Gas torch and thermit welding

Front matter

C0EXRIGHT DEPOSIT.

GAS TORCH

AND

Preface

The beginner, the practical worker, the student and tlie engineer, will find in this book a great amount of information regarding gas-torch and Thermit welding practice and equipment. No toil or expense has been spared to gather material of real and lasting value. Shops have been visited and data and photographs obtained first hand. Practically every book on welding has been carefully scrutinized for helpful suggestions. The services of experts have been engaged to give the results of long practice and research in their special lines. Each and every plan known to the experienced editor has been employed to give the reader the highest possible grade of information.

The historical references have been cut to the barest statement of facts as we have been able to obtain them, yet they are ample enough to give the inquiring mind the genesis of each class. Foreign methods and equipment have not been touched upon, except in a few instances, because such treatment would add too greatly to the bulk of this work, without adding an appreciable amount to its real value, since the methods and standard equipment here are, in general, far in advance of anything similar elsewhere.

Great care has been taken to indicate the sources of information and to give the names and addresses of the makers of equipment shown. It is believed that every well known maker of this class of welding apparatus in the United States has been mentioned at least once in these pages. This has not been done with any idea of advertising them, but because it is information every reader is entitled to have without the necessity of making a separate search for it.

Of course no recommendations regarding the best apparatus to use are made in any case. As in any other line, improvements are being constantly made, but in regard to newly invented or unknown equipment the seller should be made to prove his case before an investment is made. Apparatus which does not meet vi PREFACE

the present day requirements, soon drops out of sight. It is a good plan for a prospective purchaser of equipment to consult some well established firm which is not afraid to advertise its product in open competition. Such a firm will see that its equipment is properly installed and works .satisfactorily.

Ethan Viall.

New York City, November, 1920.

TABLE OF CONTENTS PART I— GAS TORCH WELDING.

Chapter I Page

History and Uses of the Gas Torch 1- 8

Meaning of * ' Autogenous ' ' and the Term ' ' Gas Torch ' ' Welds — The Oxy-Acetylene Gas Torch — Used for Both Welding and Cutting — Hydrogen Gas — Thermalene Gas — Blaugas — Drigas — Illuminating Gas — Benzine or Benzol Vapors — Explosive Limits of Welding Gases — The Field of Gas Torch Welding and Cutting.

Chapter II

TuE Production of Welding Gases — Oxygen and Hydrogen. ... 9- 25 Oxygen by the Liquid Air Process — Oxygen and Hydrogen by the Electrolytic Method — General Principles of the Electrolytic Method — Details of the Davis-Bournonville Electrolyzer Cell — The International Oxy-Hydrogen Generator — The Levin Type of Generator.

Chapter III

Acetylene and Medium, or Positive, Pressure Generators.... 26- 40 Acetylene — Acetylene Cylinders — Acetone Injurious to a Weld — Estimating Amount of Acetylene — Types of Acetylene Generators — The Positive Pressure Generator — The Davis- Bournonville Tj'pes — The Buckeye Carbide-Feeding Mechanism — The Portable Pressure Type — Approximate Dimensions and Weights of Acetylene Generator Sets.

CHAPTER IV Low Pressure Acetylene and Thermalene Generators 41- 53

Low Pressure Generators — The Oxweld Duplex Generators — Thermalene Generators — How the Cartridge is Packed — Action of the Thermalene Generator — Some Advantages of Thermalene.

viii CONTENTS

Chapter V Page

Types of Torches — The Davis-Bomnouville Positive Pressure Torch— The Prest-0-Lite Torch — The General Welding Co. 's Torch — The Imjaerial Torches — Calculating Amount of Gas Used — The Rego Welding Torch — The Oxweld Low Pressure Torch — The Messer Torch — The Thermalene Torch.

Chapter VI

The Davis-Bournonville Cutting Torch — The Oxweld Cutting Torch — Cutting Data — The Messer Torch — The General Welding Co. 's Torch — Imperial Torches — Caibo-Hydrogeu Torches — Airco-Vulcan Combination Torch — The Rego Torch — • The Milburn Combination Torch— The Torchweld Torch — The Davis-Bournouville Underwater Cutting Torch.

CHAPTER VII Gas-Pressure Regulators and Working Assemblies 95-115

Oxweld Oxygen Regulators and Gages — Other Regulators and Gages — Tank and Hose Colors — Regulator Adaptors — Connecting Up an Outfit — The Two Types of Tank Connections — Characteristics of the Oxy-Acetylene Welding Flame — Imperial Three-Way Outfit — Lighting the Oxweld Low Pressure Torch — Characteristics of the Oxy-Hydrogen Flame — Characteristics of the Hydrogen-Compressed Air Flame — Characteristics of the Oxy-Illuminating Gas Flame.

Chapter VIII

Typical Oxy-Acetylene Cutting Unit — Manifolds — Complete Working Outfits — Back Pressure A'alves — Lead Burning — Method of Connecting Outfits for Various Gas Combinations — A Gas Flow Indicator.

CHAPTER IX Learning to Weld with the Gas Torch 131-153

The Way to Hold a Torch — Torch Motion — Welding Two Plates — Allowing for Seam Contraction — Using the Welding Rod — Various Welding Jobs — Sources of Trouble — Built-Up Welds — Vertical Welds — Filling Up a Hole — Forming Bosses or "Putting on" Metal — Practicing on Gear Teeth — Welding Backward — Lead Burning.

CONTENTS IX

Chapter X Page

Makixg Allowance for Expansion and Contraction 154-168

Action of Metal When Heated — Using Heating Torches — Cooling Work — The Wiederwax Preheater — Suggestions Eegarding the Welding of Gratings and Pulleys — Automobile Cylinder Work.

CHAPTER XI Welding Various Metals and the Fluxes Used 169-186

Properties of Metals — Conductivity and Oxidation — Vaporization of Substances— Separation of Elements — Welding Various Metals — Welding Aluminum — Filling a Large Hole — Brass and Bronze — Cast Iron — Cast Iron to Steel — Copper — Copper to Steel— Lead — Malleable Iron — Monel Metal — Nickel — Steel — Special Steels — Manganese Steel — Nickel Steel — Vanadium Steel — Chrome Steel — Wrought Iron — Galvanized Iron — German Silver — V/hite Metal Castings — Silver — Gold.

Chapter XII

Examples o? Welding Jobs 187-220

Preparing for Welding — Examples of Special Jobs — Welding Broken Machine Tools — Preparation for Locomotive Frame Welding — Cooling Devices — Rail Bonding — Rudder Frame Welding — Large Engine Cylinder Work — Welding High Speed Steel Tips to Low Carbon Shanks for Shop Tools.

Chapter XIII

Holding Pipe for Welding — A Welding Table — V-Blocks for Holding Shafts — Jig for Holding Crankshafts — An Adjustable Crankshaft Jig — Crankcase Devices — Motorcycle Manifold Jig — Sheet Metal Roller Jig — Sheet Metal Cjdinder Jig — Apparatus for Welding Cylinder Ends — Welding Poison Gas Containers — Liberty Motor Work — Fixtures for Motor Manifolds.

Chapter XIV

The Duograph — How the Duograph Works — Drum Welding Machine — Light Seam Welding Machine — Machine for Welding Oblong Seams — Tube Welding Machines— Tube Welding by the Oxy- Acetylene Process — Arrangement of Rolls on a Tube Welding Machine.

X ~ CONTENTS

Chapter XV Page

Correct Cutting Position — Starting a Cut — Examples of Good and Bad Work — Blowing a Hole Through a Plate — Using Various Devices — Flame Control — Making a Ladle Hook — Costs of Some Cutting Jobs — Cutting Cast Iron — Torches Made to Preheat the Oxygen— Cost of Oxy-Hydrogen Cutting.

Chapter XVI

Cutting with Hand Machines — The Radiagraph — The Railograph — Circular Cutting— The Magnetogi-aph — The Camograph — The Great Western Cutter — The Pyrograph — The Universal Cutter — The Oxygraph.

CHAPTER XVII Welding Shop Layout, Equipment and Work Costs. 295-313

The Equipment Necessary for a First Class Shop — Layout of the Oxweld Shop — Keeping Track of C^osts — The Oxweld Cost Form — The Imperial Cost Form — Carbon Burning — Safety Rules for Gas Torch Workers — U. S. Railway Administration Autogenous Welding Rules — Strength of Oxy-Acetylene Welds.

Chapter III

Type of Crucible Used for Thermit Welding— Tapping a Crucible — Life of Lining Prolonged With Magnesia Tar- Crucible Ready for Baking— Thimbles— Application of Fusion Welding— Wax Pattern Molds— Ramming the Mold— Preheating the Mold — Igniting Thermit — Amount of Thermit Needed for Welds — Locomotive Frame Work — Other Railroad Work.

CONTENTS xi

Chapter IV Page

Welding Crankshafts, Mill Pinion Tektii, Etc 358-373

Y-Bloeks for Welding Crankshafts — Defects that Frequently Occur — Inaccuracy of Alignment Explained — How to Locate Minute Cracks — Welding New Teeth in "Large Pinions — Making a Wax Tooth Pattern — Another Method of Welding Pinion Teeth — Preheating Large Work.

CHAPTER Y

Welding New Necks on Large Pinions and Other Heavy Work 374-390 Two Methods of Working — Foundation and Heating Arrangements — Constructing the Mold for a Large Roll or Pinion — ■ Amount of Thermit Required — Treatment When a Cope is Used — Alternate Method — Marine Repairs.

Chapter VI

Rail Joint Work — Adjusting the Insert Between the Rails — ■ Adjusting the Mold — Preheating — The iJse of Thermit Additions — The Grinding Machine.

Chapter VII

Kinds of Compromise Joints — Using a Rail Section for a Pattern—The Clark Joint— Modified Clark Joint— Welded Cross-over — Motor Case Work — Car Truck Work.

Chapter VIII

Thermit to Use for Cast Iron — Examples of Cast Iron Welds — - Welding High Speed to Machinery Steel — Cost of Thermit Apparatus — Preheaters for Thermit Work — Cost of Materials and Apparatus for Pipe Work.

Index 426

PART 1-GAS TOECH AVELDING

Chapter I History And Uses Of The Gas Torch

According to common usage, the term "autogenous welding" is erroneously applied only to hot gas flame fusion welds. The gas combinations used for the production of the hot flame for welding or cutting are oxy-acetylene, oxy-hydrogen, oxy-thermalene or any combination that will produce sufficient heat, and is applied by means of a torch or blow-pipe. The welds so produced are strictly fusion welds, as no pressure or hammering is employed to effect the union. The word ' ' autogenous ' ' means "self-produced" or "self-generated," that is, joined with the same metal, and as such applies equally to hot gas flame, electric arc or thermit welds, although as just stated, the present custom is to apply the term generally to hot gas flame welds. However, owing to the wide field that the term "autogenous" really covers, and to the looseness with which it is often applied, we prefer to use the term "gas torch" in connection with Avelding and cutting by means of the hot gas flame.

While the use of a blow-pipe or torch in some form was known to the ancients, the high temperature gas flame is a development of the last quarter of a century. The more commonly known gas combination is oxy-acetylene. Acetlyene (CoHo) was discovered by Edmund Davy in 1836, but it remained only a laboratory gas until T. L. Willson of North Carolina and H. Moisson, the Frenchman, developed commercial methods of producing calcium carbide (CaC^) in large quantities in 1891-92. In 1895 Le Chatelier read a paper before the Paris Academy of Sciences in which he stated that : ' ' acetylene Inirned with an equal volume of oxygen gives a temperature which is 1000 deg. C. (1800 deg. F.) higher than the oxy-hydrogen flame. The products of the combustion are carbon monoxide and hydrogen, which are reducing agents." Further along he said: "this double property makes the use of acetylene in blow-pipes of very great value for the production of high temperatures in the laboratory." This statement of Le Chatelier is especially noteworthy, since he set the ratio of the gases at equal volumes, and not at the theoretical proportion of 2^ volumes of oxygen to 1 of acetylene.

The application of the oxy-acetylene gas torch to metallic welding dates experimentally from 1901, and industrially from 1903. Edmond Fouche, of Paris, who did considerable experimenting in conjunction with Picard, is generally credited with having devised the first really practical and safe torch. In February 1904 Fouche sent two of his torches to Eugene Bournonville, of New York, with which the latter repaired a machine that was still in use years later. The Fouche and Picard torch first developed, used both oxygen and acetylene under high pressure. There proved to be serious objections to this, and Fouche next produced the low pressure or injector type of torch which employed only the oxygen under high pressure. Following these was the Gauthier-Ely positive pressure or medium-pressure type which used both gases under moderate and independent pressures. This type was later brought to the United States by Augustine Davis and Eugene Bournonville in 1906. During this year Bournonville designed the first acetylene pressure generator produced in connection with the oxy-acetylene process.

In 1905 and 1906 considerable Avelding work was done but the process was handicapped by the inadequacy and poor quality of the oxygen then obtainable, and also by the imperfect knowledge and technique necessary to good work. In 1902, Carl Linde patented in England a process for liquefying air and producing oxygen and nitrogen. In 1906 a plant for the production of oxygen by the Linde process was established in Buffalo, N. Y. From that time on, oxygen plants of various

HISTORY AND USES OF THE GAS TORCH 3

kinds have constantly increased in number and the commercial production of oxygen of good quality has been a great factor in the development of gas torch welding.

At first, operations were limited to the simplest repair work on iron or steel. As the apparatus was improved and the efficiency of the welders increased, the field widened. New uses have been found for the process and the range of metals coming within its scope has steadily expanded. It has its limitations, however, which will be pointed out elsewhere.

Used for Both Welding and Cutting-. — In addition to welding, the oxy-acetylene flame, as well as a number of others, is applicable to cutting. In fact so closely allied are welding and cutting in this field, that an operator is usually called upon to do both many times in a day's work. Cutting by means of an oxygen jet was first made commercially possible by Jottrand, who took his basic patent in 1905.

Aside from the manual operation of welding or cutting torches, a large number of machines have been designed. These range from simple wheel or radius attachments for the torch itself, to huge automatic pipe making machines or others of a complicated nature.

The oxy-acetylene flame consists of two parts, a small inner luminous "cone" which is bluish white in color, and a larger enveloping non-luminous flame. The temperature at the apex of the cone is estimated to be about 6300 deg. F. This heat is not surpassed by any burning gas with the possible exception of thermalene, for which 6500 deg. F. is claimed.

For welding purposes the high efficiency of acetylene is due to its high carbon content and to the fact that it is endothermic, that is to say, heat-absorbing in its formation. Energy stored up in formation is given off again in the form of heat by the acetylene upon dissociation. It is calculated that of 1475 heat units in a cubic foot, 227 are due to the mere breaking up of the gas. "While theoretically two and one-half volumes of oxygen are needed to completely burn one volume of acetylene, the ratio in which the gases are employed in practice is about one volume of oxygen to one volume of acetylene. The flame yielded by such a mixture is the correct one, or the so-called "neutral" flame. By increasing or decreasing the proportion of oxygen, flames known as either oxidizing or reducing may be obtained, tbe appearance of the cone changing as the proportions are modified.

While the use of oxy-acetylene for welding is more commonly known than any other combination, there are several gases, which when mixed with oxygen, will produce more or less satisfactory welds. Some of them are to be preferred to acetylene for certain cutting purposes. The better known gases are described as follows, it being understood that they are to be used with oxygen.

Hydrogen gas is a chemical element which exists in nature in great quantities in various chemical combinations. The most common is its union with oxygen to form water (HoO). As a consequence, water is used as a basis for making both oxygen and hydrogen. Oxy-hydrogen welding was the first gas torch welding system employed, and it was used quite extensively until the introduction of the more advantageous system of welding with oxy-acetylene. While hydrogen may be manufactured on the premises, it is also handled commercially in steel cylinders. In using this flame for welding there is an existing danger that the oxygen may unite with the metal causing it to be overheated or burnt. To prevent the burning of the metal, it becomes necessary to use a supercharge of hydrogen so that oxygen liberated within the flame will combine with the free hydrogen instead of with the metal. This, however, increases the size and decreases the temperature of the flame. The temperature of the oxy-hydrogen flame according to Kautny, can never go higher than the dissociation temperature of water, which is estimated at 2000 dcg. C. (3632 F.) For welding thin metal sheets hydrogen is practical on account of its comparatively low heat. The quality of the weld, however, decreases as the thickness of the metal increases. While theoretically only two volumes of hydrogen are required to one of oxygen, in actual practice when employing an oxy-hydrogen toreh, it is necessary to use four or five volumes of hydrogen to one of oxygen in order to insure a non-oxidizing flame. This in itself is a wasteful process, since the maximum heat obtained is limited to the amount produced by combining two volumes of hydrogen to one of oxygen. For heavy cutting it is preferred to acetylene on account of its longer flame. It is also used extensively for lead

HISTORY AND USES OF THE GAS TORCH 5

burning, preheating, soldering, brazing, annealing, special forging or rivet heating and a number of other things.

Tliermalene is one of the latest gases to be produced. It is the discovery of Linus Wolf, Zurich, Switzerland, and it is handled in this country by the Thermalene Co., Chicago Heights, 111. It is a combination produced by the decomposition of calcium carbide and hydrocarbon oils, the heat generated by the carbide being used to vaporize the oil. It is used for either welding or cutting.

Blmigas is a liquid under pressure. It is the discovery of Herman Blau and it is made from gas oil, a product of the oil refineries. It probably has the low^est explosive range of any gas used for illuminating purposes, the range being about 4 per cent wiiile that of coal gas is about 13 per cent. Like coal gas, however, it is little used for welding, though sometimes used ft)r cutting. Blaugas is marketed in steel cylinders having the equivalent of 1300 cu.ft. of city gas, by the American Blaugas Corp., New York. Its largest field is for cooking and lighting purposes where coal gas is not readily obtainable. Owing to its portability it may be used to advantage for preheating work.

Drigas is a light oil gas, which is a vapor under pressure. It is sold in steel cylinders of about 150 cu.ft. by the same concern handling blaugas. It is especially good in combination with oxygen for cutting metal from 1 to 12 in. thick, and is also considerably used for preheating. Its explosive range is about ^ that of coal gas, and it is non-poisonous and nonasphyxiating.

Illuminating Gas (coal gas or water gas) can only be used for welding very thin pieces owing to the low temperature of the flame. It may, however, be used for preheating or cutting.

Benzine or Benzol Vapors have the same properties, approximately, as blaugas. The temperature is a little higher than that of illuminating gas, but much lower than acetylene. It is only used for welding under special circumstances.

While a number of gases, which are used with oxygen, have been mentioned, only the production and use of hydrogen, acetylene and thermalene will be described, along with that of oxygen.

Explosive Limits of Welding Gases. — In order to be explosive, a combustible gas or vapor must be mixed with a certain amount of oxygen or air, the proportions of the mixture ranging between certain limits depending on the character of the fuel. Any figures showing these explosive limits of the gases can only be approximate at best, since so many things enter into the calculations, such as the purity of the gas, means of ignition, temperature, pressure, and so on. In general, the mixture that has just enough oxygen for complete combustion of the fuel gives the highest pressures and temperatures, and very nearly the highest speed of ignition. If the proportion of oxygen (air) is increased beyond, or decreased from, the theoretical proportion, the maximum pressures and temperatures are lowered and the speed of ignition decreases until at certain upper and lower limits the mixture ceases to be explosive, and only slow combustion can occur.

The figures here given are believed to be a fair average of those given by the various authorities. The explosion is supposed to be caused by an electric spark, at atmospheric pressure and a temperature of about 65 deg. F.

Acetylene — 3 per cent gas plus 97 per cent tiir to 55 per cent gas plus 45 per cent air, or a range of 52 per cent (one writer says 73 per cent gas plus 27 per cent air).

Blangas — i per cent gas plus 96 per cent air to 8 per cent gas plus 92 per cent air, or a range of 4 per cent.

Coal Gas — 6.5 per cent gas plus 93.5 per cent air to 19.5 per cent gas plus 80.5 per cent air, or a range of 13 per cent.

Drigas — 4 per cent gas plus 96 per cent air to 8 per cent gas plus 92 per cent air, or a range of 4 per cent.

Hydrogen — 10 per cent gas plus 90 per cent air to 66 per cent gas plus 34 per cent air, or a range of 56 per cent (one writer says 6 per cent plus 94 per cent to 72 per cent plus 28 per cent).

Thermalcne — 12 per cent gas plus 88 per cent air to 30 per cent gas plus 70 per cent air, or a range of 18 per cent.

The ignition temperatures of some of the gases, at atmospheric pressure are: Acetylene, 760 to 820 deg. F. ; city gas, 1100 deg. F. ; hydrogen, 1075 to 1100 deg. F.

According to McCormack, the cu.ft. per pound of gases M'as calculated for the specific gravity and found to be : Acetylene, 14.8 cu.ft. ; coal gas, 24.3 cu.ft. ; hydrogen, 192.4 cu.ft. ; thermalene, 13.97 cu. ft.

HISTORY AND USES OF THE GAS TORCH 7

The Field of Gas Torch Welding and Cutting. — In a general way, the field of the gas torch welding and cutting may be outlined as follows, though some of the applications enumerated are more advantageously done by other methods. This is especially true with reference to the welding of heavy sections which should, as a rule, be done with thermit.

Airplane Construction. — Welding water jackets to cylinder, valve cages to cylinder, of manifolds (intake, exhaust, and cooling), flanges to the manifold connections, spark plug thimbles, tubular sections for frame, splice plates, sockets to frames, aluminum crank cases, water tank.

Automobile Industry. — Welding rear axle housings, defective gears and pinions, manifolds, shafts, steering posts, automobile bodies (aluminum and steel), tubing used in wind shields, etc., crank cases, transmission cases, wheels which are made of stamped-out parts, mufflers, valve stems to valves, rims, repairing crank shafts, frames, extending frame to make a truck out of a car.

Copper Plate. — Welding manifolds, flats, kettles, vats, tanks, copper, stills and chemical ware.

Electric Raihvay. — Welding of bonds, worn boxes, riotor housings, building in teeth of defective pinions and ge:irs, reclaiming of broken trucks, welding air receivers on air-brake system, steel trolley wires, side frames.

Forge Shop. — Welding ornamental iron, complicated parts.

Foundries. — Steel foundry: Welding up of blowholes, porous spots, blocks, cutting of risers, gates and heads ; welding moldings which are cast in parts. Cast iron foundry : Reclaiming castings.

Lead Burning. — Burning of connectors on storage batteries, battery repairs, lead linings in vats, tanks, etc., lead-pipe joints.

Piping and Gas Main WorJi. — Welding of steam, air, gas, oil, and water lines, welding for high pressure gas distribution, annnonia systems. Fittings, such as T's, Y's, S's, crosses, which are cut and welded on the job, meter connections for houses, traps, drip pots.

Plate Welding.^— Anmwma receivers, generators, air receivers, tanks for oil, vacuum driers, digesters, vats, steam driers, tanks of all kinds which are to be subjected to heat and pressure, plate assembly work for gas manufacture by-products, recovery work, stills.

Poicer Plant Maintenance. — Building up worn or broken parts, welding of cylinders, pistons, valve chests, etc. Welding of steam lines, of pump castings broken in service. Repairing of flywheels.

Railroad Repair. — Firebox repairs (including patches), replacing side sheets, welding in flues, cutting off rails, mud rings, welding cracked steam chest, valves, cross-heads, cylinders, building up worn pins, cutting out links, irregular shapes of steel, filling worn spots on wheels, welding spokes, cutting and welding up locomotive frames. Welding together parts of car seats, chair and window frames. Reclaiming bolsters, couplings, slotting forged engine rods; building up frogs and diamond crossings, scrappings. building steel cars.

Rolliny Mill. — General repair of engines, rolls, hot beds, plates, furnace equipment, fabricating open-beai"tli water jacket doors, reclaiming copper tuyeres, cutting up lost heats, cutting up "kindling" or scrap, bar stock, billets, plates.

Sheet il/<:Yrt?.— Manufacture of metallic furniture, steel barrels, transformer cases, range boilers, kitchen utensils, light air tanks, tubing, oil storage tanks.

Shipyards. — Cutting of plates, channels, special sections, welding and reclaiming of broken parts of machinery and propellers, patching of hulls, stringers, building up of worn chocks.

Small Arms Manufacture. — Reclaiming component parts, spot hardening of different parts, spot annealing.

Structural Steel. — Cutting as applied to coping, splicing and fitting rails, channels, I beams and other sha]ies. Cutting holes for rivets, welding up misdrilled holes, cutting of all kinds of gusset splice plates, cutting wrecking, welding structural parts where riveting is not possible.

Chapter II The Production Of Welding Gases— Oxygen And Hydrogen

Oxygen is a gas which constitutes about 23 per cent by weight and 21 per cent by volume of the air we breathe, most of the other percentage being nitrogen, a gas which does not support combustion. Oxygen itself will not burn, but it is the greatest supporter of combustion known. It was probably discovered by Stephen Hales in 1727, though Priestly was the first to publish a description of it in 1774. The name ' ' oxygen ' ' was later applied to the gas by Lavoisier. Pure oxygen is colorless, odorless and tasteless. For welding work it is important that the oxygen used be as pure as it is commercially possible to obtain it. The impurities which decrease its efficiency are usually hydrogen and nitrogen.

There are three ways to produce oxygen commercially; by means of liquid air, by chemicals and by the electrolytic process. When oxygen is made by the liquid air process, there is a certain amount of nitrogen present. In the chemical methods, a number of impurities may cause trouble. By the electrolytic process, the impurity is hydrogen.

Oxygen by the Liquid Air Process. — As a general rule, taking everything into consideration, it is far better for the average or small user to buy his oxygen from a reliable concern and not try to manufacture it himself. The oldest concern in this country making oxygen by the liquid air process is the Linde Air Products Co., with offices in New York City. Their cylinders are regularly furnished in two sizes of 100 and 200 cu.ft. capacity respectively. They are charged to a pressure of 1800 lb. at a temperature of 70 deg. F. Customers are furnished cylinders free and pay only for the oxygen. Empty loaned cylinders are exchangeable for filled ones at stations in practically every city of fair size in the country. A 50 ft.

size of cylinder is obtainable for those whose requirements are very limited. A number of other concerns supply electrolytic oxygen for the market, the 100 cu.ft. cylinders being about 85 in. in diameter and 48 in. high, weighing approximately 122 lb. when filled. Tlie average purity of oxygen in cylinders is about 99 per cent.

Since the production of oxygen by the liquid air process is only applicable to large installations any detailed description of the method would be out of place here. It is sufficient to say that in general, the process consists of first reducing the air to liquid form by means of the combined action of high compression and low temperature, and then separating the oxygen and nitrogen of which it is composed, by taking advantage of the different boiling points of the two. Under atmospheric pressure the boiling point of very pure liquid oxygen is — 182.7 deg. C. ( — 296.9 deg. F.) and of very pure nitrogen — 195.5 deg. C. ( — 319.9 deg. F.). This means a difference in the boiling points of 12.8 deg. C, or 23 deg. F. These respective boiling points will, of course, vary under different pressures, and various degrees of purity, but tlie difference between the two is sufficient to allow of the nitrogen lieing vaporized in suitable apparatus and carried away before the oxygen vaporizes.

The Chlorate of Potash Process. — Where circumstances make the chemical production of oxygen advisable, the chlorate of potash method is probably the most satisfactory at the present time. In this process chlorate of potash (KCIO3) and manganese dioxide (MnOo) are mixed together in the proportion of 100 to 13 parts (about 8 to 1). This riixture is placed in a retort filled as full as possible to exclude air. The retort is then heated and the oxygen is driven off. As the oxygen gas passes off from the retort it is conveyed through a cylinder or vessel containing sodium hydroxide (NaOH) which removes most of the impurities. The oxygen is then piped to a gasometer from Avhich it may be used direct or pumped into cylinders. A pound of the mixture is said to' produce about 4 or 4^ cu.ft. of oxygen. The manganese dioxide is unchanged during the process. It is used because it enables the chlorate of potash to more readily give up its oxygen and at a lower temperature than without it.