated by the
valve, F. It liquefies and collects in G.
In operation the carbon dioxide solidifies so that
the gas is cooled by the solidified carbon dioxide gas.
This apparatus was operated without exhaustion,
the natural evaporation of the carbon dioxide giving
a reduction of temperature to — 79° C. ( — no'2° F.)
The tubing is of copper, to secure good heat conduc-
tion and consequent rapid cooling. The rest of the
refrigeration is due to the expansion of the oxygen.
It is well to start with this gas compressed to 1 50
atmospheres and to utilize it down to a pressure of
100 atmospheres. The liquid air or oxygen begins to
drop in about fifteen minutes. The intensely cold
expanded and unliquefied gas rises among the coils
and cools them still more, so as to obtain a regen-
erative action. The apparatus will make 100 cubic
centimeters (about six cubic inches) of liquefied oxy-
gen in an operation.
The spheroidal state has been somewhat fully
treated in an earlier portion of this work. The orig-
inal investigators of the phenomena of the liquefac-
tion of gases never imagined how important a part it
would play in facilitating their manipulation. Thanks
to it, the hand can be immersed in liquid air. Liquid
air rests quietly in a tin dipper, and the length of time
for which it remains in the open air in a common
vessel is in many cases due to its taking the spher-
oidal state.
But liquefied gases do evaporate rather rapidly in
244 LIQUID AIR AND THE
the air, and a great desideratum was some kind of a
vessel that would hold them without the rapid loss
experienced under ordinary conditions. Liquefied
gases volatilize and disappear because they receive
heat from surrounding objects and from the atmo-
sphere. Early in his scientific work Dewar recog-
nized that it might be possible to make this loss very
much less, utilizing a vacuum as a non-conductor.
The properties of a vacuum in intercepting the trans-
mission of heat are utilized in what are known as De-
war's bulbs for holding liquefied gases. Air is often
spoken of as a good insulator, and such it is. Abso-
lutely quiet air is nearly as good an insulator as a
vacuum.
But the trouble is that air cannot be kept still, and
if it is free to move, its mass, under the influence of
heat, travels back and forth and carries heat with it,
and thus by convection destroys the heat insulation
of objects it is in contact with. Among objects in
everyday use the incandescent lamp may be referred
to as one in which a vacuum is utilized. A very con-
siderable proportion of the efficiency of an incan-
descent electric lamp is due to the vacuum within
the bulb. The vacuum is not only useful in preserv-
ing the carbon from-combustion — a filling of the bulb
with nitrogen gas would do this — but it keeps cold
gas of any kind from coming in contact with the film
and thereby cooling it.
The incandescent lamp illustrates so admirably the
heat insulating properties of a high vacuum that
some experiments may here be cited which show the
effect of filling the bulb of an incandescent lamp 'with
various gases as contrasted with having it empty.
LIQUEFACTION OF GASES. 245
As the vacuum protects the film of an incandescent
lamp from cooling, so does it protect a mass of lique-
fied gas from heating. Dewar's very elegant inven-
tion is illustrated by an appeal to the other end of the
thermometric scale from that occupied by liquid air.
In the PJiilosophical Magazine of 1894 we read that
Blenkroode filled three incandescent lamps with car-
bon dioxide, coal gas and hydrogen respectively.
A fourth lamp of the regular construction with a
high vacuum existing in the bulb was added to the
series, they were placed on a lighting circuit, and a
piece of phosphorus was placed on top of each one.
On passing a current through them, the vacuous
lamp was the brightest, the presence of the gases
chilled the other carbons, and the phosphorus was
ignited in the following order : first, on the carbon
dioxide lamp ; second, on the coal gas lamp ; third,
on the hydrogen lamp, the regular lamp being the
last on which the phosphorus ignited. The lamps
varied in brightness in the same general order, the
regular vacuous bulb lamp being by far the bright-
est. This illustrates the utility of a vacuum as a heat
insulator.
In the case of the incandescent lamp the problem
is to maintain the heat of an incandescent body in
the vicinity of relatively cold objects. In the case of
liquid air and gases the reverse has to be effected.
A very cold body is to be prevented from receiving
heat from surrounding matter. But, as is so often
the case, opposites here come together, and the same
means which will keep the film in the lamp from
losing its heat will prevent liquid air from losing its
cold, if such an expression may be allowed.
246 LIQUID AIR AND THE
A double-walled glass vessel in a measure pre-
serves liquid gases from evaporation. The inclosed
air acts as an insulator, but, by convection, carries
heat from outer vessel to inner one. A triple-walled
glass vessel is still better, as it gives two spaces filled
with air. The earlier experimenters used double-
walled vessels for another purpose. They found
that liquid gases in a single glass vessel caused ice
to rapidly form upon its outer surface, so that the
contents were hidden, as the ice was white and
opaque. They employed a double vessel and placed
some drying agent between the two vessels, on the
bottom of the outer one, to keep the air between
them dry, so that no such ice could form. We have
seen how in his early work Dewar used this device
and others did the same.
The Dewar vacuum bulb consists of a double or
treble walled glass vessel, with the space or spaces
between the vessels hermetically sealed and with a
nearly perfect vacuum therein. The conditions in
such a vessel are that the liquid in the interior one
receives practically no heat. Glass is so poor a con-
ductor that it conveys only slight traces by conduc-
tion. The liquid receives none by contact with the
air above it, as it is overlaid by the intensely cold gas
evolved from itself. The vacuum surrounding- it
cuts off any heat from warm air coming against the
sides of the containing vessel. Almost the only heat
it can receive is that imparted by ether waves or,
popularly speaking, by radiant heat.
Ether waves of this description are such as we
feel when we hold the hand near the bulb of an in-
candescent lamp when hot and giving light. They
LIQUEFACTION OF GASES. 247
pass through glass with little loss. If the glass of
the inner bulb, the one containing the liquid air or
liquefied gas, were coated with some bright opaque
substance that would reflect these waves, a further
economy would be obviously effected.
This was done for the glass bulbs by coating the
surface of the inner bulb with silver. The bright
metal reflected the ether waves, and a better effect
in preserving the gas was the result.
Then a still simpler treatment was discovered. A
little mercury — a very little suffices — was left in the
vacuous space outside the containing bulb. When
liquid gas was put into the bulb, it chilled it and con-
densed a mirror of mercury upon its outer surface,
which reflected the heat waves. When the liquid
gas was removed, the mercury disappeared again.
Direct tests showed that a vacuum preserved the
air about five times longer than would air. The fol-
lowing figures are given :
Relative Volumes of Liquefied Gases Eiaporating
from Double Bulbs.
Liquid oxygen, vacuum space, 170 volumes.
air " 840
" ethylene, vacuum " 56 "
" air " 230
If the silvering process is applied, the influx of heat
is reduced to about one-thirtieth of what it is with
an air space, or, in round numbers, 31 per cent.
Three dry air spaces, one outside the other, only
reduced the influx to 35 per cent, of what it was
with a single space.
It is interesting to find that Prof. Dewar had
248
LIQUID AIR AND THE
used metallic vacuum vessels in 1873 in calorimetric
experiments, which he describes in a paper read be-
fore the Royal Society of Edinburgh, and printed in
their Transactions, vol. xxvii.
Various Shapes and Modifications of Dewar Bulbs,
and Liquefied Gas Containers.
Various shapes can be given to the bulbs, and
several are shown in the cut. The mercury silver-
ing process is not always employed, as it may be de-
sirable to have the liquid visible, and the deposition
LIQUEFACTION OF GASES.
249
of mercury on the glass cuts the liquid off from
view.
For some reason, vacuum vessels deteriorate. The
Sectional Views of Different Forms of
Dewar's Bulbs.
vacuum cannot well be supposed to diminish, and
no satisfactory reason can be given for the change.
Prof. Dewar adopted, for the exhaustion of his
vacuum vessels, the principle of
the Torricellian vacuum combined
with that of freezing mercury
vapor.
Suppose that the drawing repre-
sents a glass bulb, K, for production
.of a vessel in which a Dewar vacu-
um, as it may be called, is to be
produced. The large bulb is the
one which will eventually form the vessel. From the
small bulb, W, the tube, H, descends a distance of
over 30 inches.
Production of
Dewar Vacuum.
2$0 LIQUID AIR AND THE
To simplify the description, the single outer bulb
alone is shown. The inner bulb is not represented
in the drawing-. It must be supplied by the reader's
imagination.
The whole affair, tube and bulbs, is filled with
mercury while inverted, exactly as in filling a
barometer tube. By heating, or by some other
manipulation, any air present may be expelled, for
mercury, mobile as it seems, invariably holds bub-
bles of air imprisoned when it is poured into a long
tube. In filling barometers, several methods of get-
ting rid of the air are employed, boiling the mercury
being one of the best. Barometers thus treated are
said to have " boiled tubes."
The long tube with the large and small bulb, be-
ing filled with mercury, is reversed in position, with
its lower end immersed in a cistern of mercury.
The mercury descends until it stands at a height
of about 30 inches. By a little inclining of the
tube, any mercury remaining in the bulbs can be
made to enter the tube, or a little may be left there
as a silvering agent. In the bulbs the Torricellian
vacuum now exists. It would be a perfect and ab-
solute vacuum except for the presence of mercury
vapor. A blowpipe flame is applied at the outlet, A,
of the small bulb, the tube melts together, and the
two bulbs are removed hermetically sealed. A trace
of mercury vapor is still in them.
The next operation is to chill the small bulb by
wiping it with a piece of cotton dipped in liquid air.
As this touches the glass, the mercury vapor is
frozen solid and is deposited on it and forms a mir-
ror. This mercury is derived from the vapor which
LIQUEFACTION OF GASES. 25 I
exists in the bulbs. A sufficient freezing removes
almost every trace of vapor, and the mercury vapor
is removed from the large and from the small bulb.
Keeping the bulb cold with liquid air, the small
neck between the bulbs is sealed off by the blowpipe
flame, and the large bulb has now within it the most
complete vacuum known. It is all but absolute.
Some infinitesimal traces of mercury vapor are pres-
ent. It responds to the most severe electrical tests
for vacua.
While a sufficiently long exposure of the small
bulb to the absolute zero, were such attainable,
might make the vacuum absolute, the difference
between it and the Dewar vacuum would be infini-
tesimal.
The calculated pressure of mercury vapor at the
temperature of melting ice is expressed by the deci-
mal 0-000,126 millimeter of mercury. The reference
is to a barometric column of mercury which has a nor-
mal length of about 760 millimeters. Therefore, the
above decimal expresses one six-millionth of an at-
mosphere, certainly low enough for almost any
purpose. But on lowering the temperature to
— i 80° C. ( — 292° F.) by sponging the outer bulb
with liquid air, the pressure of the mercury vapor
falls to the figure 0*000,000,003 millimeter, or two
and a half millionths of a millionth of an atmo-
sphere. In powers of ten it would be expressed by
25 x icr13 of an atmosphere.
If a bulb of identical size were filled with mercury
vapor at atmospheric pressure, it would, therefore,
contain two and a half million million times as great
a weight of mercury. If it were filled with air at
252 LIQUID AIR AND THE
atmospheric pressure, it would contain in round
numbers one-fiftieth the above weight of air, or
eighty thousand million times the weight of the mer-
cury in the Dewar vacuum.
Amazingly small as this quantity is, we can obtain
some concrete idea of it from the population of the
world. This may be taken at about one thousand
millions. If then we had one thousand earths, and
removed from them all of the human inhabitants
except three, they would represent three-millionths
of a millionth of the original population of our thou-
sand worlds.
Prof. Dewar seems amply justified in maintaining
that the vacuum he produces is higher than any of
which man had ever yet dreamed.
The rate at which mercury is thus deposited has
been investigated. All that was necessary was to
apply the cooling process to a vacuum bulb contain-
ing a globule of mercury. The latter supplied more
mercury vapor as fast as, or nearly as fast as, it was
deposited on the glass. The time of cooling was
taken, and then the bulb was broken and the mercury
weighed. The area over which the mercury was
deposited being known, the data are reduced to mer-
cury deposited on a given area in a given period.
In ten minutes two milligrammes of mercury were
deposited per square centimeter of surface. This
gives a rather interesting figure. These two milli-
grammes of mercury represent enough vapor to
saturate * in the Torricellian vacuum no less than
twenty liters or about twenty quarts capacity. A
globe big enough to hold this quantity, if exhausted
by the Torricelli process, would contain just about
LIQUEFACTION OF GASES. 253
two milligrammes of mercury vapor, and ten min-
utes' cooling by liquid air sponging would remove
this from the globe.
Remembering that two milligrammes are equal to
about three hundredths of one grain, and that twenty
liters are equal to about twenty quarts, and that a
twenty-liter globe would hold seven pails of water,
we again have a concrete example of the effect of
removing mercury vapor from a Torricellian vacu-
um. It also gives us an idea of how near perfection
a Torricellian vacuum is, and of what is gained by
the freezing process applied to it.
In scientific work one must always be on the
watch for side issues. New and interesting facts
constantly come out by accident, or are suggested in
investigations having widely different ends in view.
An interesting example occurs in the freezing of the
mercury vapor in the bulbs we describe.
The cut shows an apparatus designed to show the
slowness with which mercury gas diffuses through a
long, slender glass tube. Two bulbs, a large and a
small one, are connected by a capillary tube. The
latter in the experiment as executed by Dewar was 2
millimeters (o'o8 inch) in diameter and 50 millimeters
(2 inches) long. A little globule of mercury is in the
smaller tube. A Torricellian vacuum is produced
by the process already described, and the tubes are
sealed up so as to maintain it within their interiors.
The cotton wad, A, wet with liquid air, is applied
to the large bulb, and a mirror at once forms where
the same is applied. All the mercury gas in the
large globe deposits there, and, on touching another
portion of the glass, no mirror shows itself. The
254
LIQUID AIR AND THE
mercury gas diffuses with such extreme slowness
through the capillary tube that the latter for a while
acts almost like a valve to shut off the communica-
tion between the two bulbs.
If now the bulbs are inclined so that a little mer-
cury runs into the large one, then, on applying the
sponge elsewhere, a new mirror is at once formed.
Such are the Dewar bulbs, one of the most valua-
Dewar's Experiment of Freezing Mercury
Vapor in Connected Bulbs.
He of the mirror devices in connection with our sub-
ject. These bulbs and the spheroidal state are what
enable liquid air and gases to be handled almost as
if they were so much water. Certainly, the ease of
handling is comparable to the case of a volatile in-
flammable liquid, such as benzene or ether.
It is interesting to observe that sometimes the
principle has been applied in a sense unconsciously.
Thus, for the production of low temperatures, a ves-
LIQUEFACTION OF GASES. 255
sel is often surrounded by another one containing a
liquefied gas. The joint between the vessels is her-
metically tight, and the liquefied gas in the space
between is reduced in temperature by the applica-
tion of exhaustion, thus making it boil.
Although this vacuum is applied simply to reduce
temperature, one of its actions is to make the com-
bination constitute approximately a Dewar vacuum
vessel.
We now pass to some determinations of data at
low temperatures, giving as required illustrations of
the apparatus employed by Dewar and his associates.
Much ingenuity was required in carrying out some
of these determinations, but they were made possible
by the ample facilities for the production of liquid air
and liquefied gases. Had the experimenters, relative-
ly speaking, had such quantities of liquid air at their
disposal as have been produced in New York city by
Tripler, their tasks would have been still easier.
The strength of metals and their rigidity are
greatly modified by extreme cold. It is easy to
show this in a crude way. Thus a spiral of soft
metal, such as solder, an alloy of lead and tin, may
be drawn out into a straight line by suspending a
very small weight by it. But if cooled to the tem-
perature of boiling oxygen or thereabout, it will
support a weight fifteen or twenty times greater
than before, without being drawn out of a spiral, and
will spring like a watch spring.
This experiment gwes as an explanation of Tresca's
flow of solids. He found that, under great pressure
long maintained, metals would flow like a very thick
liquid, but very slowly. The soft metal, which is so
256 LIQUID AIR AND THE
easily straightened out, may be supposed at our
everyday temperatures to exist in a state of semi or
partial, perhaps much less than semi-fusion. The
same becomes fully solid when cooled by liquid air.
The same spiral will vibrate like a steel spring
\vhen intensely cold. At ordinary temperatures it is
almost devoid of elasticity.
A tuning fork or bell made of such metal will not
ring at ordinary temperatures, but when chilled the
elasticity is increased so that the metal becomes
sonorous, the bell rings and the tuning fork sounds
as if of steel or of bell metal.
As an analogy at more familiar temperatures, we
may refer to iron or glass. Either of these is rigid
and elastic, but when heated becomes soft gradually,
not melting at once, but passing through a slow
change extending over many degrees range of tem-
perature, and gradually approaching fluidity. We
may assume that such metals as lead or tin at
ordinary temperatures are undergoing a change of
state, and are approaching fluidity. The only
trouble with this view of the case is that, when such
metals do melt, the melting is sudden, and is done
within a very small range, perhaps less than a
degree.
If one of two tuning forks which are in perfect
unison is chilled in liquid air, and the two are
sounded, they are found to be no longer in unison.
The colder one is of higher pitch than before, be-
cause the intense cold has made it more elastic than
it was.
The difficulties of determining the strength of ma-
terials when cooled to the liquid air temperatures
LIQUEFACTION OF GASES.
257
have been quite successfully overcome. The cut
shows the general plan of apparatus used by Prof.
Dewar for determining the tensile strength of mate-
rials. As the piece should be of sufficient size to in-
sure absence of flaws of any kind,
the apparatus must be powerful.
Metals increasing in tensile strength
as cooled, the jaws of the apparatus
which hold them have also to be
cooled. Otherwise, the portions of
the test piece near the jaws, being
warmer than the rest, would be
weaker than the rest, and the sam-
ple would break there, and invali-
date the test.
In the cut, D is a silvered vacu-
um vessel of liquid oxygen, C is the
wire to be tested, A is a* steel rod
which runs to a set of multiplying
levers which produce the breaking
strain. At B is an arrangement for
determining the amount of exten-
sion of the wire before breaking.
When the test is to be made, the
lower part of the apparatus is im-
mersed in the liquefied gas, and the
strain is applied.
If the heavy apparatus strikes Apparatus for De-
the vessel, the glass will break, and termining Tensile
. . Strength at Low
an expensive piece of apparatus Temperatures.
will be destroyed, and the liquefied
gas will be lost. For this reason the apparatus has
to be solidly constructed, so as to be secure from
-D
258 LIQUID AIR AND THE
shaking or jarring under the heavy strains and from
the sudden breaking of the sample under test.
As a rule, Dewar used wires about one-tenth of
an inch in diameter and two inches long. He gives
the following table of his results. We quote it as
published in the Transactions of the Royal Institu-
tion. The work was published in 1894.
Breaking Stress of Metallic Wires in Pounds, 0*098
Inch Diameter, at 15° C. (59° F.) and —182° C.
(-295-6 F.)
15° C. —182° C.
(59° F.) (-295-6° F.)
Steel (soft) 420 700
Iron 320 670
Copper 200 300
Brass 310 440
German silver 470 600
Gold " 255 340
Silver 330 420
The great increase of strength is due entirely to
the reduction of temperature. When the wires are
restored to their original temperature, the increase
in strength disappears.
The inhabitant of a world where the temperature
approximated the absolute zero would have much
stronger iron and steel with which to build his
bridges, and he might make his watch springs out
of pewter and his bells out of tin.
With the same apparatus the breaking strain un-
der longitudinal tension of test pieces of various cast
metals was tried. The samples were all cast into
shape. They were two inches long, they had hemi-
LIQUEFACTION OF GASES. 259
spherical ends one-half inch in diameter and a central
cylindrical section two-tenths inch in diameter. This
gave a shape somewhat like a dumbbell.
The ends were received by cavities in the special
steel end blocks in the testing machine, in which
blocks hemispherical cavities were turned out to fit
them. Although much discordance obtained among
the results, the same general principle held as for
tensile strength of wire. The chilled metals were
stronger than at ordinary temperatures. The table
of results we give here :
Breaking Stress of Cast Metallic Test Pieces in Pounds,
0-2 Inch Diameter, at 15° C. (59° F.) and —182°
C. (-295-6° F.)
15° c. —182° C.
(59° F.) (-295-6° F.)
Tin 200 390
Lead 77 170
Zinc 35 26
Mercury o 31
Bismuth 60 30
Antimony 61 30
Solder 300 645
Fusible metal (Wood's) 140 . 450
The abnormal results with zinc, bismuth and anti-
mony are striking. These three metals are highly
crystalline, and in this feature perhaps some expla-
nation may lie hidden.
The elongation results were not considered of any
high degree of accuracy, but certain points were
brought out by them. Thus tin and lead, at ordin-
ary temperatures, elongate to the same extent be-
260
LIQUID AIR AND THE
fore breaking ; but after reduction of temperature,
tin hardly stretches at all, while lead is as ductile as
ever. Solder and fusible metal stretch less at the
lower temperature. Steel "has its elasticity only
slightly changed by refrigeration. Lead, tin, iron
and ivory balls, when refrigerated, are increased in
elasticity and bound higher than be-
fore when dropped upon an iron an-
vil. The cooled lead ball has a much
smaller distortion produced where it
strikes the anvil that it would were it
uncopled. The area of the distortion
surface is about one-ninth what it
would be in a sphere of the same
metal and size at ordinary tempera-
tures.
The cut shows how air, when lique-
fied, can be preserved practically
without evaporation, although at the
expense of the evaporation of other
liquefied air. Two vacuum tubes are
used, placed one within the other, as
shown in the cut. The inner one
connects with a tube, A, the outer
one, C, with a tube, B. The sample
of liquid air to be preserved intact is
placed in the inner vacuum tube. The
outer tube contains enough liquid air
to completely immerse the inner tube.
By India rubber perforated stoppers,
the necks of the vessels and of the tube, B, are
closed airtight, except for the passage through them
of the tubes, A and B. All heat received is cut off
Apparatus for
Preserving
and Freezing
Liquid Air.
LIQUEFACTION OF GASES.
26l
from the inner tube. The liquid air in the outer
tube boils off slowly, and the liquid air in the inner
tube is effectively preserved. If exhaustion be ap-
plied to A and />, the.
air in the inner tube
freezes to a jelly-like
mass.
The apparatus
shown in the cut was
the apparatus used for
determining latent
heat of evaporation or
the specific heat of a
liquefied gas. The
first requirement in
thermic work is tc
have a mass of the
liquid under perfect
control. It must be so
placed that it will be
permanent, and not
evaporate. This con-
dition is brought about,
by the arrangement
shown in the cut, prac-
tically a duplication of
what has just been de-
scribed, with some ad-
ditional features.
There is an outer
vacuum vessel, G. In
it is placed the refrigerant, liquid air, oxygen or
such liquefied gas as may be chosen. This vessel is
Apparatus for Determining the
Latent Heat of Evaporation
and Specific Heat of Lique-
fied Gases.
262 LIQUID AIR AND THE
corked, and a second vacuum vessel, Cy is maintained
concentric with it and immersed in the refrigerant.
Latent heat of evaporation is determined by add-
ing a known quantity of heat to the liquid and de-
termining the quantity of gas evolved. Enough
heat must be imparted to bring about evaporation,
which heat may be imparted by dropping mercury
into the liquid, as shown in the cut. Sometimes a
piece of platinum, glass or silver is used. The
weight of the substance added, its specific heat and
its temperature being known, the quantity of heat
imparted is calculated from these data. The gas
evolved is collected, and its weight being known, the
data are given for determining the latent heat of
gasification or of evaporation. The gas evolved is
measured, and its weight is calculated from its
known specific gravity.
We now know the amount of heat added, and we
know the amount of liquid which it has converted
into gas. This gives the data for calculating the
latent heat of evaporation. *To determine the speci-
fic heat, we have to ascertain the quantity of heat
required to change the heat of a given amount of
the liquid from one known temperature to another.
These known temperatures are the boiling points at
specified pressures. When such a pressure is pro-
duced, the temperature of the boiling point at that
pressure is reached. The following describes the exe-
cution of a determination of latent heat of a liquefied
gas:
The capacity of the vacuum vessel, C, being known
at given heights, it gives the quantity of liquid con-
tained in it.
LIQUEFACTION OF GASES. 263
At D is a three-way cock. When turned in one
direction, it cuts off the tube, E, and establishes com-
munication between F and the vessel, C. In another
position it cuts off the tube, F, and connects E with
the liquid gas vessel, C. The tube, F, leads to an air
pump. The tube, F, being put in connection with
C, exhaustion is applied until a vacuum of about one-
half an inch of mercury is produced. This fixes a
temperature for the liquid gas — the boiling tempera-
ture at that pressure — which temperature is known.
The stopcock, D, is turned so as to shut off F and
bring E into communication with C.
The height of column is the vertical distance from
the level of the mercury in the cistern to the level of
that in the tube. Heat is now imparted by dropping
mercury into C until the column of mercury in E
sinks to the level of that in the cistern.
Now heat enough has been imparted to raise the
temperature of the liquid gas from its boiling point
at one-half an inch pressure to its boiling point at
atmospheric pressure, the latter being taken for
each experiment from a standard barometer. The
quantity of liquid gas thus raised in temperature
being known, the data for determining specific heat
are known.
The mercury dropped into the liquefied gas in C
needs particular management. It has a propensity
for forming a stalagmite as it falls into the in-
tensely cold liquid, and this must be prevented by
dropping the mercury into different parts of the
liquid. Another difficulty is the splashing of the
liquid as the mercury falls into it.
The latent heat of evaporation of liquid oxygen is
264
LIQUID AIR AND THE
about the same as the latent heat of melting of water,
or 80 units, or the heat required to vaporize one part
by weight of liquid oxygen would raise the heat of
the same weight of water through 80° C. (144° F.)
The behavior of a jet of gas issuing from a state of
high compression may be studied by such apparatus
as that shown in the next cuts. The apparatus was
used by Dewar. In each piece is recognizable a
vacuum tube with coil.
In the first cut, C is a vacuum vessel which con-
tains a coil of tubing about 0*2 inch
diameter. The vessel in the ex-
periment is filled with a refrigerant
such as liquid air. The tube is of
silver or of copper, so as to be a
good conductor of heat. At the
end, A, is a minute aperture.
If oxygen gas at a pressure of
100 atmospheres is driven through
the tube, escaping through the
aperture, having previously been
cooled in the tube, C, to a tem-
perature of — 79° C. ( — 110-2° F.), a
liquid jet is just visible. The con-
ditions here are not nearly so extreme as with Pictet
in his experiment of 1 877, in which a pressure of 270
atmospheres was used. Dewar believes that one
reason Pictet required so high a pressure was on
account of his stopcock being massive and being
outside of the refrigerating apparatus. It is also
quite possible that Pictet used a higher pressure
than was really needed.
With air driven through the tube instead of oxy-
LIQUEFACTION OF GASES. 265
gen, 1 80 atmospheres are needed for liquefaction, and
with a reduction of temperature to — 115° C. ( — 175°
F.) liquid air can be collected in vacuum vessel, D.
This reduction is effected by applying exhaustion to
the carbon dioxide in C. Or adhering to the natural
evaporation temperature of carbon dioxide ( — 79° C.,
— i io'2° F.), a pressure of 200 atmospheres at that
temperature liquefies air. Naturally, Dewar found
that the high pressure interfered with the collection
of the liquid. An interesting point he speaks of is
that the collection of liquid air can be increased by
directing the jet against the tube above the hole.
This to some extent brings out the self-intensive
principle of Tripler's, Linde's and Hampson's appa-
ratus. By putting in a greater length of tube, as by
making a coil, B, the efficiency is increased. This is
undoubtedly because the cold gas rising produces
self-intensive action. An egg-shaped vessel acts in
the same way. Dewar terms it the cold regenera-
tive process, citing Coleman, Solvay and Linde as
users of this principle.
The next cuts show modifications. In the first
cut the pipe is coiled around an inner vacuum tube
to get better insulation from heat. The inner
tube is 9 inches long and i£ inches in diameter.
Over the end of the metal tube a glass tube is
slipped which stops the splashing about of and loss
of the liquid air. It is evident that with such an ap-
paratus the cold regeneration would be very well
carried out. The tube is coiled in a very restricted
space, and the ascending excess of unliquefied air
and of evaporated air at a very low temperature
comes in contact under conditions of high efficiency
266
LIQUID AIR AND THE
with the metal coil. It is not surpris-
ing- to hear that with a pressure of 200
atmospheres liquid air begins to collect
in about seven minutes. The apparatus
suggests one of Triplets early coils.
Another disposition is shown in the
last of the cuts, where the gas pipe is
coiled disk fashion, leaving room in the
center for introduction of a glass tube, C,
in which samples can be placed which
it is desired to subject to low tempera-
ture. The glass cap to prevent splash-
ing is seen in this cut also.
These simple jet experiments are a
good introduction to a study of the self-intensive
apparatus, whose use has excited so much interest,
both popular and scientific.
Taking the critical temperature of hydrogen as
31° C. absolute or —242° C. (— 403-6° F.), it will be
seen that the temperature of boiling air
( — 194° C., — 317-2° F.) is well above it.
— 194° C. is 80° C. absolute, so that boil-
ing air may be said to be two and one-
half times hotter than liquid hydrogen
at the critical point. It is not clear that
this is a perfectly fair way of looking at
it, however.
Wroblewski and Olszewski had con-
cluded that hydrogen had an abnormally
low critical pressure. Wroblewski gave
it a critical pressure of only 13-3 atmo-
spheres, which is about one-fourth that
of oxygen. The only trouble, therefore,
LIQUEFACTION OF GASES. 267
should be to get the temperature down. Dewar
attempted to liquefy a mixture of hydrogen with
two to five per cent, of air, and says that he obtained
solid air together with a very volatile liquid of low
density which he was not able to collect in a sepa-
rate vessel. Olszewski longed for a gas intermediate
in its critical point between air and hydrogen, to get
what has aptly been termed static hydrogen, or
hydrogen liquefied in quantity.
Accepting Dewar's view that hydrogen at 80° C.
absolute is two and one-half times as hot as it is at its
critical temperature, and taking air at two and one-
half times its critical temperature, we should find
that the liquefaction of hydrogen from the initial
temperature of boiling air would be equivalent to
the liquefaction of air from 60° C. (140° F.) or 333° C.
absolute. This figure is thus reached : The critical
temperature of air is taken at — 140° C. ( — 220° F.)
This reduces to 273 — 140 = 133° C. absolute. Two
and one-half times 133 are 333, which is the absolute
temperature, two and one-half times greater than
— 140° C. ( — 220° F.), and 333° C. absolute is equal to
333 — 273 = 60° C. (140° F.) It is possible to liquefy
air by the jet method from a still higher temperature
than this. Dewar found that starting with air at
an initial temperature equal to that of boiling water,
he could liquefy air in seven minutes by the pro-
cesses described.
It would, therefore, seem as if hydrogen at the
initial temperature of the boiling point of air should
be liquefiable by the process which liquefied air from
the initial temperature of boiling water.
Hydrogen was cooled a few degrees below this
268 LIQUID AIR AND THE
point, to — 200° C. ( — 328° F.) and was driven
through a fine aperture under a pressure of 140 at-
mospheres, but without result. A very little oxygen,
some few per cent., was mixed with the hydrogen,
and a liquid was obtained which contained hydrogen
in solution, but was principally oxygen. It gave off
hydrogen and oxygen in explosive proportions.
The experiment was now tried with the regenera-
tive coil in the first figure of the cuts, page 264. The
escaping gas cooled the coil, B, and the regeneration
brought about, apparently, a liquefaction of hydro-
gen. A liquid jet could be seen after the circulation
had continued for a few minutes, and a liquid in
rapid rotation in the bottom of the vacuum tube, D,
could be discerned.
The difficulty of recognizing a volatile, highly
mobile liquid, formed under such conditions, and so
very evanescent in duration, cannot be too strongly
insisted on. A stream of gas was rushing out of an
orifice at fifty times th': pressure of steam in an
ordinary boiler, a portion of it liquefied for a very
brief period, and then gasified. The violence of the
operation would at least tend to confuse quiet obser-
vation.
Dewar states that, owing to the low specific
gravity of the liquid and the rapid current of gas,
the latter impelled by a pressure of 140 atmospheres,
or about one ton pressure to the square inch, none
of the liquid in question accumulated. " Static hy-
drogen" was almost produced, the liquefaction was
destined to be soon accomplished, and in its proper
place (page 280) will be found described.
The jet system of cooling by impingement has in
LIQUEFACTION OF GASES. 269
several places been alluded to. Cailletet in early
days, unable to conceive of the possibility of using
liquefied gases by the gallon as refrigerants, sug-
gested the use of ethylene jets for cooling. It was
the chalumeau du froid^ or cold blast blowpipe, of
Thilorier.
Dewar tried his hydrogen jet as a refrigerant.
Liquid air and liquid oxygen were successively
placed in the bottom of the vacuum tube, Z>, so as to
cover the jet. In a few minutes, in each of the two
cases, about 50 cubic centimeters (3 cubic inches) of
the air and oxygen respectively were solidified into
hard, white solids like avalanche snow.
When the air was solidified by evaporation in
vacua, the product was a jelly ; but in the experiment
just described, the cold was so much more intense
that oxygen-ice and air-ice were produced. The
solid oxygen had the characteristic bluish color of
the liquid oxygen. Light reflected from it showed
in the spectroscope the characteristic bands shown
by light transmitted through liquid oxygen.
In the description of these experiments the Joule-
Thomson effect (page 297) was taken no cognizance
of. All was treated by Dewar as examples of cold
regeneration, not of internal intensification. There
is a very open question as to how important a role
the Joule-Thomson effect really plays in these cases.
Hydrogen, it will be remembered, does not present
the effect, but the reverse. On escape from pres-
sure under what may be termed Joule-Thomson con-
ditions— conditions adapted to bring out the Joule-
Thomson effect — its temperature rises. In the ex-
periment, as described by Prof. Dewar, the hydro-
2/0
LIQUID AIR AND THE
gen liquefaction is described as due to simple cold
regeneration. It would seem as if it was ren-
dered less powerful by the heating, or, as it may
be termed, by the negative Joule-Thomson effect
found to exist with hydrogen, unless, as Dr. Onnes
Dewar's Hydrogen Jet Apparatus.
believes, the negative effect is reversed at low tem-
perature.
The illustration shows the general scheme of
Dewar's more elaborate apparatus for cooling hydro-
gen by its own expansion. A is a cylinder charged
with hydrogen under high pressure. B and C are
LIQUEFACTION OF GASES. 2? I
vacuum vessels, each inclosing a coil of the gas de-
livery pipe. B contained solid or liquid carbon
dioxide. The vessel was closed and its interior, kept
under exhaustion so as to lower the temperature. C
contained liquid air. D is the self-intensive coil ter-
minating at G, where there is a pinhole aperture.
The first evidence of the intense cold in the freezing
of air to a hard solid led to the erection of a very
powerful apparatus, by means of which the liquefac-
tion of hydrogen was effected.
This liquefaction is the last great achievement in
the field we are studying. The subject, therefore,
will be dropped for a few pages in order to preserve
the chronological relations.
Air is always contaminated with carbon dioxide
gas, and the small quantity normally present, four
parts in ten thousand, which, however is subject to
considerable variation, suffices to produce a turbid-
ity in the liquefied product. Oxygen made as it
usually is, from potassium chlorate by ignition, con-
tains traces of chlorine, and this tends to produce
turbidity in the oxygen when liquefied.
There are cases where in a mixture of gases one
constituent liquefies while the other solidifies. It is
possible to purify a gas from some mixtures by
liquefying the mixture and filtering. In lecture ex-
periments with liquid air, it is usual to filter the
liquid in order to procure transparent samples to
show the faint blue color.
Gases, however, sometimes dissolve in other lique-
fied gases, just as they do in water. Soda water is a
solution of carbon dioxide gas in water. Thus liquid
air dissolves hydrogen. It is found that as much as
2/2 LIQUID AIR AND THE
twenty volumes of gaseous hydrogen may be dis-
solved in one hundred volumes of liquid air. This,
however, is not a large quantity. It rrust be remem-
bered that the one hundred volumes of liquid air
give when gasified about eighty thousand volumes
of gaseous or ordinary air such as we breathe.
We illustrate the apparatus with which the experi-
ments touching on this solubility of gases in liquid
air were made at the Royal Institution by Dewar.
B represents a cylindrical empty vessel of glass,
something like a pipette in shape. It fits into a
vacuum vessel, the joint between the opening of
the vacuum vessel and the neck of the tube, B, be-
ing made tight by perforated stoppers. Through
the central aperture of the cork or india rubber
stopper, which is large, a branch tube passes, and
through the center of this the neck of B, which is a
capillary tube, passes. The whole is made air-tight
by a perforated cork or india rubber stopper in the
branch tube, through an aperture in which stopper
this tube passes. A flask, A, contains liquid air, and
a siphon, H, is so arranged that it delivers liquid air
into the vacuum vessel, and keeps its level such that
the tube, B, is constantly covered with liquid air.
An a.ir pump is connected above the neck of the
vacuum vessel and keeps a high degree of exhaustion
over the liquid air in K. The tube, H, from the
flask, A, enters the vacuum vessel through the second
aperture in the rubber stopper which closes the neck
of the vessel in question.
The tube, /, leads to a gasholder full of air. This
gasholder is graduated so that the air which it de-
livers is measured. Under the influence of the in-
LIQUEFACTION OF GASES.
2/3
tense cold, air liquefies in the tube, B, coming from
the gasholder and passing through the tubes, C and
D, the lower one, C, charged with potassium hydrate,
the upper one, D, with pumice stone saturated with
sulphuric acid. Thus the air before it reaches B is
thoroughly purified.
Dewar's Apparatus for the Examination of the Least
Condensible Constituents of Air.
After forty minutes' operation with pure air the
body of the tube,' B, and the cool part of the capillary
tube were filled with liquid, showing that everything
delivered from the gasholder was liquefiable. From
two and a half to three feet of air were used in each
experiment. The capillary tube was so small and
274 LIQUID AIR AND THE
long that if only one volume out of 180,000 volumes
of gaseous air had been unliquefied, it could have
been detected. The first experiment showed com-
plete condensation or liquefaction.
To the gasholder of 283 liters capacity ( o cubic
feet) arid holding that quantity of air, one-half a liter
of hydrogen was added, which was in the propor-
tion of less than one volume in five hundred. The
experiment was repeated.
The tube, B, would not fill ; only four-fifths of its
volume was occupied by liquid, the other fifth was
occupied by gas.
At E is a stopcock of the variety termed three-
way. Turned in one direction, it connects B with 7,
C, and D, the air or gas supply. Turned in another
direction, it connects B with the tube, F. Hitherto
it had been turned so as to connect the air supply
with B. Now it was turned so as to shut off the air
and connect B with the tube, F. The temperature
was allowed to rise a little, so that the gas from the
upper portions of B bubbled up into F. The lat-
ter was originally filled with water. Its upper end,
not visible within the limits of the cut, was closed.
The gas thus collected was tested and proved to
be principally hydrogen.
Next air containing one volume of hydrogen in
one thousand volumes of air was tried, and a very
little hydrogen remained uncondenscd. Finally, one
volume of hydrogen was added to ten thousand vol-
umes of air, and this liquefied completely.
Therefore, one volume of gaseous hydrogen in one
thousand volumes of gaseous air can be almost com-
pletely liquefied. In the experiment, eighty thou-
LIQUEFACTION OF GASES. 275
sand cubic centimeters of air were condensed to
about one hundred cubic centimeters of liquid air,
and dissolved eighty cubic centimeters of gaseous
hydrogen. In other words, air liquefied at atmo-
spheric pressure dissolves about eight-tenths of its
liquid volume of gaseous hydrogen.
The apparatus just described was used for a most
interesting piece of work, the separation of helium
from the gas evolved from the water of the King's
Well at Bath, England. This element, first discov-
ered by spectroscopic observation in the sun and
named from that fact, was not known to exist upon
the earth. But some minerals were found to con-
tain it in small quantities, and the gas from the Bath
spring gave its spectrum. A good object for experi-
ment was desired, which would show how applicable
the method just described was for separation from
each other of gases of varying degrees of ease of
liquefaction.
The gas from the Bath spring contains a little over
one-thousandth of its volume of helium (0*0012 vol.)
The gasholder was filled with the gas, and the experi-
ment just described was repeated. The tube, B, col-
lected a liquid, not clear like liquid air, but turbid and
yellowish brown. The color was found to be due to
organic matter, probably of the petroleum family.
Tested with nitric acid, it gave the familiar odor of
nitro-benzoie or of artificial oil of bitter almonds.
This odor resembles that of the kernels of peach pits.
It is sometimes used for perfuming soap.
After an hour some 20 .cubic centimeters of gas
had collected in B above the liquefied gas. Seventy
liters of gas were liquefied.
2/6 LIQUID AIR AND THE
The liquid in the tube was nitrogen. By letting
the temperature rise, after properly turning the stop-
cock, E, the gas along with some nitrogen was col-
lected in the tube, F. The sample collected was
about one-half nitrogen and one-half helium.
The experiment was extremely satisfactory as
showing the practicability of using this liquefaction
method for separating traces of less condensible gases
from those which are more so. As Prof. Dewar
observes, a regular gas liquefaction apparatus could
be installed at Bath and made to produce any quan-
tity of helium, were there any demand for it.
In this class of experiment we see fractional con-
densation, long since applied in distillatory processes,
applied to gases. It is an interesting subjection of
the most elusive substances to processes hitherto
only applied to ordinary liquids.
A rather interesting demonstration of the action of
mixed gases when liquefied in presence of each other
was afforded by the liquefaction of oxygen in the
presence of an excess of hydrogen. The liquid, as
we have seen, could contain but little hydrogen. Yet
the gas given off by it contained so much that it was
explosive. In the evaporation, naturally a much
larger relative proportion of hydrogen evaporated
than of oxygen, so that the gas contained perhaps
over one-half its volume of hydrogen, while the liquid,
as we have seen, could contain but a little more than
a trace dissolved.
One of the recent triumphs of chemistry was the
isolation of fluorine. For generations of chemists it
had proved an element which could not be separated
from its compounds. It has most intense affinities
LIQUEFACTION OF GASES. 2//
for other elements, and attacks glass with much
energy. Moissan, a French chemist, succeeded in
separating it in the elemental state. In 1897 Mois-
san and Dewar, working together, liquefied it.
From theoretical considerations it appeared that
fluorine should be more difficultly liquefiable than
chlorine. Thus boron fluoride and silicon fluoride
are gases, the corresponding chlorides are liquids.
The same holds with many organic compounds—
those containing chlorine being liquid and those con-
taining fluorine being gaseous. This, obviously
enough, was taken as indicating that fluorine was
more difficult to liquefy than chlorine.
The experimenters made fluorine by electrolyzing
a solution of potassium fluoride in hydrofluoric acid.
The gaseous fluorine evolved was passed through a
platinum condenser tube which was cooled by solid
carbon dioxide mixed with ether. This was intended
to condense all impurities. It passed through another
platinum vessel filled with perfectly dry sodium flu-
oride and then into the liquefaction vessel.
One of the great troubles of fluorine, as a subject
for experiment, is that it attacks glass. For this rea-
son platinum vessels are used for accurate work with
it and its compounds. Lead stills and flasks are used
for rough work, and the natural mineral fluorspar
has even been suggested as a material for vessels.
The liquefaction vessel was a glass capsule into
whose upper part a platinum tube was soldered.
The tube from the fluorine evolution and purifica-
tion apparatus entered the outer tube and passed
down the annular space into the glass cylinder or
capsule. The latter was immersed in liquid o-rygen,
2/8 LIQUID AIR AND THE
which, boiling at atmospheric pressure, gave a tem-
perature of — 183° C. ( — 297-4° F.) The glass was
not attacked at this low temperature, and the fluor-
ine did not liquefy. Exhaustion was now applied
to the oxygen, and the reduction of pressure reduced
the temperature to about — 187° C. ( — 304-6° F.) A
dew of liquefied fluorine began to appear upon the
glass.
In the first experiments the platinum tube leading
out of the vessel had no cock. Upon closing it with
the finger, fluorine at once began to collect in the
glass capsule, which rapidly became partly filled
with it. It was a clear, very mobile liquid of yellow
color. The intensity of the color was stated to be
equal to that which would be given by a column of
gaseous fluorine one meter long.
The liquid was so cold as to have little chemical
power left. A number of substances were tried.
Silicon, boron, carbon, sulphur, phosphorus and
iron reduced in hydrogen could, after cooling with
liquid oxygen, be dropped into it without any reac-
tion. Ordinarily, fluorine would attack them vio-
lently. At the. temperature of — i8o°C. (—292° F.)
it attacked benzene and turpentine. It could not
separate iodine from potassium iodide. Hydrogen
burned upon the surface of the liquid when caused
to impinge thereon.
It was cooled to — 2io°C. (— 346° F.) by boiling
liquid air, in hopes that it ' would solidify, but it re-
mained liquid. By accident, some air got into the
capsule of liquid fluorine. It liquefied and floated
upon it, a colorless or faint blue liquid upon the
pale yellow fluorine. But, by passing a current of
LIQUEFACTION OF GASES. 2/9
fluorine through liquid air, a flocculent precipitate
formed. This was filtered out, and on heating ex-
ploded with great violence. In a subsequent experi-
ment the same layer of fluorine under the liquid
oxygen just described was formed by passing
fluorine to the bottom of a vessel of liquid oxygen.
Tvidences were found that liquid oxygen would
dissolve it under certain conditions, the fluorine be-
ing admitted, not to the bottom, but to the surface
of liquid oxygen. The subject remains obscure.
The specific gravity was determined by placing
in it different substances of known specific gravity
and observing which ones floated and which ones
sank. Ebonite, caoutchouc, wood, amber and methyl
oxalate were taken. The pieces were placed in the
empty tube, and fluorine was liquefied in it. Wood,
caoutchouc and ebonite floated, the methyl oxalate
sank, and amber was almost indifferent. This gave
it the same specific gravity approximately as that of
amber, or 1*14.
The amber could only be seen with difficulty, so
that the refractive index of liquid fluorine is almost
the same as that of amber.
On cooling it from —187° C. (—304-6° F.) to
—210° C. ( — 346° F.), it diminished one-eleventh in
volume. It possessed no magnetic features as far as
tested.
Its capillarity is less than that of liquid oxygen.
The relative heights to which it and other- liquids
rise in a capillary tube were determined, with the
following results :
Liquid fluorine.. 35
Liquid oxygen. . . 50
Alcohol 140
Water.. .220
280 LIQUID AIR AND THE
Water, therefore, rose about seven times as high as
fluorine.
May 10, 1898, is one of the classic dates in our
subject, for it was on this day that Dewar liquefied
hydrogen, and obtained it in quantity as a " static
liquid."
A very powerful train of liquefying apparatus had
been set up in the Royal Institution, its erection ex-
tending over a year's time. It weighed two tons
and contained 30,000 feet of piping.
Hydrogen was cooled to — 205° C. ( — 337° F.) at a
pressure of one hundred and eighty atmospheres.
The gas was allowed to escape continuously from
the nozzle of a coil of pipe, at the rate of ten or fif-
teen cubic feet a minute. When it is stated that an
ordinary gas burner burns about six cubic feet per
hour, it will be seen that hydrogen was used most
profusely. The jet issued into a doubly silvered
vacuum vessel, surrounded by another vessel, the
intervening space being kept at — 200° C. ( — 328° F.)
Soon drops of hydrogen began to appear, and in
five minutes twenty cubic centimeters had collected.
The goal was won. Static hydrogen lay quietly in
a vessel.
The jet then closed with frozen impurities from the
hydrogen. . One per cent, of the gas had been col-
lected in the liquid form.
A small glass bulb was weighed in the liquid and
gave a specific gravity of 0*08 — an amazingly low
figure. The end of a long glass tube sealed at the
bottom was placed in it, and at once became filled
with solid air. Liquid oxygen was placed in a tube
and immersed in it, when a blue solid was produced
LIQUEFACTION OF GASES. 28 1
from the frozen liquid. It was solid oxygen, or
oxygen ice.
A glass tube closed at its upper end was placed in
a vertical position with its lower open end immersed
in a vessel of mercury. It was so arranged that its
upper end could be cooled by liquid hydrogen. On
doing so, the mercury rose in the tube as the air
solidified, until it stood within a minute fraction of
an inch of the height of the barometric column.
If liquid hydrogen were placed in a double-walled
non-exhausted vessel, it froze the air in the inter-
space solid, and the inner vessel became coated with
a hoar frost or coating of solid air, literally of air-ice.
The liquid hydrogen manufactured its own Dewar's
bulb.
A metal rod dipped in it became so cold that, on
removal, liquid air fell from it in drops, liquefied by
the cold of the rod due to its immersion in the liquid
hydrogen.
A sample of the helium obtained by Dewar from
the gas of the Bath spring (page 275) was at hand in
a sealed bulb with a narrow tube attached to it. The
tube was dipped into the liquid hydrogen. Liquid
helium formed in it as a distinctly visible liquid.
As a control experiment, the same tube was put
into boiling air and no liquid formed. This showed
that the cold of boiling air was insufficient to pro-
duce a liquid from it ; the liquid hydrogen gave a
degree of cold sufficient to do it.
The boiling point of the liquid hydrogen in the
first experiments was determined by a platinum -re-
sistance thermometer. At o° C. (32° F.) this had a
resistance of 5-3 ohms. In the liquid hydrogen the
282 LIQUID AIR AND THE
resistance fell to cri ohm. From the observation the
temperatures of —238-2° C. (—39676° F.), —238-9° C.
(—398° F.) and —237° C. (—394*6° F.) were calcu-
lated on slightly differing bases. These temperatures
are about 8° C. (14-4° F.) higher than Wroblewski's
calculated temperature of boiling hydrogen, and
5° C. (9° F.) higher than that given by Olszewski's
calculation.
. In later experiments the following results were ob-
tained : The resistance of the platinum wire resist-
ance thermometer sank from 5*338 ohms at o° C.
(32° F.) to 0-129 ohm at the boiling point of hydro-
gen. This gave the boiling point as — 238° C.
( — 396*4° F.) The resistance of the platinum wire in
liquid oxygen was eleven times that of its resistance
in liquid hydrogen, both at atmospheric pressure. At
its boiling point the pressure of air, which is solid at
that temperature, is but O'OO2 millimeter of mercury.
This is one three hundred and eighty thousandth
of the normal pressure. The vapor density of hy-
drogen at the temperature of its boiling point is
eight times greater than at ordinary temperatures,
or about one-half as heavy as air at ordinary temper-
atures.
The critical temperature is about 50° C. absolute
(90° F. absolute) and the critical pressure is less than
fifteen atmospheres. The latent heat is about two-
fifths that of oxygen. The application of a vacuum
to liquid hydrogen, therefore, cannot lower its tern-
perature very much, compared with the cases of
other gases.
An approximate determination of the density was
made by measuring off ten cubic centimeters of the
LIQUEFACTION OF GASES. 283
liquid, and collecting and measuring the hydrogen
gas from it. The result was 0*07 — not far from that
obtained by weighing the glass bulb in "it. It is
about one-sixth that of liquefied marsh gas (0*41 ).
The light, evanescent liquid is, nevertheless, per-
fectly visible, has a denned meniscus, and can be
readily manipulated in vacuum vessels.
The atomic volume at the temperature of its
ebullition is 143 (oxygen=i37; nitrogen--=i6'6).
The gaseous hydrogen at this temperature has a
specific gravity of 0-55 (air=i). The ratio of the
specific gravity of the gas, compared to that of the
liquid at the ebullition point, is as i : 100 (oxy-
gen=i:255).
The specific heat of gaseous hydrogen and of
hydrogen occluded in palladium is 3*4 ; of liquid
hydrogen, 6-4. The specific heat of the liquid, per
unit volume, is 0-5, or about that of liquid air.
Liquid hydrogen affords a rapid means of obtain-
ing one of the nearest approaches to a perfect
vacuum which man can produce. We have just
seen that air is solidified by the cold of liquid hydro-
gen. A tube is filled with air and sealed. The end
of the tube is placed in liquid hydrogen. With sur-
prising rapidity the air in the tube solidifies and
collects in the lower end where immersed in the
liquid, and a vacuum, almost perfect, is formed in
the rest of the tube. An immersion of one minute
in never exceeded. The tube, while its end is still
immersed, is softened with the blowpipe flame above
the hydrogen vessel, or as near where it emerges
therefrom as possible, and under the effect of atmo-
spheric pressure it closes and is sealed off. Thus a
284 LIQUID AIR AND THE
vacuum tube is produced without pump or other
apparatus of similar function. The process is so
simple and efficacious that it would seem to give a
suggestion for the production of other vacuous ves-
sels, such as incandescent lamps. A. more easily
solidified gas could be substituted for air, and liquid
air could take the place of hydrogen. Sir William
Crookes, celebrated for his work on high vacua,
from whom the vacuum tubes used in high vacua
experiments are named, examined these tubes. He
found that a higher vacuum was produced than he
was in the habit of getting in his own tubes, after
several hours' work with the mercury pump.
On spectroscopic examination, the spectrum of
carbon and of hydrogen was obtained. Neon and
helium lines were also found. The carbon spectrum
is attributed to carbonates in the glass.
An actual trial was made to determine what low-
ering of temperature would result from reducing the
pressure under which the hydrogen boiled. As
has been already stated, no great reduction was
anticipated; not over 9° C. (16-2° F.) Under
an exhaustion of one inch of mercury, very
little lowering was effected. The extent of reduc-
tion due to the partial vacuum only amounted to
i° C. (r8° F.) Possibly the platinum thormometer
did not give the right result ; possibly the connec-
tions conducted heat ; possibly the resistance curve
of platinum cannot be relied on at such excessively
low temperatures.
With the liquefaction of hydrogen in bulk the
story of the liquefaction of gases culminates. The
date is but a few months before the period in which
LIQUEFACTION OF GASES. 285
this book was written. It seems a most appropriate
time in which to put together the long chronicle of
a hundred years' efforts to liquefy gases, and whose
final triumphs are no less Tripler's great buckets of
liquid air, made in the city of New York, and sent
off hundreds of miles by rail, than they are the few
teaspoonfuls of liquid hydrogen liquefied by Dewar
and his colleagues in the Royal Institution in Lon-
don.
Hydrogen has been treated as a metal. In its
liquefaction many expected that a metallic liquid
like mercury would result. But the product was
not in the least metallic, and was a non-conductor
of electricity, so that a much mooted question as to
the nature of hydrogen is at last settled.
LIQUEFACTION OF GASES. 287
CHAPTER XII.
CHARLES E. TRIPLER.
The life of Charles E. Tripler — His early experiments with
gas motors — Mechanical difficulties encountered — His
electrical experiments — Chemistry — His work in fine art
— Exhibition of his paintings — Return to the investiga-
tion of compressed gases — Liquefaction of air — He en-
deavors to utilize the low grade heat of the universe —
Simplicity of his apparatus — The plant — The compressor
— General plan of operations — Capacity of his plant —
How he transports liquid air — His lectures — Raoul Pictet
in Charles E. Tripler 's laboratory.
Charles E. Tripler was born in New York, August
10, 1849. From his early years he showed a great
fondness for mechanics and experimenting, which
fondness soon developed into practical work. In the
early seventies his attention was directed toward
the production of a motor to be driven by gas. He
experimented on an engine driven by ammonia. His
work was different from that of others in one im-
portant respect. The endeavor had been to actuate
an engine by the pressure of ammoniacal gas, and to
reduce its pressure by dissolving it in water.
This process Tripler wished to avoid. He desired
to work the ammoniacal gas in a continuous cycle
without having resource to solution. Gasolene and
naphtha were next tried, much trouble being expe-
rienced in those early days with the joints in the
288 LIQUID AIR AND THE
apparatus, high pressure work in engineering having
greatly developed during the last twenty-five years.
One of the objects was to produce a motor for use
on street cars.
Electricity and chemistry were now (1873-76)
taken up. Edison was at the same time engaged on
electrical problems, and Tripler left the field and
took up art.
An artist by nature, he painted and exhibited
paintings, and left his mechanical and scientific work
almost untouched for a few years.
About 1884 he worked on gold extraction and
amalgamation and then returned to his first love
and experimented with gases of many kinds, ethyl
chloride, methyl chloride, and at last with carbon
dioxide. During these researches he discovered the
principle on which his work on the liquefaction of
air has been based.
Nitrous oxide was the next gas to be experimented
with, and an explosion brought about during the
generation of the gas nearly cost the investigator his
life. His work, being at high pressure, and with
many gases, has always been attended with peril, and
the wholesale manipulation of liquid air is far from
safe, irrespective of the question of pressure and dan-
ger of explosion. All sorts of gases were made and
liquefied, and about 1891 air was liquefied.
The key to his life's work has been the effort to
use gases for motive power, Carnot's cycle giving
the clew to what he has desired to accomplish.
He desired to utilize the heat of the sun. If the first
chapters of this book have been followed out to their
conclusions, it will be seen that the utilization of the
LIQUEFACTION OF GASES. 289
low grade heat energy of the universe, in accordance
with Clerk Maxwell's dream, presents nothing of the
essentially impossible. This heat Tripler hopes to
utilize. If it is utilized, there will be a further de-
mand made upon the heat of the terrestrial system,
which will involve a reduction of temperature due
to the conversion of low grade heat energy into
mechanical energy. This involves a theoretical
loss of temperature by the earth and its atmosphere
from self-contained causes, and the loss would have
to be replaced by heat derived from the sun.
Perhaps the most striking feature about the Tripler
process, apparatus and plant is that there is compara-
tively little to be said about it. While Dewar, work-
ing on the lines laid down years before by Pictet and
assisted by liberal gifts from one of the London
guilds and from private individuals, liquefied gases
at vast expense, here in the metropolis of this coun-
try a private individual has erected a plant at his
own expense, and for years past has liquefied air on a
scale which Dewar and his associates never dreamed
of. In order to preserve air, Dewar devised his cel-
ebrated vacuum bulb, an apparatus of the highest
merit. Tripler took common tin cans, lined them
with felt, filled them with two to five or more gallons
of liquid air, and sent them off hundreds of miles by
rail.
In the reports of papers and discussions in English
scientific gatherings incredulity is still expressed, or
was until very recently, when the sending of liquid
air about in common tin buckets was spoken of.
In England, Dewar has excited the greatest enthu-
siasm by his lectures on liquid air and liquefied gases.
290
LIQUID AIR AND THE
The enthusiasm was deserved, and it is a hopeful
sign of the times that a popular audience can still be
so stirred to a high pitch of interest in a scientific
subject. But, meanwhile, Charles E. Tripler, in his
private laboratory, with boiler, air compressor and
simple liquefying apparatus, has repeatedly shown
liquid air, in quantities that
until recently scientists
would scarcely have be-
lieved possible of produc-
tion, has poured it out on
the floor by gallons to show
its rapid evaporation and
production of dense clouds
of condensed moisture, has
blown iron pipes to pieces
with it, and has permitted
physicians to try its effects
as a cautery upon patients.
Mr. Tripler's apparatus is
of the type which employs
no extraneous sources of
cold. All the liquefaction
is done by its own powers
and within its own system.
A steam boiler is installed
in one corner of the labora-
tory in which his plant has
been erected. This supplies
steam to a Norwalk straight line compressor. The
steam pressure is about 85 pounds to the square
inch.
The compressor is a steam engine with three com-
Pouring out Liquid Air on
the Floor in Tripler's
Laboratory.
LIQUEFACTION OF GASES.
29I
2Q2 LIQUID AIR AND THE
pression cylinders in line of the prolongation of the
axis of the cylinder. The piston rods run in one
line through the four cylinders. The engine is rated
at 90 horse power when working- at 150 revolutions.
For the work done in Mr. Tripler's laboratory the
rate is about 100 revolutions.
The stroke of the engine, and, consequently, that
of the four compression pistons, is 16 inches. The
steam cylinder is of 16 inches diameter, the first or
low pressure air cylinder is of io£ inches diameter,
the intermediate cylinder is of 6f inches diameter,
the high pressure, the last of the three, is of 2| inches
diameter. The pressure is brought up by three
steps. The first compression raises it to a pressure
ranging from 55 to 65 pounds above the atmospheric
pressure; the next compression, from 350 to 400
pounds; and the final from 2,000 to 2,500 pounds per
square inch. The areas of the pistons in the three air
compressing cylinders are in the ratio of 1 10 : 44 : 6?
the air pressures successively produced as 55 : 350 :
2,500.
The cut gives a diagrammatic representation of
the general arrangement of the apparatus in Tripler's
laboratory, and the cut on page 291 gives a view of
the interior. On the left is seen the boiler, and in
the background is the compressor. The three air
cylinders of the compressor are arranged in tandem
or in line with each other. Between the first and
second and between the second and third air cylin-
ders are surface condensers which cool the air.
Compression, as has been explained, heats a gas.
The air is drawn down from the roof of the build-
ing through a pipe, and goes through a washer
LIQUEFACTION OF GASES.
293
which removes the dust. This is a case containing
baffle plates over which water is kept trickling. It
is marked "duster" in the diagrammatic cut. The
294 LIQUID AIR AND THE
air then goes through the compressor with its cool-
ers and leaves the third cylinder at high pressure
and hot.
The heat is removed by a final cooling in a surface
condenser designated ' cooling tank " in the diagram.
The moisture in the cooled air is pretty thorough-
ly precipitated by the compression. There are some
traces of oil present, derived from the lubricating
oil of the pump. Such of this material as is carried
forward is removed in a separator, which is virtually
a steam-trap, and the air is ready for liquefaction.
The construction of the liquefiers has not been
fully divulged. The lower end of one is seen in the
cut on page 291. They appear as long felt-covered
cylinders. Inside the felt wrappings are cylindrical
cases containing coils of copper pipe. At the bot-
tom of the coil of pipe is a special valve, the inven-
tion of Mr. Tripler. The compressed air escapes
from the valve and, expanding suddenly, experiences
a drop in temperature. Some of the cooled air
works its way up through the chamber and cools the
coils of pipe. Thus there is established an intensive
or accumulating action. The air entering the lique-
fier at a normal temperature is cooled by the reverse
flow of expanded air. It escapes from the valve at
the bottom at a temperature which constantly grows
lower until air begins to liquefy, and collects in the
bottom of the liquefying chamber. Now all is in
working order, air is liquefying and collecting, and
in a short time liquid air can be drawn off by the
gallon just like water.
Three or four gallons of liquid air are produced
in an hour in the usual operation of the plant, but
LIQUEFACTION OF GASES. 295
power enough is present to produce far more.
Every part of the liquefiers is insulated with non-con-
ducting covering. Only the handles of the valves
protrude, and these become white with a thick de-
posit of hoar frost.
The diagrammatic cut gives a general idea of the
distribution of parts, but is not given as a representa-
tion of the plant in any sense.
One of the most remarkable things about Mr.
Tripler's work is its simplicity even in detail.
There is no refrigerant used, and nothing is to be
seen but the ordinary objects which meet the eye in
any steam plant. There are no cylinders of liquefied
ethylene or carbon dioxide. Even the compressor
is of a normal type. Yet in this apartment the most
impressive achievement in physics of the century is
repeated week after week, and air is liquefied by
the bucketful and handled as if it were so much
water.
Its transportation is interesting. No vacuum bulbs
are needed for this. A tin bucket is. wrapped with
boiler felt and is thrust into a larger one. The liquid
air is poured into the inner bucket, a piece of felt is
placed over the mouth, and the air is ready for re-
moval. In such buckets it has been taken hundreds
of miles.
In the cut on the next page are given sections of
two of the buckets, one holding twice as much as the
other. The scale is i-J inches to the foot.
Mr. Tripler has given many lectures on the subject
of liquid air, and in the next chapter are illustrated
a number of the experiments which he shows. But
his goal is the practical, and his lectures are merely
296
LIQUID AIR AND THE
a side issue and express only his deep interest in the
subject.
An interesting occasion was the presence of Prof.
Raoul Pictet at one of Mr. Tripler's demonstrations.
The American inventor tells of Pictet's enthusiasm
at witnessing the demonstrations executed with such
1
m
/&•
^&&SJ^Q#r£
^&^g¥&
Tripler's Buckets for Transporting Liquid Air.
prodigality of material. The originator of the cas-
cade or closed cycle system of liquefaction met the
originator of the self-intensive system only to be
delighted at his demonstrations.
LIQUEFACTION OF GASES. 297
CHAPTER XIII.
THE JOULE-THOMSON EFFECT.
First attempts at liquefying gas — Joule and Thomson and
their discovery — Coal a cheap chemical — Substitution of
mechanical for chemical energy — Sir William Siemens '
regeneration of cold — Self-intensive refrigeration — Nega-
tive Joule-Thomson effect — Mathematics of the theory —
Conditions of pressure for economical application.
The first attempts at liquefying gases were based
on the application of great pressure. This was at
once useless and unnecessary in many cases ; useless
because an insufficient lowering of temperature was
applied and the gases did not liquefy, and unneces-
sary because the high pressure was not needed, had
a sufficient refrigeration been applied. Cailletet,
and probably Pictet, got useful effects indirectly
from high pressures. By sudden release of high
pressure a great refrigeration was produced, the
temperature of the gas fell below the critical point
and it liquefied.
The discoveries due to Joule and Thomson that air
and most gases are not perfect gases, that there is
really no perfect gas, and that hydrogen is an ultra-
perfect gas, has already been spoken of on pages 60
et seq. The change of temperature in a given mass
or volume of gas brought about by letting it flow
under pressure through an orifice, an effect not to be
confused with cooling due to expansion, while so
298 LIQUID AIR AND THE
trifling as to have entirely escaped recognition by
Joule in his early experiments, has been taken as the
starting point for the operation of refrigerating ma-
chines. The movement, whether we accept the
theory of action offered or not, was in the direction
of purely mechanical production of cold, and hence
was in the direction of economy. Dewar speaks
often of the great expense of his liquefactions, in
effecting which a very large expenditure was in-
curred in the production of liquid ethylene alone, so
that the cost of this and of other refrigerants was
a large item of expense in the Royal Institution
work.
In general terms we may say that coal is the
cheapest chemical we possess. Could the old
time experimenters have seen the possibility of sub-
stituting coal for the expensive liquefied ethylene
and other gases, they would have been most de-
lighted. In the processes of liquefying air and oxy-
gen which we are now to describe this in a sense is
done. Air is liquefied by the application of power,
and neither liquid ethylene, solid carbon dioxide nor
other refrigerant is needed. Even coal may be
dispensed with, for the energy of a waterfall might
be utilized to produce liquid air.
As a general rule, it may be stated that the sub-
stitution of mechanical power for chemical and for
other special agents is one of the most impressive
movements of the age. The electric battery giving
way to the mechanically impelled dynamo is an ex-
cellent example of the movement alluded to. In the
field of refrigeration the substitution of a purely me-
chanical process for refrigeration by boiling liquefied
LIQUEFACTION OF GASES. 299
gases was to be greatly desired, and in the applica-
tion of the Joule-Thomson effect the possibility has
been claimed of effecting the substitution.
When gas expands under terrestrial conditions, it
practically always falls in temperature. It is not
easy to see how conditions could be established which
would expand a gas without such fall. This fact was
well known for many years, and over forty years
ago the idea of applying it to refrigeration and of
making it more effective by cold regeneration was
suggested. It was William Siemens who saw the
possibility of utilizing it by a regenerative process
for the production of still lower temperatures. It is
fair to presume that his mind was, at the period in
question (1857), deeply occupied with the subject of
the regeneration of heat, and the regeneration of
cold seemed a natural sequence of the other. He
simply thought of the cold due to the energy de-
veloped by an expanding gas. This development of
energy calls upon an equivalent quantity of energy
for its development, and in the case of an expanding
gas the energy which is called upon is the heat
energy of its molecules. This heat energy is con-
verted into mechanically exerted energy and dis-
appears as heat— therefore cold is produced.
Leaving out of account this refrigeration, we know
that, if a gas is expanded, there is another change in
temperature outside of and independent of the
natural cooling due to energy developed in expan-
sion. This is what we have termed the Joule-Thom-
son effect. The apparently slight refrigeration thus
produced is the principle claimed to underlie the
operation of two of the most prominent of the gas
300 LIQUID AIR AND THE
liquefaction processes now in use. Linde's and
Hampson's apparatus are the ones alluded to.
There is nothing of efficiency involved in the
small orifices or porous diaphragm as used in the
experiment. It is simply a way of localizing expan-
sion and of producing it. As it is an element of the
most practicable way of rendering possible the ex-
pansion of a gas from a high degree of compression,
it is always used, but there is nothing occult about it
as far as the valve or aperture is concerned, outside
of mechanical advantages.
The term self-intensive refrigeration is perhaps
etymologically preferable to regeneration. This pre-
ference would be based on the idea that the produc-
tion of cold is not, properly speaking, an operation
involving production, but destruction. Cold is the
negation of heat, and, properly speaking, cannot be
said to have an existence of its own. But William
Siemens, doubtless thinking over his methods of re-
generating heat, in his 1857 patent prescribes the
regeneration of cold.
The origin of the methods used by Tripler,
Hampson and Linde can be studied in the records of
the patent offices as well as in the literature of pure
science. •
The primary idea of the self-intensive process is
found in the Siemens provisional specification of the
English Patent Office. He simply contemplates
cooling air by expansion, thereby causing its heat
energy to disappear. This cooler air is caused to
act upon the entering air, and give it a lower tem-
perature before expansion, so that the cold grows
constantly more intense. But Siemens has no idea
LIQUEFACTION OF GASES. 30!
of utilizing the expansion through a small orifice,
which is the system so much employed at present.
The Joule-Thomson effect was not known at the
early date which we speak of.
In 1893 Tripler applied for and was granted a
patent by the English Patent Office for a gas lique-
fying process and apparatus. This most interesting
document gives a clear description with drawings of
an apparatus based on self-intensification for the pro-
duction of cold. The Joule-Thomson effect is not
appealed to in it.
It is far from certain that the Joule-Thomson effect
is the principal factor in the operation of modern
self-intensive gas-liquefying machines, even if we ad-
mit Onnes' theory that the negative effect which
obtains with hydrogen is reversed under more ex-
treme conditions. We are justified in attributing
especial importance to such utterances as those con-
tained in Siemens' early provisional specification,
and in Tripler's early patent, which is full and com-
plete and is illustrated by drawings.
The use of an aperture for expanding gas through
is more justly regarded as an expedient for readily
bringing about a great difference in pressure in a gas
or, what is the same thing, for causing a great expan-
sion and sharply locating it.
But whatever influence the Joule-Thomson effect
has, whether great or small, Linde and Hampson
have both invoked it as the principle on which their
machines operate. It is easily stated, and involves
in its study but little mathematics. In Cailletet's
and in Wroblewski and Olszewski's liquefactions by
release there was no thought of appealing to this
302 LIQUID AIR AND THE
almost trifling effect to account for the mists of
oxygen and other gases observed when they sud-
denly expanded. The cloud of moisture seen in the
receiver of a common air pump with the first strokes
of the pump were never supposed to be due to it.
It is not clear why it has to be invoked as the factor
in liquefying air by the gallon.
The theory may be thus stated :
If air be expanded through a fine orifice, the
change in temperature due to the Joule-Thomson
effect is thus calculated :
Fall in temperature = -
In this formula /2 is the pressure in atmospheres
before passage through the orifice or before expan-
sion, pl is the pressure after passing through it or
after expansion, Tl is the temperature of the gas
before passing through it in degrees Centigrade re-
ferred to the absolute zero.
The work which a pump has to do in forcing a
continuous circuit of air round and round through
/
this aperture varies with - This is because the
/
work of the pump depends on the ratio of pres-
sures on the front and back of the piston. The
greater the pressure in front in proportion to the
pressure back of it, the more work it has to do.
To get a good reduction of temperature, it is evi-
dent that the quantity/2 — j>1 of the first formula
must be as large as possible and the quantity T1 of
LIQUEFACTION OF GASES. 303
the same formula must be as small as possible. The
first of these is regulated by the proportions given
the different parts of the apparatus, the second quan-
tity grows smaller as the temperature of the gas to be
liquefied falls. In circulating apparatus, this tem-
perature, as we shall see, falls continuously, the longer
the apparatus is worked, until air begins to liquefy.
/
The ratio — may be kept small and the difference
/
{P — pl large by giving high values to /2 and /'; in
other words, by working at high pressures.
A formula often seems uninteresting, but if the
substitutions of real values for the letters are made,
it acquires concrete interest.
Assume that the air, in passing through the orifice,
falls 3*6 atmospheres in pressure, and assume that
we start with a temperature Tl=o° C.=2^° C. ab-
solute. The fact that the fall in pressure is y6
atmospheres makes /2 — pl=y6. Our formula now
reads :
Fall of temperature *-**• (fff)2=i° C. (1-8° F.)
This seems a very trifling fall of temperature.
But assume that the air is driven more vigorously
through the orifice until a difference of pressure of
ten atmospheres is maintained, then the formula
reads :
Fall of temperature = -V- (if I)2==278° C. (5° F.)
which is at least somewhat more appreciable. So it
follows that by changing the mechanical relations
we can produce falls of temperature of various de-
grees.
On inspection of the formula another thing be-
304 LIQUID AIR AND THE
comes evident. The lower the temperature before
passing the orifice is, the greater will be the fall in
temperature. To assume Tl to be — 91° C. ( — 131*8°
F.), which is in absolute degrees C. 273 — 91=182°
/289\2
C., the quantity — reduces to the factor 2*52 in
\T1I
round numbers ; so that if the gas, as it reaches the
diaphragm, can be got down to this temperature, the
fall in temperature will be greater in the ratio of
(l?t)2 : (fll)2==I*12 : 2*52> or l '• 2'2$> also in round
numbers. Hence, at this temperature, for the two
pressure differences we have taken, the tempera-
tures would be i° x 2*25 = 2*25° C. (4*05° F.), and
278° x 2-25 = 6-26° C. (i 1-26° F.)
The first substituted formula has been purposely
constructed so as to give a temperature fall in round
numbers of i° C. If there is a different pressure
drop employed, the fall of temperature due thereto
when Tl = 273° C. absolute or o° C. is found by
dividing the pressure drop expressed in atmospheres
by 3*6 and multiplying by unity. This gives directly
the fall in temperature.
Thus, if a fall of 10 atmospheres were to be as-
sumed, we have 10-7-3*6 = 278, which, multiplied
by unity, gives 278° C., as calculated by the second
substituted formula.
Assume now that we are working with a different
temperature, T1. Then we may divide it by 273
and square the product and divide unity with it, and
the result will give the degrees Centigrade of fall of
temperature at a pressure drop of 3*6 atmospheres.
Thus suppose the temperature T1 to be — 91° C.
LIQUEFACTION OF GASES. 305
This is 182° C. absolute, iff = f> which squared is
f . To divide unity with it, we invert and multiply,
which is expressed thus : f x I = 2-25. This is the
factor used in the third substitution example.
It is evident that with a formula for a fall of
temperature = ^6- (f fl)2 = i °, we can, by applying
thereto the two methods of calculation last described,
make it apply to any case. Thus, if we assume that
the pressure drop is 10 atmospheres and that Tl =
— 91° C., we have simply to multiply unity by one of
the factors already determined, and this product
must be multiplied by the other. These factors are
278 and 2-25 ; we have, therefore :
i x 278 x 2-25 = 6-255° C. (i 1-27° F.)
The same result could be reached by substitut-
ing directly in the equation
Fall of temperature =
4
These examples merely illustrate different ways of
reaching the same results.
The statement has been made that the power re-
quired to force air through the aperture varies with
/
- in which /2 is the pressure in the inlet side of the
/
aperture and/1 the pressure of the gas after it has
passed through it. The reason of this propor-
tion existing is due to the fact that gas is diminished
in volume by pressure. Thus, if a given weight of
air is to be pumped through an aperture by a pump,
it may be done at very low pressure or at high pres-
sure. At first sight it might be thought that at high
306 LIQUID AIR AND THE
pressure, when the pump is working- against a pres-
sure of fifty pounds to the square inch, more power
would be required than when it works against a
lower pressure. But, air being compressible, the
pump at high pressure has a less volume of air to
force through, and hence has fewer strokes to make.
The air which enters the suction end of the pump
may be looked upon as reinforcing its action.
Hence the higher its pressure is, the less work will
the pumps have to do. Hence the smaller/2 is and
the larger/1 is, the less work will the pump have
to do.
LIQUEFACTION OF GASES. 307
CHAPTER XIV.
THE LINDE APPARATUS.
Linde's apparatus — The simplest form of apparatus — Its
operation — Its storing of air at atmospheric pressure —
Avoidance of atomization and waste — Subdivision of
pressure-drop — Laboratory apparatus — A feature of ineffi-
ciency in it— Its power of liquefaction — Continuous oxy-
gen-producing apparatus — Date of Linde's first successful
use of his apparatus.
Linde's apparatus, which is described as utilizing
this small increment of cold, if the expression may be
allowed, and by constant summation of such incre-
ments bringing about a high degree of refrigeration,
caused much interest when its supposed principles
were first stated and its operations were first dis-
closed. The term self-intensive has been aptly coined
to describe machines of this type.
What the apparatus of the original Linde type does
is this : Air is pumped through a circuit of pipes ;
the pipe from the outlet of the pump, after going
through the given circuit, returns to the inlet, so
that the air under treatment goes constantly around
the same circuit. When a gas is pumped against
resistance, it is compressed or diminished in volume
and heated. The outlet pipe from the pump is kept
at a uniform temperature by cold water circulating
in contact with the outside of the pipe, like a surface
condenser.
308 LIQUID AIR AND THE
The air thus cooled is forced through a small aper-
ture, and the passage from high to low pressure, with
consequent expansion, causes cooling. Between the
water cooling apparatus and the aperture a long
length of pipe intervenes. The cooled air is carried
back to the pump so as to circulate around this pipe
on its way back, and it abstracts heat from the air
already cooled by the water. Hence the air reaches
the aperture constantly at a lower temperature,
but leaves the water condenser always at a uniform
temperature. The real cold production is done
after the air leaves the water condenser. The degree
of cold keeps increasing until liquid air drops from
the aperture and lies in the bottom of the apparatus.
By a cock it can be drawn therefrom like water.
It seems at first sight impossible that the small de-
crease of temperature, due to the imperfection of the
gaseous state as it exists in air, should be able to pro-
duce such refrigeration. What Hampson calls ther-
mal advantages are to be aimed at. The surface on
which the cooled air acts on its return must be
large, the material of the pipes thin. These elements
provide for a rapid cooling by the returning air
of the counter-stream on its way to the aperture.
The entire mass to be cooled must be as light as pos-
sible. The action of the pump is constantly heating
the gas by compression, and this heat is removed by
the water. The atmosphere surrounding the appara-
tus constantly heats the portions colder than itself
by contact. The colder portions, therefore, must be
protected from this action by thick jacketing or other
means. Concentric air spaces produce a good effect,
and doubtless if it were practicable Dewar's vacuum
LIQUEFACTION OF GASES. 309
heat insulation might be applied with excellent
effect.
Linde made quite a sensation by his description
of his apparatus, which, by purely mechanical means,
liquefied air, although his first results were far from
encouraging.
What is called Linde's simplest form of apparatus
is illustrated in the cut, and will be readily under-
stood, especially if the reader has grasped the very
simple general theory on which its operation depends.
It will be understood that the drawing is not a repro-
duction of the exact apparatus, but is diagrammatic,
being purposely made as clear as possible without
permitting detail to interfere with intelligibility.
^ P represents a pump which aspirates air from the
pipe, G, and forces it out, under pressure, through H.
The air forced out through // goes through a
complete circuit of pipes and returns through Gt
thus constantly and repeatedly going around the
circuit.
J is a water condenser or more properly a cooling
apparatus. It is a cylindrical vessel, and the air pipe
goes through it in a coil. Water enters at K and
emerges at Z, so that as the gas leaves the vessel it is
always at the temperature of the inflowing water.
The arrows show the direction of the current of gas,
and all is perfectly clear to the point, C. The arrows
might be taken to indicate that the gas, on reaching
C, goes down directly to G, but they do not indicate
this. The pipe, B, is of small diameter, and, without
any opening or break, runs straight on to D, is bent
into a coil, and descends to E and T. But from C to
F it is surrounded by a second pipe concentric with
3io
LIQUID AIR AND THE
it, and it is this outer pipe which is connected to
the pump suction by the vertical pipe extending
downward from C and ending in G.
The cylindrical vessel on the right is simply a non-
conducting casing or jacket to protect the pipes from'
the heating effect of the outer air. In the illustration
Linde's Apparatus for Liquefying Air.
the iptenoi of the coil is shown, a part of the pipe
being supposed to be broken away to show this.
In the course of the air in the pipes to the right of
the point, C, lies the soul of the apparatus. The
small pipe running down through the protecting
vessel terminates in the chamber, T. A valve, R, is
provided which may be opened or shut so as to reg-
ulate the pressure drop, and this valve constitutes
LIQUEFACTION OF GASES.
the aperture through which the gas passes and ex-
pands with attendant cooling.
The end of the pipe, E, enters the small airtight
box or chamber, T. From the chamber rises a
larger pipe, Ft which, just above the top of the
chamber, receives within it the smaller inlet pipe, E,
and winds up through the protecting vessel concen-
tric with the smaller pipe. On the second and third
turns from the top the interior arrangement of the
pipes is shown very clearly.
The operation is now clear. The air enters the
pump at Gy is forced through H and compressed,
thereby being heated. The heat is removed in the
cooling apparatus, Jt and the compressed air, at the
temperature of the water, goes on to D. There it
descends in the inner pipe of the double coil, expands
through R and is cooled thereby, passes through T
and up through F, the outer pipe of the coil. There
it cools the air in the inner pipe of the double coil.
The air, therefore, reaches the valve, R, at a lower
temperature than before, so that it is constantly fall-
ing in temperature, reaches R at lower and lower
temperatures, and eventually the critical temperature
of liquid air is reached and passed, and liquid air
begins to collect in the chamber, F, as shown in the
cut. By the faucet, V, it can be drawn therefrom as
required.
If air is liquefied in the apparatus, every cubic inch
of liquid represents about one-half a cubic foot of air
withdrawn from circulation in the apparatus. Once
the apparatus begins to liquefy air, it has to have new
material supplied it, just as a grist mill needs a sup-
ply of grain to keep the stones in operation. A pipe
312 LIQUID- AIR AND THE
at A connects with a second pump which pumps in
new air as required, so as to maintain an advan-
tageous pressure in the system — one which will give
an economical relation between the pressures on the
opposite sides of the aperture.
A minor yet important feature of this apparatus
is that the liquid air collects at atmospheric tempe-
rature, or thereabout. The effect is twofold. It
can be withdrawn much more easily than when it
has to be taken from a receiver in which it is sub-
jected to 50 or 100 atmospheres pressure. In the
latter case it rushes out, only controllable by the
faucet, and the mechanically atomizing effect plays a
part in wasting it and facilitating its loss by gasifica-
tion. But, stored under atmospheric pressure, it not
only is quietly withdrawn, as required, but, by vola-
tilization, it keeps its own temperature down. The
maintaining it in a quiet state and in bulk operates
to make it evaporate more slowly, the battle of the
squares and the cubes, as it has aptly been termed,
being involved. H
It is evident that to make the difference of pres-
sure/2— pl (page 302) large, recourse may be had to
the expedient adopted in steam engineering for ex-
pansion engines of high initial pressure. These are
constructed with two cylinders (compound engines)
or with three or more cylinders working in series,
the steam passing seriatim from one cylinder into
the next (triple, quadruple, etc., expansion engines).
Just as in these engines the expansion is divided be-
tween several cylinders, so it is practicable in self-
intensive refrigerating machines to force the air or
gas through several apertures, letting each one take
LIQUEFACTION OF GASES.
313
care of its fraction of the total difference of pres-
sures,/2—/1.
Linde has done this in a partial way in his labora-
tory apparatus, and the cut shows the modification
Laboratory Apparatus.
in question. If the description of the simple appa-
ratus has been understood, the drawing alone will be
almost self-explanatory. There are, however, vari-
ous refinements introduced in this machine which
need explanation.
314 LIQUID AIR AND THE
A double-barreled pump is used which takes in
air from the open room, the pipe on the right, with
the arrow pointing down it, being the intake. The
right hand pump cylinder pumps the air through
the coil in the water jacket, e, and thence it passes
into the cylinder on the other end of the pump. On
its way to the other or left hand end of the double
pump, it is joined by a stream of air from the inter-
changer or refrigerator, which air enters by the pipe,
P1. From the left hand pump barrel the air, now
twice compressed, goes through a second water
jacket, d, and by the pipe, P'2, passes to the left.
These water jackets cool the air but partially. In
order to more thoroughly cool it water is injected,
and at / is a trap which removes most of the water.
The air then goes through a coil in the small tank,
g, which is surrounded by ice and salt. This cools
the air thoroughly and removes the last of the water.
It will be remembered that in the first described
apparatus an auxiliary pump was used to supply
the deficiency of air, due to liquefaction of a portion
thereof. In the laboratory apparatus the right hand
pump barrel performs this function, compressing
the air to 16 atmospheres only ; the second or left
hand pump barrel, taking in the air from the right
hand barrel, and also the air from the pipe, P1, com-
presses it all to 200 atmospheres.
The air thus compressed we have followed to its
exit from the coil in g. Cold and dry, it rises to the
top of the refrigerating case, entering it at P2 and
going down a spiral pipe. This spiral pipe is the
inner one of a triple concentric coil, whose construc-
tion is shown in the small sectional cut in the upper
LIQUEFACTION OF GASES. 315
right hand corner of the illustration. It descends
through the interior coil to a, where it passes
through an aperture regulated by a valve. Just be-
low a is another valve, b. This valve is slightly
opened, so that, of the air which passes a, one-fifth
as near as may be passes b. The four-fifths of the
air which does not pass through b rises through the
annular space between the interior tube and the in-
termediate tube. This four-fifths of the air rises to
the top of the refrigerating chamber and goes back
to the pump by the pipe, Pl Pl. This circuit is com-
parable to that in the first described machine.
The one-fifth of the air which passes through b
has undergone a double expansion. It has expanded
through two apertures, a and b. A portion of it
when the liquefaction has begun passes on to the
annular space between the intermediate pipe and the
outside pipe of the coil, and, after passing through it,
escapes into the open air at the top of the chamber.
The outlet pipe is there shown leading from the out-
side tube up into the air. Three-quarters of it thus
escape, one-quarter is liquefied and collects in the
double-walled vessel, c. Thus, the air from the
pump, entering the inner pipe at P2, is cooled on its
descent by the expanded air in the intermediate
pipe. But this air is still further cooled by the con-
stant uprising stream of still colder air rising in the
outer pipe.
There is one peculiarity to be noted in the accu-
mulative cooling action. The air from the pump
entering at P2 is working in the opposite direction
to the colder air in the intermediate annular space
or pipe. This is the correct method. But the cool-
316 LIQUID AIR AND THE
ing effect of the air in the outer tube is differently
applied. This air rises, and cools in its rising the
air in the intermediate tube, which is also rising.
This is the wrong way of working, but its inefficiency
is lessened by the fact that the entire quantity of air
does not pass through the outer tube. It is only a
question of one-fifth multiplied by three-quarters,
which is three-twentieths of the original air. This
is the quantity which passes up the outer tube. It
operates, perhaps, more as a jacket than as a cooler.
The air, after it collects in the liquid state in the
vessel, c, can be withdrawn by opening the cock, //.
Enough back pressure is maintained in the vessel, c,
to force the liquid air out at //, exactly like water
from a soda water siphon.
It will be seen that the right hand pump barrel has
to supply not only the deficiency in air caused by
liquefaction of a portion of it, but has also to pump
in air to supply the loss of that which escapes into
the air after passing through the valve, b.
Another peculiar feature will be noticed. All of
the air is not twice expanded. The majority is only
once expanded, and all the liquid air which is pro-
duced is derived from the one-fifth of the total which
is twice expanded through a and through b.
A pressure gauge is mounted on top of the trap,
/, to enable the operator to maintain the proper
pressure.
This apparatus, with the expenditure of three
horse power, is credited with the production of
nearly one quart of liquid air per hour.
The makers of liquid air, confronted with their
great success, as yet scarcely know what to do with
LIQUEFACTION OF GASES.
317
their wonderful product. One of their projects is
to utilize it for the production of a highly oxygen-
ated air, as it may be termed, for the production
of a mixture of nitrogen
and oxygen which will
be very rich in oxygen.
The next illustration
shows in diagram how
Linde proposes to effect
this by a continuous pro-
cess. In the cut are
shown a double set of
annular or concentric
pipes, forming two coils
such as used in the first
described apparatus.
These coils are in paral-
lel with each other. The
air from the pump enters
both coils by the small
branched tube seen at the
top of the apparatus and
designated by a. It goes
down the two interior
tubes of the coils through
the valves, c and d, and,
leaving the outer con-
centric pipes, the tubes
unite to a single pipe, b.
Thence the single tube
passes through the liquid air vessel, S, and emerges
at the bottom. The air expands through the valve,
r\ and part of it liquefies and collects in 5.
Linde 's Oxygen-producing
Apparatus.
318 LIQUID AIR AND THE
When air is liquefied and allowed to stand, it gives
off nitrogen much more rapidly and in larger quan-
tities than it does oxygen. Hence, a gas rich in
nitrogen is given off by the liquid air in S, and this
gas rises through the annular space between inner
and outer pipe in the coil, which starts from the left
of the liquid air vessel.
The liquid air, constantly growing richer in oxy-
gen, passes out of a pipe leading to the right out of
the bottom of the liquid air vessel and, controlled by
the valve, r2, evaporates into the annular space of
the other coil. The nitrogenous gas in the one
annular space and the gas rich in oxygen in the
other annular space cool off the gas from the pump
so as to form the true self-intensive heat interchang-
ing system.
The two outer pipes are kept separate as they
emerge from the interchanger. One, marked n, de-
livers a product poor in oxygen. This may be allowed
to escape. The other, marked o, delivers a product
rich in oxygen, which may be utilized for many
technical purposes.
If the gases from the outer pipes of both coils are
allowed to escape, one into the air, the other into an
oxygen receiver, the pump will have to work upon
new air constantly. There will no longer be a ques-
tion of supplying a loss of a fraction of the air — all
will have to be pumped in during the operation.
Linde's first successful experiments were per-
formed in May, 1895. Fifteen hours' pumping was
required to liquefy air, and then he collected some
three quarts of liquid air per hour, containing about
70 per cent, of oxygen. He used in his interchanger
LIQUEFACTION OF GASES. 319
iron tubes over 300 feet long, r2 and 2-4 inches
in internal diameter respectively. His pump was a
carbon dioxide or carbonic acid gas compressor,
and he got from it a compression varying from 22
to 65 atmospheres. The liquid was crystal clear and
bluish in color.
The inventor's own words describe his apparatus
as eliminating heat from gas " exclusively by ex-
penditure of internal work." This internal work he
holds to be the work of separating the gas's own
sluggish molecules from each others' vicinity.
320 LIQUID AIR AND THE
CHAPTER XV.
THE HAMPSON APPARATUS.
Hampson 's apparatus — Its general features of construction —
The jet and regulating device — Thermal and mechanical
advantages — Data of its operation — Use of cylinders of
compressed gas instead of pumps — Application of pre-
liminary cooling to the air or gas to be liquefied.
The Hampson apparatus is the invention of Dr.
W. Hampson. It is very simple and resembles very
much the Linde apparatus, and it works precisely on
the same lines.
The cut shows a section of the apparatus. A
cylindrical case is lined with non-conducting mate-
rial. It contains three coils of pipes, each coil con-
sisting of a single range of pipes arranged almost in
the shape of a cylinder. The coils of pipe are laid
in what may be termed the grooves of helices or
screws, formed by winding partitions whose course
is parallel with the axes of the coils of pipe, so that
the section of the apparatus shows the circular tube
sections, each in a little square. The perspective
view of the end of the innermost coil c n page 322
shows how the pipes and partitions are disposed.
The air enters by the small tube at the upper right
hand portion of the case. It goes down the long
outer helix, passes to the bottom of the intermediate
one, and rises through its coils to the top. Here it
LIQUEFACTION OF GASES.
321
passes into the central coil and descends to the bot-
tom of it, near the lower end of the liquid air
reservoir. The air here issues -=^
through a jet into the body of
the apparatus. It follows the
course of the helically bent
pipes ; first up the center, then
down the intermediate cham-
ber, and then up the exterior
chamber, escaping1 at the larg-
er pipe. Its course, it will be
observed, is exactly contrary
to that followed by the air on
its journey within the pipe.
The helical partitions guide
it on its return course.
The jet through which the
gas expands is shown in the
next cut. Its delivery capa-
city is regulated by screwing
toward its face or away from
it the flat, or nearly flat, p:ece
shown. The smaller its deliv-
ery capacity at a given pres-
sure, the greater is the differ-
ence of pressure or degree of
expansion which it establishes
at any pressure.
In illustration on this page,
showing the internal arrange-
ment of the coils, it will be
Hampson's Gas Lique-
faction Apparatus.
seen that the upturned jet points to the center of a
threaded aperture, a pipe from which extends to the
322
LIQUID AIR AND THE
top of the apparatus. Through this aperture a long
stem passes, with a screw near its bottom and an
almost flat end. By screwing the rod up or down,
the flat end is brought near-
er to or withdrawn from the
jet, as described, the deliv-
ery of the aperture is made
greater or less, the whole
operating as a regulating
valve, and, there being no
interior parts, the chance of
any obstruction is minim-
ized. The valve rod is
shown in place in the cut
showing the full apparatus.
The pipes are made as
thin as possible, in order to
facilitate rapid and efficient
cooling. The compressed
and the expanded air are in
finely subdivided volumes,
so that they readily inter-
change temperatures, and
the long and devious course
in opposite directions, fol-
lowed by the two divisions
of the air, conduces to the
same end.
The action has been fully
explained already in the
description of the Linde
machine. The compressed air expanding becomes
cool. The cooled gas following the coils cools the
Jet, Regulating Apparatus,
and Regenerative Coil
of Hampson's Gas Li-
quefaction Apparatus.
LIQUEFACTION OF GASES. 323
air within them. The temperature constantly falls,
and presently liquefaction occurs. The liquid air
collects in the reservoir below the main case.
The apparatus is operated by a compressor or by
the use of cylinders of compressed air.
The compressor must deliver air at a pressure of
80 atmospheres or over. An engine power of 3*5
horse power is required to drive the compressor,
and about 1*2 quarts of liquid air are produced in
an hour. No preliminary cooling is required.
If the compressor delivers air at a pressure of
120 atmospheres, air begins to liquefy in 16 minutes ;
if at a pressure of 130 atmospheres, only 10 minutes
are required.
If a cylinder of compressed oxygen is used instead
of the pump, the conditions are less favorable, as the
pressure constantly falls. Cylinders adapted for the
purpose can be procured. When such are employed,
an auxiliary cylinder of liquid carbon dioxide is
needed. This is used to cool the apparatus prelim-
inary to the admission of oxygen. The latter is
compressed to 120 atmospheres. One hundred and
twenty-five cubic centimeters can be collected there-
from.
The preliminary cooling by the carbon dioxide is
effected by passing the gas, intensely cold from its
gasification, in at the bottom of the apparatus, so
that it follows the general path followed by the
escaping air or oxygen in the regular operation of
the apparatus.
It will be seen that the idea of circulating the
identical air over and over again is not carried
out. All that does not liquefy escapes. But this is
324 LIQUID AIR AND THE
merely a detail. If oxygen or any expensive gas
were being condensed, the cheapest way would be
to use it over and over again, and this could readily
be done by a compressor with its inlet connected
to the outlet of the apparatus.
There is one important point to be considered in
working with a compressor as contrasted with the
use of a cylinder of compressed gas or air. The
action of the compressor heats the gas or air; so
it is advantageous to cool it by water, or otherwise,
before admitting it.
But if a cylinder of compressed gas is used, there is
no heating. There is even a reduction of temperature,
due to expansion ; so that an advantage is gained.
This applies to any similar liquefaction apparatus.
In Dr. Hampson's laboratory apparatus the liquid
air or oxygen can be withdrawn from its recipient
by siphon, or the receiver can be removed with its
contents by unscrewing a vulcanite cap at the bot-
tom of the apparatus.
The disposition of pipes varies somewhat in differ-
ent types of apparatus, but the same principle is fol-
lowed in all of them. The great object to be attained
is lightness of the interchanging system of pipes, in
order to increase thermal conductivity.
LIQUEFACTION OF GASES.
325
CHAPTER XVI.
EXPERIMENTS WITH LIQUID AIR.
Experiments with liquid air — Formation of frost on bulbs —
Filtering liquid air — Dewar's bulbs — Liquid air in water
— Tin made brittle as glass — India rubber made brittle —
Descending cloud of vapor — A tumbler made of frozen
whisky — Alcohol icicle — Mercury frozen — Frozen mer-
cury hammer — Liquid air as ammunition — Liquid air as
basis of an explosive — Burning electric light carbon in
liquid air — Burning steel pen in liquid air — Carbon
dioxide solidified — Atmospheric air liquefied — Magnet-
ism of oxygen.
We shall now describe some of the lecture experi-
ments with liquid air. These are generally repro-
ductions of experiments shown
by Charles E. Tripler at his lec-
tures and demonstrations. For
most of the illustrations our
thanks are due to the Scientific
American and to McClures Maga-
zine.
When liquid air is poured into
a glass flask it boils energetically,
and the outside soon becomes
covered with hoar frost, and
clouds of moisture condensed
from the atmosphere descend
from it. From its mouth the
same cloud is seen apparently
326
LIQUID AIR AND THE
escaping. But this cloud has nothing to do with the
liquid air itself. It is simply the moisture of the
atmosphere condensed by the cold of the air as the
latter evaporates from the liquid state.
By courtesy of McClure'a Magaiine. Copyright, 1898, by The S. & MeClure Company.
Filtering Liquid Air — Frost-coated Bulb.
The above cut shows the filtration of liquid air
into a Dewar bulb. Ordinary filtering paper is em-
ployed, and the solid or cloudy matter, such as solid
carbon dioxide, is effectually removed, and a beauti-
LIQUEFACTION OF GASES.
327
fully clear bluish liquid drops into
the bulb. The bulb on the right is
one just showing a coating of hoar
frost.
If a Dewar bulb is substituted
for the flask, the air lies compara-
tively quiet. In a good bulb only
one or two tiny threads of bub-
bles rise through the liquid, re-
minding the observer of cham-i
pagne whose effervescence has
nearly exhausted itself. On first
introduction the liquid air may be
quite agitated and steam may ap-
pear escaping from the neck.
On dropping liquid air into a flask of water, the
action is very violent. The air at first is lighter
than water, but it grows heavier as it loses nitrogen.
It sinks, after a little, partly gasifies, floats up, and
forms ice about itself, and at last disappears. A
larger vessel of water than is indicated in the cut
may be advantageously used.
The small cut gives an almost
conventional representation of
I what occurs when liquid air is
• poured into a narrow-necked
flask of water. In the actual
experiment, which is best per-
formed in a wide-mouthed bottle
of water, there is much agitation
and disturbance. The globules
rush about, vapor forms about
the mouth of the vessel, and
328
LIQUID AIR AND THE
the appearance which is so well presented in the
cut below is seen.
Many substances are made brittle by immersion
By courtesy of McClure's Magazine. Copyright, 1898. by The 8. S. MoClure Company.
Liquid Air in Water.
in liquid air. We have seen that lead becomes elastic
and that the pitch of a tuning fork is raised by im-
mersion. It is quite possible to make a tuning fork
LIQUEFACTION OF GASES.
329
out of soft metal which will become resonant, on
immersion for a few seconds in liquid air. A tin dip-
per after a few minutes' immersion becomes almost as
brittle as glass and is broken by a blow.
India rubber, such as children's balls are made
of, becomes almost as brittle as glass after floating
a few minutes in it. The cut showing a ball in
liquid air brings out another point of interest — the
formation of the cloud of moisture and its descent.
The air which volatilizes from the liquid air is very
cold and pours over the top of the vessel like water
and carries the cloud with it. The cloud is com-
posed of moisture condensed from the outer atmo-
sphere.
330
LIQUID AIR AND THE
The freezing of an alcoholic liquid gives a good
proof of the low temperature of liquid air. Liquid
air is poured into a glass of whisky or alcohol, and
the liquor freezes. The cut shows a sort of icicle
By court««y of Mefflvre't Magazine. Copyright, 1898, by The 8. S. McClure Company
Alcohol Icicle.
of alcohol lifted up on the end of a roa out of a
glass of alcohol thus frozen.
A test tube containing liquid air is placed in a
glass of whisky. The latter is soon frozen solid,
and can be lifted out of the tumbler in a lump. On
standing a few minutes after the air has evaporated,
LIQUEFACTION OF GASES.
331
the test tube can be taken out, and a sort of tumbler
whose material is frozen whisky is
produced.
Mercury is often frozen by liquid
air as an example of its frigorific
power. The experiment as shown
in the cut consists in freezing a bar
of mercury in a mould by immers-
ing it in liquid air. Screw eyes
are frozen into the ends of the bar.'
A heavy weight is sustained. A
striking presentation of this experi-
ment has been effected by a man
hanging from such a bar of mercury. ,
Another example of the effect of cold
upon mercury consists in making a
tuning fork out of it. It is easy to
see that the changes which may be
rung upon this phase of low tem-
perature are very numerous.
Another experiment consists in
casting a hammer head out of mer-
cury. A mould is prepared with a
handle thrust into it, and mercury is
poured in. Liquid air is poured
upon the mercury. After a few min-
332
LIQUID AIR AND THE
utes' standing the mercury freezes so hard that it can
be withdrawn from the mould, and a nail can be
By courtesy ot JfeO/f«'« Magunne. Copyright, 1898, The S. S. McClure Company.
driven with it. We are not
aware that a mercury nail has
ever been driven into wood.
The gasification of liquid air
is nearly irresistible in the pres-
sure it produces when confined.
A quantity is poured into a metal
cylinder closed at the bottom
and a plug of wood is driven
into the top. In a few seconds
the plug is expelled as if by the
explosion of gunpowder, with a
loud report.
If a piece of paper is saturated
with liquid air and lighted, it
burns with much energy. The
longer the liquid air has been
kept, the more violent is the
LIQUEFACTION OF GASES.
333
combustion. The standing of the air causes it to
grow richer in oxygen. A piece of boiler felt, which
ordinarily cannot be made to burn, if saturated with
liquid air rich in oxygen, burns most brilliantly, and
if liquid oxygen is used, almost explodes. This is in
the air. If confined, a violent explosion ensues.
334
LIQUID AIR AND THE
An electric light carbon brought to a red heat and
plunged into the liquid burns beneath it. The car-
bon dioxide formed by the combustion remains in
great part in the liquid, freezes
solid and sinks to the bottom.
A steel pen or a watch
spring can be burned in liquid
air which has been kept stand-
ing a few minutes. A bit of
sulphur may be placed on the
end of the steel and ignited to
start the combustion. An in-
teresting variation on this ex-
periment is to place the liquid
air in a tumbler made of froz-
en whisky, as described on
Page 33°- The pen or watch
spring is burned in this. The white heat of the burn-
ing pen, the intense cold of the air, and the alcoholic
liquid hard frozen form a set of incompatibles which
it would be hard to equal. The
combustion of steel, a metal once
supposed to be incombustible, is
occurring more vividly than that
of the most familiar inflammable
substances and in a vessel made
of a frozen liquid once supposed
to be incapable of congeal-
ment. The material of the pen
is practically that out of which
grates and stoves are made. The material of the
tumbler is approximately one-half alcohol, which lat-
ter liquid has long been used to prevent freezing.
LIQUEFACTION OF GASES.
335
A kettle of liquid air placed on a cake of ice boils
actively because of the heat of the ice which supports
By courtesy of McClure't Magazine. Copyright, 1398, by The S. S. MftClure Company.
it. If the boiling is not
rapid enough, it may be
accelerated by adding ice
water or even a lump of
ice to the kettle. This
shows that ice is hot.
If carbon dioxide gas
is directed by a jet upon
liquid air, it is liquefied
and also forms carbon
dioxide snow.
336
LIQUID AIR AND THE
Bat far more impressive than this is the experi-
ment illustrated in the diagram, which is self-explana-
tory. A tube of liquid air is connected to an air
pump and exhausted. The cold is so intense that,
after a few minutes, liquid air drips off the outside of
Vacwrrt
Outside Covered
with Snow
(Moisture in Air)
&.
a**-%!
and Dropping \ f '/,
the tube. This is the air of the atmosphere reduced
to the liquid state by the intense cold of the tube,
due to the boiling of the air within it.
The phenomenon reminds us of Dewar's experi-
ment with liquid hydrogen, whose cold was so
intense that it liquefied the atniospheric air. It is
LIQUEFACTION OF GASES.
337
also useful in bringing before us the dependence of
liquefaction upon temperature and its independence
of pressure.
Oxygen was discovered to be diamagnetic by
Faraday. A tube with outlet is filled with liquid
air and is suspended by a thread as shown. A pow-
erful magnet attracts it as if it were a bar of iron or
steel.
This is an incomplete presentation of the experi-
mental side of our subject. Changes in colors of
chemicals and many other phenomena can be shown.
The description falls far short of the actual witness-
ing of the experiments.
338 LIQUID AIR AND THE
CHAPTER XVII.
SOME OF THE APPLICATIONS OF Low
TEMPERATURES.
Frigotherapy — The frigorific well — Pictet's experiment —
Effects of the first trial of the system — Medical uses of
liquid air — Critical point as test of purity of chemicals —
Purification of chemicals by low temperature crystalliza-
tion— Low temperature distillation — Regulation of chemi-
cal reactions by cold — Liquid air explosives — The princi-
ple of their action — Liquid air in electric power trans-
mission— Liquid air as a reservoir of energy.
Prof. Raoul Pictet has during the last few years
given much attention to the uses of the intense cold
produced by the application of liquefied gases. The
purification of chemicals, the testing of the same for
minute quantities of impurities by intense cold and
by the observation of the critical point, and the
regulation of reactions, are included in the scope of
his work. Another of the uses to which he pro-
posed to put the application of intense cold is the
treatment of disease.
He conceived the idea that simple exposure of the
system to a very low temperature for a short time
might be productive of important effects. The
human system in the Arctic regions has endured
very low temperatures without any effect upon the
personal hygiene as far as discernible ; but it re-
mained to be seen whether, by descending far below
LIQUEFACTION OF GASES. 339
these natural extremes, a constitutional effect could
not be produced.
He constructed what he termed a frigorific well, a
small chamber, double walled, and lined with thick
non-conducting material, to protect the subject from
contact with the walls or floor. Such well was
about 6 feet deep and 2 feet in diameter. By use of
the cold derived from the liquide Pictet (page 169)
the temperature within the well could be reduced to
— 1 10° C. ( — 1 66° F.) A foot stool was placed upon
the floor. This was so arranged that the patient
could stand upon it, with his head in the open air. i
A woolen cover was thrown over his shoulders, so
that the head alone emerged, and the rest of the per-
son was immersed in the chilling atmosphere as if in
a cold bath. The clothing was not removed. The
chill penetrated it readily.
The effects of the immersion were very marked.
The body had to maintain its heat, and this can only
be done by a more vigorous process of oxidation.
As Prof. Pictet expresses it, the body becomes auto-
phage or self-devouring. The temperature taken by
a thermometer in the mouth rises in amount from
0-2° to 09° C. (0-36° to r6° F.) The temperatures of
the human body, it will be remembered, are always
expressed in this country in Fahrenheit degrees, so
that the above temperatures are expressible as
98'760-ioo0 F., taking 98*4° F.° as the average human
temperature.
A slight feeling of epigastric constriction is some-
times felt by the subject, a slight momentary paraly-
sis in the lower extremities may be experienced, but
all is quickly succeeded by a feeling of general in-
340 LIQUID AIR AND THE
vigoration. A reaction generally occurs before the
patient leaves the well.
After a while the temperature falls below the
normal, and a slight vertigo may appear and the
pulse may slacken.
A two hours' exposure proved fatal to a dog.
Pictet himself reports that in his own case he
'effected a remarkable cure by the use of the cold
well. He had suffered for years with stomach
trouble of the dyspeptic type, and resolved to try
the effect of extreme cold upon himself. His respir-
ations were at the rate of fifteen and one-half per
minute ; his pulse beat at a frequency of sixty-three.
He descended into the cold well, wearing a heavy
wrap. A plank lay upon the bottom for him to
stand upon. In order to keep, in motion, he lifted his
feet successively six inches high, with a frequency of
forty-two per minute. For four minutes no especial
sensation was experienced. After five minutes, or
thereabout, an indefinable sensation was felt, and a
desire for nourishment appeared, marking the begin-
ning of what he terms a frigale. The pulse beats
rose in frequency to sixty-seven per minute, and the
respiration to nineteen. Each respiration was deeper
than usual.
After eight minutes' exposure he emerged, feeling
a sort of prickling sensation all over the body, but
no cold affected the skin. A well defined hunger
was present, almost disagreeable in its craving ef-
fect.
On walking homeward, after two or three min-
utes a reaction set in, exceeding in intensity that due
to a cold bath. The body seemed penetrated by a
LIQUEFACTION OF GASES. 341
myriad of fine needles. He states that this expres-
sion gives but a feeble idea of the physiological con-
sequence of the restoration of the normal circula-
tion. The reaction lasted at least fifteen minutes.
This was on February 23, 1894. He states that
on that day, for the first time in six years, he ate a
full meal with enjoyment.
During February and March of that year he made
eight experiments in the descent into the cold well.
The periods varied from eight to eleven minutes
each. The same sensations and reactions accom-
panied each trial. He gained weight rapidly after
the treatment, and found his health radically im-
proved.
In the year 1895, at Geneva, Pictet was invited to
exhibit his work before the National Exposition.
Among other things, he installed two cold wells
which could be brought to a temperature of — no0
C. (—166° F.)
The apparatus was placed in charge of two physi-
cians, Drs. Cordes and Chossat.
The wells were thoroughly protected by fur.
They were entered by a ladder or the patient was
lowered into them by ropes. Footstools of various
height were provided, so that patients, whether tali
or short, could be properly immersed. A woolen
covering was provided for the shoulders.
The working temperature rarely rose above
— 90° C. ( — 130° F.), and was often much lower.
It became quite the fashion to take a cold air bath.
So many presented themselves that the physiological
examinations were somewhat restricted. The desire
on the part of the management, however, was to
342 LIQUID AIR AND THE
facilitate the trial of the cold air wells by as many
patients as possible.
The patients were examined carefully in many
cases ; the temperatures were taken before and after
an exposure of ten or twelve minutes. In a few
instances the exposure exceeded fifteen minutes.
Some visitors descended only once, others a dozen
times.
Full reports on the subject will be found in Science
Frangais of November 6, 1896, and a report was pre-
sented to the Medical Academy of Paris by Dr.
Cordes at its meeting on October 29, 1897. Finally,
a most elegant presentation of the subject is given in
Prof. Pictet's book " La Frigotherapie, ses Origines,
son But," Paris, 1898. Curves indicating the changes
of pulse frequency and of temperature, with other
observations for ninety-seven cases, are given.
A method of quickly applying frigotherapic
treatment locally is due to Dr. Ribard. He uses
solid carbon dioxide alone or mixed with ethyl
chloride as the source of cold. This he applies
locally to the skin, protected by felt.
Dr. G. Fish Clark, of New York, writes that he
has removed cancer, certain forms of bunions, corns,
warts and superfluous hair by means of this agent.
The tissue, when the air has thoroughly worked
upon it, is practically cut off by means of a tempo-
rary status in the circulation of the blood. The cir-
culation is riot renewed if a certain amount of care,
obtained by experience, is taken, as may be indicated
in each individual case. The parts beneath the mor-
bid tissue or morbid growth not affected by the low
temperature of the liquid air are held intact, and use
LIQUEFACTION OF GASES. 343
their circulatory system by means of anastomosis and
returning of arterial blood (after it has become deox-
idized) to the veins by means of infiltration through
the interstitial spaces. This process forms a new
skin surface under the morbid and frozen surface.
The result is an upheaval of the super-tissue, which,
as it dries and shrinks, eventually falls off like a scab.
The process of applying must be studied, and it is
dangerous to place it in inexperienced hands, as the
freezing of vital organs, the danger of involving large
distributing arteries and veins, and the involvement
of osseous tissue, must be avoided. It must be de-
termined accurately by the physician how deep an
application is going in a certain interval of time.
From his own observation, he has failed to draw
the same conclusion as to its effect upon bacteria as
M. D'Arsonval, Paris, has arrived at. He has, as far
as he has investigated, found an utter destruction of
microscopic life. He has not, however, experimented
with the bacilli D'Arsonval used. He affirms that \j
he has the greatest faith in liquid air as a means-
whereby humanity will receive great aid, and that in
many cases where the knife is now used this agent
will be found a most welcome substitute. The pain
in its application is at no time sufficient to require
an anaesthesia, it is complicated with no hemorrhage,
and the patient, after its proper application and
dressing, feels no additional inconvenience. " If by
inventing this process of manufacturing liquid air
Mr. Tripler has accomplished nothing else than this,
his name will be treasured at least in medical his-
tory as that of one of its most valued contributors."
Pictet has applied a curious observation which he
344 LIQUID AIR AND THE
made in determining whether chemicals are pure.
He found that an infinitesimal amount of impurity,
while it affected the boiling point very little, would
make a difference from ten to sixty times as great in
the temperature of tne critical state.
An apparatus was made by which a group of tubes
of various liquids could be heated to known tempera-
tures under observation. The disappearance of the
meniscus was taken as indicating the critical state,
which was supplemented by the nebulous effects
which occur at the same point.
To chloroform were added a few drops of alcohol.
The boiling point was barely affected, but the critical
temperature was changed several degrees. A num-
ber of other chemicals were tried with analogous
results. For a certain class of substances, therefore,
a delicate test of purity exists in the determination
of the critical point.
The great degree of cold which the liquefaction of
gases puts in the chemist's hands extends an old
time method of purification to new fields. For gen-
erations past crystallization has been the great agent
in purifying salts. If a chemical salt is dissolved in
water and the solution is evaporated down until it
becomes a relatively strong one, a point is often
reached at which the dissolved substance tends
to separate. With the majority of salts this point is
attainable. If the strong solution is left to stand,
the salt will gradually separate in crystalline form.
The phenomena above described in a few words
naturally do not occur with all substances, not even
with all soluble substances. Again, the phenomena
are not restricted to solutions in water ; they may
LIQUEFACTION OF GASES 345
occur with other solvents. But water is the great
solvent, and we are more familiar with crystalliza-
tions from water than from other substances.
In all nature there is no more wonderful example
of mathematical exactitude than that supplied by
the laws of crystallization. The forms of the crystals
are based on exact laws formulated originally by
the Abbe Hauy.
The fact that a crystal is an exact, mathematically
determined form almost implies that when a sub-
stance forms a crystal it must be a pure substance.
If the substance dissolved were dirty and impure,
crystallization, should it occur, would have at least
a tendency to purify it.
An impure substance is dissolved in water, is crys-
tallized therefrom, the crystals are removed arid
drained from the liquid — mother liquor, it is called
— and are found to be much purer than was the orig-
inal substance. They may be redissolved and re-
crystallized, when the second crystallization will
impart a still higher degree of purification.
This process has long been employed by chem-
ists and manufacturers to purify salts, and is still
the great process used to obtain pure chemicals.
When water is exposed to cold it solidifies, and its
solidification is a species of crystallization, although
the crystalline formation is, as a rule, not visible. It
is brought to view by melting ice under proper con-
ditions, and all are familiar with the beautiful crys-
talline forms which are discernible in snowflakes.
We should expect, therefore, that the freezing of wa-
ter would have a purifying effect upon it.
It has this effect. Ice is purer than the water from
346 LIQUID AIR AND THE
which it is made. If cider is exposed to cold, the
water freezes out in a relatively pure condition, and
the cider is left as a sort of mother liquor, so much
stronger than" before that what is almost a brandy
results. Here the cider constituents are the impuri-
ties, and they are left in the mother liquor in greatly
concentrated condition, and the water is crystallized
out as ice in a relatively pure state.
Water is ordinarily purified by distillation. It
would be perfectly practicable to purify it by re-
peated freezings, if distillation could not be effected.
Liquefied gases, by their innate cold and power of
absorbing heat energy or rendering heat latent, ex-
tend the range of the freezing processes to new fields.
Liquid air can solidify and thereby purify alcohol.
A number of very important chemicals can be puri-
fied by intense cold. One of the most familiar of
these is chloroform. Used as an anaesthetic, it is un-
certain how much of the bad effects of chloroform
are due to its impurities. Irrespective of any dan-
ger to life, there are after effects which it is desirable
to overcome or minimize. The purer it is, the less
are these after effects, and it is quite possible that
with absolutely pure chloroform, deaths of patients
from the effects of its administration would be far less
frequent than they now are.
Chloroform is purified by freezing. On subjection
to a proper degree of refrigeration, the pure chloro-
form crystallizes out almost like sodium sulphate
from water. The very cold crystals are removed
and melt, and an extremely pure product is the re-
sult. The process is termed one of rectification at
low temperature, and can be applied to a number of
LIQUEFACTION OF GASES. 347
liquids. Chloroform is taken as a typical substance,
and as one for which a great demand exists. Ether
is another chemical product which is thus purified
with success, and alcohol can be purified by the
freezing process until it is 100 per cent, pure, or is
what is known as absolute alcohol. Various anaes-
thetics are purified by freezing.
Formerly these methods were inapplicable, simply
because the degree of cold requisite for their execu-
tion was unattainable.
Distillation by heat is attended with the objection
that the heating may impair the product. Low tem-
perature distillation is made practicable by utilizing
the intense cold of liquefied gases to condense the
distillate. In this way so high a vacuum is produced
that a liquid will distill with relative rapidity at ordi-
nary temperatures. It is a reversal of the ordinary
course of operations. Instead of applying heat to the
retort and forcing off the gasified liquid against the
pressure of the atmosphere, the latter is removed and
the gases which take its place are condensed by in-
tense cold, so as to maintain an almost perfect vacuum
over the liquid, which distills without artificial heat.
Chemical reactions are so greatly modified by
temperature that the cold of boiling liquefied gases
may bring about radically different results in these
cases. Thus, if organic substances are treated with
nitric acid, the products will vary according to the
temperature at which the interacting substances are
kept. As illustrations of compounds produced by
the action of nitric acid on organic substances, nitro-
glycerine, guncotton and many similar substances
may be cited. These have extensive uses as explo-
348 LIQUID AIR AND THE
sives, and by deoxidation give a host of products such
as the aniline dyes. Any process which affects these
reactions would affect the most important field of
chemical industry. Heat, in the popular sense, has
hitherto been the great agent in producing chemical
reactions and in modifying them. Intense cold may
now be looked on as a supplementary agent.
An explosive is a substance whose action may de-
pend upon various chemical and physical actions.
If two volumes of hydrogen are mixed with one
volume of oxygen, a colorless mixture of gases re-
sults. If an electric spark or other source of heat is
applied to the mixture, they at once combine sud-
denly, and with production of great heat. The re-
sult is an explosion, and the operation of combina-
tion produces a sound like a pistol shot. The mix-
ture can be made to discharge a shot from a gun or
to blast rocks.
Another class of explosives operate by simple
breaking up of a feeble chemical combination. Chlo.
rine and nitrogen can be made to unite and produce
an oily liquid — a chemical combination of one atom
of nitrogen and three of chlorine. On the least dis-
turbance, or without any apparent reason, the com-
pound will explode, simply reproducing chlorine and
nitrogen. But, simple as it seems, the explosion is
of fearful violence, and it is truly appalling to read
of Davy's and Faraday's work with this substance,
one of the most dangerous known to humanity.
It is unnecessary to go further. When a substance
can be made in which a very violent chemical action
can be induced, the heat produced and the changes
in volume may be so sudden and great that an ex-
LIQUEFACTION OF GASES. 349
plosion results. Such a substance is termed an ex-
plosive, and there are a great many of such now in
service.
One of the proposed uses of liquefied air is as a
constituent of an explosive. If air is liquefied, it
occupies about one eight-hundredth of its former
volume, so that there is involved in its liquefaction a
concentration of its oxygen to that extent. Then,
we know that, by standing, the nitrogen evaporates
more rapidly than the oxygen, so that a constant
action of enrichment in ox_f gen is taking place as re-
gards the unevaporated liquid. Thus, the liquefac-
tion of air and subsequent enrichment may amount
to a concentration of its oxygen of sixteen hundred
or more times.
Even this is not so remarkable as it might seem.
We are very familiar with oxygen in liquid and
solid form in combinations of the chemical order.
Thus, water, which we know most familiarly as a
liquid, or as a solid, contains eight-ninths its weight
of oxygen. Startling as it seems, it is no paradox to
say that water is approximately pure liquid oxygen.
This assertion would be based on its chemical corn-
position by percentages or proportions by weight.
But there is more than this to be looked at. By
its affinity for hydrogen it is locked fast in the water
molecule, so as to be comparatively inert. Those
who have seen the fierce combustion produced by
soaking organic matter in liquid air and then igniting
it would never think of employing it as a material
to put out fires. Yet we use water for this purpose,
although it is far richer in oxygen than is liquid air.
Under certain conditions water can support com-
350 LIQUID AIR AND THE
bustion. If steam is passed through a mass of red
hot copper borings, iron borings, coal and many
other substances, it gives up its oxygen to them, the
hydrogen severs its alMance, and a true combustion
ensues at the expense of the oxygen of the water.
It is hard to bring about a combustion in water
vapor, and in liquid water it is all but impossible,
owing to its cooling powers.
The air we breathe contains about one-fifth of its
volume of oxygen, and fires burn in it with far
greater energy than in ^team, which contains one-
third its volume of the same gas. This is because
oxygen in air is free and uncombined, and can unite
witn anything that claims it, without having to dis-
solve any bonds which unite it to other elements.
We are familiar with oxygen in the solid state in
innumerable compounds. For purposes of com-
bustion and explosion, we select those that are rich-
est in oxygen and which have it most feebly united
or combined. The " villainous saltpeter," potassium
nitrate, contains in round numbers 48^ per cent,
by weight of oxygen, which is very feebly com-
bined, and is, therefore, so ready to combine with
carbon, sulphur and other compounds that for cen-
turies it has figured as an ingredient in the great ex-
plosive gunpowder, which has ended many a life on
the battlefield, a service some may be weak enough
to consider of very questionable utility. The sci-
entist cannot but consider the human body as a
very exquisite mechanism, and must regard its de-
struction by one who cannot adjust and create its
mechanism as a work opposed to every ethic of true
science. Science always contains for its true vota-
LIQUEFACTION OF GASES. 351
rles elements of admiration and wonder. Destruc-
tion of that which cannot be created or resynthe-
sized is an abject confession of weakness that should
be most discordant with every note of the scientific
student's nature.
Now take liquid air which by standing has become
rich in oxygen. It is liquid and of about one-third
the specific gravity of typical solid oxygen-contain-
ing compounds. One-half of its weight may be oxy-
gen which is absolutely free and uncombined, ready
on provocation to unite with many elements without
having any bonds of union to sever. It is evidently
an available substance for a constituent of an explo-
sive or for an inciter of violent combustion.
It is found that if liquid air, after standing a little
while, so as to evolve nitrogen and become rich in
oxygen, is poured upon organic matter, such as cot-
ton, felt, powdered charcoal and similar substances,
a violently combustible product is formed. A piece
of heavy felt which can hardly be induced to burn in
the open air, when soaked with liquid air, burns
with the brilliancy of a piece of pyrotechnics.
This is combustion. Rapid combustion is explo-
sion, and with such mixtures explosion can be
brought about by confinement before ignition and
by ignition with a detonator. The shock and heat
set the whole off at once, and an explosion compara-
ble to that of gunpowder results.
The following are the general features of Dr.
Linde's practical trials of the liquid air explosive for
blasting rock and coal : Charcoal is broken up into
grains about the coarseness of beach sand. The
effect of pouring liquid air upon the porous mass
352 LIQUID AIR AND THE
with its many points is to eliminate the spheroidal
state and to provoke violent ebullition. This would
be so great as to scatter the charcoal to right and
left. Accordingly, to keep it together, the charcoal
is mixed into a sort of sponge, with one-third of its
weight of cotton (cotton wool or waste).
Liquid air, which has stood long enough to con-
tain about half its weight of oxygen, is poured upon
the mixture of wool and charcoal. An ebullition at
first occurs, during which more nitrogen than oxy- \ /
gen goes off, and a further concentration of oxygen
is effected. The moist mixture is rapidly charged
into insulated paper cartridges, and is ready for use
within five or ten minutes. It must be at once placed
in the shot holes and exploded by a detonator, pre-
ferably an electric one. But any detonator which
can be rapidly exploded will answer. Delay is fatal
in one sense — it destroys the efficiency of the cart-
ridge. After fifteen minutes to half an hour the
liquid air will have so completely evaporated that
no explosion can be produced.
This might seem a defect, but it is quoted as a
merit. Countless accidents have happened in mining
and tunneling operations from cartridges hanging
fire, as it is called, in blast holes, only to go off unex-
pectedly, and killing and maiming the workmen.
Half an hour after a liquid air cartridge has been
placed in the hole it is innocuous.
By using air which has stood a longer or shorter
time, the power of the explosive and the heat pro-
duced in its explosion can be controlled at least to
some extent, even if it must be considered largely
guesswork.
LIQUEFACTION OF GASES. 353
The explosive was used for several months in a
coal mine at Pensburg, in Bavaria, near Munich,
with good results. Where power costs nothing the
explosive is a very cheap one. In tunneling opera-
tions it often happens that there is a surplus of
power derivable from streams that flow in the
vicinity. The European engineers show a great
aptitude for utilizing such sources of energy.
Where such are available, this would be the cheap-
est possible explosive, as well as the safest.
In America, Tripler has experimented in this di.
rection, and has found that he could blow heavy
steel tubes open as if with dynamite.
Elihu Thomson presents the possibilities of liquid
air in electric power work. Few realize how large
an item capitalization plays in the problem. The in-
stallation of a long line of copper is an expensive
matter, and successful efforts are made to reduce
it by employing high potential difference. But
could the temperature be reduced to that of liquid
air, a thin \vire would carry a large current at rela-
tively low potential difference, or at the high poten-
tial difference a very much larger one. As far as the
cost of copper went, the capitalization of the line
would be slight, in proportion to the power trans-
ferred. There would be every excuse for an expen-
sive construction of a line which would carry a
large current. The capitalization per unit would be
quite small.
The idea of Elihu Thomson is expressed by refer-
ence to the power of Niagara Falls. An expensive
power installation is there established which works
to its full capacity for only a little over one-third of
354 LIQUID AIR AND THE
each day. He suggests that the power might be
used during the night hours for making liquid air
which could be stored in tanks well insulated from
the outer air temperature. The inevitable evapora-
tion of air could be utilized to perfect the heat in-
sulation by being led down through the jacketing
of the tank.
-A furnace in a steel works or other industrial es-
tablishment may have a temperature on its hearth
and working chamber of two or three thousand de-
grees above that of the air, yet there is no difficulty
in insulating it by a firebrick lining and, perhaps,
ordinary brick exterior, so that the hand can be
placed upon the outer surface without being burned.
Between liquid air and the atmosphere there is but
one-eighth the difference of temperature that exists
between the heat of a furnace and that of the air.
The copper conductor could be inclosed in a pipe
which could be kept cold with liquid air. Such a
line need not involve a loss in the energy trans-
ported of more than one or two per cent. In most
long distance lines a loss of ten or fifteen per cent,
of the energy is allowed for. It is possible that
the saving of most of this might pay for the cost of
liquid air, irrespective of the increased capacity of
the line.
A few years ago it would have seemed absurd to
make such a suggestion. But there is not a particle
of absurdity in it. The achievements in the produc-
tion of liquid air by Tripler and others, and the
carrying of it hundreds of miles by rail in jacketed
buckets, show how easy a substance it is to handle,
once a sufficient quantity is brought together.
LIQUEFACTION OF GASES. 355
The surfaces of solids of identical shape vary with
the squares of their linear dimensions. Thus, if there
are two of Tripler's air buckets exactly alike, except
in size, and if one is twice as large as the other, the
surface of the tin and of the open top will be four
times as large in one as in the other. The volume
varies as the cube of linear dimensions. Therefore,
in the case cited, the larger bucket will hold eight
times as much liquid air as will the smaller one.
Therefore, if we state the relation of surface to
volume in the small bucket as a : by the ratio in the
large one will be 4 # : 8 £. That is to say, there will
be half as much surface exposed in proportion to the
contents in the large bucket as in the small one.
The heating and wasting of the air by evaporation
is due to the surface exposed. Therefore, the larger
the vessel, the less in proportion will the waste due
to heating from the exposed surface be. If a bucket
were five times as large, the ratio would be still
more favorable — 25 a : 125 £, or i : 5, and so on.
By carrying out what the French would call the
audacious idea of making liquid air by the barrelful,
Tripler has demonstrated the possibility of handling
it on the large scale pretty nearly as water is hand-
led. The English scientists, as late as 1897, find it im-
possible to credit the accounts of what is done in this
country. Prof. Fleming says that " nothing was
effectual in storing liquid air until Prof. Dewar in-
vented the silvered, vacuum-jacketed glass vessel
as a container, and the even more effective and in-
genious mercury vacuum process for introducing
the high vacua required, without which none of our
research work could have been done." This is not
356 LIQUID AIR.
the only quotation which might be used to show
how incredible the achievements on this side of the
ocean seem to foreign investigators.
Liquid air, if it could only be produced cheaply
enough, would represent an ideal substance for the
production of energy. It is calculated that in one
pound of it there are stored 139,100 footpounds of
energy. An electric storage battery varies from one-
tenth to one-twentieth of this amount per pound of
its own weight, and compressed air is about one-
tenth. A pound of water compressed to 400 pounds
pressure to the square inch has only one-quarter
the energy of an equal weight of liquid air. In the
compressed air and liquid air calculations the
weight of the reservoir is not included.
The peculiarity of liquid air as a material for the
storage of energy is that it can be made to give any
pressure, from the slightest up to many atmospheres,
nearly a thousand in number. It represents the
water in a boiler, the containing vessel is the boiler,
and the atmosphere represents the hot gases and
flames of the furnace. By exposing more or less of
the surface of the vessel to the air the evaporation
could be controlled. Its expansion would tend to be
adiabatic, but by further use of an air reheater,
identical in construction with an air condenser, the
disadvantageous adiabatic element may be sup-
pressed, and isothermal, or nearly isothermal, ex-
pansion substituted. The condition is as it steam
were superheated between boiler and engine, and as
if the engine itself were heated by an external fire.
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INDEX.
Absolute cold 19-20
Absolute zero 40-41
Acetylene, Cailletet'sworkon,
J75. * 79-i8i, 182-183
Adiabatic expansion and contrac-
tion 69
Air, a conveyor of heat 244
Air and water contrasted 85-86
Air, Cailletet's liquefaction of ..186-187
Air, composition of 87
Air, constancy of composition of .89-90
Air, dry and wet compared 14-15
Air, experiments with liquid. ..325-337
Air, how to preserve liquid indefi-
nitely 260-261
Air, liquefied, giving two liquids 220
Air, liquid, defined 9
Air of atmosphere not a chemical
compound 86-87
Air, physicists' and chemists'
views of V 88-89
Air, Wroblewski's experiment on
liquefaction of 220
Alcohol frozen by liquid air. 330
Alcohol frozen by Wroblewski and
Olszewski . 212
Aniagat 147
Ammoniacal gas, Faraday's lique-
faction Of III-II2
Ampere and Colladon, anecdote
of 133-135
Andreef 214
Andrews, memoir on life of, by
Tait and Brown 150
Andrews, Thomas. 19, 133, 147-150,
169, 176
Apparatus and experiments, Cail-
letet's liquefaction 177-182
Apparatus and process, Trip-
ler's 290-295
Apparatus, Hampson's, for lique-
fying air 320-324
Apparatus, lyinde's, for liquefying
air 307-319
Apparatus, Pictet's liquefaction. 157-163
Apparatus, Thilorier's 137-141
Argon. 87
Arseniureted hydrogen, liquefac-
tion of 122
Atmosphere, its relation to ani-
mals and birds 85-86
Atmosphere liquefied 336
Autophage state of human sys-
tem 339
Babbage 119-120
Barker, George F 199, 240
Barleycorn as unit of space 25-26
Bath well, helium from 275-276
Battle of squares and cubes 355-356
Baucalari 115
Benjamin Thompson 93
Bianchi's modification of Natter-
er's apparatus 142-145
Blenkroode 245
Blenkroode's experiment illus-
trating vacuum 245
Boiling a cooling process 76-77
Boiling by producing a vacuum. .77-78
Boiling gases 76-77
Bonty 201
Brunei's carbon dioxide engine .99
Buckets, Tripler's, for liquid
air , .289-296
Bulbs, efficiency of different 247
Bulbs, vacuum, mercury silvering
of 247,253-254
Cagniard de la Tour 128-133
Cailletet, L. P.. .22, 24, 58, 135, 150,
151, 155, 156, 165, 172-202, 204,
212, 214, 215, 2l8, 219, 220, 226
360
INDEX.
Cailletet and Hauteville on spe-
cific gravity of oxygen 197
Cailletet, honors received by 174
Cailletet, life of 173-1 74
Cailletet, liquid acetylene, his
work on 197-199
Cailletet on conductivity of metals
at low temperatures . . 201
Cailletet on critical state pheno-
mena 190-192
Cailletet performs I,a Tour's ex-
periment 202
Cailletet's cold blast blowpipe,
141, 198-199
Cailletet's continuous liquefac-
tion process 200
Cailletet's control experiment
with hydrogen 184
Cailletet's controversies with De-
war 232-233
Cailletet's frozen mercury stop-
per 187
Cailletet's letter to Academy of
Science 183-184
Cailletet's liquefaction of hydro-
gen 218
Cailletet's manometers ... 187-189
Cailletet's thermometric methods,
trials of 201-202
Callendar 57
Carbon bisulphide, frozen by
Wroblewski and Olszewski 212
Carbon burned in liquid air 334
Carbon dioxide in air 9O-91
Carbon dioxide in liquid air 336
Carbon dioxide, liquefaction of,
Faraday's in
Carbon dioxide, solid 15-16
Carbon monoxide dispatch, Wrob-
lewski and Olszewski's 213
Carnot's cycle 70, 288
Celsius thermometer scale .38-39
Centimeter 25
Chemical reactions governed by
cold 347-348
Chlorine, Faraday's liquefaction
of 1 06, 1 10
Chlorine, Northmore's liquefac-
tion of 106, 117-118
Clark, Dr. G. Fish 342
Clausius 204
Coal as a chemical 298
Cold, absolute ... 19-20
Cold, distillation by 347
Cold, regeneration of 299
Cold regenerative process 265
Coleman. 265
Colladon and Ampere, anecdote
of 133-135
Colladon, Daniel . 133-137, 174, 176,
179, 200, 207
Colladon, his original apparatus. . .136
Conservation of energy 29-36
Contraction, adiabatic 69
Cordes, Dr 341
Count Rumford 92-95
Critical pressure 19
Critical state of matter 19-20
Critical temperature 19
Crookes layer 80-82
Crookes layer, protection due to 84
Crookes, William 2^4
Cubes and squares, battle of. . .355-356
Cyanogen, liquefaction of, Fara-
day's in
Cycle of reversible engine 70
Davy-Faraday Research Labora-
tory 115
Davy, Sir Humphry 96-99, 102,
103, 105, IIO, 115, 120 121, 126
Debray 211-212,218
Dewar and Moissau's liquefaction
of fluorine 276-280
Dewar, James.. 96, 99, 112, 115, 151,
157, 168, 198, 200, 206, 215, 219,
225, 227, 229, 230-285
Dewar's apparatus of 1883 233
Dewar's apparatus of 1895 238-239
Dewar's bulbs . 244-254
Dewar's bulbs, mercury silvering
of 247, 253-254
Dewar's colleagues 232
Dewar's controversies with Cail-
letet.... 232-233
Dewar's early apparatus 233-2-57
Dewar's gas jet experiments. . .264-266
Dewar's hydrogen jet experi-
ments 266-271
Dewar's life 231-232
Dewar's liquefaction of helium 281
Dewar's liquefaction of hydro-
gen 280-285
INDEX.
361
Dewar's separation of helium. .275-276
De war's small gas liquefaction
apparatus '. 241-243
Dewar's suggestion of marsh gas
as a refrigerant 232-233
Dewar's use of Pictet's cycles ... .233
Dewar's vacuum 249-253
Diffusion 18
Dog killed by low temperature . . . 340
Double and triple glass gas
bulbs 245- 247
Ducretet 206
Dufour, Prof Henri 155-156
Edison 288
Effects of intense cold on human
system 339-341
Eiffel Tower manometer ... . 188-189
Elasticity of metals affected by
cold 255-256, 260
Electric power transmission,
liquid air in 353-354
Electric resistance of metals
affected by cold, Wroblewski
on 219-220
Electrolysis of water 148-149
Elements, fundamental in physics .25
Elongation of metals affected by
cold. . . 259-260
Energy 29
Energy and force 24-25
Energy, conservation of 29 36
Energy converted into useless
heat 29
Energy, kinetic 31
Energy, low grade heat 288-289
Energy, low grade heat and liquid
air 35-36
Energy, potential 30
Energy, reduction of available. ..71-72
Energy, reservoir of. 32-33
Energy, unutilizable of world 34-35
Energy, waste of, in railroads and
steam navigation 33-34
Entropy 34
Ethylene 197-199
Ethylene, liquid as refrigerant. 197-198
Ethylene, Wroblewski and Ols-
zewski's results with. 212
Euchlorine, Faraday's liquefac-
tion of in
Evaporation by stream of gas. 201. 214
Expansion, isothermal 68-69
Experiment, Blenkroode's, show-
ing utility of vacuum .... 245
Experiment, Count Rumford's. 118-119
Experiment illustrating conser-
vation of energy 32
Experiment in boiling by a
vacuum ••••77
Experiment, Joule and Thom-
son's 61-62
Experiment, Joule's 60-61
Experiment on low grade heat
energy 35-36
Experiment with chlorine hy-
drate 126
Experiment with india rubber
band.... 32
Experiment, Villard's. 24
Experiments, Dewar's hydrogen
jet 266-271
Experiments, Dewar's, on solu-
tions of gases in other lique-
fied gases 271-274
Experiments, Dewar's, with gas
jets 264-266
Experiments, early, of Faraday.. .103
Experiments in spheroidal state.82-83
Experiments, I,a Tour's 129-132
Experiments, Pictet's, of 1877 . . 160-161
Experiments with liquid air. . .325-337
Explosions in Faraday's and
Davy's early work no
Explosive, liquid air 348-353
Faraday as fellow of the Royal
Society 106-107
Faraday, Michael 28, 42, 95, 99,
100-115, "7-129. 131, 226, 240
Faraday, Michael, his life too 115
Faraday on Davy's continental
tour 105
Faraday's bent tubes .123-128
Faraday's death 115
Faraday's discovery of magnet-
ism of oxygen 114-115
Faraday's engagement at Royal
Institution. 104-105
Faraday's failures in liquefactions
of gases 114
Faraday's liquefactions of gases,
106-112, 113-114
Faraday's solidification of gases . .114
362
INDEX.
Faraday's thermometer 39
Fleming, J. A 232
Fluorine, liquefaction of 276-280
Force 27-29
Force and energy 24-25
Force, conservation of, an errone-
ous doctrine 28-29
Force, living 29
Formula, Joule-Thomson effect,
300-306
Frigotherapy 338-342
Fuller, Mr. John 95
Fullerian professorship in Royal
Institution 95, 96
Gas cooled by expansion 299
Gaseous state of matter 12
Gases, boiling 76-77
Gases, Davy's experiments in in-
haling 97-98
Gases, Davy's views of the utility
of liquefying 98
Gases, determining latent heat of
liquefied 261 264
Gases, determining specific heat
of liquefied 261 264
Gases, molecular motion in 17-18
Gases, permanent 149-150
Gases, solution in other liquefied
gases 271-274
Gas heavier than liquid . 21
Gas jets, Dewar's experiments
with 264-266
Gas, receiver for liquefied, Cail-
letet's 195-196
Gas, the perfect... , 59-62
Galbanum 191
Galitzine 22
Gramme 25
Griffiths 57
Hampson 226, 238, 265, 300, 301,
309, 320-324
Hannay 23
Hauteville 197
Heat, latent 72-76
Heat, measurement of . . . 37
Heat of ice n
Heat, specific. See specific heat.
Heat, utilization of unavailable . . .72
Helium, liquefaction of Dewar's. . .281
Helium, separation of, Dewar's,
275-276
Helmholtz 204
Hervy, death of 138
Hogarth 23
Hydrochloric acid, Faraday's
liquefaction of 112
Hydrogen, Cailletet's liquefaction
of 184-185
Hydrogen, constants of liquid by
Olszewski 227-229
Hydrogen dispatch, Wroblewski's.2i8
Hydrogen, jet process of liquefy-
ing 266-271
Hydrogen, liquefaction of, De-
war's 280-285
Hydrogen, liquefaction of, Pic-
tet's 164-165
Hydrogen, liquefaction of, Wrob-
lewski's 218-219
Hydrogen, Wroblewski and Ols-
zewski's attempt toliquefy.2i3~2i4
Hydrogen, Wroblewski on criti-
cal pressure of .. 266
Ice, liquid air boiled on 335
India rubber affected by intense
cold — 329
India rubber band experiment 32
Isothermal expansion and con-
traction 68-69
Jamin . 21
Joule 60, 61
Joule and Thomson's experi-
ment 61-62
Joule's experiment 60-61
Joule-Thomson effect .. 269-270, 297-306
Joule-Thomson effect, negative ... 301
Kinetic energy 31
Kirchoff 204
Laboratory liquid air apparatus,
Linde's 313-316
patent heat 72-76
La Tour, Cagniard de . . 202
LaTour'slaw 20-21,128-129
Lavoisier 94
Law-, La Tour's 20
Layer, Crookes 80-82
Leyden University, Cailletet's
pump in 193
Leyden University, Pictet's cycles
in 157-158
Liebig's account of accident with
Thilorier's apparatus 138-139
INDEX.
363
Linde 226, 238, 265, 300, 301, 307-
319, 322
Linde's liquefaction process and
apparatus 307-31$
Liquefaction in tubes, Davy's sug-
gestion for 126-127
Liquefaction of gases, Faraday's
first work on 106,110
Liquefaction of hydrogen, Pictet's
experiment in 164-165
Liquefaction process and appara-
tus, Linde's .. ..,. 307-319
Liquefied gas receiver, Caille-
tet's... 195-196
Liquid air accelerating combus-
tion 332-333
Liquid air apparatus, Linde's 309-312 __
Liquid air as source of oxygen. 316-318
Liquid air as source of power 356
Liquid air defined 9
Liquid air dropped into water. 327-328
Liquid air, experiments with. .325-337
Liquid air explosive 348-353
Liquid air, filtering 326-327
Liquid air, gasification of 332
Liquid air giving two liquids.... 22p
Liquid air in Dewar bulb 327
Liquid air in flask . .325
Liquid air, medical uses of ... .342-343
Liquide Pictet 24, 169-171
Liquid floating on a gas 21
Liquid fluorine, data of 278-280
Liquid helium, Dewar's produc-
tion of 281
Liquid hydrogen 280-285
Liquid hydrogen, data of 280-283
Liquid hydrogen, Olszewski's de-
termination of constant of .227-229
Liquids and solids, solutions of,
in gases 23-24
Liquids, molecular motion in 18
Liquid state .12
Liveing, G. D 232
Living force 29
Low temperatures, applications
of 338-356
Machinery, Dewar's, Royal Insti-
tution 239
Magnetism of oxygen 337
Manometer, Faraday's 124-125
Manometers, Cailletet's 187-189
Marsh gas, liquid, as refrigerant.. 215
Mass 26
Matter, critical state of 19-20
Matter, three forms or states of. . . n
MaxwelJ, J. Clerk 150, 204, 225, 289
Maxwell, J. Clerk, on low grade
heat energy . . 289
Medical uses of liquid air 342-343
Meniscus defined 21
Mercury frozen by liquid air. . . 331-331
Mercury vapor, experiment in
freezing 453-*54
Metals affected by intense cold. 328-329
Metals, effect of intense cold on
elasticity of 255-256, 260
Metals, effect of intense cold on
elongation of 259- 260
Metals, effect of intense cold on
strength of 256-259
Metals, Tresca's flow of .255 256
Mixture, Thilorier's 113
Moissan and Dewar's liquefaction
of fluorine 276-280
Moissan, Prof 232, 277
Molecular attraction 11-12
Molecular death 18
Molecular motion of gases 17-18
Molecular motion of solids n
Mond, Dr. Ludwig 115
Monge and Clouet . no
Natterer, J. .19, 42, 141-147, 169, 194,
211, 213, 216
Natterer's apparatus and experi-
ment 141-147
Natterer's freezing mixture 145
Natterer's thermometer 145, 211
Natterer's tube 23, 213, 216
Negative Joule-Thomson effect 301
Nitrogen, anomalies of 88
Nitrogen, Cailletet's liquefaction
of 184
Nitrogen dispatch, Wroblewski
and Olszewski's 213
Nitrogen, solidification of, by
Wroblewski and Olszewski. . . .214
Nitrous oxide, Faraday's liquefac-
tion of ;... in
Nitrous oxide, Natterer's liquefac-
tion of 145
Nitrous oxide, suggested by Fara-
day as cooling agent 114
364
INDEX.
Northmore, Thomas. .106, no, 117-
Il8, 121, 122, 143
Northmore, Thomas, liquefac-
tions by 106,117-118
Onnes, H. Kamerlingh 49, 270, 301
Olszewski, K. .42, 145, 151, 157, 165,
168, 169, 185, 203-229, 266, 267, 301
Olszewski's and Pictet's appara-
tus, defect in 223
Olszewski's determination of con-
stants of liquid hydrogen . . 227-229
Olszewski's liquefaction appara-
tus of 1890 221-226
Olszewski's liquefaction of hydro-
gen, approximate 221
Olszewski's static oxygen. .-. . 221-226
Oxygen, Cailletet's liquefaction
of 183-185
Oxygen, critical pressure of,
Wroblewski and Olszewski's
determination 216-217
Oxygen, critical temperature of,
Wroblewski and Olszewski's
determination 217-218
Oxygen dispatch, Wroblewski
and Olszewski's 211-212
Oxygen, Linde's method for pro-
ducing 317-318
Oxygen, magnetism of 337
Oxygen, specific gravity deter-
mination of, Wroblewski and
Olszewski's 214
Paris, Dr. John Ayrton, and Fara-
day 107-109
Perkins' alleged liquefaction of
air 116-117
Permanent gases, the six so-called. 150
Pictet, Raoul....22, 24, 133, 135, 150,
151, 152-171, 185, 192, 200, 105,
220, 223, 225, 233, 064, 189
Pictet, honors received by 156
Pictet's cycles used by Dewar 133
Pictet's cycles praised by Wrob-
lewski 005-106
Pictet's determination of tempera-
ture 167
Pictet's experiment in cold well,
340-341
Pictet's frigotherapy 338-34*
Pictet's Intellectual and Moral
Philosophy 157
Pictet's life and character 153-155
Pictet's liquefaction of oxygen
dispatch 161
Pictet's original liquefaction ap-
paratus 157-163
Pictet's liquid 24,169-171
Pictet's work, importance of 168
Pleischl's lecture on Natterer's
apparatus 144 -146
Pneumatic Institution 96
Potential energy 30
Power expended in I^inde's ap-
paratus " 316,318
Power, liquid air as reservoir of 356
Pressure affecting state of mat-
ter ... 16-17
Pressure, critical 19
Pressures, enormous, in Natter-
er's experiments 146
Pump, Cailletet's mercury. .. 191-195
Pump, Faraday's 113
Pump, Pictet's 166
Purification of chemicals by
cold 344 347
Purity, critical state test of 343-344
Ramsay 21, 22
Reaumur thermometer scale.. 38, 44-45
Regnault's mercury pump 193
Release, Cailletet's 182
Ribard's local application of in-
tense cold 342
Ribeau, George, Faraday's em-
ployer 102
Regeneration of cold 299
Royal Institution of England. 10, 92-99
Rumford, Count 92~95. 118-119
Rumford's, Count, experiment in
liquefaction of gases 118-119
Second 25
Self-intensive refrigeration .'. 300
Siemens, William 299, 300, 301
Silvered gas bulbs 247
Skating rinks, Pictet s . . . I54-J55
Solid state of matter 11
Solid carbon dioxide and Crookes
layer 84
Solids and liquids, solutions of,
in gases ....23-24
Solids, flow of 13
Solids, vaporization of 15-16
Solution, gaseous, utilized 24
INDEX.
365
Solution of solids and liquids in
gases 23-24
Solvay 265
Specific heat at constant volume
and at constant pressure 64 65
Specific heat, atomic 66
Specific heat of gases 64-65
Spheroidal state 78-84, 243
State of matter affected by pres-
sure 16-17
State of matter, intermediate. 13-14, 20
State of matter, volume affected
by 18-21
Steel burned in liquid air 334
Strength of metals affected by
cold 256-259
Stromeyer 122
Sulphur dioxide, liquefaction of. . .no
Sulphureted hydrogen, liquefac-
tion of iio-in
Surface tension 78-79
Thermodynamics, second law of. 70-71
Thermometer, calorimetric 58
Thermometer, electric resist-
ance 54-57
Thermometer, Fahrenheit's 39
Thermometer, gas or air 44-51
Thermometer, Natterer's 211
Thermometer scales 37,44
Thermometers, substances for
filling 37, 42
Thermometer, thermo-electric. ..51-54
Thermometric methods, Caille-
tet's trials of 201-202
Thilorier ... 112, 113, 137-141, 198, 269
Thilorier's apparatus exhibited
by Faraday 112
Thilorier's apparatus, fatal acci-
dent with 138-139, 143, 145
Thilorier's cold-blast blowpipe,
141, 198
Thilorier's experiments 137-141
Thilorier's freezing mixture; 141
Thilorier's solid carbon dioxide 137
Thomson, Sir William 61, 62
Thomson, Fylihu 219
Thompson, Benjamin 93
Torricell ian vacuum 249, 252-253
Tour, Cagniard de la .... 22
Transition phenomena 22-23
Tresca's flow of metals 255-256
Tripler and Pictet 296
Tripler, Chas. E- .226, 235, 255, 266,
285, 286-296, 287, 289
Tripler on low grade heat energy,
288-289
Tripler's apparatus and pro-
cess 290-295
Tripler's buckets for liquid
air 289,296
Tripler's life 287-289
Tubes, Faraday's bent 123-128
Vacuum, a heat insulator 244-246
Vacuum and air space bulbs, effi-
ciency compared 247
Vacuum, Blenkroode's experi-
ment illustrating utility of 245
Vacuum bulbs or vessels 244-254
Vacuum produced by liquid hy-
drogen 283-284
Vapor 63-64
Vaporization of solids 15-16
Villard 23,24
Volumes, relations of, in change
of state 18-21
Water and air contrasted ...... .85-86
Water, three states of 11-13
Water vapor 64
Well, frigorific 339
Whisky frozen by liquid air.... 330-331
Witowski 55,57
Work 25, 31-32
Wroblewski and Olszewski's ap-
paratus . . ..206-211
Wroblewski and Olszewski's car-
bon monoxide dispatch 213
Wroblewski and Olszewski's
nitrogen dispatch 213
Wroblewski and Olszewski's oxy-
gen dispatch 211-212
Wroblewski and Olszewski's oxy-
gen liquefaction 211 212
Wroblewski, Sigmund von . ... 42,
145, 151, 157, 165, 168, 203-229,
266, 301
Wroblewski's life 203-205
Wroblewski's liquefaction of hy-
drogen 218-419
Wroblewski on liquefaction of air. 220
Zambiasi 22
Zero, absolute 40-41
Zero of thermometer scales 37-38
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employed in various shops, determine which is best adapted to his particular case,
and adopt the method that will save the most time and money for their employer.
No machinist can read it without finding new methods and ideas which will be of
ralue to him —Machinery, March, 1896.
•'A strongly bound cloth book, 400 pages, entitled "Shop Kinks" by that
living encyclopaedia of mechanics, Robert Grimshaw. As might be expected, the
author covers almost every possible subject that could come up in a machine shop.
The articles are well illustrated, and the different processes clearly explained.
Mr. Grimshaw is not one of those who think there is nothing known outuide of
himself, but is ever gleaning " Kinks " from other men's brains. A copy should be
on the desk of every machinist in a factory repair shop, for the right "Kink " at the
rieht time will often prevent the stoppage of a factory."— Wade's Fibre and Fabric,
Feb. 15, 1896.
NORMAN W. HENLEY & CO., PUBLISHERS,
132 Nassau Street, New York.
Special circular describing the above sent on request, or IB* will $end copies
on receipt of the price .
JUST PUBLISHED.
The Modern flachinist,
By JOHN T. USHER, Machinist.
PRICE, $2.50.
Specially Adapted to the Use of Machinists, Apprentices,
Designers, Engineers and Constructors.
A practical treatise embracing the moat approved methods of modern machine-shop practice,
embracing the applications of recent improved appliances, tools, and devices for facilitating, duplicating,
and expediting the construction of machines and their parts.
A NEW BOOK FROn COVER TO COVER.
Every illustration in this book represents a new device in machine-shop
practice, and the engravings have been made specially for it.
8vo. 32% Pages. 357 Illustrations. Price, $2.50.
What is said of "The Modern Machinist."
This is a new work of merit. It is on " Modern Machine Shop Methods," as Its name implies.
It is thoroughly up to date, was written by one of the best-known and progressive machinists of the day,
is the modern exponent of the science, and all its subjects are treated according to latest developments.
In short, the book is new from cover to to cover, and is one that every machinist, apprentice, designer,
engineer, or constructor should possess. — SCIENTIFIC MACHINIST, JULY 15th, 1895.
This book is the most complete treatise of its kind that has yet come under our observation, and
contains all that is most modern and approved and of the highest efficiency in machine-shop practice,
etc., etc.— AGB OF STKSL, JUN*, 1895.
There is nothing experimental or visionary about this book, all devices being in actual use and
giving good results. It might perhaps be called a compendium of shop methods, showing a variety of
special tools and appliances which will give new ideas to many mechanics, from the superintendent to
the man at the bench. It will be found a valuable addition to any library, and will be consulted
Whenever a newer difficult job is to be done.— MACHINERY, JULY, 1895.
NORMAN W. HENLEY & CO.,
132 NASSAU STREET, NEW YORK.
*** Copies of the above sent prepaid on receipt of price.
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