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 University of Illinois Library 
 
 INE oo Gee 
 
 APR 2.6 199 
 
 L161—H 41 
 
LIQUID AIR 
 
 f 23) BBS BY mG = 
 
 LIQUEFACTION OF GASES 
 
 Tab Ohiee Wie hy: DIOGKAPHY 
 PRAGHICAL ACELICATIONS 
 MANUFACTURE 
 
 BY 
 
 Ee Ci CONGR SLOAN bore. Db. 
 
 ILLUSTRATED 
 
 NEw YORK 
 NORMAN, Wee HENLEY ~& CO, 
 132 NASSAU STREET 
 
 1899 
 
COPYRIGHTED 1899 . 
 BY 
 NoRMAN W. HENLEY & Co. 
 
 COMPOSITION, ELECTROTYPING AND 
 PRINTING BY 
 MaACGOWAN & SLIPPER 
 NEW YorK, N.-Y:, U.S. A. 
 
mn) 
 
 APTOS BDI 
 
 es S es | 2 Fp 
 
 gE 
 
 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 uncgncernedly 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 
 
 ECO 
 par 22 a4 ee, Ae 
 
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 overa 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. 
 
LAB EE Or CONLEN Ts. 
 
 CHAPTER I.—Puysics. 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—Klectrolytic 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—Latent heat of melting, of vaporization, of expansion—Boil- 
 ing a cooling process—Expansiona 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.—Puysics AND CHEMISTRY OF 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- 
 stituents. 
 
TABLE OF CONTENTS. 
 
 CHAPTER V.—THE RovaL INSTITUTION OF 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.—MIcCHAEL FARADAY. Pages IOI-I1I5 
 
 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—Kuropean 
 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 I16-151 
 
 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—Thilorier—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.—Raovut PIcrer. 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 11, 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-PavuL CAILLETET. Pages 173-202 
 
 The life of L.-P. Cailletet—His education—Honors received—His modification 
 
TABEEOF 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—Ljiquefaction of nitro- 
 gen—Of hydrogen—Rival claims of Cailletet and Pictet—Mercury stopper 
 method—Manometers—Original methods of testing—Hiffel tower mano- 
 meter—Carbon dioxide experiments—Mercury pump—High pressure gas 
 reservoir—Ethylene 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—Ljiquefaction 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 XI.—JAMES DEWAR. Pages 231-285 
 
 Dewar’s life and education—His associates—Controversies with Cxilletet as to 
 priority—Karly 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—Hlongation 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 
 —Ljiquefaction 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 EK. 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-THOMSON 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.—SoOME OF THE APPLICATIONS OF LOW 
 TEMPERATURES. Pages 338-356 
 
 Frigotherapy—The frigorific well—Pictet’s experiment—Effects of the first 
 trial of the system—Medieal-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. ad 
 
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LIQUID AIR 
 
 ANDY PEs 
 
 LIQUEFACTION OF’ GASES 
 
 GHAPTER: Tf. 
 PHYSICS. 
 
 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’s tube—Physical units—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 isnot some . 
 occult mystery attending it. Liquid air is simply 
 aix 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 
 
{0 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 is 
 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 pieccs 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 cnd 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 betore 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 4f 
 tin cans. 
 
 The long record should not be read until the® 
 answer to the query cited above has been given; the * 
 
LIQUEFACTION OF GASES. II 
 
 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. 
 
 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. Wecannot 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. Amolecule 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 
 néver ceases its travels: } As the molecules slide 
 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 of the liquid state of matter. 
 
 Let us apply more heat. Our water is already 
 shapeless. We have to keep it in a containing vessel. 
 Evenadropof water hanging from the window shutter 
 ona rainy day is held ina little sack of water-film. 
 Later on we shall see what an important bearing the 
 liquid film has inthe 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 1s 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. Asthe 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 
 
 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 
 elosedsevcnywuere. dite third state” ot matter is 
 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 AIRSAND: 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, asa 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 cvaporating surface of the 
 leaves of the vegetable world assumes the gaseous 
 form and mixes with the air. The specific gravity 
 
LIQUEFACTION OF GASES. 15 
 
 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 passe 
 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. 
 fodine 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 
 
16 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 liquehes— 
 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 
 allects it greatly. The greater the pressurcierae 
 higher is the temperature at which a liquid becomes 
 agas. A gas just hot enough to hold that form may, 
 under some conditions, be converted into a liquid 
 by applying pressure, without any change in tempera- 
 ture being required to effect the change of state. 
 This, too, is very natural. Foralquid, 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 thermai 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. Leys 
 
 secondary matter. [or 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, if the latter grows 
 smaller on liquefaction. So that it is quite conceivable 
 that a point might be reached where pressure would 
 help to convert aliquid 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. Thisis 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. 19 
 
 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 stateis 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 init. 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 bea 
 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. BY 
 
 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 asort 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 ordown alittle. 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 ae 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 striaz, and so character- 
 istic is this feature that it is used by Pictet in some 
 
LIQUEFACTION OF GASES. 23, 
 
 of his most recent work as an indicator of gasefac- 
 tion. 
 
 If a tube is partly filled with a liquid, is sealed and 
 heated, fhe first indication of a change of state to be 
 looked for is the disappearance of the meniscus. As 
 it vanishes, the flickering striz 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 || |//|jll 
 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. |i. 
 If it is to be shown to an audience, the ii 
 image of the tube is projected upona 
 screen by the magic lantern, and the phe- | 
 nomena are produced so as to be visible ||) 
 by a roomful of spectators. The sealed ee ) 
 tube is termed Natterer’s tube. ot 
 
 Hannay and Hogarth, in 1880, in experi. N@tterer's 
 ments on the critical state of matter, found oat 
 that several salts, such as potassium iodide and bro- 
 mide, would dissolve or volatilize in gaseous alcohol | 
 fepoetenipetatureO1.375,4.0. (707, H:), 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 
 
 NUNN 
 
 Nl 
 ATI 
 
 {| 
 i 
 1 
 
24 LIQUID, ATRZAND AA EE 
 
 solids and liquids. As a liquid, bromine may be 
 cited. This was placed ina 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 “guzde Pictet 
 (page17o) 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 of 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 
 
20 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 ina body. 
 It is a somewhat unfortunate unit, as it is constantly 
 confused with weight. A piece of iron hasa 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 
 ot 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 forone 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. 27 
 
 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 of 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 “bitum just as motion does. A 
 man may run or wa.-k or stand still. He thereby 
 creates or annihilates motion. Hemay 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 lessonin 
 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 itis who gave one of 
 the first blows to this name. 
 
 There is one survival of the erroneous doctrine 
 
LIQUEFACTION OF GASES. 29 
 
 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 action 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- 
 perly 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 frictional 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- 
 mento sencroy.s). lo, “do swork,y..is. 10, 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 hfting 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 1s now’ stretched: 
 The ‘energy’ of the® éxperimenter: is ~ spentesonm 
 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 
 
 yee 10mn.. rout: toysrest alter ats<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 runsa 
 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- 
 izcd by man, and these energies are called available 
 energy orentropy. 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 ina 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 pepular 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 shghtly heated. Then it loses the 
 heat ina 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 tne air, by heat such as is usually 
 
26 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 che 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, a7 
 
 CHAPTER II. 
 FEAT. 
 
 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’ i1lstrument 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, 
 andeetiree mares in, -eeneral@ use, - Ehermometers 
 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 forthis 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. Onc 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. Inthisthe 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, ashe interpreted it, his thermometer 
 contained 11,124 parts of 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 11,336 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 1 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 1 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. AI 
 
 clusion that, when the temperature has been lowered 
 273 degrees, the gas, losing 1 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 ina very 
 crude way, but it gives a simpler presentation of tne 
 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 1 degree, the 
 -volume of a gas will increase by z4 3 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 had to be discarded because the metal 
 solidified at a comparatively high temperature when 
 referred to the degrce of cold attained in the experi- 
 ments. Even in Faraday’s experiments the mercurial 
 thermometer was discarded in favor of the aicohol 
 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 —110° 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 glanzende Bestatigung) is given by an experi- 
 ment of Natterer, who shows that the incredible 
 pressure of 3,00) 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 (Wiedemann’s 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 —116° C.(—177° F.) It melts, 
 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 —130°5° C. (—203° F.) Methyl 
 alcohol (wood alcohol) was easier to freeze than 
 ordinary alcohol. Phosphorous chloride froze at 
 about —111°8° C.(—169° F.) These substances, it is 
 claimed, were never frozen before this period 
 (Wiedemann’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 
 
 Celsius 
 
 Scale2728- 
 
 - 180 
 
 100 
 
 30 
 
 ~100 
 
 -150 
 
 C 
 
 r= 
 
 LIQUID AIR (AND. THE 
 
 Absolute 
 Scale 
 
 500 
 
 450 
 
 100 
 
 350 
 
 200 
 
 150 
 
 100 
 
 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 &. Mercury, J, lies 
 in the tube, cutting off the end from 
 the bulb. As “the air -expandsiig 
 forces the mercury up; as it con- 
 tracts, the mercury descends. This 
 isa 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 
 scientinc,; work:. it iscalledase ae 
 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 1s —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 hquefies. 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- 
 R struction is given, 
 
 which can be readily 
 followed by the 
 reader. 
 
 A bulb, A, is filled 
 with perfectly dry 
 pure hydrogen. 
 From its top acapil- 
 lary tube; a, arises 
 
 | and connects with 
 Details of Hydrogen Thermometer, a mercury tube, 5S, 
 
 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, ¢, of glass, ivory, steel, or 
 
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, k, 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 ona firm stand and attached to the 
 tube enables this to be done. The tubes, #&: and 5S; 
 contain mercury. 
 
 If the tube, A, is raised or lowered to the proper 
 point, the mercury in S 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 aninch. 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, ¢. 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 & will 
 
4% LIQUID AIR AND THE 
 
 be lower; the readings being taken only when the 
 mercury in S has been brought to its exact level by 
 raising or lowering the manometer tube, &. The 
 
 ivan Thin 
 
 Bi 
 
 O mw 
 
 AA 
 he ea 
 hi 
 
 Hydrogen Thermometer. 
 
 greater pressures  corre- 
 spond to greater heat of 
 the contents of the bulb, A, 
 the lesser pressures to lower 
 heat. By measuring the 
 difference of level potmmaue 
 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 
 
 and down until the image 
 
 oe 
 
LIQUEFACTION OF GASES. 49 
 
 of the surface of the mercury in the manometer 
 tube, A, exactly coincides with the cross-wire as seen 
 in the telescope. The telescope is now swung ina 
 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, S; the difference gives the 
 pressure of the hydrogen in units of a column of 
 mercury. 
 
 As the point, ¢, is supposed never to change posi- 
 tion, the scale may be adjusted so that its zero is at 
 the level of the point. Fora 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, S the 
 mercury tube, & the manometer, 7 J the frame, 
 and & 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 Leyden, prepares 
 hydrogen tor 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 S just reaches the point, ¢. (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 Sy) be the specific gravity of the gas in the bulb, 
 let V, be the volume of the bulb, and ~ the volume 
 of the capillary tube; let H’ be the height of mer- 
 cury column, measured from the fixed level of the 
 point, ¢, to the level of the upper surface of the mer- 
 cury in the manometer tube increased by the height 
 of the barometric column. S,is taken at 0° C. and 760 
 mm. barometer. The weight then will be expressed by 
 
 - Ely 
 So | VG = Vo ———= 
 76) 
 
 Next the bulb is placed in the substance whose 
 temperature-is to be. determined. Let 2 be vthe 
 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 
 
 I+aiz H 
 Ik? 760 
 
LIQUEFACTION OF GASES. 51 
 And equating we have: 
 
 lot le gad H 
 So Vo + YW) = So v; + a] == 
 760 It+kt 760 
 
 Solving these with respect to ¢, we find that— 
 ey (Vo + %) (A—H’) 
 V, (4 H’—a H)—  & (H—H’) 
 
 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 
 
52 LIQUID AIR AND THE 
 
 Kamerlingh-Onnes’ 
 Thermo-electric 
 Thermometer. 
 
 copper, nickel and zinc. Other 
 couples are German silver—cop- 
 per sulphide (Becquerel’s); Ger- 
 
 ‘man silver—zinc-antimony alloy 
 
 (Noé’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. ~ Ina, journal recently 
 
LIQUEFACTION OF GASES. 53 
 
 started in Berlin, and which is devoted to the topic of 
 compressed and liquefied gases (Zeztschrift 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- 
 electric 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 
 (o‘00001) 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 sucha 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- 
 gine 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 
 
56 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 which 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- 
 7 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 itis 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 
 
 ane to the changes of temperature 
 Sar eie ee by separating it as far aS possi- 
 A vnrniometen 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 
 
 (r 
 
 iii 
 
 SS 
 
-LIQUEFACTION OF GASES. By 
 
 coil. It isa 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 o'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 .-hermometer was 
 constructed with a view to 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 resistance 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 by passing 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.» —Atter sits 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 
 
 GRAB PEAR ELE 
 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 variationsrof 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 #5 
 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 
 
60 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 
 
 Vacuum 
 
 — AirA B 
 
 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 atube. One is charged with gas under pressure, 
 the other has a vacuum produced within it. A cack 
 
LIQUEFACTION OF GASES. 61 
 
 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, ahd 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 fail, 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. 
 - Ourancestors had their own way of looking at 
 gases. They at- 
 N tempted to classi- 
 \ oe c fy them into per- 
 N 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 
 enoughis introduced, an excess of liquid may be leit, 
 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 tem- 
 
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 
 nydrogen, 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. Thenenergy has to 
 pe supplied to the gas to enable it in turn to expend 
 energy onits 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 1 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 1°4058. 
 
 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 OSH wit Oe IE 
 expansion or contraction. Canuistd | a “Ke 
 
 Suppose that a gas is placed ina sspidioH 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 encrgy 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 is adiabatic. 
 
 The condition rarely exists in practice, except in 
 approximation, because as we work with gases under 
 confinement, there isa 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 abouta 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 are 
 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 1°4058 (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 intemperature. 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 1 cubic foot of air at a temperature of 
 100° 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 
 
7O 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 isa 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. 71 
 
 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 9, and let 
 6 and © indicate two temperatures, ©' being the 
 higher, the second law states that in a reversible 
 heat engine— 
 
 , G1 — & 
 
 Efficiency —= 
 1 
 
 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 convertcd 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 1s 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 ora 
 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 
 ep ©. (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 
 ato° C. Weshould find at the end of the process that 
 we had a pound of water at exactly the same tem. 
 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 tem- 
 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. 77. 
 
 toa 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. 
 pone el ;) 
 
 The way in which water is made to boil is usually 
 by applying heat toit. 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 
 to 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 coidness, and 
 get rid of its oid 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 attracticn 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 tike 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 
 spout ireely, . 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 hes 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. SI 
 
 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 ona 
 Crookes layer. The real 
 layer is exceedingly thin. 
 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 
 
 Theory of Spheroida! State. 
 
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, whichis 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 froma 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 hght 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 the 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 
 
 CELA P Dr he Lv 
 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—lIts 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 ; im 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 init. 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 
 
£6 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. | 3 
 
 Thus, our atmosphere has a far different relation 
 to us than is held by the true ocean of liquid matter 
 that spreads over so large a proportion of the 
 earth’s surface toits 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 cubicinch 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. 
 
 4 
 
LIQUEFACTION OF GASES. 87 
 
 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 trom 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 infinitesiinal 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 squareinch. 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 onthe earth. Itis 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 
 
gO 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 at aslight 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. or 
 
 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 later. 
 
 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 
 
 GHAP GEARS Ve 
 THE ROYAL INSTITUTION OF ENGLAND. 
 
 The Royal Institution—Its origin and objects—Count Rum- 
 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 Dewar 
 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. In 
 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- 
 fer with Count Rumford on the matter, subscriptions 
 
‘MOIJNyYsUy [eAOY oq} Jo Aroyer0qe’yT 
 
 semznioyy 8,04p ep Jo fs N0Gy 
 
 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 Woburn, Mass. His life 
 
04 LIQUIDVATRVAN DSi 
 
 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. 
 
 = 2S Anil W/ 
 == Oly 
 SS TT 
 pT WINN 
 
 + 
 
 Lecture Room at the Royal Institution. 
 
 Courtesy of McClure’s Magazine. z 
 
 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 of 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 of George the Third, and in 1810 
 its powers and functions were eniarged 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 43,333 6s. 8d. each, which 
 sums constitute two-thirds of 410,000, 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 18 of that year, on account of the death of 
 Mr. Fuller, who had done so much for the Institution. 
 
96 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. Q7 
 
 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 hecalled 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, Brunel 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 
 abouta 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 4100, 
 
 and eventually the Fullerian professorship, appoint- 
 ing him for life, with the privilege of giving no 
 lectures. The salary was then placed at £100. 
 
 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. 
 
ie 
 
LIQUEFACTION OF GASES. Io] 
 
 CEEAP TER. Vi 
 MICHAEL FARADAY. 
 
 Michael Faraday—His early life—KEarly 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—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-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 Sived 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 extremeiy 
 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 dent 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 hisway. 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, andthe 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 savs 
 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 bcen 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 buta 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 
 
2OA. 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 lfe 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 1, 1813, Faraday was engaged as assist- 
 
LIQUEFACTION OF GASES. TO5 
 
 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 ¢ry 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 
 
106 LIQUID AIRGAND IEE 
 
 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 urdertaken 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, Northmore, whose work is 
 recorded later in this book. 
 
 On May 1, 1823, he was proposed tor a fellow of 
 
LIQUEFACTION OF GASES. 107 
 
 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 asa fellow of the 
 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 
 
108 : LIQUID ‘AIR AND HE 
 
 intimate fend 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: 
 
 “T 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. 109 
 
 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.’ 
 
 “Early on the next morning I received from Mr. 
 ' Faraday the following laconic note: 
 
 “DEAR SIR: The oc/ 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. 
 
I1o 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 (pagerr8) 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. III 
 
 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 ogo. 
 
 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 
 360 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 drv 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 too grains of silver chloride would 
 absorb 130 cubic inches of the gas. This highly 
 charged salt of silver, heated in the sealed tube, 
 
I12 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 firs: 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. I13 
 
 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, 1845. 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 —76:7° C. (—106° F.) 
 To increase the. cold he placed the mixture under an 
 
114 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. 7 
 
 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. Ils 
 
 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. 
 
116 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 ina 
 drill holein 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 of 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 1,1co 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. Li7 
 
 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. Theair 
 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 1805 and 1806 papers by Thomas Northmore 
 appeared in WVicholson’s Journal, xil., 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 oi 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 
 such 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. 
 
118 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 fuzd.”’ 
 
 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 319. 
 
 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 ef ‘seg., a -papereon 
 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. 18 fe) 
 
 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 tailow, 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- 
 locks 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 history of the lque- 
 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 Setence, 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 tem- 
 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 
 ‘27-7 chlorine, 72°3 water, or 1 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 CLOH;. 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 Soctety of London, 1823, vol. 
 xlll., page 160 e¢ seg.—a most sumptuous publication 
 wherein the work is described in full detail by Fara- 
 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 106and 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; Mcholson’s Journal, xii., page 
 368, Klli., page 232). 
 
 The arseniureted hydrogen experiment, however, 
 has a great subjective interest, as it illustrates the 
 danger inherent in the work o1 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 
 itin quantity, by digesting an alloy of 15 parts tin 
 and 1 of arsenic in strong muriatic acid, collecting 
 it over the pueumatic trough, and exposing it to the 
 temperature pede by mixing snow and calcium 
 chloride, in which, as a test of its coldness, several 
 pounds or quicksilver had been frozen in the course 
 o1 afew minutes. This was certainly a most-power- 
 ful freezing mixture. Yet Faraday doubtsif the gas 
 was really liquefied, as he himself had tried it at nearly 
 —18° C. (o° F.) at a pressure of three atmospheres. 
 
 Had any accident happened during these experi- 
 - ments, had aretort 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 inthe 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 5 
 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, 6 andc. A long-stemmed fun- 
 nel was used to pour the liquids through, if liquids 
 were used. The ends, a and d, were then sealed, 
 and, by turning the tube over, everything collected 
 
 in one end, a. The tube was placed 
 o 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 
 aly ° \ any liquid that distilled over was 
 caught in the intermediate bend. 
 
 To determine the pressure pro- 
 duced in the tube, a small tube 
 i closed at one end, o, and with a 
 | short bit of mercury, z, in its bore, 
 was placed in the experimental 
 tube before closing it. As the pres- 
 
 renee os aiming oni, foe: the mercury was forced 
 
 Tahessand toward the end of the small tube 
 Manometer. containing it. This it did because 
 the air confined between the mer- 
 cury and the ae 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. 
 
LIQUEFACTION OF GASES. 125 
 
 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 were 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- 
 cury, 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 lke 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 ina 
 straight closed tube, occurs in the liquefaction of 
 chlorine from the hydrate. Chlorine hydrate, a 
 compound of chlorine and water (Cl.OH;), 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 asa 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. P27 
 
 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 known, 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 ieast, 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 Aznales 
 de Chimte 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 
 
 a 
 
 Dela Tour’s 
 Apparatus. 
 
 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 @ie 
 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: (Ihe other end)2a;5 was" alsa 
 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 
 
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 Ax- 
 nales, and, like Faraday’s bent tubes, is an interesting 
 example of early methods. The levels g, e’, 4, &, 
 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 4,c,d,e, in the cut on page 130 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 f, were sealed by melting the 
 glass witha 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’, 6’, g’, 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 cme sim- 
 ple apparatus. 
 
 One tube was two-fifths filled with alcohol sp. gr. 
 0844. The liquid expanded to double its volume and 
 then,.at a temperature: of 258°7° C. (497°7° 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” Ofsa75 
 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 Ampére, 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. 
 
 Ampére 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 m:.ker. 
 
 Those who are familiar with the Ampére 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. 
 
 Ampére began his lecture and gave his demon- 
 stration “on the ‘blackboard; “He waseinst re. 
 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. 
 
 Ampére 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. 
 
 Ampére left the hall with Colladon. No one else 
 was with them. They followed the Boulevard 
 St. Michel toward the Seine, the tears running 
 down Ampére’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 Ampére was trying to forget 
 his sorrows 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 Ampére. 
 
 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 
 
 ARTO SOO se wee pew ecececesecc-coe 
 
 ny, 
 Ba ccorcascce 
 
 ome cconweerse A, 
 
 pital ae aaa ey ——  y 
 
 Ld 
 eecossaa 2000 secs. 
 
 2 TSE Sewers © 
 
 D. Colladon’s Apparatus of 1828. 
 
 which rose from 
 it was from 006 
 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. Bya tube, 
 C, counection 
 could be made 
 with its interior. 
 An extension, 4 
 A, was bolted 
 firmly :to’ Tit.aaee 
 glass gas tube, 
 T T, open: at the 
 bottom, with a 
 long capillary 
 tubese2"%, “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, 2. 
 
 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 4oo 
 atmospheres pressure, without result. 
 
 The principal parts of his apparatus are still in ex- 
 istence, carefully preserved in the offices of the So- 
 ciété 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 Chimie 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 ies 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, 
 Bohl gletter x:, pares. 130,-131:) 
 
 The Thilorier improved apparatus is shown in the 
 
 Thilorier’s Apparatus for Liquefying Carbon Dioxide. 
 
 illustration. The rignt 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 init. 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 inthe 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 — 
 4o° C. (104° F.) the pressure would rise to one hun- 
 dred atmospheres. 
 
LIQUEFACTION OF GASES. I4I 
 
 Thilorier did some good work on liquid carbon 
 dioxide. As far back as 1835 we find a paper of his 
 in the Axnales de Chimie 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 frotd—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 108 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, anew one was produced by an 
 Austrian scientist, which apparatus was compara- 
 tively safe. Ina 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 hadasolid piston. At 
 the point where the pump barrel connected with the 
 reservoir wasa 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 inthe 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 aman, 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, 7, 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; , 2,0, the drainage pipes and cock; C, 
 the cylinder or pump barrel cooling jacket; and be- 
 low is seen the small jacket for cooling the piston 
 
LIQUEFACTION OF GASES. 145 
 
 rod. The piston rod, ¢, with pitman, 4, works in 
 the slides, P, Q, in the massive metal frame. The 
 gas from the bag, A, dried in its passage through 
 pie bottle, /, enters by the’ pipe; A. 
 
 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 (Wzedemann’s Annatlen, 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 11 are embodied, 
 at which exhibition carbon dioxide snow produced 
 by Natterer’s process was shown to adelighted 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. xi. 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, Z, which is held by screw bolts on 
 the end of a copper tube, X. A perforated 
 block with screw thread cut in the per- 
 foration closes the lower end, and a steel 
 screw, S, 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. pee 
 
 ‘ ; pressing 
 
 To 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 Tvansactions 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 init. 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 wires, 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 compressed 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 7vansactions of the Royal Society, 
 as quoted, with very elegant cuts of the apparatus. 
 It appears in a translation in the Aznalcs 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 mentioncd 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 
 afew 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. I5!I 
 
 reduction to the vesicular state of the gases con- 
 muned. _ 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 Re VITk 
 RiOuLebICEErt: 
 
 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 11, 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 /iquzde 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 
 Ecole 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 
 
1§4 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 enterea 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 
 oecupied 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 Société 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 
 Cellérier 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 Société 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 Aztude Critique du 
 Matcrialisme et du Spiritualisme 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, WV. 
 
 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 isa 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, J7, 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, 4 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, 4 and JB. 
 
 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, 4, contains liquid or solid 
 carbon dioxide, which constantly evaporates. The 
 pumps, & and /, pump gaseous carbon dioxide out 
 of the upper end of 7 and condense it in the tube, 
 K, where it is cooled by the boiling sulphur dioxide. 
 The small pipe, 4, 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, JZ, 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 eae 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, J, by the 
 evaporation of the cold carbon dioxide, was kept 
 at a temperature of —140° C. (—220° F.) 
 
 In the improved apparatus, the tube, 1/7, was made 
 of copper, and the liquefied gas was withdrawn at JV; 
 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, 7. 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. 161 
 
 and the tube, JZ, was filled to one-third of its length 
 with the liquid. The tube being of 1 centimeter (0°4 
 inch) internal diameter, it will be seen that this was 
 a considerable quantity of oxygen—about 22 cubic 
 centimeters or 14 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 
 l’orifice en inclinant lappareil”). 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, 7. 
 
 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: 
 
 “Oxygéne liquéfié aujourd’hui sous 320 atmo- 
 spheres et 140° de froid par acide sulphureux et 
 carbonique accouples. 
 
 iene, 
 “ RAOUL PICTET.” 
 (TRANSLATION. ) 
 
 “ Oxygen liquefied to-day under 320 atmospheres 
 and 140° of cold by suphurous and carbonic acid 
 working together. 
 
 “Signed, 
 sh AQUI RICTED.” 
 
 The terms sulphurous acid and carbonic acid are 
 synonyms for sulphur dioxide and carbon dioxide. 
 
 The substitution of the open copper tube J/ for the 
 closed one and the use of the manometer, &, and cock, 
 NV, are later modifications. The temperature of the 
 oxygen generating retort, Z,is now put at 485° C. 
 
162 LIQUID AIR AND THE 
 
 a af 12747 
 
 | 
 j 
 
 Annaratn 
 
 Pictet’s Gas Tignleariad 
 
7 
 
 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 J of 500 atmospheres. The gas began to liquefy 
 and the pressure fell to about 320 atmospheres. On 
 opening JV, 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 fare 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 4 and /of the diagram on page 158. 
 
 ~ In @ is the carbon dioxide tube, where the gas 
 
 from the outside tube in / is cooled by boiling sul- 
 phurous oxide, which is in a tube inclosing and 
 concentric with the carbon dioxide tube. These are 
 Kand C of the diagram. 
 
 G is a gashclder filled with carbon dioxide gas. 
 K isareservoir of liquid sulphurous oxide. VP are 
 the pumps, and # 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 
 
104 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. \xxxvi. 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 —14 9° 
 C. (—220° F.) Enough gas was generated to meas- 
 ure 252 liters at 0° 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 Olszewski tried to throw some doubt 
 on the method followed in the hydrogen experiment 
 of Pictet. He published in the Phzlosophical 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 
 
166 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 thisarrangement 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. 167 
 
 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 Chimte et de Physique, Paris, fifth series, 
 vol. xiii., or in the Archives des Sciences Physiques et 
 Naturelles, 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 vwestble 
 by condensing it in transparent apparatus. The pro- 
 blem is very complex, bristling with practical diff- 
 culties. We must avoid the condensed ice (gzvre, 
 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 
 
168 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 3co 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, 
 i261 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 wasall 
 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, J7, 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. \t is still used by him for the pro- 
 duction of low temperatures. The paper will be 
 found in the Comptcs Rendus, 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- 
 pertics 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 gascs, and in the paper in question 
 discusses at some length the use of such liquids, 
 which at relatively low temperatures separate into 
 
170 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. (—95° 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 “guide Pictet (formula CSQO,) with sulphur- 
 ous oxide. At high temperatures the vapor ten- 
 
LIQUEFACTION OF. GASES. 171 
 
 sion of the “guide 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 /éguzde 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. 173 
 
 GLEARA BRAK: 
 BOUISS PAUL GC AICLE TET: 
 
 The life of L.-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 ChAatillon-sur- 
 Seine, in the Céte d’Or, France, on September 21, 
 1842. He studied at the Lycée 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 136) for the purpose of his inves- 
 
LIQUEFACTION OF GASES. 175 
 
 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 
 agas. 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 résumé 
 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 Axnales de 
 Chimte 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 
 
170 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 uepended 
 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 érouillard. We find here an indirect 
 appeal to the criticaltemperature. 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 136and 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. 177 
 
 in the Comptes 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 liquetactions 
 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, 7P. Thisis 
 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, 4, screws down against 
 the flange on the bottom of 4, 
 squeezing it against the packing 
 shown under A. JJ 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 
 amatter of security. The darkly 
 shaded part within B and J re- 
 presents mercury; the lighter 
 shaded portion in Bis water. A 
 cock serves to draw to draw off 
 the refrigerating agent from J. 
 Uis a pipe joined by the coup- 
 ling, R £,to the mercury vessel. S is the platform 
 which supports the shade, C, and refrigerant ves- 
 sel, M. 
 
 When the apparatus is first set up, the level of the 
 
 tion Apparatus. 
 
178 LIQUID AIR AND THE 
 
 mercury in Z 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, P7, 
 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 180. A valve in the compress- 
 ing press or pump was suddenly opened by the han- 
 dle, O, 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. i79 
 
 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, 8. 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 
 
LIQUID2 AIR AND TALE 
 
 180 
 
LIQUEFACTION OF GASES. 181 
 
 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. 4 is a steel cylinder with plunger 
 actuated by a screw, /, and held in brackets, B Z. 
 M 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, O, was provided, 
 and it was this valve which constituted the distin- 
 guishing feature of Cailletet’s process and apparatus. 
 
 At S is a cross-connection to bring into connection 
 the hydraulic cylinder, 4, the liquefaction apparatus 
 of page 177, and the gauges. Two of these are shown. 
 One, designated by WV, is a Thomasset manometer ; 
 WN’ is a Cailletet glass bulb manometer, such as 
 spoken of on page 187. 
 
 The liquefaction apparatus, #, stands upon a shelf 
 of iron, 4, with set screws, d d, to secure ae mercury 
 reservoir, a, 
 
182 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 formuia, should give a lowering of tempera- 
 ture of 200° C. (360° F.) This release constitutes 
 the advance in his work over all his predecessors. 
 Asa 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. 3 | 
 
 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, page 1017,1n which he says that 
 he has liquefied nitrogen dioxide, using a tempera. 
 ture of —11° C. (12°2° F.)and a pressure of 104 atmo- 
 spheres. At 18° 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 : 
 
 “T hasten to tell you, you first, and without losing 
 a moment, that I have liquefied to-day both carbon 
 monoxide and oxygen. 
 
 “T am, perhaps, wrong in saying liquefied, for at 
 the temperature obtained by the evaporation of sul- 
 phurous acid, say —29° and 200 atmospheres, | 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. 
 
184 LIQUID: AIR AND PHE 
 
 ‘“‘T 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. 3 
 
 “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 (frévzstons) prophecies of M. 
 Berthelot are completely realized. 
 
 | ‘ LOUIS _ CAIEEET Eas 
 
 -~December27 1377.5 
 
 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 ‘“ 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 (/weur),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 Rendus, vol. |xxxv.) 
 
 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 
 
186. 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 7ransac- 
 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 1 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 ved 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 downa tube and 
 found that it gave the same effect as he had seen in 
 his aemaeesler 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 1n number. 
 
 Continuing the compression until 310 atiehheees 
 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. 187 
 
 frozen mercury was covered with hoar frost, which 
 he thought was solid air. 
 
 This closing the tube with a stopper (douchon) 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 ee a EpCg 
 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. Thesteel 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 hquefaction apparatus. The manometer was kept 
 ata uniform temperature by meltingice. 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 ‘ades 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. — we ; 
 
 He also constructed an open end mercurial mano-: 
 
188 LIQUID AIR AND THE 
 
 meter, which wasa 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 
 4 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 PHM ES 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 3,5, of their length 
 or height. This was a very minor matter. But 
 the mercury for the same range expanded y1,;. The 
 
LIQUEFACTION OF GASES. 189 
 
 heat expansion of the mercury, therefore, had to be 
 corrected. The compressibility of the inercury 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 well 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 STIOUIDFAIR GAN Dearie 
 
 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 aliquid ina gas. It 
 reminds us of the solution of a solid in a gas shown 
 when a solution of a solidin a liquid is heated: to a 
 point above the critical one for the solution in ques- 
 tion. Thus,if potassium iodide or chlorophy]l 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 Bano 
 and Hogarth, page 23. _ 
 
 Guilletet noted the same thing with le 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. 191 
 
 Galbanum is a resin imported from the Levant, 
 used in medicine, and of somewhat uncertain origin. 
 Those who are interested in the archzology of sci- 
 ence will find it mentioned in Exodus xxx. 34. The 
 old name for it was chelbenah. 
 
 This ancient member of the pharmacopceia 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 Seeuliar 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 Rendus, vol: xc. 
 Years later he returns to this aleston 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- 
 
192 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 
 anda gas above it are capable of mutually dissolving 
 each other in all proportions. 
 
 His condensing pump, without harmful clearance 
 or lost space (saus espace nutstble), excited considera- 
 ble attention. If acondensing 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 upperend. To avoid clearance 
 he placed a quantity of mercury over the piston. As 
 
LIQUEFACTION OF GASES. 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 lquid 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. 
 
 ec icut ives alséction- of the, barrelolsthe 
 pump. & Z#is the barrel with plunger, 4. The dark 
 portion over the plunger is mercury. At a, 6 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. S is an ebonite valve through 
 which the gas is forced by the plunger into the bon- 
 net which surmounts the barrel. The tube, 7 7, de- 
 livers the compressed gas. A flexible copper pipe 
 fjeconnected to ithe tube, 7 7, 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, &, closes. 
 The plunger then drives the gas before it through 
 
194 LIQUID A 
 
 IR AND THE 
 
 the valve, S, and as it reaches the upper part of the 
 cylinder, the mercury rising into the: narrow ‘tube 
 below S expels the last traces of gas. As the 
 
 Shy 
 
 wy 
 
 : 
 § 
 
 Cailletet’s Mercury Plunger - 
 Air Pump, — 
 
 insure the tightness of th 
 
 plunger descends, an almost 
 perfect vacuum forms above 
 the mercury until the valve, 
 R, 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, S, 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. acre | 
 tihe> base cotethe zbarret 
 
 “screwed into a socket or 
 
 base piece, which held some 
 glycerine ‘or. mercury, .to 
 e packings, 2 and J. 
 
 The presence of mercury made. the lubrication ~ 
 
LIQUEFACTION OF GASES. 195 
 
 problem somewhat troublesome, as ordinary oils 
 and grease coming in contact with the mercury 
 formed almost solid compounds. Eventually Cail- 
 letet adopted 
 vaseline and 
 glycerine as lu- 
 bricants. 
 Wath this 
 pump a man, 
 without over- 
 exertion, readi- 
 ly liquefied 
 20. t.0: 5 0.0 
 grammes of 
 carbon dioxide 
 in an hour. 
 Recognizing 
 the danger of 
 the larger cyl- 
 inders used for 
 holding lique- 
 Med oases, 
 Cailletet re- 
 placed them by 
 a group of nine 
 Bopper tubes, = 
 arranged in a ~ 
 Eylindrical.:. 9.7, 
 group, and all Sates 
 
 connected by ~ Cailletet’s High Pressure Reservoir 
 for Liquefied Gases. 
 
 small copper 
 tubes, @ a, to one central delivery cock, V, and 
 outlet coupling, O. The group was mounted on 
 
all 
 
 196 LIQUID AIR AND THE 
 
 trunnions, #,in a frame, as showninthe 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 inproved form, doing ser- 
 vice at the cryogenic laboratory of the University 
 of Leyden. 
 
LIQUEFACTION OF GASES. IQ7 
 
 Cailletet 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, 0° C. (32° F.) 
 and at —23° C. (—9'4° F.), it was for various pres- 
 sures expressed in atmospheres : 
 
 Pressure. Soe ek cee) —23° C. (—9'4° F.) 
 200 0°58 sp. gr. 0°84 Sp. gr. 
 275 C05.) OS3e es 
 300 O7Os O8Oul a 
 
 As a control, a similar experiment with nitrous 
 oxide, substituted for carbon dioxide, gave at 300 
 atmospheres and at —23° C. (—g°4° F.) a specific 
 gravity of 0-94. 
 
 Another of Cailletet’s classic discoveries is the use 
 of liquid ethylene as a cooling agent. According to 
 
198 . LIQUID AIR AND THE 
 
 him, it liquefies at the following pressures and tem- 
 peratures: 
 
 As, atmospneres ataie-C.<(39°oegn) 
 
 50 a3 66 4° Ce (Go -28 F.) 
 56 “ “ 8° C. (464° F.) 
 60 . EOS Ge tus O aecey 
 
 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- 
 iny together alcohol and concentrated sulphuric acid. 
 The latter, with its high affinity for water, takes the 
 elements of water from the alcohol, and gaseous cthy- 
 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 OMS HAs into snow, like carbon 
 dioxide. 
 
 The classic interest of this~ ieee 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 highdegree 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, pee 
 played an important role in technology. 
 
 An objection to ethylene, as a refrigerating agent, 
 is its cost. It is no great matter to make afew 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 Io 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 Bnirecisted 
 this state of affairs and tried to work with léss 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 atime, 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 greatlv 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 tem- 
 
LIQUEFACTION OF GASES. 201 
 
 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 : 
 
 “Tt seemed probable that this resistance would 
 become extremely small, and consequently the con- 
 ductivity very great, at temperatures below —2o00’, 
 although our first experiments did not permit us to | 
 form a definite idea of that which would occur under 
 
 such conditions.” (Comptes Kendus, vol. c., page 
 1189.) 
 
 This isin 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 determini: g low temperatures. They were 
 
202 LIQUID AIR AND THE 
 
 the following: 1. 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 Comptes 
 Rendus, vol. cxii. 
 
eae 
 
 LIQUEFACTION OF GASES. 203 
 
 GHAPTER? UX 
 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 Ecole 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 Wrede- 
 mann’s Annalen, 1883, is published an article which 
 gives the tull account of their first important work 
 
LIQUEFACTION OF GASES. 205 
 
 in the liquefaction of gases. The authorship is given 
 adualform. 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 “‘ezmer von uns” (“one of us”) is 
 always used. 
 
 Wroblewski died in 1888. As early as 1684 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 Wiedemann’s An- 
 nalen 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 
 Wredemann’s 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 
 
207 
 
 LIQUEFACTION OF GASES. 
 
 aah 
 ' —— 
 
 —= 
 
 a 
 
 I 
 Wily —— se 
 
 f 
 MMMM 
 
 a / 
 
 In the gas refrigerating por- 
 LZ 
 
 tion will be found a reminder of Pictet’s circuits, not 
 J 
 
 Z Wh 
 Wroblewski and Olszewski’s Gas 
 Compression Vessel 
 
 me) 
 a 
 = 0. SOLO. ge ah Agee Fs a, ro Ee aS, et eh iy ans ce ee ana ee 
 Bra Deco Oe ae re HS a AR eco ere Tore coe ae 
 mony 9 St eS Se AO eo gee Pies S$ Bde z 
 Fatale nA BESE Oo 2a Oo eee ace cei a 
 Rms ec eoP rt 'vagh ve oe SRCU Sak ator ae Me Sop ae OO Sl at ees 
 oO DSN . ct O — o mH 8 Dm & a MW 4. 
 st gy GG " or Summa rPoe Pad or ceeg Sern en eae og 
 © tO. + Aa QD Poin, = - on a, ) fs} 
 ra n 2 HE A oa Bo, Cp OW 8 Bea ope 0 Ve ae So oa 
 par Go Ay FS neh PO aS SO Gok fee 2 B88 Oo bon ee | fotos Ste 
 
208 LIQUID AIR AND THE 
 
 centimeters (23°2 inches) deep and 85 centimeters 
 (3°4 inches) wide. ¢ ando isa bronze piece which 
 forms a tight connection between the gas tube, z, 
 and the upper tube, ¢, 7, g,¢ 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 f. The steel 
 tube was inserted in place, a groove along the line, 
 e, é, 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, #, the steel tube expands, and they 
 glass gas tube, z, is cemented into it. At & the 
 bronze steel-lined piece has aconicalend. mis a 
 glass tube cemented in place, and all is secured by a 
 coned piece, /, with screws, 7, as shown, the Screws 
 uniting all parts to an airtight joint. 
 
 At-patube is connected which leads to a force 
 Put: 
 
 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 Wiedemann’s Annalen. 
 
 We have, as before, the vessel, z, with its steel con- 
 taining vessel, 6, only the top of which is shown. 
 The capillary tube, g, was o’g centimeter (0°36 inch) 
 external diameter and a little over o'2 centimeter 
 (o'08 inch) internal diameter. The glass vessel, z, 
 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, s, is provided with an india rubber stop- 
 per of its own, perforated for three tubes. One is 
 
 AIT ORD 
 
 NN RLS 
 = 
 
 a} 
 
 . 
 NZ 
 LL 
 
 Uv 
 
 g 
 Z 
 ZN 
 Z 
 g 
 Zs 
 
 Wroblewski and Olszewski’s Apparatus for 
 Liquefying Gases. 
 
 the end, g, of the gas tube, 2, the other the stem of the 
 hydrogen thermometer, ¢. The third receivesa T 
 shaped tube, «. Liquid ethylene is contained in the 
 
210 LIQUID :ATRVAND. 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, 0’, 
 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, w, by the tube, z, 
 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, z, mercury was contained in the vessel, 4, 
 and the pressure was increased to any desired extent 
 by pumping water into 4. 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 24 millimeters of 
 mercury, which is a small fraction of an atmosphere. 
 The ethylene, when first admitted to the vessel, s, 
 boiled tumultuously, but soon quieted down and 
 kept slowly boiling, thereby producing a a 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 tothe 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. (— 02° 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: 
 
 “ Oxygéne liquéfié, completement liquide, incolore 
 comme l’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 Rendus 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”’ (‘uz de nous’), 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 9g: 
 
 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, liquéfiée 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: 
 macors: 
 
 “Oxyde de carbone liquéfié dans les mémes con- 
 ditions que l’azote. Ménisque 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 evena 
 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 
 S1ze. | 
 
 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 was known, the experi- 
 menters using Andréeff’s determination (Lzebzg’s An- 
 nalen, vol. cx., page 1). The calculations are too com- 
 plicated. to -be here reproduced: » The -resultvobs 
 tained for oxygen at about —130° C. (—202° F.) and 
 the pressure of liquefaction was C899. 
 
 Wroblewski, still longing to produce liquid oxy- 
 gen in quantity, says, in December, 1883, that it is 
 merely a question of appliances to produce liquid 
 
LIQUEFACTION OF GASES. 215 
 
 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. I[n- 
 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. Asan example 
 
216 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, g, of the apparatus, page 209, by the aid of 
 boiling ethylene contained in the vessel, s, as already 
 described. As the oxygen liquefied its level rose in 
 the tube, g, and eventually reached a point above 
 the level of the liquid ethylene in s. Now it is evi- 
 
 = 
 
 dent that, as the liquid oxygen reachesa pointin 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. 217 
 
 experiment. Thesame 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- 
 caltemperature 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 
 
218 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 poses 
 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: 
 
 “ Hydrogéne refroidi par oxygéne bouillant s’est 
 liquefié 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 o*2 
 cm. to 0°4 cm. (0°08 inch to o*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 gypsay_ 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 div- 
 
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, in 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 2I°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. 1 UZ2y 
 
 this distinguished investigator. He seemed to pos- 
 sess the rare faculty of not disputing with any of his 
 confréres. 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 résumé 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 18 millimeters (0°56 to 0°72 inch) in in- 
 ternal diameter. The walls were 3 to 4 millimeters 
 (o'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 sla 
 
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 Budle- 
 tin internationale de 1 Academie 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 lque- 
 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 1883 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 isacylinder of oxygen gas compressed to 100 
 atmospheres. It is connected by a tube to the steel 
 reservoir, 8. From the lower end of the steel reser- 
 voir a tube with stopcock, 4, descends. A gauge,.a, 
 indicates the pressure of the oxygen. It is obvious 
 that any considerable diminution of pressure would 
 indicate liquefaction. 
 
 ag : 
 
 Ge pees 
 
 Olszewski’s Liquefaction Apparatus of 1890. 
 
 The reservoir, 4, 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, ¢, and is bent into a coil between C and D. 
 
LIQUEFACTION OF GASES. 225 
 
 The coil is contained in a vessel, £, which is charged 
 with a mixture of ether and solid carbon dioxide. 
 A tube, a, leads from this vessel, which is absolutely 
 tight, to an exhausting pump. JZ contains liquid 
 ethylene, which is kept cold by ice and salt mixture 
 in the outer vessel, /. 
 
 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 liquid 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, 4, filled with 
 the liquid. It could then be drawn off by opening 
 the cock, 8. 
 
 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. It 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 instrument. 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. 227 
 
 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. 
 oy AOC e Sl eS Weer es Ce haere 1000 ohms. 
 Se (LOS Boe Es) ait pcs ermie 9.5 Sone 
 Bem 2 eek e200 Gas) iene wats oie m os nix Pees 
 = aa TRE | ORTA ESE i te Sealed ea ern aera ee AGS ate 
 
 This shows the decrease in electrical resistance due 
 to reduction of temperature which is utilized as a 
 thermometric factor. But moreis shown. The fall 
 in electrical resistance per degree fall in tempera- 
 ture grows greater as the temperature descends. 
 
 Thus: 
 Ohms. 
 
 Between 0° and —78:2°C. the fall per degree is 2°557 
 66 —78°2° 66 —182'5° C 66 66 66 66 2°655 
 (6 —182'5° 66 —208'5° @ (6 6 66 66 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 Io 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 7o 
 atmospheres, the mist appeared at pressures of 14, 16 
 and 18 atmospheres respectively. Allconstancy 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. 229 
 
 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. 
 
ee 
 
LIQUEFACTION OF GASES. 231 
 
 PCHAPTER: XI 
 
 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 Inst1- 
 tution apparatus—Cooling cycles employed—Laboratory 
 apparatus—Vacuum vessels—Air as a heat conveyer— 
 Experiments with incandescent lamps—-Reflection of ether 
 waves from vacuum vessel-_Keeping power of vacuum 
 vessels—The Dewar vacuum—lIts 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—A pparatus 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—Ljiquefaction 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 EIQUTD*ArR TANT San 
 
 Cambridge. He is Fullerian Professor of Chemistry 
 in the Royal Institution of England, thus being 
 Iaraday’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 1833 
 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 
 —100° 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 Mature 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 becn 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 gastube by the magic lantern. It is of interest 
 
(2 
 o 
 oe 
 Z 
 < 
 a 
 < 
 < 
 = 
 a 
 _ 
 ma 
 
 ine, 
 
 zu 
 
 's Maga 
 
 ? 
 
 Courtesy of McClure 
 
 in the Laboratory of the Royal Institution. 
 
 f. Dewar 
 
 Pro 
 
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 
 andthe 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 ly 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 
 
236 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 /, and the gas from C reaches it through 
 a fine copper tube, 2. Dis a manometer to show the 
 
 Dewar’s Early Oxygen Liquefaction Apparatus of 1883. 
 
 pressure of the gas, and /is an air pump gauge to 
 indicate the vacuum under which the refrigerant 
 boils. 7 is the point of attachment of an air pump 
 for producing this vacuum. 
 
LIQUEFACTION OF GASES. 237 
 
 The gas liquefaction tube, 7, 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 #/, and that the exhaus- 
 tion takes place from its bottom. Its top is hermeti- 
 cally sealed, and holes at & 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 hquid nitrous oxide or solid 
 carbon dioxide is used in G, then the pressure of 
 the oxygen must be brought up to 80 to too 
 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, 4, 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 
 <pparatus 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 go at- 
 mospheres and was evaporated in a condenser jacket 
 so as to give a temperature of —go° 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 
 
 IN 
 
 Wn NE 
 |" 
 
 \[-— 
 
 ayer N 
 i BR < | 
 Bl VCO Neale: h \s ff 
 ‘| U% By — \ - 
 Us eh ye a aa 
 
 <2 
 
 Courtezy of McC lure’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. 241 
 
 air or oxygen. The small cylinder above and 
 in a central position contains the liquefaction appa- 
 
 = TEL | Mm 
 Tl] ) \ © 
 ! ‘( Jil 
 
 M11 \\\ TASS 
 
 Nl 
 
 Dewar’s Small Gas Liquefaction 
 Apparatus. 
 
 ratus. It forms avery 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 
 
 WY} 
 
 WG 
 
 ex Xer XOX Jom 
 WWW 
 
 OSGi OT «EM © 0 EF o RE° Hil 9 AK © Io BRS AO 
 
 @X Yex XOr Yel Xe 
 ANN 
 
 een 
 
 a 
 
 Section of Dewar’s Small Gas 
 
 GG aan ae 
 2a 
 
 = 
 
 | eae PO BO BOSOGO OO S— 
 
 ANN 
 
 NON 
 
 WW 
 
 WN 
 
 O_O O O_O 
 
 ee 
 XK KERR 
 z) 
 
 (ome mre) 
 
 WILL 
 
 hay 
 
 B 
 
 Liquefaction Apparatus. . 
 
 rated by the 
 
 the inlet, &. 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, 4, 
 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- 
 hand 
 wheel above C. 
 
 The air or oxygen, 
 after going through 
 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, /. 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.(—110°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: 150 
 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 atin 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 knownas 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 anincandescent 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 Philosophical 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 ona 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. Wehave 
 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 hquid 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 Liqueficd Gases Livaporating 
 from Double Bulbs. 
 
 Liquid oxygen, vacuum space, 170 volumes. 
 
 ifs (<5 air cc 840 (<9 
 fo ethylene vacuuin, |“ 56 : 
 “6 7 air 66 230 See 66 
 
 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, 34 per cent. 
 
 Three dry air spaces, cne 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 7ransactions, vol. xxvii. 
 
 Courtesy of MceClure’s Magazine. 
 
 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, A, for production 
 of a vessel in which a Dewar vacu- 
 
 . : Production of 
 Meee sori inay bescaiied: 15 tO be’) pawar Vacuum. 
 
 produced. The large bulb is the 
 
 one which will eventually form the vessel. From the 
 small bulb, W, the tube, 7, descends a distance of 
 over 30 inches. 
 
250 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 
 asa 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, 4, 
 of the small bulb, the tube melts together, and the 
 two bulbs are sameradl hermetically sealed. se trace 
 of mercury vapor is still in them. 
 
 The next operation is to chill the small buib 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. BET 
 
 exists in the bulbs. A sufhcient 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 
 —180° 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 10-* 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. Ifit 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 Torriceilian 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 widély 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 (0°08 inch) in diameter and 50 millimeters 
 (2inches) 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 apphed 
 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 une 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. 
 
 ble 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. 258 
 
 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 reduccd 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 gives us 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 
 
250 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 
 when 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 1s increased so that tne 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, Disa silvered vacu- 
 um vessel of liquid oxygen, C is the 
 wire to be tested, 4 is a steel rod 
 which runs to a set of multiplying 
 levers which produce the breaking 
 strain. At Bis 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 enae for De- 
 the vessel, the glass will break, and epee ue Tensile 
 
 i , rength 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 
 
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 Zyvansactions of the Royal Institu- 
 tion. The work was published in 1894. 
 
 Breaking Stress of Metallic Wires tn Pounds, 0°098 
 Inch Diameter, at 15° C. (59° FF.) and —182° C, 
 (—295°6 J) 
 
 eh Be —182° C. 
 
 (59° F.) (—295°6° F.) 
 Pteel (scotty were eee 420 700 
 ITON eek cp teen eee ee 320 670 
 (CODDEL Inhcenie ae es 200 300 
 ISTASSS IL. beet ae orn 310 440 
 Eras Vela 470 600 
 Gro Te Dasete pee eta tay wae! 255 340 
 DIWVGr ay at eeth. eae 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, 
 o'2 Inch Diameter, at 15° C. (59° F.) and —182° 
 C. (—295°6° F.) 
 
 pnd OF —182° C. 
 
 Sorte) Ss 20540 aks) 
 (ETN ak 2, SI AMIE fos Maat 200 390 
 eats atic oe Fe 170 
 TENA In eR eee a 35 26 
 BYLGRCUL Vey ew yc. ee O 31 
 ISISIUUL ee ence cre ae 60 30 
 BVI OU eg ae ee toa: 61 30 
 POL leet Most lets Gn « 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. Stcel 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 
 uncooled. 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- 
 Ibes, 
 
 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, &. The sample 
 of liquid air to be preserved intact is 
 Apparatus for placed inthe inner vacuum tube. The 
 
 Preserving = outer tube contains enough liquid air 
 and Freezing | E F 
 
 Liquid Air, to completely immerse the inner tube. 
 
 By india rubber perforated stoppers, 
 the necks of the vessels and of the tube, 4, are 
 closed airtight, except for the passage through them 
 of the tubes, A and &. All heat received is cut off 
 
LIQUEFACTION OF GASES. 261 
 
 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 4, 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- 
 
 Apparatus for Determining the 
 
 ditional features. Latent Heat of Evaporation 
 There is an outer Ae Specific Heat of Lique- 
 vacuum vessel, G. In ed. Gases. 
 
 it is placed the refrigerant, liquid air, oxygen or 
 such liquefied gas as may be chosen. This vessel is 
 
262 LIQUID AIR AND THE 
 
 corked, and a second vacuum vessel, C, 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 Dis a three-way cock. When turned in one 
 direction, it cuts off the tube, Z, and establishes com- 
 munication between / and the vessel, C. In another 
 position it cuts off the tube, / and connects & with 
 the liquid gas vessel, C. The tube, /, leads to an air 
 pump. The tube, /, 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 £ 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 & 
 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, Cis.a vacuum vessel: which cons 
 tains a coil of tubing about 0°2 inch 
 diameter. _ The vessel #in the vem 
 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 1877, 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 Presse 
 than was really needed. 
 
 With air driven through the tube instead of oxy- 
 
LIQUEFACTION OF GASES, 265 
 
 gen, 180 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., 
 —110'2° F.), a pressure of 200 atmospheres at that 
 temperature liquefies air. Naturally, Dewar found 
 that the high pressure interfered with the collection 
 of the hquid. 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, 5, 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 14 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 regeneratior 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 Tripler’s 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, 
 
 a 
 ny 
 
 i 
 
 PLT 
 
 UL 
 
 i 
 I 
 Vi 
 
 (( 
 
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 wou!d be equivalent to 
 the liquefaction of air from 60° C. (140° F.) or 333° C. 
 absolute. This figureis 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.) Its 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 httle 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, 4, 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 the 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, VD, 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 zz 
 vacuo, 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-T homson effect really plays in these cases. 
 Hydrogen, it will be remembered, does not present 
 mie-etiect, but the reverse. On escape trom; 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 bydro- 
 
270 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. A#and C are 
 
LIQUEFACTION: OF. GASES. agit 
 
 vacuum vessels, each inclosing a coil of the gas de- 
 livery pipe. #& contained solid or lquid carbon 
 dioxide. The vessel was closed and its interior kept 
 under exhaustion so as to lower the temperature. C 
 contained liquid air. J 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 hquid 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 isa 
 solution of carbon dioxide gasin water. Thus liquid 
 air dissolves hydrogen. It is found that as much as 
 
272 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 must 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, BZ, 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, /#, is so arranged that it delivers liquid air 
 into the vacuum vessel, and keeps its level such that 
 the tube, &, is constantly covered with liquid air. 
 An air pump is connected above the neck of the 
 vacuum vessel and keepsa high degree of exhaustion 
 over the liquid air in K. The tube, A, 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. 273 
 
 tense cold, air liquefies in the tube, 8, coming from 
 the gasholder and passing through the tubes, C and 
 D, the lower one, C, charged with potassium hydrate, 
 the upper one, JY, with pumice stone saturated with 
 sulphuric acid. Thus the air before it reaches 2 is 
 thoroughly purified. 
 
 SS 
 
 SSS PUMICE 42s 
 SS =. }1 3004S 
 
 TO EXHAUST PUMP, | 
 
 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 anda half to three feet of air were used in each 
 experiment. The capillary tube was so small and 
 
274 LIQUID AIK. AND Gre 
 
 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) and 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, 2, would not fill; only four-fifths of its 
 volume was occupied by liquid, the other fifth was 
 occupied by gas. 
 
 At £is a stopcock of the variety termed three- 
 way. Turned in one direction, it connects B with J/, 
 C, and D, the air or gas supply. Turned in another 
 direction, it connects & with the tube, / 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 2 with the tube, 7 The temperature 
 was allowed to rise a little, so that the gas from the 
 upper portions of & bubbled up into /. 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 uncondensed. 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 (00012 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. 
 
270 LIQUID AIR AND THE 
 
 The liquid in the tube was nitrogen. By letting 
 the temperature rise, after properly turning the stop- 
 cock, £, the gas along with some nitrogen was col- 
 lected in‘the tube, #. ~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. Itis 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. 2/7 
 
 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 lquefaction vessel was a glass capsule into 
 whose upper part a platinum tube was soldered. 
 
 Vhe 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 oxygen, 
 
278 LIQUID AIR AND THE 
 
 which, boiling at atmospheric pressure, gave a tem- 
 perature of —183° C. (—2y7°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 
 olass. 
 
 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 
 withit. 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 —180° 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 —210° 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. 279 
 
 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. 
 Evidences 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 
 —z210° 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 : . 
 
 iquidsiioriners635 4Alcohol 4... 2.4: 140 
 eiaudwoxy Tent eco ater. Bir oni. 6 220 
 
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.) ata 
 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 o7o8—an amazingly low 
 figure. The end of along 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. 281 
 
 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 toit. 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 0° C. (32° F.) this hada 
 resistance of 5°3 ohms. In the liquid hydrogen the 
 
282 LIQUID AIR AND THE 
 
 resistance fell too'1 ohm. From the observation the 
 temperatures of —-238°2° C. (—396°76° 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 o129 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'002 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 tem- 
 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 0o°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 defined meniscus, and can be 
 readily manipulated in vacuum vessels. 
 
 The atomic volume at the temperature of its 
 epullition ) is’ 14°3). (Oxygen—=13°7; nitrogen=-16'6). 
 The gaseous hydrogen at this temperature has a 
 Secilic’ Sravity, O1.0°55 (air—=1)."> The ratio of the 
 specific gravity of the gas, compared to that of the 
 liquid at the ebullition point, is as 1: 100 (oxy- 
 gen—1I: 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° Co (i625 "P.) indes 
 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 
 1° C.(1°8° F.) Possibly the platinum thcrmometer 
 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 
 teaspoontuls 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 
 
 CTEAR TER tl: 
 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 pairitings—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. Inthe 
 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. 
 Pon ne toe ton A steam boiler is installed 
 the Floor in Tripler’s 1 One corner of the labora- 
 Laboratory. 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- 
 
291 
 
 LIQUEFACTION OF GASES. 
 
 o~ ae fb 
 
 ‘Tripler’s Laboratory, Showing Air Compressor and End of Liquefier, 
 
292 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 15 inches diameter, the first or 
 low pressure air cylinder is of 103 inches diameter, 
 the intermediate cylinder is of 6% inches diameter, 
 the high pressure, the last of the three, is of 23 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. Theareasof the pistons in the three air 
 compressing cylinders are in the ratio of 110: 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 
 
 4aslog 
 
 o) 
 pete 
 © 
 vQ 
 + 
 E 
 © veoeteea py 
 fa ti Steam Exhaust 
 > § 
 4 . To Froof 
 © tn ! ; 
 a S Ih Air Intake 
 g pea er 
 =) a OS 
 Cg | QS &, 2 
 x 
 i 
 = 
 ae | 
 Sera. 
 2 § 
 ‘oe D 
 wo & 
 > 
 vy ‘4 
 a : 
 S 3 
 5 ve 
 ag (t Ia 
 oe I 
 ary U———S (_ i) 
 Liquetier_No./ 1 
 ae ae Seestoen 
 — 
 © SERRE Se 
 B “pe aren oe ae 
 co = |é\= 
 
 Liquefier No.2. 
 
 > | a 
 
 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 ATR VAND? 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 liquetying and collecting, and 
 in a short time liquid air can be drawn a 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 anormal 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 14 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 
 
 mah 
 
 +} | 
 =e 
 
 Sh 
 
 / 
 NS 
 a 
 
 — 
 
 : 
 
 x 
 
 , 
 y 
 
 \(/ 
 
 AN 
 
 \ 
 VE 
 
 MK 
 
 pee ll 
 
 \. 
 ( 
 (ea 
 
 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 
 
 GHAPTERS XI. 
 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 seg. 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 caseof 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 
 
 eee nemo 
 
 ve nareneanene: 
 
ety 
 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 
 SE1lence. 
 
 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. 301 
 
 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 farfrom 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 agreat 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 — 
 
 Val — p} a 
 an 
 
 In this formula 7’ is the pressure in atmospheres 
 before passage through the orifice or before expan- 
 sion, f' is the pressure after passing through it or 
 after expansion, 7! 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 
 
 2 
 
 this aperture varies with — This is because the 
 yo 
 
 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 7’ — p' of the first formula 
 must be as large as possible and the quantity 7‘ 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. 
 2 
 The ratio— may be kept small and the difference 
 P 
 f—' large by giving high values to f” and f'; 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 7‘—o0° C.—273° C, ab- 
 solute. The fact that the fall in pressure is 3°6 
 atmospheres makes /’—/'—3°6. Our formula now 
 reads: 
 
 Fall-of temperature 23 (243)—1° C. (18° FE.) 
 
 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 — 12 (883)—2:78° 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- 
 
204 LIQUID AIR AND THE 
 
 v 
 
 comes evident. The lower the temperature before 
 
 passing the orifice is, the greater will be the fall in 
 
 temperature. To assume 7! to be —g1° C. (—131°8° 
 
 F.), which is in absolute degrees C. 273—g1—182° 
 289\? 
 
 C., the quantity —) reduces to the factor 2°52 in 
 
 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 
 (Bee)? s (239) 112 (252,00 tc2:25, -alsosine note 
 numbers. Hence, at this temperature, for the two 
 pressure differences we have taken, the tempera- 
 tures would :be! 1°-X 2°25 —= 2°25" GC.) ( (Oh ie eae 
 278° 225 = b'20° Cems ean 
 
 The first substituted formula has been purposely 
 constructed so as to give a temperature fall in round 
 numbers of 1° C. If there is a different pressure 
 drop employed, the fall of temperature due thereto 
 when, 71—= 273°C. absolute.or:0° .C. 1s ioundwby 
 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+ 3°6— 2°78, which, multiplied 
 by unity, gives 2°78° C., as calculated by the second 
 substituted formula. 
 
 Assume now that we are working with a different 
 temperature, 7’. 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 71 to be —g1° C. 
 
LIQUEFACTION OF GASES. 305 
 
 This is 182° C. absolute. 4$2—%, which squared is 
 §. To divide unity with it, we invert and multiply, 
 which is expressed thus: }x 1— 2:25. This is the 
 factor used in the third substitution example. 
 
 It is evident that with a formula for a fall of 
 temperature — 38 (343)? — 1°, 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 71— 
 —g91° 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 
 2°78 and 2°25; we have, therefore: 
 
 Deyo 6 22h Ons. Ce( 11:27 eis) 
 
 The same result could be reached by substitut- 
 
 ing directly in the equation 
 
 Fall of temperature = 
 
 p—P' (=) 
 
 4 273 
 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 
 
 9 
 
 es in which 7’ is the pressure in the inlet side of the 
 P 
 
 aperture and #' 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 todo. Hence the smaller 7’ is and 
 the larger ' is, the less work will the pump have 
 to do. 7 
 
LIQUEFACTION .OF GASES. 307 
 
 GHAPRTER == XLV; 
 THE LINDE APPARATUS. 
 
 Linde’s apparatus— The simplest form of apparatus—lIts 
 ‘ 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. 
 
 W hat the apparatus of the original Linde type does 
 is this: Airis 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 1s 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. 
 
 W hat is called Pade 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 /7, 
 The air forced out through ff goes through a 
 complete circuit of pipes and returns arent G, 
 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 allis 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, J, is of small diameter, and, without 
 any opening or break, runs straight on to D, is bent 
 into a coil, and descends to £ and 7. But from Cto . 
 F it is surrounded by a second pipe concentric with 
 
310 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 interior 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, 7. <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. 3II 
 
 the aperture through which the gas passes and ex- 
 pands with attendant cooling. 
 
 The end of the pipe, 4, enters the small airtight 
 box, orm Chamber, 7. Prom the chamber rises“a 
 larger pipe, /, which, just above the top of the 
 chamber, receives within it the smaller inlet pipe, Z, 
 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 G, is forced through AH and compressed, 
 thereby being heated. The heat is removed in the 
 cooling apparatus, /, 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 & and is cooled thereby, passes through 7 
 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 inthe chamber, /, 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 itis 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. 
 
 It is evident that to make the difference of pres- 
 sure ~?—/! (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. cats 
 
 care of its fraction of the total difference of pres- 
 sures, p*—p'. 
 
 Linde has done this in a partial way in his labora- 
 tory apparatus, and the cut shows the modification 
 
 ia) 
 
 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, ce, 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, 
 f:, From the left hand pump barrel the air, now 
 twice compressed, goes through a- second water 
 jacket, d, and by the pipe, P*, passes to'the left. 
 These water jackets cool the air but partially. In 
 order to more thoroughly cool it water is injected, 
 and at f 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, P!, com- 
 presses it all to 200 atmospheres. 
 
 The air thus compressed we have followed to its 
 exit from the coilin g. Cold and dry, it rises to the 
 top of the refrigerating case, entering it at P*? and 
 going down a spiral pipe. This spiral pipe is the 
 inner one of atriple 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, 6. This valve is slightly 
 opened, so that, of the air which passes a, one-fifth 
 as near as may be passes 4. The four-fifths of the 
 air which does not pass through @ 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, P! P'. This circuit is com- 
 parable to that in the first described machine. 
 
 The one-fifth of the air which passes through 4 
 has undergone a double expansion. It has expanded 
 through two apertures, @ and J. 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 P”, is cooled on its 
 descent by the expanded air in the intermediate 
 pipe. But this air is stili 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 /” 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. Itis 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 4, 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, 0. 
 
 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 4. 
 
 A pressure gauge is mounted on top of the trap, 
 f,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. 
 
 their wonderful product. 
 
 317 
 
 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- 
 GCesseeethe they.cut sare 
 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 toa single pipe, &. 
 Thence the single tube 
 
 , i 
 aS SS SS SS eS 
 
 Linde’s Oxygen-producing 
 Apparatus. 
 
 passes through the liquid air vessel, S, and emerges 
 atthe bottom. The air expands through the valve, 
 r', and part of it liquefies and collects in S. 
 
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, 7’, 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 x, de- 
 livers a product poor in oxygen. This may be allowed 
 to escape. The other, marked 2a, 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, 1°2 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 
 
 GHARTIER eXVe 
 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 on 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, escaping 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, piece 
 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- Hampson’s Gas Lique- 
 ment of the coils, it will be CARREY ca) PENCE 
 seen that the upturned jet points to the center of a 
 threaded aperture, a pipe from which extends to the 
 
 NIG 
 oe a 
 Nae 
 
 N 
 
 ae : 
 
 2UMURUoUUUoS 
 
 . Smita ee 5 
 z ca aN 
 
 Prater a os: 
 
 bly ative ay Ay 
 
 pay 
 ‘aa 
 
 ated 
 
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, 
 
 Jet, Regulating Apparatus, 
 and Regenerative Coil 
 
 of Hampson’s Gas Li- 
 
 ' quefaction Apparatus. 
 
 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- 
 izedai.s The. valve sradme 
 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 
 
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 saa 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 1s 
 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 ts 
 no heating. There is evena 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 OX VE 
 EXPERIMENTS WITH LIQUID AIR. 
 
 Experiments with liquid air—Formation of frost on bulbs— 
 Filtering liquid air—Dewar’s bulbs—Ljiquid 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 asammunition—Ljiquid air as 
 basis of an explosive—Burning electric light carbon in 
 liquid air—Burning steel pen in liquid air—Carbon 
 dioxide epee ants 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 prinout lc cel 
 by Charles E. Tripler at his lec- ! . 
 tures and demonstrations. For 
 most of the illustrations our 
 thanks are due to the Sczentzfic 
 American and to McClure's 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’s Magazine. Copyright, 1898, by The S. & McClure 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 les compara- 
 tively quiet. Ina good bulb only 
 one or two tiny threads of bub- 
 bles rise through the liquid, re- 
 minding. the observer of cham- 
 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 
 what occurs when liquid air is 
 poured into a narrow-necked 
 flask of water. Inthe 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 
 me? 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 S. S. McClure Company, 
 
 Liquid Air in Water. 
 
 in liquid air. Wehave 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 ballin 
 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 courtesy of McClure’s Magazine. Copyright, 1898, by The S. 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 tumblerinalump. On 
 standing a few minutes after the air has evaporated, 
 
a 
 
 & 
 
 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- 
 
53" 
 
 LIQUID AIR AND THE 
 
 utes’ standing the mercury freezes so hard that it can 
 be withdrawn from the mould, and a nail can be 
 
 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. 
 
 a 
 
324 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 ina tumbler made of froz- 
 en whisky, as_ described on 
 page 330. 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. 
 
 pi 
 i , | 
 
 | 
 i 
 
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 
 
 it.) li. the boiling «is. not 
 rapid enough, it may be 
 accelerated by adding ice 
 water or even a lump of 
 ice to the kettle. <his 
 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. 
 
B26 LIQUID AIR AND THE 
 
 But 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 
 
 To Vacuurn Pump 
 
 Rubber 
 4 otonper” 
 
 RS 
 S 
 Liquid Air AOE: be 
 Boiling Violently --- 4S 
 pd ecmat Chree: 
 % Oe : a) 
 i ee wenz 
 + ) f 4 Outside Covered 
 Ra Fe ty 4 with Snow 
 4 ‘ A) (Moisture inAir) 
 ‘ ae 
 \\ et es 
 4; \ \) a if if 
 Air Condensea } | y, 
 and Dropping '\ | Li 
 x 
 4 
 
 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 atmospheric air. It is 
 
 ov - 
 
LIQUEFACTION OF GASES. Sys 
 
 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 
 
 CHARTER xXVi1, 
 
 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—Ljiquid 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 
 
 a 
 
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 /iguzde Pictet (page 169) 
 the temperature within the well could be reduced to 
 —110° C. (—166° 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. 
 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 
 acold 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 o'9° C. (0°36° to 1°6° 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 
 98:76°—-100° 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 ALK 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, witha 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- 
 teres 
 
 On walking homeward, after two or three min- 
 utes a reaction set in, exceeding in intensity that due 
 to acold 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 —110° 
 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 tall 
 or short, could be properly immersed. A woolen 
 covering was provided for the shoulders. 
 
 The working temperature rarely rose above 
 —go° 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 Sczence 
 Francais 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 Frigothérapie, 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 not 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 
 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 anzesthesia, 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 the 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 Abbé 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 and 
 drained from the liquid—imother 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 
 
340 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 asa 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 anesthetic, 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 anzs- 
 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 latteris 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 mgs 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- 
 
 + aa 
 
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 oxygen 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 com- 
 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 alliance, 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 steam, 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 
 
 ries 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, soas 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 . LIOUID ATRAAND Crh 
 
 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 afurther 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 beat 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 SAD OA gS that 
 no explosion can be produced. 
 
 This might,seem a defect, but it is quotedgasea 
 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. ane 
 
 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 wire would carry a large current at rela. 
 tively low potential difference, or at the high poten- 
 tial difference a very much largerone. 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 init. 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: 4, the ratio in the 
 large one will be 4@a:8 06. 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 @:125 6, or 1:5, 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 foot pounds 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 if steam 
 were superheated between boiler and engine, and as 
 if the engine itself were heated by an external fire. 
 
Oo ON AN FW NH 
 
 = Ss eS 
 Si) asi So 
 
 H 
 Ww 
 
 Te ee ed! 
 Nun + 
 
 HoH 
 on 
 
 H 
 Ne) 
 
 SUBSTANCE, 9 
 a 
 B 
 MVERISIP os Sa = yal BOW) 
 Hyd. selenide.| HgSe 
 Ammonia ....| NH, 
 Propane... C3H, 
 Acetylene.....| CoH» 
 Nitrous oxide] N,O 
 FAthamMe tees ee | Coble 
 Carb. dioxide | CO, 
 OZONE see sen Os 
 Ethylene. . CoH, 
 Methane .eens| Orla 
 Nitric oxide ..| NO 
 Oxygen..a.64 Os 
 Argon.,... A 
 Car. monoxide] CO 
 EN dite cece chal vee PAs 
 Nitrogen.. Ne 
 Hydrogen Ho 
 sKVbiverl As, Boga) 8sle 
 
 Critical 
 temperatures, 
 Degs. | Degs. 
 Cent |ebali: 
 
 365 689 
 138 280°4 
 130 266 
 97 206°6 
 37 986 
 35 96 
 34 93°2 
 31 88 
 5) 50 
 — 81°8 | —II5°2 
 Se OS hehe, 
 —118°8 | —181°4 
 —I2I —185°8 
 = 39"5,.| 219 £ 
 —I40 | —220 
 —146 —231 
 ns i eta 
 
 Temp. of satu- 
 
 PHYSICAL CONSTANTS. 
 
 rated vapor at}, ; 2 Pressure 
 Critical atmospheric Freezing point.! ‘at which 
 pres- pressure. freezing 
 cite point was 
 ‘ determined. 
 Degs. | Degs. | Degs. | Degs. mm. 
 Atmos;| Centi a) Habr Cent) |i halt, 
 200 100 212 fe) a2 760 
 gi — 4I — 41°8| — 68 | — 904 Son 
 ve | 38 | | oti tiqluid at 
 an ae ill liqjuid a 
 4 45 49 —151| ° C. sees 
 ae — 85 —I2I — 81 —113°8 950 
 75 | 89 \ | =128 re =a175 760 
 é ., {Still liq)uid at 
 DO) AN 93 leek Sort —151/°C tees 
 75 |—80 |—112 |— 56 |—69 760 
 cites —-I06 , —1588 aie 
 51°7 | —102 —150 —169 —272 birt 
 54°9 | —164 —263°4 | —185°8 | —302°4 80 
 71°2 | —153°6 | —254 | —167 —369 138 
 50°8 | —181°4 | —294°5 munavie 5 On 
 50°6 ; —187 —304°6 | —189°6 | —309°3 aseele 
 35°5 | —190 —310 —207 | —340°6 100 
 39 —I9QI°4 | —312°6| .... Becht BOOS 
 35 | —194°4|—318 | —214 | —353°2 60 
 20 —243 | —405 ies eed Beck 
 Below 
 AOE -— 264 —443"2 2 . 
 
 Den- 
 sity 
 of 
 gas. 
 
 2°02 
 
 Density of 
 liquid at 
 temperature 
 given. 
 
 rat 6-426. 
 
 0°6364 
 atom Ce 
 
 Data collected and tabulated by Walter H: Dickerson, M.K, 
 
 1 
 J 
 
 Color of 
 liquid. 
 
 Colorless. 
 
 “ae 
 ce 
 
 ac 
 «6 
 
 ae 
 
 66 
 
 Dark blue, easily 
 exploded. 
 Colorless. 
 ae 
 
 ce 
 
 Blue. 
 
 Colorless. 
 
 oe 
 
 Light blue. 
 
 Colorless. 
 e 
 
uv 
 
 oy 
 
 hed 
 
INDEX. 
 
 Absolute cold.... 
 Absolute zero. 
 Acetylene, Cailletet’s work on, 
 
 175, 179-181, 182-183 
 Adiabatic expansion and contrac- 
 
 ss ee eetesee +s 
 
 19-20 
 
 TiOiete ee bee eat Re ets an 69 
 Air, 2. CONVEYOE-OL Heat” 2)... vess.c 244 
 Air and water contrasted......... 85-86 
 Air, Cailletet's liquefaction of ..186-187 
 AGT COMPOsitiGn:Olr ee -sese eee hei 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- 
 
 MNICELY oe ee tence score . 260-261 
 Air, liquefied, giving two liquids 220 
 Adar, liquid, defined..:...... De. Stee biel 9 
 Air of atmosphere not a chemical 
 
 COMIDOUNC 45 NEN ae ay ae ie alae 86-87 
 Air, physicists’ and chemists’ 
 
 views of Ee 88-89 
 Air, Wroblewski’s experiment on 
 
 Hieivetactioniol asses wre eee 220 
 Alcohol frozen by liquid air.... ... 330 
 Alcohol frozen by Wroblewski and 
 
 OISZEWSKIZA coe pares cs 212 
 Jagecvehedsh dk Aah eS Raa eee eed 7, 
 Ammoniacal gas, Faraday’ Ss ie 
 
 PACIIOM Olmeen pene «cee a ties III-I12 
 Ampere and Colladon, anecdote 
 
 OL ee eaten eee Ee. cme eine 133-135 
 ASIGECEL eee te mee) Garters anaes 214 
 Andrews, memoir on We of, by 
 
 atte articles Ovaries aa. . 5 comers 150 
 Andrews, Thomas.19, 133, 147-150, 
 
 169, 176 
 Apparatus and experiments, Cail- 
 
 letet’s liquefaction.......... 177-182 
 
 Apparatus and process, Trip- 
 
 ler’s .. 
 
 Apparatus, Hampson’s, for lique- 
 
 EVATIOVAIE army cae e ee , 320-324 
 Apparatus, Linde’s, for liquefying 
 
 BAG See mne bs, Sie Ga Ao wares thier 307-319 
 Apparatus, Pictet’s liquefaction. 157-163 
 Apparatus, Thilorier’s......... 137-141 
 Argon. See italic ere lesan Taher aires) satecater’ 87 
 Arseniureted edrogen: liquefac- 
 
 RIO OL. inter noek dane weet 122 
 Atmosphere, its relation to ani- 
 
 ialsand birds: 5, 22.ees vnc 85-86 
 ALMOSpHEereNiguetliedu=a. aces. 336 
 Autophage state of human sys- 
 
 Le o0le Amar Rreyepesete Rete cee caer Ratio ance, 
 Babbage.. ap «+e LIQ-120 
 
 Barker, eesiee F, gee Aen 240 
 
 Barleycorn as unit of space...... 25-26 
 Bath well, helium from..... . «275-276 
 Battle of squares and cubes....355-356 
 Baucalati: . Bi. se CR ee LS 
 BenjamineLnontpsol aes 93 
 Bianchi’s modification of Natter- 
 
 ers apparatus: .. 23.2% ee. 142-145 
 BlenkerOOdGra ememue. meta et .. 245 
 Blenkroode’s experiment  illus- 
 
 (amalernele? UAE TR es oa Mobo dos 245 
 Boiling a cooling process......... 76-77 
 Boiling by producing a vacuum. 77-78 
 Bollinie PASS seem ce eeeticccte scone 76-77 
 BOWE Areata clos et ER SEK. Malisveha en: 201 
 Brunel’s carbon dioxide engine ...99 
 Buckets, Tripler’s, for liquid 
 
 Eby Cone UR ye ete a ede . 289-296 
 Bulbs, efficiency OMditerent mrss: 247 
 Bulbs, vacuum, mercury silvering 
 
 Ol eee |) asta ee wee. -247, 253-254 
 Cacmardideia Outed. 0--.. 128-133 
 
 Cailletet, L. P...22, 24, 58, 135, 150, 
 I51, 155, 150, 165, 172-202, 204, 
 212, 214, 215, 218, 219, 220, 226 
 
360 INDEX. 
 Cailletet and Hauteville on spe- Coal.as a cheniical ios. .anisese eee Soe 
 cific gravity of oxygen.......... 197 >|, Cold) absoluten-seesnaice. tee een 19-20 
 Cailletet, honors yeceived by .. -.),.174 | Cold, distillation by 2.22.2 e, ame 347 
 Cailletety lie ofgeeee aco: 2173-174 |. Cold, regeneration of) .e-en. afore 
 Cgilletet, liquid acetylene, his Cold regenerative process.. .,.....265 
 WW OL Ky O11G eee fe ee 197-199. |. Coleinatlrs men eer seek eee ere ears 
 Cailletet on conductivity of metals Colladon and ere anecdote 
 at low temperatures . .........201 Of Ei caer oi Sieleisieie ste cia vate R LOS 
 Cailletet on critical state pheno- Colladon, patel; . 133-137, 174, 176, 
 SVEN Fete, onc cate doe ca nie 190-192 179, 200, 207 
 Cailletet performs La Tour’s ex- Colladon, his original apparatus... .136 
 PELIUIME ME eee raceree side Gaeete 202) || Conservation of energy, ose eeee 29-36 
 Cailletet’s cold blast blowpipe, Contraction, adiabatic. 2... sees Oe 
 TAT, 168-199 1.) Cordes; Dr. 2.0. os seeiehiee a eee 341 
 Cailletet’s continuous liquefac- Count iwiniordiess ee eee eee 92-95 
 Lion process ze. acs cet ccaisisieus yeOO na CLitical precsu reqs ams eapteciaie ieieepretie 19 
 Cailletet’s control experiment Critical state of anatter,,. son caee 19-20 
 with hydrogen inte escalate log Ciiticalitem peratiine anes 19 
 Cailletet’s controversies with De- Crookes ayers mse Jisee = |) HOO=BS 
 WALT Scale de see eee eee as 232-233 | Crookes layer, protection due to....84 
 Cailletet’s frozen mercury stop- Crookes, William seen ee vaio ton 
 POL Sirs: cassie ssuemeroae idee ..187 | Cubes and squares, battle of...355-356 
 Cailletet’s letter to oem of Cyanogen, liquefaction of, Fara- 
 SSeS. soak Age nkc . 183-184 Gay) S 5 hu ycee eermeente wiereie sieie ere efep alee 
 Cailletet’s liquefaction of hydro- Cycle of réversible ensine 77... ens 7o) 
 SOU ered ae 5 Os oe cannes ..218 | Davy-Faraday Research Labora- 
 ‘Cailletet’s manometers .... . 187-189 LOLy Ja. thease ee eee II5 
 
 ‘Cailletet’s thermometric methods, 
 trials Of seroma aioe: 201-202 
 Callendat ae metas Rae noes Bok yi 
 Carbon  bisulphide, frozen by 
 Wroblewski and Olszewski,...212 
 Carbon burned in liquid air........334 
 Carbon dioxidein air.... .-.....90-9I 
 Carbon dioxide in liquid air........336 
 Carbon dioxide, liquefaction of, 
 
 Hatad ay |S cceeccn avs Taipdon set, Cote 
 Cartpon dioxidensoliduersiest tier 15-16 
 Carbon monoxide dispatch, Wrob- 
 
 lewski and Olszewski’s ....... 213 
 Catnots Cy clegannats arene ae 70, 288 
 Celsius thermometer scale....... 38-39 
 Centimeter? avsschs aon so ones eeu 
 Chemical reactions governed by 
 
 COld Sites comet sree e tener meses 347=348 
 Chlorine, Faraday’s liquefaction 
 
 Ole eee Atay eet Ara. 106, IIO 
 
 ‘Chlorine, Northmore’s liquefac- 
 tiomofee ee ceded ani pLOO L710 
 
 Clark: "Dit Gaehisihiat..@s aeeee ere 342 
 
 <OLAUISIUGE= Aree aanee Seleissresisie esa treet 24. 
 
 Davy, Sir Humphry.. ...96-99, I02, 
 103, 105, IIo, pit. 120 121, 126 
 
 DEDLAY sae eee Sieve s (ae meee Deo ee 
 Dewar and Mbiseaas s Tiqueiacare 
 of fluorine ...... Serene 276-280 
 
 Dewar, James. .96, 99, 112, II5, I5I, 
 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 ... ...... he eae 244-254 
 Dewar’s bulbs, mercury silvering 
 Olt ean tere a eee 00247, 253-254 
 Dewar’s colleagues.... ... .... Seren 232 
 Dewar’s controversies with Cail- 
 ete tee esiedieleiesrialsielelsiole 2522 ae 
 Dewar’s early apparatus. ,,....233-237 
 
 Dewar’s gas jet experiments. . . 264-266 
 
 Dewar’s hydrogen jet experi- 
 IMLETIUS, «1s cn omni eee fey «200-271 
 
 Dewar’s life ..... « 2 fi enmelets 1231-232 
 
 Dewar's liquefaction of helium, ...28r 
 Dewar’s liquefaction of hydro- | 
 WEN cio ase Aponon placcucnadcese as: 
 
INDEX, 
 
 Dewar’s separation of helium. ,275-276 
 Dewar’s small gas liquefaction 
 
 AP PAPALUS woe ane. Wetec sees . 241-243 
 Dewar’s suggestion of marsh gas 
 
 as a refrigerant..... pases 252-233 
 Dewar’s use of Pictet’s cycles.... .233 
 iMananeS VES enoees Ghosaer 249-253 
 Diffusion aeirdonicness 
 Dog killed by low temperature ...340 
 
 SC eC 
 
 Double and triple glass gas 
 DULDS een ee ete eine cca eee es 245-247 
 PVE CKELE Rac tecielets taie ¢.5 eiaeieres ers 206 
 Dufour, Prof. Henri............155~156 
 FVGASON ae ms Sacer wie segma set os 2200 
 Effects of intense cold on human 
 SYSUCIILE Genie setetcteicictalslevessss « © 339-341 
 Eiffel Tower manometer .....,188-189 
 Elasticity of metals affected by 
 ebld- fa EONS S Se ee 255-256, 260 
 Electric power transmission, 
 hoquidiaira nae eee + 353-354 
 Electric resistance of metals 
 
 affected ne cold, Wroblewski 
 
 CI rr sods ck geese tees .»..219-220 
 Electrolysis of water .148-149 
 Elements, fundamental in physics .25 
 Elongation of metals affected by 
 
 Cold ere Shek Uebitis ca vee ae 6259-200 
 OSes Meteors Sa were nee eae STORES, 
 nervy, atid forces) ae wacccoas 24-25 
 Energy, conservation of ......... 29 -36 
 Energy converted into useless 
 
 MEAE sates. AR ciao ciound eae eek!) 
 Energy, kinetic: 1.5: eee SERA TaN RS 
 Energy, low grade heat.. . .288-289 
 Energy, low grade heat fae paid 
 
 Alice Mere a tae Nels ote e330 
 Energy, potential ....... Aan eter 30 
 Energy, reduction of available. ..71-72 
 Energy, reservoir of........ ey 2433 
 
 Energy, unutilizable of world. ...34-35 
 Energy, waste of, in railroads and 
 steam navigation 
 tLOpYaieee ne cara ceets Se ese 
 ISCO I ce essiee's e's .. 197-199 
 Ethylene,. liquid as perigerant: 197-198 
 Ethylene, Wroblewski and Ols- 
 zewski’s results with. ..212 
 Kuchlorine, Faraday’s licuefac- 
 TLOMS ODM i uae cet cts 
 Evaporation by stream of gas. 201, 214 
 
 C—O 
 
 Expansion, isothermal...... 
 Experiment, Blenkroode’s, show- 
 ing utility of vacuum . ee ZAS 
 Experiment, Count Rumford’s.118-119 
 Experiment illustrating conser- - 
 
 VALIOMIOL Cllet Sy ea tnereer saan 32 
 Experiment in boiling by a 
 
 MAGGI cons, Veils cele Pepe's < hesagee ee 77 
 Experiment, Joule and Thom- 
 
 SONS hele eraeiiners Meise ois ewig OLaO2 
 
 iHxpetiment,, Joules 7 .a..02s5 400 00-02 
 
 Experiment on low grade heat 
 CULES Y seicieies siennes 000 0 0 35-30 
 
 Hxperiment with chlorine hy- 
 
 eeeeee 
 
 Grate, crest sede eee Sone cae el 20 
 Experiment with india rubber 
 
 Danae eee eee nent eur 
 Pcerimicht: Walland Serer coe . 24 
 
 Experiments, Dewar’s yvdnoven 
 OU iaran canine eee eale eos Pas. 200-271 
 Experiments, Dewar’s, on solu- 
 tions of gases in other lique- 
 fiedePAaSeS wees eat tetas 271-274 
 Experiments, Dewar’s, with gas 
 jets 
 Experiments, early, of Faraday...103 
 Experiments in spheroidal state.82-83 
 Experiments, La Tour’s..... . «129-132 
 Experiments, Pictet’s, of 1877..160—-161 
 Experiments with liquid. air.. .325-337 
 Explosions in niet rs and 
 Dayy’s early work.. aieierecieLLO 
 Explosive, liquid air........ ge ae 
 Faraday as fellow of the Peover 
 SOCELY x wrest Gir aiers'e seein e lates 106-107 
 Faraday, Michael..... 28, 42, 95, 99, 
 100-1i5, I17-129, 131, 226, 240 
 Faraday, Michael, his life....., 100-115 
 Faraday on Davy’s continental 
 
 LOWLseteiolois oiel ce stonister Sonne tee ste 105 
 Faraday’s bent tubes........ . .123-128 
 Faraday’s death......... ystems pew tlS 
 Faraday’s discovery of magnet- 
 
 ism of oxygen..... .. 114-115 
 
 Faraday’s engagement at Royal 
 
 Disk ohgbhalore oe WAG Sens . 104-105 
 Faraday’s failures in liquefactions 
 OL FaSeSWac ow. sca aes LRP Care Oe II4 
 
 Faraday’s liquefactions of gases, 
 106-112, I13-I14 
 Faraday’s solidification of gases ..114 
 
362 INDEX. 
 Faraday’sthermometer....... MOCHSCe) Meiniholtza te. Wee Shuaje telat ee one oer 204 
 Fleming ays Aus sense see SOR ont 232 Heéeryvyscdeashior peo caer foctaelge 
 Fluorine, liquefaction of,......276-280 | Hogarth.... ........ ade meee 28 
 HOLCE 75 th jes sem lee cee wake ents 27-29 | Hydrochloric acid, Faraday’s 
 FOLCemnds CNeErsy sin nce eee 24-25 liquefaction of..... A ts II2 
 Force, conservation of, an errone- Hydrogen, Cailletet’s liquefaction 
 ous: docttiie spt eee an 20=29 OLE ere on Oneraenee . 184-185 
 Bored, HVine sce ea ees mero oene ...29 | Hydrogen, constants of liquid by 
 Formula, Joule-Thomson effect, Olszewski. . ; ; . . 227-229 
 300-306 Hydrogen dispitcin a¥roblewsikitst 218 
 Frigotherapy........+ Pre 338-342 | Hydrogen, jet process of liquefy- 
 Fuller, Mr) ohne i teens eee ier 95 ba ari herr cca . 266-271 
 Fullerian professorship in Royal Hydrogen, liquefaction of, De- 
 Unis titittOn re tee winner er: 95, 96 Will, Siemyroceisse ieee perestion 280-285 
 Gas cooled by expansion ........299 Hydrogen, liquefaction of, Pic- 
 Gaseous state of matter.......... Leet? EGE). hg nde Ane ose, uGhiC’ se eeee 164-165 
 Gases, boiling. ...4... 2623 Se mite 76-77 | Hydrogen, liquefaction of, Wrob- 
 Gases, Davy’s experiments in in- ENV SIGNS yo he eee . 218-219 
 Helin. 7.2 caries 97-98 | Hydrogen, Wroblewski and Ols- 
 Gases, Davy’s views of the utility zewski’s attempt to liquefy.213-214 
 of liquefying....... a ree 98 | Hydrogen, Wroblewski on criti- 
 Gases, determining latent heat of calipressure Ofiat sso ae 266 
 liquefied,........ aera ..)..261 264 | Ice; Hquid air boiled ont. meas 335 
 Gases, determining specific heat India rubber affected by intense 
 OiMGiehe des: meee tir & 261 264 Cold ete ree Seay hee .eneeseg 
 Gases, molecular motion in...,..17-18 | India rubber band experiment... ..32 
 Gases, permanent 1.2 27 oes. 149-150 | Isothermal expansion and con- 
 Gases, solution in other liquefied traction. ete. ns . 68-69 
 gasess 5 AP ip nhieu. eee. -271-274 | Jamin Sees cosy wpe cia oa) nemne 
 Gas heavier than liquid ........ 21 Joules. 25s eee os fase 60, 61 
 Gas jets, Dewar’s experiments Joule and Thomson’s experi- 
 AALAEY Ape. GeND eh) SAGAOOoS . .264-266 ment..5. | aah owe eae 61-62 
 Gas, receiver for liquefied, Cail- Joule’s experiment), 2 60-61 
 letet’s joe cielo ect embstem § «+++. 195-196 Joule-Thomson effect ..269-270, 297-306 
 Gas, the perfect... ..e0. sseee+e-59-62 | Joule-Thomson effect, negative... 3o1 
 
 Galbanmui Hy, waste eeraelete eet OL 
 
 Galitzine. 35: SOC OSE ATE Ono eens 22 
 Grama onc sedorsise ai Mass ta, tae aes 25 
 Griffiths. Fonte. So eae ne eteet tee wes 57 
 Hampson.....226, 238, 265, 300, 391, 
 
 309, 320-324 
 Ha nti yee cicehiarelnele er seals . a2 
 Fiautevilie. 4% arti ae eecteer 197 
 Heat. latent oes: setae ne ois a 72-76 
 Heat, measurement of... ....... 37 
 Heat.or-1cew eee eee ciate rereiete II 
 Heat, specific. See specific heat. 
 Heat, utilization of unavailable .. .72 
 
 Helium, liquefaction of Dewar’s... 281 
 Helium, separation of, Dewar’s, 
 
 275-276 
 
 Kinetic Cher sy Mia satan canteese 
 1-Ghael olen ye Solace Steen wan aicin eee 204 
 Laboratory liquid air apparatus, 
 Lindes! tease A ee ice AC el 
 Latent Heat <3. co dew sls eeetneee te 2a 
 Ta ToursCagniard des. ene OT 2Oe 
 La Tour’s law... . ..20-21, 128-129 
 Lavoisier ne: ..asGee Higiwins wee OR 
 
 Taw, La “DOUrl’S wees efasarices eens 
 ayer, Crookes icy. nae . 80-82 
 
 Leyden University, Cailletet’s 
 piUInip in... ij lesenteweeieas Palos 
 
 Leyden University, Pictet’ s cycles 
 ieee: Sthundaishe L5G LS 
 
 Liebig’s abet of aceidoue with 
 Thilorier’s apparatus....... 138-139 
 
INDEX. 
 
 Linde.....226, 238, 265, 300, 301, 307- 
 319, 322 
 
 Linde’s liquefaction process and 
 AV PATAlUS,.. cies cetenge~! Po 307-319 
 
 Liquefaction in tubes, Davy’s sug- 
 SeSLIOMsLOL Me wecieeree ey ire 126-127 
 
 Liquefaction of gases, Faraday’s 
 Pest awohs= Oly, 2 tees PLOOMLTO 
 
 Liquefaction of hydrogen, Pictet’s 
 experimentin «... . 164-165 
 
 Liquefaction process and appara- 
 
 ENG SALLITELS Ge ne Nee ore 307-319 
 Liquefied gas receiver, Caille- 
 
 EUS TR ca rae one cata . 195-196 
 Liquid air accelerating combus- 
 
 RAIN Ba oe Aeeten WOM Meee ee 332-333 
 
 Liquid air r apparatus, Linders 309-312 
 Liquid air as source of oxygen.316-318 
 Liquid air as source of power......356 
 Liquid air defined........ 69) 
 Liquid air dropped into mater pane 
 Liquid air, experiments with. .325-337 
 
 Liquid air explosive.... .. 0348-353 
 Liquid air, filtering..... pure nert a 20=3 27, 
 Liquid air, gasification of........ rg 2 
 Liquid air giving two liquids.... 220 
 Liquid air in Dewar bulb....... eso 
 *haquid airan flask £.\..22..< an 53 
 Liquid air, medical uses of ....342-343 
 aquade Pictets ca. cae. snack 24, 169-171 
 ( Liquid floating on a gas......see. wei! 
 Liquid fluorine, data of.... . ... 278-280 
 Liquid helium, Dewar’s produc- 
 tion of THUR relosicerstete r roe col 
 Piquidihy drogenintses ar . . 280-285 
 Liquid hydrogen, data of...... 280-283 
 
 Liquid hydrogen, Olszewski’s de- 
 termination of constant of .227-229 
 Liquids and solids, solutions of, 
 
 TASES Meet ee ee My ct  Oay 23-24 
 Liquids, molecular motionin..... apes) 
 Liquid'state: 2 .....3% desubootudcdssc vel 
 Liveing, G.D. w oete/al ele aie's' «wis ieiere es 232 
 ANAS LOLCE LSS cr tyacm ees «oe ie ere tone 29 
 Low temperatures, applications 
 
 Oy then Tole ee oe ECON ee . .338-356 
 Machinery, Dewar’s, Royal Insti- 
 
 RUC ate Ais. fae to Sif aeRO Ox 239 
 Magnetism of oxygen...... .. aay 
 Manometer, Faraday’s.......,.124-125 
 
 Manometers, Cailletet’s,.......187-189 
 
 363 
 
 Marsh gas, liquid, as refrigerant..215 
 
 WRA SS Aare eter trea s Ate iretin.. a ledereaiaiotele eee 
 Matter, icritical staterof, 5 .6c%i5- 19-20 
 Matter, three forms or states of. .. 11 
 
 Maxwell, J. Clerk. ....150, 204, 225, 289 
 Maxwell, J. Clerk, on low grade 
 
 NEAMEHera Verne he ee Sees 289 
 Medical uses of liquid air...... 342-343 
 Meniscus defined ... Beit cathe ae 21 
 Mercury frozen by liquid air... 331-332 
 Mercury vapor, experiment in 
 
 PUCeZIT haan ere er, 253-254 
 
 Metals affected: by iatense cold,.328-329 
 
 Metals, effect of intense cold on 
 elaSlicity, 0 tae el 255-256, 260 
 
 Metals, effect of intense cold on 
 
 elon Sationioteanee eae 259-260 
 Metals, effect of intense cold on 
 
 Strencthyoigse. aie eee 256-259 
 Metals, Tresca’s flow of........ 255 256 
 Mixtures ENiOrien Se ieds.cccsne ot 113 
 Moissaun and Dewar’s liquefaction 
 
 (on ishblevmnuvs: AP pen) Le . .276-280 
 IMOISsatin PLOle ener 2320277) 
 Molecular attraction.............II-12 
 Molecular death... ..t.... HAPRaE Re es eis doy 
 Molecular motion of gases...... .17-18 
 Molecular motion of solids...,......11 
 Mond yer, Ludwis ines seen eal 
 Monge and Clouet......... boat .IIO 
 Natterer, J..19, 42, 141-147, 169, 194, 
 
 2URI2L3 210 
 Natterer’s apparatus and experi- 
 
 SILC MUCH roti dese shednteseemrevers «ers 141-147 
 Natterer’s freezing mixture ...... 145 
 Natterer sithermometer. 1... atAS Wore 
 INALLeEreIy Ste meat er 23. 2135210 
 Negative Joule-Thomson effect..... 301 
 Nitrogen, anomalies of ........:.... 88. 
 
 Nitrogen, Cailletet’s liquefaction 
 
 Nitrogen dispatch, Wroblewski 
 and Olszewski’s 
 Nitrogen, solidification of, by 
 Wroblewski and Olszewski....214 
 Nitrous oxide, Faraday’s liquefac- 
 tI OLA 2 aa eee ACK See ELL 
 Nitrous oxide, Natterer’s liquefac- 
 tionloh 7 Sawer: . 145 
 Nitrous iicides ptimeeatid ‘by Bote 
 day as cooling-agent ...........114 
 
304 
 
 Northmore, Thomas, .106, 110, 117- 
 
 ETS wL20 22 et AS 
 
 Northmore, Thomas, liquefac- 
 LIONS DY, Ce eis toe OO LL EO 
 Onnes, H. Kamerlingh......49, 270, 301 
 
 Olszewski, K..42, 145, I51, 157, 165, 
 168, 169, 185, 203-229, 266, 267, 301 
 Otszewski’s and Pictet’s appara- - 
 US ,GGlectinee emeae eee oc 223 
 Olszewski’s determination of con- 
 stants of liquid hydrogen. .227-229 
 Olszewski’s liquefaction appara- 
 
 tus of 1890...:. ena oi teeea Ree . 221-226 
 Olszewski’s liquefaction of hydro- 
 Cel aApproximaleseneen notes 221 
 
 Olszewski’s static oxygen..-.. 221-226 
 Oxygen, Cailletet’s liquefaction 
 
 Oxygen, critical pressure of, 
 Wroblewski and Olszewski’s 
 Aeterimination! scene e ee 216-217 
 
 Oxygen, critical temperature of, 
 Wroblewski and Olszewski’s 
 
 determination eee 217-218 
 Oxygen dispatch, Wroblewski 
 
 and Olszewslals 2 eeere eae 211-212 
 Oxygen, Linde’s method for pro- 
 
 ducing... SOTO Ly ec hes 
 Oxygen, imapaceen Ole Shenk Sy 
 
 Oxygen, specific Pavia detec! 
 mination of, Wroblewski and 
 Olszewskils ne ater ae 214 
 
 Paris, Dr. John Ayrton, and Fara- 
 Gay gee ee nae SiG Sao ae Gata 107-109 
 
 Perkins’ alleged liquefaction of 
 
 Permanent gases, the six so-called.150 
 Pictet, “Raowl.26.22024 T29.5125 A750, 
 I5I, I52-171, 185, 192, 200, 205, 
 
 220, 223, 225, 233, 264, 289 
 
 Pictet, honors received by..... ...156 
 
 Pictet’s cycles used by Dewar......233 
 Pictet’s cycles praised by Wrob- 
 
 TeWSKi. eee conte ree e+ 205-206 
 Pictet’s determination of tempera- 
 CULE Ts. cevare ce eto eee ae ee OT, 
 Pictet’s Experiment: in cold well, 
 340-341 
 Pictet’s frigotherapy ....... ..338-342 
 Pictet’s Intellectual and Moral 
 Philosophtyaen eee os coe 57 
 
 INDEX. 
 
 Pictet’s life and characteér......153-I55 
 
 Pictet’s liquefaction of oxygen 
 dispatch... ....cssitaeisls a ghana 
 
 Pictet’s original liquefaction ap- 
 
 PaTatus swale as rere eyo 
 Pictet sdiquidi, «eee 24, 169-171 
 Pictet’s work, importance of.......168 
 
 Pleischl’s lecture on WNatterer’s 
 apparatus .... «++ 6144-146 
 
 eeeceecece 
 
 Pneumatic Institution,......... Apnnce): 
 
 Potential energy...... AP ae Ree: 
 
 Power expended in Linde’ Ss ap- 
 PaTracuseeeeees CRU ea tees 316, 318 
 
 Power, liquid air as reservoir of....356 
 Pressure affecting state of mat- 
 
 1S Oat see ere ete et . 16-17 
 Pressure, critical....... PEE ee i seg 
 Pressures, enormous, in Natter- 
 
 et’s ex petitients sey neeee «ge 
 Pump, Cailletet’s mercury..... IQI-195 
 Puntp, Kataday:S “aa-ea nee pons 
 Pump, Pictet}Staaacqaceetee eee 166 
 Purification of chemicals by 
 
 Coldum..: saohemeen Sits ctor 344 347 
 Purity, critical state test of....343-344 
 RAMSAY io cae ence eer Jon pono oe 
 Reaumur thermometer scale..38, 44-45 
 Regnault’s mercury pump......... 193 
 Release, Cailletet’sm eee aero 
 Ribard’s local application of in- 
 
 tense coldec. > «as jeee es eee 
 Ribeau, George, Faraday’s em- 
 
 ployer: (ses eoree mingonedos ce 
 
 Reseneration of cold.-ewesetan 299 
 Royal Institution of England.10, 92-99 
 Rumford, Countier.- swe 92-95, 118-119 
 Rumford’s, Count, experiment in 
 liquefaction of gases. .... .118-119 
 Secondaaes. Peon mean Seed idles 
 Self-intensive refrigeration........300 
 Siemens, William. .... . 299, 300, 301 
 Silvered gas bulbs ..... Sin ean 
 Skating rinks, Pictet's .... 154-155 
 Solid state of matter.......... sav au be 
 Solid carbon dioxide and Crookes 
 LAYOT oe s'n's sas ssh ptsak es eta . 84 
 Solids and liquids, solutions of, 
 LEASES. . diss s,chtop ocd e Geese ae 
 Solids, flow of “siewscsd.u seuss eee eee 
 Solids, vaporization of ... ......15-16 
 Solution, gaseous, utilized..........24 
 
 UU 
 
 a.) 
 
 —— 
 
 Ee 
 
 Ee 
 
INDEX. 
 
 Solution of solids and liquids in 
 
 gases EDO OOO eee 
 SOLVAY eersceelen aes a tio arise steer eters 265 
 Specific heat at constant volume 
 
 and at constant pressure..... 64-65 
 Speciic Meat Atomics, wot een. ee 66 
 Specific heat of gases............54-65 
 Spheroidal state....... et ae 78-84, 243 
 State of matter affected by pres- 
 
 SULC cca sweets eraistes ealO=r7 
 
 State of matter, intermediate.13-14, 20 
 State of matter, volume affected 
 
 IDVies easiest ieee maine as or LOL 
 Steel burned in liquid air..... ~...334 
 Strength of metals affected by 
 
 COld ees oe daaeieers cee ee 256-259 
 SUPOMIEY Ely falas cisles See ce Cae 122 
 
 Sulphur dioxide, liquefaction of...110 
 Sulphureted hydrogen, liquefac- 
 
 HlOMMOL Pees <c Reis ee oie ELO=T i 
 SilcLace tenSio tie wes see. dso cece 78-79 
 Thermodynamics, second law of.70-71 
 Thermometer, calorimetric.....,..- 58 
 Thermometer, eléctric . resist- 
 
 aTiCeM ems eae: eh ATES 
 
 Thermometer, Fahrenheit’s.........39 
 Thermometer, gas or air.........44-51 
 ‘Bhermometerenatterer’ sac...) 2IL 
 
 hhermometer scalesayarn.: ace. 37, 44 
 Thermometers, substances for 
 fPLLT OR ee ere er es eta ta 6 Meee aT AZ 
 
 Thermometer, thermo-electric...51-54 
 Thermometric methods, Caille- 
 tetistiia [Sloe geen amen cs ee 2OL—202 
 chvorier wes. II2, II3, 137-141, 198, 269 
 Thilorier’s apparatus exhibited 
 by Faraday.... Katha B= oxalate 19D 
 Thilorier’s apparatus, fatal acci- 
 dent with). 22.422 138-139, 143,145 
 Thilorier’s cold-blast blowpipe, 
 I4I, 198 
 Thilorier’s experiments........ 137-14a 
 Thilorier’s freezing mixture..... I41 
 Thilorier’s solid carbon dioxide... .137 
 Thomson, Sir William,..........61, 62 
 AhoOmSOM, Flint pena ets ays eile si) 
 STOMIP SOME Heil) Ali een 2 st.ce eens S 
 
 Torricellian vacuum.. .... 249, 252-253 
 FLOUt Cao naar elas. -. eae 22 
 ‘ltansition phenomena, ,7........ 22-23 
 Tresca’s flow of metals......... 255-256 
 
 tiple an dePictetan mame. teeters 296 
 Tripler, Chas. BE. .226, 235, 255, 266, 
 
 285, 286-296, 287, 289 
 Tripler on low grade heat energy, 
 
 288-289 
 Tripler’s apparatus and _  pro- 
 CESS Tal ei eat nl aetied oon s 2. . 290-295 
 Tripler’s buckets for liquid 
 ALT OR i SEA, alia ote: ZOO K 200 
 Tripler's Hie. 172% sian oe nahn 287-209 
 Tubes, Faraday’s bent.......... 123-128 
 Vacuum, a heat insulator,..... 244-246 
 Vacuum and air space bulbs, effi- 
 CIENCY COM PaLedmesrae. east 247 
 Vacuum, Blenkroode’s  experi- 
 ment illustrating utility of..... 245 
 Vacuum bulbs or vessels ... ..244-254 
 Vacuum produced by liquid hy- 
 MrOSGiieerce rece a eee tela . . 283-284. 
 Wapor a 5 Acinic era OL Oe ae 63-64 
 Vaporization of solids.... ....... 15- 16 
 Villard pee... ane RS cr etereetts ee 6 235 24 
 Volumes, relations of, in change 
 OLAS eos ie woes we ee A fag iseZit 
 Water and air contrasted .......85-86 
 Water, three states of....... dene LI=l3 
 Wiateh Val DOs. vacle atsfals\elelolereticisteteiere ts 64 
 WWE seaneopmiMe ney  mancdedde nec 339 
 Whisky frozen by liquid air....330-331 
 Witow Ska ve caiccsncue ore oe 55, 57 
 WOOL amass emvecigk te cere een 25, 31-32 
 Wroblewski and Olszewski’s ap- 
 PALALUS eae see . ..206-211 
 
 Wroblewski and Olszewski’s car- 
 
 bon monoxide dispatch........213 
 Wroblewski and  Olszewski’s 
 TC TOT ENT GIS Palen yy aeias delet 213 
 Wroblewski and Olszewski’s oxy- 
 SCUMISPALC Ui Aunt desis oe Z an i 
 Wroblewski and Olszewski’s oxy- 
 Pen liquetactionmn..tees eee 211-212 
 Wroblewski, Sigmund von. ...42, 
 145, 151, 157, 165, 168, 203-229, 
 266, 301 
 Wroblewskis™ifer...6+...- 203-205 
 Wroblewski’s liquefaction of hy- 
 UTOSSi ne Wem Ge. poke 218-219 
 Wroblewski on liquefaction of air.220 
 Zambiasi........+. plate, one aysasleie nines 22 
 LET Osa DSOLULE Ha fa eer sa: Maes 4Ordle 
 
 Zero of thermometer scales...... 37-38 
 
We were the first in this country. | 
 
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 DEWAR 
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 in his experiments and de- 
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 various lectures and exhibi- 
 
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 As makers of the best X-ray tubes in the coun- 
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 on the desk of every machinist in a factory repair shop, for the right ‘‘ Kink ” at the 
 3 cht time will often prevent the stoppage of a factory.”’— Wade's Fibre and Fabric, 
 
 eb. 15, 1896. 
 
 NORMAN W. HENLEY & CO., PUBLISHERS, 
 
 132 Nassau Street, New York. 
 
 Special circular describing the above sent on request, or we will send copies 
 on receipt of the price. 
 
JUST PUBLISHED. 
 
 The Modern [lachinist, 
 
 BRON USL ER ae 
 
 PRICE, = = - = $2.50. 
 
 Specially Adapted to the Use of Machinists, Apprentices, 
 Designers, Engineers and Constructors. 
 
 A practical treatise embracing the most 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 FROI 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. 322 Pages. 257 Illustrations. Price, $2.50. 
 
 What is said of “The Modern Machinist.” 
 
 This is a new work of merit. Itis 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.—Screntiric Macuinist, Juty 15th, 1895. 
 
 This book is the most complete treatise ofits 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.—AGE or STEEL, JUNE, 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 new or difficult job is to be done.—Macuinery, JuLy, 1895. 
 
 NORMAN W. HENLEY & CO., pustisners, 
 132 NASSAU STREET, NEW YORK. 
 
 %* Copies of the above sent prepaid on receipt of price. 
 
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