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THE ART OF GALVANIZING 
 
 By Alfred Sang, Pittsburg. Pa. 
 
 One of the most persistent problems 
 which confront the worker in iron and 
 steel is the prevention of corrosion. We 
 cannot rid ourselves of the agents which 
 effect the corrosion of iron without at 
 the same time ridding ourselves of the 
 agents which are essential to life itself. 
 Air is indispensable both to human res- 
 piration and for the formation of rust 
 and other oxides for which it supplies 
 the oxygen ; moisture is necessary for 
 the formation of clouds which make the 
 earth fertile, and it also supplies the 
 medium in which rusting takes place 
 and hydrates the oxide; carbonic diox- 
 ide is an animal by-product, and a raw 
 material for the vegetable world, and 
 the exchange of carbonic dioxide and 
 oxygen, which is continually taking 
 place between the animal and vegetable 
 kingdoms is of vital importance; then, 
 on the other hand, rust is not readily- 
 formed — if at all — unless there be an 
 acid present, and the acid which is most 
 universally distributed is carbonic acid 
 or hydrated carbonic dioxide. There is, 
 as you see, a close relationship between 
 the processes of living and rusting, but 
 while human beings make up for the 
 rusting or decaying of their tissues by 
 nutrition, it has not yet been discovered 
 how to feed or regenerate iron, and un- 
 til such a discovery is made we are com- 
 pelled to take our cue from the ancient 
 Egyptians and resort to embalming. 
 Methods for Protecting Iron and Steel. 
 
 There are two general ways of em- 
 balming iron to prevent its decomposi- 
 tion, which might be called respectively 
 the non-metallic and metallic methods. 
 In the non-metallic method, the articles 
 are coated with an organic substance, 
 usually oil or varnish, the efficiency of 
 which depends on its being more or less 
 air tight; when coloring matter is add- 
 ed to the oil it becomes a paint, but I 
 understand from authorities on the sub- 
 ject that a varnish free from pigments 
 is preferable to anything else. The 
 metallic method consists in coating the 
 
 iron with some other metal, and it , 
 this method which I have come to discuss 
 with you. 
 
 The Composite Nature of Steel. 
 
 Iron rusts less readily than does steel; 
 this is perhaps due to steel being a very 
 composite material. In the iron, which 
 forms the bulk of its composition, are 
 dissolved or immersed a great variety 
 of other substances; some of these are 
 simple, such as graphite, silicon and 
 manganese, and others are compound, 
 such as carbides, sulphides, phosphides 
 and silicides; the carbon compounds are 
 very numerous and diversified, being due 
 to different heat treatments; the best 
 known are cementite, pearlite and mar- 
 tensite. Just as variety is, to some 
 people, the spice of living, so is hetero- 
 geneous composition the spice of rusting, 
 in the present instance at any rate; nor 
 is this by any means a solitary instance; 
 it is a well £nown fact that chemically 
 pure zinc is dissolved very slowly by cer- 
 tain acids, whereas the commercial prod- 
 uct, especially if it be high in iron, is 
 rapidly dissolved.* 
 
 When -"'steel is attacked by an acid 
 pickle its surface is due to the iron dis- 
 solving first* and the impurities be- 
 ing left ai a poorly adhering black 
 powder. For some work which has 
 to be coated, and especially if the 
 coating is non-metallic, it is desirable 
 to remove the surface "rottenness'' by 
 means of the sand-blast; the sand-blast 
 is often inconvenient or undesirable, but 
 a high pressure water jet is also ef- 
 fective and will remove at the same 
 time the gelatinous or colloidal salts of 
 iron which are left on the surface of 
 the steel. 
 
 Metallic Coatings. 
 
 If the metallic coating is considered 
 merely as a garment which protects the 
 
 * The theory has been advanced by Weeren 
 that this passiveness of pure zinc is due to 
 the formation of a condensed layer of hydro- 
 gen on the surface, which prevents further 
 action of the acid. It is difficult to see how 
 the presence of iron would prevent the ac- 
 cumulation of hydrogen. 
 
98 
 
 TRAN^4CTT KS AMERICAN FOUNDRYMEN'S ASSOCIATION 
 
 / 
 
 iron article i^" atmospheric influences, 
 the point3^P" cn ™ust receive special 
 consider;]** 3 ' 11 are tne closeness of the fit 
 and th/- irnpenetralile qualities of the 
 coa tins'- A close fit is more readily ob- 
 tain/" by depositing the metals electric- 
 , ;/?. In hot processes the uneven con- 
 fraction of the coating and coated met- 
 als — the latter usually having the lower 
 coefficient — will cause blisters which are 
 not always noticeable to the naked eye 
 but which are none the less present. 
 This poor adherence due to uneven con- 
 traction is evidenced by the flaking 
 which will take place when the articles 
 arc bent; with articles which do not 
 undergo bending, such as castings, there 
 may not be any flaking, but the air 
 spaces are there just the same and oxi- 
 dation will take place under the blisters, 
 out of sight, slowly but surely, if the air 
 is given access. Unfortunately the air 
 has free access to these spaces because 
 no hot coated surface which has not re- 
 ceived a mechanical treatment in the hot 
 state, such as rolling, is free from faults 
 and crevices: especially is this the case 
 in rough and irregular work like cast- 
 ings where the variety of strains taking 
 place at the moment of setting of the 
 coating metal produce an equivalent va- 
 riety of microscopical fissures. Through 
 these fissures the air, moisture and car- 
 bonic dioxide have free access to the 
 iron. 
 
 An electrically deposited coating ad- 
 heres a great deal better than does a 
 hot coating, and this is the greatest 
 point in its favor ; unfortunately, it is 
 almost impossible to obtain a sur- 
 face free from pores. Every pho- 
 tographer knows how specks of dust 
 will cause pinholes in his negatives: a 
 particle of dust is more or less light- 
 proof and protects the point of the film 
 on which it rests from the chemical ac- 
 tion of light In electrolytic work each 
 speck of impurity prevents the metal-ions 
 of the electrolyte from depositing on the 
 spot covered by the impurity and a pin- 
 bole or pore is the result. These pin- 
 holes are like weds with a spot of rust, 
 a -speck of dirt or a particle of oil at the 
 bottom, each of which is sufficient in 
 itself to prevent the deposition of the 
 coating metal, but none of which is able 
 
 to prevent the access of the corroding 
 agencies. Under the microscope rust 
 will be found to originate in all cases in 
 the pores, and I have examined speci- 
 mens where the rust seemed to fairly 
 ooze out of them. If articles could be 
 made perfectly clean before being coated, 
 the electrolytic process would be perfect 
 as regards the two points of quality re- 
 quired of a coating considered as a cov- 
 ering only. 
 
 The Coating as a Mechanical 
 Protection. 
 Considered merely as a mechanical 
 protection, the coating should be resist- 
 ant to impact and to abrasion, the latter 
 being the most important. The soft met- 
 als, such as tin and zinc, do not stand 
 up well against abrasion, but unless 
 their adherence be very defective, they 
 will stand impact well, on account of 
 their malleability at ordinary tempera- 
 tures. It would be desirable to obtain a 
 coating which would be as good a pro- 
 tection as zinc but tougher and harder. 
 Aluminum is being used with some suc- 
 cess and if the metal were cheaper it 
 would become an interesting competitor 
 of zinc. 
 
 Different Behavior of Tin Plate and 
 Galvanized Iron. 
 But there is a more important feature 
 of metallic coatings to be taken into con- 
 sideration. This feature I shall intro- 
 duce by the following example: If you 
 make an incision in the surface of a 
 sheet of tinplate and a similar one in a 
 sheet of galvanized iron and expose the 
 two sheets together to the same oxidiz- 
 ing agencies, you will soon note a very 
 great difference in the behavior of the 
 two mutilations. The cut in the gal- 
 vanized iron will rust very slightly or 
 nut at all and the zinc at the edges will 
 be oxidized, but the cut in the tinplate 
 will not only show much more rapid and 
 intense oxidation of the iron but the cor- 
 rosion will extend beyond the edges of 
 the cut. and in spite of the tin. A pin- 
 hole in a galvanized sheet will not rust; 
 a pinhole in a tinplate will spread out 
 like a star. 
 
 Metals in Contact. 
 T must now call your attention to a 
 few scientific principles which are all- 
 important when considering metallic 
 
 Gift, 
 
 ; 180r 
 
 (kU<*-' 
 
TRAXSACTIOXS AMERICAN FOUXDRYMEX'S ASSOCIATION 
 
 99 
 
 coatings. In order to understand the 
 reason for the different behavior of the 
 galvanized iron and the tin-plate, it is 
 necessary to thoroughly understand what 
 takes place when two metals are in con- 
 tact. For the purpose of the present dis- 
 cussion we must consider four cases of 
 metals in contact as follows : 
 
 First — In the presence of electricity. 
 
 Second — In the presence of heat. 
 
 Third — In the presence of corrosive 
 agents. 
 
 Fourth — Apart from any exterior 
 agency whatever. 
 
 In the Presence of Electricity. 
 
 As regards the first case, it is important 
 to note that copper conducts electricity 
 better than does iron, iron better than tin, 
 tin better than lead, lead. better than zinc 
 and zinc better than antimony. The 
 metals first mentioned are negative to 
 those which follow ; iron is negative in 
 relation to zinc and zinc is positive in 
 relation to iron. The conductivities of 
 these metals are the reciprocals of their 
 resistivities, in other words, the better 
 conductivity of copper over iron is due 
 to the smaller resistance which it op- 
 poses to the passage of the electric cur- 
 rent. Again, the better the metal con- 
 ducts electricity the less capacity it has 
 for storing it: this is the same as in the 
 case of heat, the poorer the body as a 
 conductor, the more difficult it will be 
 to heat it, but the longer it will take to 
 cool. The wooden handle of a silver tea- 
 pot does not heat up as well or as rapidly 
 as does the pot itself, but when the tea- 
 pot is cooled the metal part cools quick- 
 est and becomes colder than the handle. 
 If, now, two metals, say iron and zinc, 
 are put in contact and immersed in an 
 electrically charged medium., the iron be- 
 ing the better conductor will not absorb 
 as much electricity as the zinc, and there 
 will exist what is known as an electro- 
 motive difference of potential, there will 
 be a difference of electrical pressure be- 
 tween the iron and the zinc in contact, 
 and therefore a steady current of elec- 
 tricity will flow from the zinc to the 
 iron, and this current will be kept steady 
 by the leakage which is directly propor- 
 tional to the absorbing power. If no 
 leakage were possible the potential of the 
 two metals would reach the same level 
 
 and they would be in electrostatic equili- 
 brium equivalent to a closed circuit. 
 
 An apt comparison to what takes place 
 would be that of two water tanks of 
 equal dimensions, connected at the bot- 
 tom and at the top by open pipes, and 
 one tank having a larger intake at the top 
 than the other ; if both tanks are filled 
 simultaneously by steady streams of 
 w r ater, the tank with the larger intake 
 will fill more rapidly and there will be 
 a continual flow through the lower con- 
 necting pipe from the tank with the larger 
 intake to the tank with the smaller in- 
 take to maintain the level. When the 
 tanks are full they will be in equilibrium, 
 and if they are turned upside down the 
 outflow through the intake pipes will be 
 proportionate to the previous inflow and 
 the current will be reversed, passing from 
 the tank with the smaller outflow to the 
 tank with the large outflow in which the 
 level is going down more rapidly. It is 
 this operation of maintaining, or rather 
 the effort to maintain the electrical level 
 which produces the flow between metals 
 of different conductivity when they are 
 in contact and immersed in an electrically 
 charged medium. The medium itself may 
 be perfectly static, or at rest, but the 
 flow from the iron to the copper will 
 manifest itself as dynamic, or moving 
 electricity ; nothing in nature, be it ma- 
 terial or immaterial, can be manifested 
 to our senses unless there be a motion, a 
 difference, a relation. 
 
 Electricity is always present on this 
 planet, and everything is fairly impreg- 
 nated with it, if, therefore, we bring two 
 dissimilar metals into mutual contact we 
 shall obtain a flow of electricity from one 
 to the other, caused by an ineffectual ef- 
 fort to equalize potentials, which will 
 produce sensible galvanic effects. The 
 contact need not be direct ; a suitable con- 
 ducting connection, such as moist air, 
 will act as an electrolyte and enable the 
 action to take place, the space in be- 
 tween constituting what is known as a 
 field of force. Besides atmospheric and 
 telluric electricity we are often called 
 upon to take into consideration, in our 
 engineering problems, the electricity arti- 
 ficially produced for industrial and do- 
 mestic purposes, the diffusion of which, 
 or "stray currents" as they are called, 
 
100 TRANSACTIONS AMERICAN FOUNDRYMEN'S ASSOCIATION 
 
 will hasten the corrosion of water pipes 
 and structural steel, even when they are 
 embedded in concrete. 
 
 The reverse of the order in which I 
 have previously placed the metals in re- 
 lation to their conductivities — i. e.. anti- 
 mony, zinc, lead, tin, iron and copper, 
 indicates the positive direction in which 
 the current will flow from metals having 
 the higher to those having the lower po- 
 tentials ; it is known as an electromo- 
 tive series. 
 
 In the Presence of Heat. 
 
 The second case is that of metals in 
 contact exposed to heat. The electrical 
 conductivity of substances will vary with 
 temperature, that of metals decreasing 
 with an increase of temperature. There 
 are notable exceptions to any generaliza- 
 tion which might be attempted that the 
 conductivity is inversely proportional to 
 the temperature, and one of these excep- 
 tions happens to be iron. 
 
 When two metals in contact are sub- 
 iei ted to heat the voltaic or galvanic 
 action of which I have spoken will be 
 influenced either favorably or unfavor- 
 ably because the thermo-electric series is 
 different from the electro-motive series 
 which I have given you. The thermo- 
 electric series runs as follows : lead, tin, 
 copper, zinc, iron and antimony. The 
 order of these metals indicates the direc- 
 tion in which the current tends to flow 
 with an increase of temperature, this 
 tendency may lie, and is in most cases, 
 exhibited as. either a resistance or as an 
 aid to the electromotive current; for in- 
 stance, increase in temperature will re- 
 duce the current from zinc to iron in a 
 lesser degree than from antimony to iron. 
 This principle has been used in the con- 
 struction of electric pyrometers in which 
 the variation in the temperature of a 
 couple formed of dissimilar metals is 
 recorded very sensitively at a distance 
 from the source of heat, by means of a 
 galvanometer. 
 
 The galvanic effect between metals is. 
 therefore, modified in a very complicated 
 manner and to a considerable extent by 
 the temperature at the point of con- 
 tact. This galvanic action seems to be 
 intimately related to the natural tendency 
 towards chemical action exhibited by all 
 substances in contact and to that chemi- 
 
 cal affinity which exists to some degree 
 or other between all kinds of matter. 
 In the Presence of Corrosive Agents. 
 The third case is that in which corro- 
 sive agents are present which attack both 
 of the metals. A decrease of electrical 
 potential seems to aid chemical action 
 and an increase of this potential opposes 
 it. The metal towards which the flow 
 of current is directed is, so to speak, 
 over-saturated on. account of the persist- 
 ence of effect which, when it refers to 
 magnetism is called hysteresis, and its 
 potential is greater than normal. The 
 How of current from zinc to iron will 
 over-saturate the iron and will prevent 
 its decomposition, when it is exposed to 
 corrosive influences, whereas the zinc 
 which is under-saturated is in poor physi- 
 cal condition to withstand chemical at- 
 tacks. It will decompose into oxide and 
 carbonate more rapidly than if it were 
 out of contact with the iron. If only one 
 of the metals is attacked by the corro- 
 sive agents under normal conditions, 
 there will lie no galvanic protection and 
 this is why nickel-plating which is unaf- 
 fected by ordinary atmospheric condi- 
 tions is nothing more than a protective 
 skin and if it is partially removed the 
 exposed surface of the irons rust very 
 readily. Copper-plating is no better, and 
 if the iron is exposed the galvanic action 
 is slightly unfavorable because the cop- 
 per is in negative relation to the iron. 
 Copper rolled over iron and then drawn, 
 forms a good protection, but in this case 
 the iron i^ nothing but a core. Lead 
 would be a good coating metal if it were 
 only harder and more readily attacked by 
 acids. 
 
 Apart From Any Outside Agents. 
 
 The fourth and last case is that of 
 metals in contact without any exterior 
 agents being taken into account. Care- 
 ful investigation has shown conclusively 
 that if two metals are placed in close 
 contact there will be a slow exchange of 
 molecules, which will result in the metals 
 alloying at their surface. If great pres- 
 sure is applied during this exchange, the 
 metals may be actually welded together. 
 This action does not take place in a 
 minute, nor even in a day or a month. It 
 is very wonderful what pressure will do; 
 certain salts in a finely powdered state 
 
TRANSACTIONS AMERICAN FOUNDRYMEN'S ASSOCIATION 101 
 
 have been compressed beyond a critical 
 point where the cohesion became equal 
 to that of the substance before it was 
 pulverized and even transparency was re- 
 covered. What enormous power must 
 exist within the atom to bring about the 
 same results by rapid and unimpressive 
 reaction; such as the recovery of crys- 
 tals by dissolving a pulverized substance 
 and then evaporating it. 
 
 This exchange of molecules between 
 metals in contact is a simple case of dif- 
 fusion. The diffusion of metals takes a 
 great deal longer than that of liquids or 
 gases because the internal friction is 
 vastly greater; if the molecular cohesion 
 is reduced by fusing the metals, the al- 
 loying will take place as readily as when 
 whisky and water are mixed to form the 
 alloy, which is known as a "high-ball." 
 If the metals could be brought to a state 
 of vapor, the diffusion would be practi- 
 cally instantaneous, and even if only one 
 of the metals were in a state of vapor 
 this should hasten the process to a con- 
 siderable extent. I must ask you to take 
 good note of this statement, because it 
 has a very important bearing on the pro- 
 cess and nature of dry galvanizing. 
 
 The effect of pressure is to hasten the 
 action, but diffusion will always take 
 place between metals provided there is 
 some kind of contact. According to this 
 theory the metals of alloys should be- 
 ' come more thoroughly incorporated with 
 time, and a zinc coating which has passed 
 through the early stages of its existence 
 without being destroyed should, like wine 
 and love, improve with age; the two 
 metals should gradually become alloyed 
 at their surface of separation. If the 
 old Ninivites or Egyptians had pro- 
 duced galvanized work there would be 
 people to worry over the lost art of al- 
 loying iron and zinc just as others still 
 persist in claiming that some useless art 
 of hardening brass has been lost, al- 
 though it has not even been proved as 
 yet that it ever existed. 
 Specifications For an Ideal Coating. 
 
 On looking back at the four cases of 
 metals in contact which I have discussed, 
 you will readily see that all are closely 
 related and that they must in all nor- 
 mal cases be present at one and the same 
 
 time. What then are the specifications 
 for an ideal metallic coating for iron? 
 
 First — It must be as far as possible 
 from iron towards the positive end of 
 the electromotive series and must ful- 
 fill the same requirements in the thermo- 
 electric series. 
 
 Second — It must be affected by the 
 same agents which corrode the iron. 
 
 Third — It must present as large a sur- 
 face as possible to the corroding agents. 
 
 Fourth — It must be in very close con- 
 tact with the iron. 
 
 Zinc is, of all the commercial metals, 
 the one which most closely fulfills the 
 first and second requirements ; the third 
 and fourth in regard to surface exposed 
 and contact with the iron, are matters 
 of process, and I shall, therefore, now 
 proceed to describe the various processes 
 which have been used to apply zinc to 
 metal surfaces, but before doing so I 
 want to point out that all these princi- 
 ples which I have enumerated apply as 
 well to the salts of the metals and that 
 is undoubtedly one reason why red lead 
 and zinc white give such good protection 
 against corrosion. 
 
 Cold Galvanizing. 
 
 In the early years of the last century 
 the process of electrolytic zincing, which 
 is nowdays known as cold or electro-gal- 
 vanizing, was first discovered, but until 
 about 10 years ago the lack of suitable 
 equipment prevented its commercial ap- 
 plication. The articles to be treated by 
 this process are first thoroughly cleaned 
 of scale, rust and grease by an acid pick- 
 le, sand-blasting, hot lye or by other 
 means, singly or in combination, and are 
 then placed as cathodes in a solution of 
 some salt of zinc — usually the sulphate — 
 in presence of zinc and which regenerate 
 the solution, while a current of low volt- 
 age is passed through the arrangement 
 and deposits zinc from the solution upon 
 the articles. Numerous factors must be 
 taken into account; the composition and 
 temperature of the bath; the voltage and 
 density of the current; the quality, shape 
 and position of the anodes, and many 
 other points which are all of prime im- 
 portance if the results are to escape first 
 criticism and then corrosion. 
 
 The surface of an electrically galvan- 
 ized article is matt or frosted, provided 
 
102 
 
 TRANSACTIONS AMERICAN FOUNDRYMEN'S ASSOCIATION 
 
 the work has been properly done. It al- 
 ways shows a few pores. If improperly 
 done, or if the work was not perfectly 
 clean before treatment it is either hon- 
 eycombed with pin holes or spongy. 
 Above a certain limit of thickness, below 
 which the coating is worthless, first class 
 electro-galvanizing is superior to hot- 
 galvanizing and it is cheaper to produce 
 where automatic machinery can be em- 
 ployed, although less zinc is deposited 
 than by a hot dip. This is no doubt due 
 to the better contact between the zinc 
 and iron. 
 
 Hot Galvanizing. 
 
 Sixty years ago the process of hot-gal- 
 vanizing was introduced on a commercial 
 scale. It consists in dipping the articles 
 into a bath of molten spelter, with or 
 without other metallic additions, at tem- 
 peratures ranging from 750 to 900 de- 
 grees Fahr. The articles must be first 
 cleaned as for electrolytic work, but a 
 slight falling short of perfection does 
 not have such disastrous effects on the 
 quality of the result. Very heavy pieces 
 may be heated before dipping so as not to 
 chill the bath. The coating is crystalline 
 or amorphous and does not adhere as 
 perfectly as does the electrolytic one. 
 Properly treated sheet metal goods have 
 an attractive spangled - appearance hut 
 most articles look like castings and sharp 
 edges are lost. Metallic chlorides are 
 used as fluxes, they are expected to re- 
 move the injurious salts of iron left by 
 the pickling, hut it is a question if it is 
 not another case like the introduction of 
 rabbits in Australia, and if they them- 
 selves are not the main cause of the de- 
 cay which starts underneath the coating 
 in hot-galvanizing work.* 
 
 Dry Galvanizing. 
 
 The latest process for applying a zinc 
 coating, is the dry process, and I am go- 
 ing to endeavor, not only to describe the 
 process itself, hut to show you also how 
 it fulfills the requirements which I have 
 indicated, how it permits the extension 
 of galvanizing to articles which have 
 never been protected in this manner and 
 how by divulging the mystery of the na- 
 ture of zinc dust it permits us to specu- 
 
 ' The fumes eiven off in hot work are in- 
 jurious to machinery ami in a manufacturing 
 concern it is necessary to erect a separate 
 building for this work. 
 
 late along new lines in metallurgy which 
 may lead to the discovery of some princi- 
 ples of great industrial value. 
 
 The process of dry galvanizing or 
 Sherardizing metals was awarded a gold 
 medal at the St. Louis exposition of 1904 
 and the president's gold medal for 1903 
 was presented to its discoverer by the 
 British Society of Engineers. The in- 
 ventor, Sherard Cowper-Coles, is one of 
 the most eminent metallurgical engineers 
 in Europe and is well known for his re- 
 introduction on a commercial scale of the 
 process of electric galvanizing, the regen- 
 erating of electrolytes by the coke and 
 zinc dust filter, the electrolytic spinning 
 of copper into sheets, wire and other 
 forms, and innumerable other invent'cms 
 and improvements in connection with the 
 electro-deposition of metals. 
 
 The Practice of Dry Galvanizing. 
 
 For the purpose of Sherardizing, the 
 articles are placed, after cleaning, in a 
 retort — usually a drum— and are covered 
 with zinc dust, which is commonly called 
 blue-powder, and is the flue-dust, and, 
 therefore, a by-product of the zinc smelt- 
 ing furnace known as the Belgian fur- 
 nace. It contains as a rule from 75 to 
 90 per cent of pure zinc; the supply of 
 zinc-dust is ample at a price below that 
 of spelter, and if the demand increases it 
 can lie produced in any quantity that may 
 lie required. A small amount of pou - 
 dered charcoal is added to prevent oxida- 
 tion of the zinc by the air inside the re- 
 tort at the beginning of the operation, 
 and the receptacle is closed and heated 
 to a temperature about two hundred de- 
 grees below the melting point of zinc. 
 Ideal conditions would obtain if the air 
 were exhausted from the drums. Where 
 the size of the plant warrants the con- 
 trol of the zinc-dust consumption to 
 within so fine a margin, the drums might 
 be filled witli some inert gas such as car- 
 bonic dioxide which is supplied to soda 
 fountains and other uses in steel bottles 
 at a very low cost. It is, however, to be 
 feared that if the temperature is allowed 
 to go too high the carbonic dioxide 
 might act as an oxidizer on some of the 
 dust. 
 
 By Sherardizing, a homogeneous de- 
 posit of zinc is obtained, varying in thick- 
 ness according to the length of time the 
 
TRANSACTIONS AMERICAN FOUNDRYMEN'S ASSOCIATION 103 
 
 article is allowed to remain in the re- 
 tort, its lower portion being an alloy of 
 zinc and iron or of zinc and copper, as 
 the case may be. In the case of copper 
 the alloy is a true and hard brass. The 
 drum is occasionally turned a fraction of 
 a revolution to insure an even coating 
 where the articles are crowded together, 
 and the heating may last from a few 
 minutes to several hours and two or 
 three drums can be used in connection 
 with one furnace. 
 
 A Sherardized surface resembles in 
 general appearance an electrically coated 
 surface. It is, however, of a soft silver- 
 gray, more lustrous and metallic and, on 
 that account, it is to most people, more 
 pleasing to the eye, and it is distributed 
 with great uniformity, which is not the 
 case in hot galvanizing. Whereas in hot 
 galvanizing the amount of zinc which is 
 alloyed to the metal of the article is very 
 small and most of the coating forms an 
 exterior perishable skin, in Sherardizing 
 the coating is thoroughly incorporated 
 with the metal which it protects, forming 
 an alloy having the appearance of pure 
 zinc but much harder and more durable. 
 It is on account of this thorough alloy- 
 ing that the protection afforded by Sher- 
 ardizing is so superior to that afforded 
 by either hot or electric galvanizing. 
 The zinc having penetrated the iron, the 
 old surface cannot be recovered by either 
 chemical or mechanical means. 
 
 If an excessive amount of zinc is de- 
 posited by Sherardizing, the outside sur- 
 face is composed of zinc somewhat hard- 
 ened by the presence of a small percent- 
 age iron, and zinc-dust accumulates and 
 clusters in a way which renders the sur- 
 face rougher and much less attractive in 
 appearance under magnification than it is 
 to the naked eye. No special advantage 
 is derived from the additional expense 
 unless the conditions under which the 
 articles are to be used are exceptionally 
 severe. 
 
 The process of Sherardizing is not con- 
 fined to zincing; the dusts of antimony 
 and of other metals can be used in a 
 similar manner. The fact that zinc-dust, 
 even at temperatures higher than its 
 melting point, does not melt or cake, is 
 of great value in Sherardizing, as 
 it eliminates the danger of spoilt 
 work from carelessness in hand- 
 
 ling the temperature. Furthermore, zinc- 
 dust containing as little as 35 per cent of 
 pure metal can be used. The presence of 
 the oxide is probably necessary, as it 
 seems to play a part in the process. 
 Some Anomalies of the Process. 
 But why is it that zinc-dust acts in this 
 peculiar manner, depositing zinc at a 
 temperature several hundred degrees be- 
 low its melting point, and why is it that 
 the comparatively cold zinc alloys itself 
 to the iron or other metal when the mol- 
 ten zinc of the hot process fails to do so, 
 or at best only does so in a cumbrous 
 limited way? I can only answer these 
 questions by giving you my own theory 
 of the nature of zinc dust and of its 
 action under the conditions of Sherard- 
 izing. This theory is quite new to the 
 very best of my knowledge and was not 
 published by me until quite recently;* it 
 is founded on observed facts but is not 
 entirely empirical, because so far it has 
 seemed to satisfy all the theoretical tests 
 to which I have been able to put it and 
 it answers a number of unexplained phen- 
 omena which I shall mention later. 
 The Nature of Zinc-Dust. 
 The vapor of zinc which is given 
 off at a temperature of 1,000 degrees 
 Cent., or more, at the inception of 
 distillation, comes into contact with 
 the comparatively cold atmosphere of 
 the flue, the sudden chill causes a 
 rapid condensation of the vapor, so 
 rapid indeed that it skips the liquid 
 stage and drops in the shape of per- 
 fectly spherical particles of which 
 about 30,000 million can be crowded 
 into a cube measuring one-sixteenth 
 of an inch in every direction. This 
 impalpable powder which, notwith- 
 standing its high specific gravity — 
 for it is only about 10 per cent light- 
 er than zinc — can be blown about like 
 lycopodium, is used mostly by paint 
 manufacturers and is sold packed in 
 barrels holding about 1,500 pounds. 
 It is 10 or 15 per cent cheaper than 
 virgin spelter at equal content of 
 free zinc. It cannot be melted into 
 slabs on account of its rapid oxida- 
 tion at a very low temperature. 
 The peculiar properties of zinc-dust 
 
 *Electro Chemical and Metallurgical Industry, 
 May, 1907. 
 
10+ TRANSACTIONS AMERICAN FOUNDRYMEN'S ASSOCIATION 
 
 have been ascribed by some to the 
 presence of cadmium, which being a 
 more volatile metal is distilled first 
 from the ore and condensed in the 
 flues; one observer found quantities 
 ranging from 0.283 to 0.794 per cent 
 in flue dust after two hours of fur- 
 nace operation. Others have claimed 
 that these properties are due to the 
 presence of zinc oxide or other im- 
 purities. No plausible reasons for 
 these theories have as yet been ad- 
 vanced. 
 
 Most of the zinc-dust is produced 
 in Belgium or in Silesia, and a sam- 
 ple which I have had analyzed 
 showed the following composition: 
 
 Metallic zinc 88.95 
 
 Zinc oxide 6.88 
 
 Lead 3.45 
 
 Cadmium 0.62 
 
 Sulphur 0.55 
 
 Iron 0.04 
 
 G. Williams, an English chemist.* 
 has shown that zinc-dust takes up 
 water and decomposes it and gives 
 up its hydrogen on heating; he has 
 also shown that it absorbs hydrogen 
 at ordinary temperatures when sur- 
 rounded by it in a moist condition, 
 and that heated alone it yields 50 
 times its volume of hydrogen, but 
 when heated to redness with an equal 
 weight of zinc hydroxide it gives off 
 535 times its volume of hydrogen. All 
 this may have some bearing on the 
 antics of zinc-dust and on Sherard- 
 izing, but as I am about to show it 
 is unlikely and lacks confirmation, 
 both theoretical and practical. 
 
 It is my belief that these impuri- 
 ties have little or nothing to do with 
 the properties of zinc-dust and that 
 the reasons should be sought for in 
 its mode of production. 
 
 If under similar conditions of rapid 
 cooling we produce other solid bodies 
 we get unstable and brittle results. 
 If a bead of fused glass is dropped 
 into water a "Ruperts' tear" is the 
 result. As you know, a Ruperts' tear 
 is very unstable and whereas for a 
 drop of normal glass of similar di- 
 mensions several good strokes of the 
 hammer would be required to pulver- 
 ize it, the Ruperts' drop can be shiv- 
 ered to fragments by breaking off its 
 
 * Chemical News, Vol. 52. 
 
 tail with two fingers, or by scratch- 
 ing the surface film where tension 
 keeps the drop together. The dif- 
 ference of energy required to effect 
 the destruction of the normal drop 
 and the Ruperts' drop is enormous. 
 
 If we assume that zinc-dust is in 
 this critical state we can explain al- 
 most every one of the effects which 
 have puzzled chemists during the past 
 forty years. Douglas Carnegie* found 
 that zinc-dust instantly reduced fer- 
 ric to ferrous salt, and this even in 
 neutral solutions (the italics are his); 
 this action he states was consider- 
 ably quicker than with granulated 
 zinc in the presence of sulphuric acid. 
 He was at first inclined to ascribe 
 this wonderful efficiency to the oc- 
 cluded hydrogen mentioned by Wil- 
 liams, but further experiments, which 
 I need not detail, showed that he was 
 mistaken. Referring to another chem- 
 ical operation in which zinc-dust act- 
 ed with equal promptness, he writes: 
 "Zinc-dust merely effects instaneous- 
 ly the dechlorination which I found 
 zinc foil required several hours to 
 effect." 
 
 It is so well known that zinc-dust 
 has a great affinity for oxygen at a 
 low temperature that it has been 
 used for a long time in the dis- 
 charge style of ' printing of cotton 
 goods. The fabric is first dyed a 
 plain color and it is then printed on 
 with a discharge paste. The zinc 
 c'.ust acts as a reducing agent at the 
 temperature of the boiling water in 
 which the cloth is dipped to effect 
 the discharge. 
 
 A fact that is undoubtedly respon- 
 sible in a great measure for the mys- 
 tery attaching to the action of zinc- 
 dust is its readiness to oxidize. It 
 is only when oxidation is put out of 
 its power, as in the closed Sherard- 
 izing drum, that heat will produce 
 sufficient overstrain to cause the par- 
 ticles to burst into vapor. This va- 
 por so suddenly released will con- 
 dense instantly on the coolest spaces 
 it can find. In Sherardizing the cool- 
 est spaces arc on the articles in the 
 
 *Trans. Clicw. Soc., London, yr. 188S, p. 
 46S. 
 
TR.1XSACTI0XS AMERICAN FOVXDRYMEX'S ASSOCIATION 105 
 
 drum, and the drum itself being al- 
 ways hotter does not receive any de- 
 posit. One drum has already lasted 
 two years without being coated. Zinc- 
 dust appears to break down into va- 
 por ' at about ISO to 200 degrees 
 Cent., although it undoubtedly begins 
 to disintegrate at a lower heat; as 
 the pressure increases it takes a 
 greater amount of heat to cause the 
 breakdown; as the vapor condenses 
 the pressure is relieved and the hot- 
 ter particles of dust are vaporized 
 and re-establish an equilibrium. In 
 reference to this question of the vap- 
 orization of zinc, it is a well-known 
 fact that zinc will at ordinary tem- 
 peratures affect a photographic plate. 
 This has always been ascribed to 
 zinc vapor which exhibits in that 
 state great chemical activity. Radi- 
 ology, the new science, is expected 
 to bear the burden of all such ac- 
 tions and I suppose I ought to say 
 that the action of zinc on photo- 
 graphic plates is due to the slow dis- 
 integration of its atoms into energy 
 and helium. 
 
 In a small way it is a significant 
 fact that zinc-dust is intensely exo- 
 thermic in its reactions, which means 
 that these reactions are accompanied 
 by the production of heat. I could 
 also mention the property first point- 
 ed out by Schwarz, which zinc-dust 
 has of combining violently with sul- 
 phur by percussion. 
 
 It has been known for some time 
 that a cement made out of certain 
 oils and zinc-dust possesses the use- 
 ful property of becoming exceedingly 
 firm and adhering closely to iron, 
 steel and other metals, when heated 
 to a temperature of ISO degrees Cent., 
 or even less, if treated for a suf- 
 ficient length of time. The theory of 
 the nature of zinc-dust which I have 
 given explains this hardening by the 
 release of the zinc from its peculiar 
 condition to form a solid without the 
 formality of passing through the liq- 
 uid stage. In the body of the ce- 
 ment it is protected from oxidation 
 and the zinc becomes mechanically 
 continuous. It is an excellent com- 
 
 position for calking cracks and crev- 
 ices in metallic objects, for packing 
 joints and for smoothing off the sur- 
 face of castings. 
 
 I think that I have given you a 
 sufficient number of examples to 
 show that zinc-dust is a substance in 
 a very abnormal physical condition 
 and if I have spent so much time in 
 doing so, it is because I feel certain 
 that by taking advantage of this ab- 
 normal condition the metallurgical in- 
 dustries will before long reap im- 
 portant benefits. 
 
 Zinc Vapor and Ferro-Zinc. 
 
 I must tell you more about zinc 
 vapor. This vapor is a gas just like 
 air or any other gas and subject to 
 the same physical laws, but as it is 
 produced by the breakdown of zinc- 
 dust particles at a very moderate tem- 
 perature, it finds itself in the gaseous 
 state at a point below its critical 
 temperature and it will therefore 
 readily assume the solid state by con- 
 densation under its own pressure, 
 confined as it is within a retort. 
 
 When iron is pickled, hydrogen is 
 given off on the surface and rises to 
 the top of the vat. The pickle works 
 its way into the metal and hydrogen 
 is given off below the surface and 
 remains occluded. This occlusion has 
 very surprising results ; the surface of 
 the iron is hardened and if it is to 
 be drawn through a die or worked 
 in any way, it is necessary to bake 
 out the gas. Hydrogen has been long 
 suspected of metallic proclivities; it 
 is often classed as a metal. It is 
 known to form an alloy with palla- 
 dium and it is supposed to alloy it- 
 self to the iron to produce the hard 
 skin of which I have spoken. Zinc 
 vapor acts in the same way in Sher- 
 ardizing, but it forms an alloy all the 
 more readily because in its normal 
 condition it is itself a metal as we 
 generally understand that rather ar- 
 bitrary term. 
 
 Being a gas, the zinc vapor can 
 force itself into the pores of the 
 metal and form a deposit to a depth 
 which will increase with the dura- 
 tion of the treatment. A small piece 
 
106 
 
 TRANSACTIONS AMERICAN FOUNDRYMEN'S ASSOCIATION 
 
 can be alloyed throughout. An alloy 
 of zinc and iron produced by fusion 
 would be a sorry article when it came 
 to be tested; "zinc-eisen," as it is 
 called, is zinc ruined by the addition 
 of a quantity of iron, which renders 
 it brittle and worthless. By alloying 
 with vapor at a low temperature the 
 qualities of the metal cannot be in- 
 jured, but they may be greatly im- 
 proved by the zinc forming an inter- 
 molecular binding, which fills spaces 
 which would otherwise allow motions 
 of the particles under stress which 
 might injure their cohesion; the va- 
 por deposit should increase tough- 
 ness and it is quite possible that this 
 theory may have some bearing upon 
 the general subject of the nature of 
 alloys. 
 
 By using carbon as a condenser for 
 free zinc vapor, out of contact with 
 the dust, I have obtained a perfect 
 zinc dew. I used a common arc lamp 
 carbon and the drops on the top were 
 large and reduced in size down to 
 microscopical proportions on the 
 edges. Here and there on the in- 
 side were traces of zinc, showing that 
 the gas had penetrated the mass. The 
 zinc vapor had not alloyed to the 
 carbon, the specific heats being wide 
 apart, whereas I have observed that 
 the closer the specific heats of the 
 zinc and the material to be coated at 
 their working temperatures, the more 
 quickly and firmly would they com- 
 bine. It is no doubt on this account 
 that copper Sherardizes so much 
 more rapidly than does iron. 
 
 Improvements in Sherardizing will 
 undoubtedly be founded on the intelli- 
 gent control of the temperature, but to 
 this end temperature readings will 
 have to be taken inside the retort and 
 not in the furnace as heretofore. 
 
 Working with gas alone and under 
 the special conditions necessitated by 
 the peculiar circumstances of the ex- 
 periments, I was able to obtain quite a 
 variety of deposits. Rapid cooling 
 will cause (lie zinc to condense as 
 crystals the adherence of which to the 
 iron is, however, inversely proportion- 
 al to their size. Normal cooling would 
 
 seem to yield in all cases a fine glossy 
 surface of what can be appropriately 
 termed ferro-zinc. 
 
 Examining this 1 ferro-zinc under 
 about 400 diameters of enlargement it 
 exhibits the structure of the original 
 metal. A piece of mild steel which 
 had been thoroughly pickled and which 
 had been treated by vapor only, and 
 was, therefore, free from any exterior 
 zinc coating, such as would have con- 
 cealed the alloy if operated on in con- 
 tact with the dust, exhibited the usual 
 structure of an etched mild steel. This 
 ferro-zinc appears to be harder than 
 the original iron and its rust-proof 
 qualities are the true secret of the ex- 
 ceptional efficiency of Sherardizing. 
 
 The Creece test with sulphate of 
 copper is not a fair test for Sherardiz- 
 ing. it is almost without significance 
 for the following reasons: The outer 
 coating of the slightly oxidized zinc 
 particles resists the text better than 
 does the brighter hot coating or the 
 porous electrolytic one, but the alloy, 
 obtained by vapor treatment alone, 
 and which is present in all Sherardiz- 
 ing, readily takes the copper just as 
 the iron itself would, and yet it will 
 resist corrosion perfectly. The copper 
 will deposit without destroying the 
 zinc and the test is, therefore, worth- 
 less. The only way to test Sherardiz- 
 ing is to put it into service. 
 
 The alloy known as nickel steel does 
 not rust easily and yet in a nickel 
 plated article if the nickeling is partly 
 removed the iron will be corroded. 
 This shows that we must not expect 
 contact theories to adapt themselves to 
 perfection to metals in solution, and to 
 alloys. The alloy of nickel and iron re- 
 sists corrosion and in my opinion it is 
 a parallel case to that of ferro-zinc. 
 
 The Romans to make their brass, 
 which they called "Orichalcum," threw 
 cadmia, (oxide of zinc) on highly 
 heated copper. The more recent cal- 
 amine brass, process which was in use 
 until about one hundred years ago, 
 consisted in heating calamine (zinc 
 ■ silicate), granulated copper and coke — 
 dust in crucibles, the fusion and alloy- 
 ing taking place at a temperature con- 
 
TRANSACTIONS AMERICAN FOUNDRYMEN'S ASSOCIATION 107 
 
 siderably lower than the melting point 
 of copper. I thought these two points 
 of history might interest you by com- 
 parison and as aids to the digestion 
 of the most recent developments. 
 The Theory of Dry Galvanizing. 
 
 Let us enter the Sherardizing retort 
 and endeavor to find out what takes 
 place. Which guess will offer the 
 most plausible explanation? It is an 
 established fact that in Sherardizing 
 the presence of zinc oxide is neces- 
 sary. We might suppose, therefore, 
 that a molecule of oxide is reduced by 
 voltaic action when it comes into con- 
 tact with the iron; the zinc attaches 
 itself to the iron which acts' therefore, 
 as a cathode in electrolysis, and the 
 oxygen travels in the opposite direction, 
 combines with a free molecule of zinc 
 to form a molecule of oxide, and goes 
 through the same performance as be- 
 fore. 
 
 I have excellent reasons, which I 
 must keep for later publication, for 
 believing that this hypothesis is pret- 
 ty close to the truth if not the true 
 explanation of the action in dry gal- 
 vanizing. 
 
 The outer coating is composed of 
 reduced zinc in granular form and the 
 silver gray appearance may be due to 
 slight oxidation of the surface. 
 
 Whatever the true explanation may 
 be it is of little immediate interest to 
 "practical" men, but it is of great in- 
 terest to scientists who are expected 
 to continue furnishing their abstract 
 facts to serve as souls to the concrete 
 bodies created by inventors. The in- 
 ventors, while claiming all the credit, 
 usually sell or lose most of it to men 
 who put these inventions into practi- 
 cal use. He laughs best who laughs 
 last, and by the time the invention has 
 become an industry the poor scientist 
 has been entirely forgotten, — except to 
 be occasionally dubbed a theorician, a 
 dreamer, a simple soul, a mild and 
 childlike, — for of such is the kingdom 
 of heaven. 
 
 The Efficiency of Dry Galvanizing. 
 
 The efficiency of dry galvanizing, 
 which has been proved by thorough 
 testing both in England and Germany, 
 
 is' due to its fulfilling the conditions 
 which I have set forth in the early 
 part of this paper. 
 
 Considered merely as a covering, it 
 fits as closely as does an electrically 
 deposited coating and it is impenetra- 
 ble because free from pores or cracks. 
 
 As a mechanical protection it resists 
 both abrasion and impact better than 
 hot or cold work because of the qual- 
 ities' of the ferro-zinc alloy. Zinc itself 
 is superior to both tin and lead in 
 ductility and tenacity. 
 
 Considered in relation to contact ef- 
 fects the zinc distilled as vapor and 
 alloyed to the iron is absolutely pure 
 and the span between it and the iron 
 in the electromotive series is, there- 
 fore, extended as compared with a 
 zinc containing a percentage of impur- 
 ities. Its contact with the iron in the 
 body of the alloy is as perfect as is 
 possible. In relation to corroding 
 agents its granular structure offers a 
 maximum surface for them to decom- 
 pose and, therefore, increases the ratio 
 in which the coating acts by its own 
 decomposition as a protection to the 
 iron. 
 Commercial Scope of Dry Galvanizing. 
 
 It is a noteworthy fact that while 
 many articles have appeared in techni- 
 cal and scientific journals about Sher- 
 ardizing, not one word of criticism or 
 denial of its claims has' as yet been 
 offered. I have been looking for seri- 
 ous criticism for some time past but 
 when I have found doubters I have 
 only succeeded in making new con- 
 verts. The process has always ap- 
 pealed to scientific men because they 
 are in position to appreciate the solid 
 scientific foundations of its claims. 
 
 The new process has not entered the 
 field as a competitor to galvanizing 
 alone: in a great many instances it 
 can take the place of coppering, of 
 nickel-plating and of tinning, where 
 the articles are not to be used for the 
 preparation or handling of foodstuffs. 
 To these I should add the large 
 amount of copper and brass articles, 
 from tubing to typewriter and sewing 
 machine parts which are now nickel- 
 plated. An interesting point in rela- 
 
103 TRANSACTIONS AMERICAN FOUNDRYMEN'S ASSOCIATION 
 
 tion to the various methods of protect- 
 ing metals is the price of the metals 
 themselves. Nickel is 7u times, tin 
 and aluminum 7 times, copper 4Vg times 
 and antimony 3 r 4 times as high in 
 price as spelter, and at equal efficiency 
 against corrosion the lightest coating 
 is one of zinc as applied by dry-gal- 
 vanizing. 
 
 Analyzing the various items which 
 go to make up the cost of Sherardiz- 
 ing, we find that in every instance 
 there is a saving either over the hot 
 process or over the electric process. In 
 most cases the saving is over both of 
 the older processes. 
 
 Initial Expense. 
 A plant for Sherardizing is less ex- 
 pensive than a hot plant and very 
 much less so than an electric plant. 
 Every part of it is of a simple nature 
 and calls for neither feat of engineer- 
 ing nor for the solution of any out-of- 
 the-way problems. It is very much 
 like a plant for close annealing, and 
 whereas the depreciation on a hot 
 plant is usually taken at 50 per cent 
 per annum, the depreciation on a 
 Sherardizing plant would not exceed 
 10 per cent, which is the depreciation 
 commonly figured on an electrolytic 
 plant. The drums are not made of 
 perishable hard rubber or wood as are 
 those for electrolytic galvanizing. The 
 process can lie carried on in the main 
 manufacturing building, and the pick- 
 ling done in the cheapest kind of an 
 outhouse. 
 
 The Saving in Cost of Zinc. 
 For an equal thickness of coating, 
 the zinc actually deposited is about the 
 same in value whether derived from 
 dust or from spelter slabs. It is less 
 than the anodes used in electrolytic 
 work which have to be cast specially 
 and are very often of odd or compli- 
 cated form. Even less zinc is re- 
 quired than in the electric process be- 
 cause an equal thickness is more ef- 
 fective and because the distribution is 
 fully as even. In Sheradizing there is 
 nothing to throw away, but sufficient 
 dust (from 1 to 5 per cent) is added 
 from time to time to replace that of 
 the weight of the articles coated 
 
 which has been used. There is no 
 equivalent to the unsatisfactory results 
 due to using spelter recovered from 
 dross and therefore contaminated by 
 the presence of iron. 
 
 In electro-deposition an unobstructed 
 path is required between the anode and 
 the object, for, the dissociated ions of 
 the salts in solution to travel. If any 
 part is hidden or recessed no deposit 
 is made and the parts furthest from 
 the anodes have the lightest coating. 
 In addition to this it must be under- 
 stood that the anodes are not entirely 
 used up and part of them is lost at 
 the bottom of the tank, and as eaten- 
 out remnants they cannot be used to 
 the vanishing point. 
 
 It is hardly necessary to point out 
 the enormous saving in the quantity 
 of zinc used as compared with the 
 hot process. Hot galvanized articles 
 have, as a r.ule, a much thicker coat- 
 ing than is necessary because most of 
 them cannot be conveniently wiped 
 like wire or band iron. In Sherardiz- 
 ing all the zinc is consumed and the 
 thickness of deposit is regulated just 
 as readily as in the electric process. In 
 the hot process a large percentage of 
 spelter is converted into dross and 
 skimmings, and while much of it is re- 
 covered, the net loss cuts quite a fig- 
 ure on the cost sheet. 
 
 The Saving in Labor. 
 
 Sherardizing is like annealing in that 
 it requires but a small amount of la- 
 bor, and that unskilled, placed under 
 proper superintendence. A drum 
 holding one or more tons of articles 
 can be left to itself for half an hour 
 or more subject to an occasional turn; 
 in the meantime another drum is be- 
 ing prepared for Sherardizing while 
 the first will be cooling. Suitable par- 
 titions will allow of several classes of 
 small articles being Sherardized in one 
 drum without mixing. 
 
 Hot galvanizing requires constant 
 attention and handling, which can 
 seldom be done by one man even with 
 the aid of overhead trolleys and sim- 
 ilar fixtures. It is not a mechanical or 
 automatic process, but one of hard 
 manual labor, and the regulation of 
 
TRANSACTIONS AMERICAN FOVNDRYMEN'S ASSOCIATION 109 
 
 temperature and methods of dipping 
 require the attention of an experienced 
 galvanizer. 
 
 As a leading authority on hot work 
 has written: "Considerable skill is re- 
 quired to bring a piece of work out 
 of the metal and cool it so that the 
 surface will be smooth, free from blis- 
 ters and with no lumps of surplus 
 metal attached." 
 
 For the electric process at least one 
 man possessing some knowledge of 
 electricity and of all the whims of 
 electrolytics is needed. In electro- 
 deposition irregular shapes — excepting 
 in the case of very small articles — re- 
 quire regular shaped anodes, but in 
 Sherardizing the dust, every particle 
 of which may be considered as a min- 
 ute anode in itself, is used just as it 
 comes from the refiners for any size 
 or shape of article. 
 
 By combining the advantages of 
 both the old processes, Sherardizing en- 
 ables a manufacturer to galvanize with 
 one plant only, articles which have hith- 
 erto been divided between the two 
 processes, the small ones being elec- 
 tro-galvanized and the large ones 
 dipped. Less care is needed in clean- 
 ing the articles to be Sherardized, and 
 oil or grease, far from being objection- 
 able, are helpful to the process, be- 
 cause their volatile hydrocarbons help 
 to prevent oxidation of the dust; the 
 addition of grease or vaseline has in- 
 deed been found to be of some advan- 
 tage in many cases. Furthermore, the 
 articles can be put into the drums wet, 
 as they come from the washing tank. 
 The labor of recutting threads is 
 eliminated. Bolts, screws and nuts 
 can be put in the drum just as they are 
 delivered from the machines, covered 
 with oil or cutting compound. 
 
 With small installations the process 
 can be worked intermittently. The 
 low cost of the plant warrants a man- 
 ufacturer in running a drum two or 
 three days a week instead of sending ■ 
 his work out. thereby saving time, 
 freight and jobbers' profits. The tem- 
 perature required is so low that it 
 takes very little time to start the fur- 
 nace and where gas is used this ele- 
 
 ment of time may be almost disre- 
 garded. This' low temperature also 
 suggests using the waste gases of an- 
 nealing and other furnaces, and in 
 many cases it will be found economical 
 to place a whole day's production in 
 the retort and leave it in overnight 
 with the night watchman to keep his 
 eye on the pyrometer. There is no 
 labor for skimming and drossing; no 
 pots to scrape at unexpected times, nor 
 furnaces to destroy and rebuild at all 
 too frequent intervals. 
 
 The Saving in Fuel and Power. 
 
 The plainest fact about hot galvan- 
 izing is its thermal inefficiency. The 
 pot must be kept going day and night, 
 whether in use or not, and even dur- 
 ing its operation most of the heat is 
 lost by radiation and by having to 
 bring the articles to the temperature of 
 the bath. On the other hand, power is 
 seldom an item of any consequence, 
 whereas in electrolytic work the 
 amount of current consumed is quite 
 large, for a deposit which is meant for 
 something more than exhibition pur- 
 poses or to be buried out of sight and 
 forgotten. This is seldom appreciated 
 because electricity is unobtrusive in 
 its action; the cost of electro-galvan- 
 izing thin sheets is prohibitive on ac- 
 count of the amount of current con- 
 sumed. In Sherardizing the heat is 
 very low and is kept in by a lining of 
 refractory material; the articles do 
 not have to reach the temperature of 
 the zinc dust and the apparatus is al- 
 ways ready for work on short notice. 
 The temperature does not have to be 
 varied to suit the different sizes and 
 classes of articles to be coated and as 
 I have suggested, waste gases can be 
 used under many circumstances. 
 Other Factors of Economy. 
 
 With the new process, less acid is 
 used than in the electrolytic process 
 because the cleaning does not have to 
 be so thorough. The vapor works its 
 way under specks of dirt and bare 
 spots cannot exist. No flux of any 
 kind is needed as in hot galvanizing, 
 and there are no comparatively high- 
 priced electrical supplies to be bought. 
 
 There is no danger whatever from 
 
110 TRANSACTIONS AMERICAN FOUNDRYMEN'S ASSOCIATION 
 
 explosions, no broken castings nor dis- 
 torted iron work to replace, and the 
 temper of the finest steel blades and 
 of steel springs is in no way injured by 
 the low temperature used. This may 
 at first seem strange and will not be 
 perfectly clear until we know some- 
 thing more about the temperatures ex- 
 isting and the reactions taking place 
 in the retort. 
 
 Various Applications of Dry Galvaniz- 
 ing. 
 
 Sherardizing will not full an uncalked 
 seam and act as a solder, this is its one- 
 limitation but it has a great variety of 
 new applications to make up for it. Fly 
 screening can be galvanized and the 
 business parts of agricultural imple- 
 ments such as mower and harrow teeth 
 can receive adequate protection at a 
 low cost without impairing their qual- 
 ities. 
 
 Flashing a surface electrically to dis- 
 cover flaws has been in use for some 
 years and Sherardizing will render the 
 same service; it is, in fact, being used 
 at the present time for this very pur- 
 pose for boiler tubes. However, while 
 electric flashing is worthless against 
 corrosion, a flashing with zinc dust or 
 vapor is very effective as a rust pre- 
 ventive, and of particular service for 
 articles which are to be shipped across 
 the ocean. 
 
 Within reasonable limits innumera- 
 ble machined articles, tools, locomo- 
 tive and engine parts can be flashed 
 with zinc and be effectively protected 
 against rust under the conditions of 
 their operation, whereas at present 
 they must be periodically cleaned at 
 the expense of their appearance and of 
 the accuracy of their fit. Articles 
 such as wire, tubes, etc., either flashed 
 or coated with a heavy deposit can be 
 drawn out, the coating drawing out 
 with the material itself. 
 
 A brilliant and permanent polish 
 which can hardly be distinguished 
 from nickel-plating, but bluer and 
 more like silvrr. and a better reflector 
 of light, can be given to Sherardized 
 articles by means of the usual burn- 
 ishing tools and machines, but unlike 
 nickel-plating it is absolutely rust- 
 
 proof. This polish is not temporary 
 like that of electro-galvanizing, and it 
 is hard and durable if worked down, as 
 it should be, t > > the ferro-zinc. The rea- 
 son that it does not whiten by corro- 
 sion, as might naturally be expected, is 
 because the surface has flowed to an 
 inpervious film and the iron is shielded 
 from any contact effects. In this con- 
 nection it should be remembered that 
 highly polished steel is relatively rust- 
 proof. If, however, nickel-plating is 
 preferred a light Sherardizing before 
 plating, instead of coppering, will en- 
 sure very thorough adherence of the 
 nickel to the ferro-zinc and superior 
 rust-proof qualities will be obtained. It 
 has been shown that it is very difficult 
 to volatilize zinc from alloys where 
 there is any nickel present.* 
 
 Sherardized aluminum can be elec- 
 tro-plated and the objectionable soft 
 surface be overcome, not to mention 
 the finish and appearance. 
 
 Sherardizing has been found to pro- 
 tect silver from sulphated hydrogen 
 which blackens it; it can be applied 
 very lightly before polishing without 
 altering the color. When aluminum 
 has been Sherardized it can be readily 
 soldered; this is expected to do away 
 with the very unsatisfactory riveting 
 of articles made from aluminum sheets. 
 The latest application is for inlaying 
 or damascening and this art is being 
 carried out in England on a commer- 
 cial scale. A variety of colors can be 
 obtained by using different dusts and 
 by varying the time, thereby obtain- 
 ing alloys of different tints. The de- 
 signs shade off in a pleasing manner 
 beyond the edges of the stopping-off 
 material which acts as a stencil in set- 
 ting graphical limits to the action of 
 the dusts and vapors. 
 
 It is very seldom that in the his- 
 tory of invention we find an improved 
 process which corrects so many de- 
 fects', removes so many limitations oi 
 the processes in use and creates so 
 many new and novel applications as 
 does dry-galvanizing. 
 
 * See A. R. TTaslam in Chcm. News, Vol. 51. 
 
SCIENCE APPLIED TO THE BRASS 
 INDUSTRY 
 
 By Andrew M. Fairlie, Copper Hill, Tenn. 
 
 For the sake of progress in the 
 brass industry, as well as for the ad- 
 vancement of science, it is highly de- 
 sirable that the brass and scientific 
 men learn to know each other better. 
 Science is not nearly so formidable as 
 many believe. She should be respect- 
 ed, it is true, but not treated with awe; 
 for the benefits she has bestowed, she 
 should be admired, not feared and 
 shunned; and while she continues to 
 promise aid, economically lightening 
 the labors of men, improving the qual- 
 ity of products and the efficiency of 
 processes, she should be cherished, not 
 ignored, maligned not abused. 
 
 Science, it must be admitted, is a 
 forbidding word. Yet it need not be. 
 As indicated by its derivation, science 
 is' nothing more nor less terrible than 
 knowledge. More specifically, it is 
 the knowledge of nature's laws. An 
 incident that occurred in the course of 
 this day's work will illustrate at once 
 the meaning of science, and its value 
 to the brass industry. Mr. X. was 
 superintending the manufacture of a 
 new metal, an alloy of nickel and lead. 
 He weighed the metals himself, and 
 was particular that the percentages 
 should remain exactly as' planned. He 
 was out of the foundry when the lead 
 was added, but stepped in just as the 
 men were skimming, and as he did 
 so, saw a heavy lump fall from the 
 crucible to the floor. 
 
 "What's that?" asked X. suspiciously. 
 
 "Slag from the coke," was the reply, 
 and this statement was corroborated 
 by a fellow workman. 
 
 Not content, X plunged the lump 
 into water to cool it, scratched the sur- 
 face with a file, and saw that the lump 
 was not slag, but metal. Application 
 of the magnet indicated that the metal 
 was either nickel or iron, and a simple 
 chemical test excluded the latter, so 
 
 that the deduction was plain. The 
 men chilled the nickel by adding the 
 lead too fast, then skimmed off the 
 frozen nickel, which had come to the 
 surface of the lead, and so, entirely 
 ignorant of this fact, spoiled their 
 work. In this case only very ele- 
 mentary science, or knowledge, if you 
 will, was required to detect the error 
 and apply the remedy — a new casting. 
 
 Contemplating the help that science 
 has already given the brass maker, ana- 
 lytical chemistry at once claims our 
 attention. This branch of chemistry 
 detects injurious impurities in the com- 
 mercial metals from which brass' is 
 made; it locates and measures the 
 losses in the business; by pointing out 
 the sources of inaccuracy, it standard- 
 izes the mixtures of a casting shop; 
 it shows the exact composition of any 
 metal submitted for reproduction; by 
 selecting the good and bad qualities of 
 molding sands it improves the quality 
 of sand castings; it distinguishes good 
 coal and coke from poor, and in many 
 ways\ discovers the cause of trouble. 
 
 Metallurgy, in its turn, has been of 
 serviceV The methods of recovering 
 metal ftom scrap have been improved. 
 The cause of porosity in castings has 
 been found, and the soundest castings 
 are now possible by the use of de- 
 oxidizers, such as silicon, phosphorus, 
 aluminum or. magnesium. The oxida- 
 tion of metals\in the foundry has been 
 diminished by. keeping the molten 
 metal surrounde^d as much as possible 
 by reducing gases, both while melting 
 and while pouring. The pernicious 
 effect of the iron stirrer for mixing al- 
 loys has been demonstrated, and one 
 of graphite substituted. 
 
 Physics has furnished the conduc- 
 tivity bridge and the pyrometer. Since 
 extremely small proportions of certain 
 impurities in copper have a powerful 
 
LIBRARY OF CONGRESS 
 
 112 TRANSACTIONS AMERICAN FOUNDRYMEN'S A: 014 634 178 4 
 
 effect in depressing the electrical con- 
 ductivity, the former has been adopted 
 as' a quick and accurate means of test- 
 ing the purity of refined copper. The 
 pyrometer, by controlling the temper- 
 ature, tends to render furnace pro- 
 cesses more exact. The microscope, 
 extending its researches to the exam- 
 ination of the non-ferrous metals, has 
 been directed upon polished and etched 
 sections, of copper, brass and bronze, 
 and has revealed the varying structures 
 resulting from different degrees of heat 
 in melting and pouring, as well as from 
 forging, rolling, and other mechanical 
 pri icesses 
 
 In the electro-plating industry the. 
 value of circulating the electrolite, 
 either by rotating an electrode or* 
 otherwise, has been recognized and 
 the principle applied. 
 
 But it is not possible, nor, indeed, 
 is it necessary, to enumerate within 
 the limits of an association paper all 
 of the scientific discoveries and inven- 
 tions adopted in practice by the brass 
 industry since the days when, eighty 
 years ago, sheet brass was made in 
 Waterbury, Conn., by alternately pass- 
 ing the ingot between heavy steel rolls 
 and annealing in the flames of a 
 chestnut wood fire. So much for the 
 past and present — what is the outlook 
 for the future? Completeness applied 
 to the future is. of course, out of the 
 question, and one must be content with 
 a study of the signs of the times. 
 Even thus the limitations of time and 
 space serve an injunction against com- 
 pleteness, and we can consider here 
 only a few of the problems which con- 
 front this generation. 
 
 We had in mind just now the elec- 
 tro-plating industry. The electro-plat- 
 ing shop needs the chemist and metal- 
 lurgist more, perhaps, than any other 
 branch of the non-ferrous metal in- 
 dustry. An examination of the inquiry 
 columns of the trade papers demon- 
 strates that rule-of-thumb methods in 
 the plating room do not meet the re- 
 quirements. The trouble experienced 
 by the "platers in controlling their so- 
 lutions and costs and the quality of 
 their work is simply evidence that the 
 
 electro-plating shop ought to be, and 
 must become an electro-chemical and 
 metallurgical laboratorj r on a commer- 
 cial scale; that the handful of this, 
 the pinch of that, and the bucketful of 
 the other — yes, even the dram and 
 ounce and gallon — must give place to 
 the gram and the liter; in short, that 
 science must foster an industry that 
 was born of science. It is too much 
 to say that science is now prepared to 
 solve off-hand any electro-plating pro- 
 Idem that might be presented. Pro- 
 blems in practice require scientific in- 
 vestigation, and as electro-plating pro- 
 blems have been neglected, much 
 painstaking work will be required for 
 their solution. Let us see what prob- 
 ability of success is offered to stimu- 
 late efforts in this direction. 
 
 Ideally, the metal dissolved from an 
 anode showed equal the metal depos- 
 ited on the cathode, the bath remain- 
 ing unchanged. Practically, this de- 
 sideratum is today seldom achieved. 
 Impurities in the anode dissolve in the 
 bath, polluting it. and at the same time 
 metal is deposited on the cathode more 
 rapidly than it is dissolved from the 
 anode. The excess is derived from the 
 bath, with consequent variation in com- 
 position. Furthermore, certain impuri- 
 ties, insoluble in the electrolyte, either 
 form a coating on the anode, partially 
 insulating it, or, falling off. foul the 
 bath; consequently the electrolyte has 
 to be regenerated or renewed from 
 time to time. Such obstacles' should 
 not be regarded as insurmountable. 
 On the contrary, experience shows that 
 patient application of scientific princi- 
 ples will overcome such difficulties. 
 For example, several years ago Dr. 
 N. S. Keith was confronted with a pro- 
 blem in the electrolytic refining of lead 
 base bullion.* His solution of lead 
 acetate and lead nitrate became de 
 posed, with the formation of insoluble 
 salts which interfered with the d< : 
 tion. The problem was finally solved 
 by substituting for the original bath 
 an electrolyte composed of lead sul- 
 phate dissolved in sodic acetate. Dr. 
 Keith avers that the integrity of this 
 
 'Electrical Industry, June, 1903, p. 345. 
 
014 634 178 
 
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