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MONTHLY REVIEW

Published by the American Electroplaters Society

Publication and Editorial Office, 3040 Dirversey Ave., Chicago

VOL. XVI   SEPTEMBER, 1929   No. 9

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EDITORIAL

Our annual convention and meeting at Detroit from every point of view, was a most successful meeting, and we American Electro-platers Society remembering the hospitality of our previous meeting at this city, responded by attending in large numbers, resulting in very fine debates and of diversified opinions, which tends to hasten progress of many mysteries now pending to be solved by our fellowship research at Bureau of Standards.

The different expressions by many of the men in the discussion and debates gave research members many things to aid them in the determination of what is most interesting subjects to the industry to investigate first, and each year as we get better acquainted with these men and understand each other better, more progress will be made in the investigations.

It is hoped that our branch officers will see fit to revive interest of their members in our research fund, and when chairman of the Research Committee sends out the plans of that committee relative to the continuity of this work at the Bureau of Standards, get behind the movement personally and put it over in real A. E. S. style.

If this is done throughout the society the report of this committee will bring a thrill of pride to every member of the society, as it will demonstrate the A. E. S. is still most unselfish and progressive society in the world.

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SOME OBSERVATIONS ON THE CORROSION
OF CHROMIUM PLATE

C. F. Nixon

MR. REINHARDT: Unfortunately, Mr. Nixon can’t be here today—my name is Reinhardt, and I am with the Western Clock Company. The work on this paper was done in the laboratory of the Western Clock Company at La Salle, Ill. The stork deposited an eight-pound electroplater at Mr. Nixon’s house a couple of days ago, and that is why he can’t be here (Reads Mr Nixon’s paper. )

As the use of chromium plate becomes more general and commonplace it is of increasing importance that its limitations be clearly recognized. When its electrodeposition was new it was thought chromium plated ware was permanently beautified, that its lustrous surface would survive any exposure undimmed and unmarked. But now that the honeymoon is over the faults of electrodeposited chromium become more apparent especially to those platers who find their brass plumbing fixtures coming back with chromium flaked and to those whose chromium plated auto parts, watch backs, and so forth, have presented unexpected difficulties—and a paper such as this seems appropriate.

It is our purpose to deal with the corrosion of chromium from a rather broad point of view; to observe the behavior of chromium and chromium plate under a variety of conditions, and from the data obtained to derive, if possible, an hypothesis by means of which the performance of chromium plated metals under conditions of exposure not studied may be predicted. With this end in view it seems desirable to consider the properties of chromium alone before undertaking to discuss chromium plated metals.

Since electrodeposited chromium is passive and owes many of its noble metallic properties to this fact, our first concern is with the nature of this passivity. Passivity has been thought by some to be due to two allotropic forms of the same metal, one active and the other passive, by others to high surface tension, by still others to a wide variety of causes. Ulick R. Evans, however, at a recent meeting of the American Mining and Metallurgical Engineers, convincingly supported the oxide film theory. In this paper he demonstrates that a thin film, usually of oxide, invisible but continuous, protects, in particular iron, and in general all passive metal, from the action of materials normally corrosive. When a strip of iron, he points out, is heated to a high temperature at one end a layer of oxide is formed which diminishes in thickness with the distance from the hot end. Toward the middle of the strip, the thickness of the film is such as gives rise to tempering colors, which fade from deep blue to light straw, and finally to an area where the film is continuous but so thin that it is invisible. In this area, indistinguishable in appearance from the cold end, a drop of copper nitrate does not produce a deposit of copper on the iron. At the cold end where the film is not continuous and at the hot end where the film of oxide is thick and cracked, deposition of copper takes place. Mr. Evans found, also, that pure iron exposed in dry air will develop the protective film of oxide in more or less time depending upon the temperature. To clinch the argument Mr. Evans succeeded in separating the invisible film from the bare metal by immersing the passive specimen in an iodine solution He proved its identity by microscopic examination, showing the surface irregularities of the film corresponded to the irregularities of the base metal, and even succeeded in photographing fragments of film. With this much established for iron, it seems reasonable to assume that the passivity of other metals, including chromium, is also due to a protective film. It is an attractive theory in the case of chromium; as will be seen, this theory makes it possible to explain chromium’s peculiar surface properties.

A discussion of the solubility of chromium in various corrosive solutions is a necessary preliminary to this explanation. ”(Active) Chromium,’’ according to Treadwell and Hall, ”dissolves in hydrochloric, hydrobromic, sulfuric and oxalic acids with evolution of hydrogen and formation of chromous, or of a mixture of chromous and chromic salts. The metal is easily made passive, however, by immersion in nitric acid or by anodic polarization. Passive chromium retains its luster in the air, is insoluble in dilute acids, and resembles the noble metals.” It might be inferred from this quotation that chromium is usually active, but such an inference would be false. Numerous investigators have demonstrated that chromium is always passive in air, and becomes active only under extreme provocation, such as immersion in hydrochloric acid or sulfuric acid, only to revert to the passive state as soon as removed from the acid. G. C. Schmidt says that chromium is attacked-by Cl, Br and I at high temperatures. To expand this rather scanty data, fragments of pure, electrodeposited chromium varying from .050 in. to .075 in. in thickness—obtained by plating sheets of copper back to back, subsequently removing the copper by means of nitric acid—were immersed in a wide variety of solutions. The following solutions were without corrosive effects on chromium in ten days at room temperature:

N/10 nitric acid, conc. nitric acid N/1 sodium hydroxide, N/1 sodium carbonate, N/1 citric acid, N/1 tartaric acid, 570 lactic acid, N/10 sodium sulphate N/10 sodium nitrate, N/10 ammonium hydroxide, synthetic sweat (common salt—100 g., acetic acid— 100 cc., lactic acid—10 cc., citric acid—5 grams, water up to 1 liter) N/1 acetic acid, pure orange juice (fresh daily), pure lemon juice (fresh daily), lemon, lime and cherry fountain syrups; soot and water mixture, iron rust and water, 10% formic acid.

Chlorides found non-corrosive to chromium in 10 days at room temperature are: N/10 sodium chloride, N/1 zinc chloride, N/2 barium chloride, N/2 stannous chloride and N/2 chromium chloride.

Two oxidizing agents out of seven, namely ammonium persulphate and potassium chlorate, were without effect on chromium in 10 days also at room temperature. The results obtained with the group of oxidizing agents are tabulated below.
(Itemized in Table No. 1, attached)

When chromium is attacked by pure bromine or, more slowly by bromine water, the action is peculiar. Corrosion apparently starts at a point or a number of points and spreads concentrically, the original spot in the center being etched most deeply. In the light of the oxide film theory the explanation is simple: bromine, unable to dissolve the protecting film as a whole, breaks through the film at a weak point and works out, gradually undermining the oxide layer.

Chromium does not resist the action of all chlorides; calcium, ferric, cadmium, cobaltous, cuprous and silver chlorides (dissolved in weak NH₄OH) seem to attack chromium. Both in the case of cuprous chloride and silver chloride the metal was deposited by immersion on the chromium in spots, evidently indicating areas where the film producing passivity was broken.

Chromium is also soluble in warm chromium plating solution.

Before passing on to a discussion of chromium plated metals it may be found interesting to pause a moment to consider the relation between the film of oxide and chromium’s peculiar surface properties. Accepting the film theory it becomes obvious that the low coefficient of friction and ability to shed water and molten solder without becoming wet, are not properties of chromium but of the oxide. It is well known, to continue, that other metals than chromium do not adhere to chromium when electrodeposited thereon, which is a natural result if there is a film of oxide covering the chromium.

Before any plate will adhere therefore it is necessary to remove the oxide. When the attempt is made to chromium plate chromium the usual advice is to hold the part to be plated in the solution long enough to bring it up to the temperature of the bath—and also to allow time for the dissolution of the protective layer of oxide.’ It is logical to predict that other plated metals will stick to activated chromium. To test out this deduction, strips of chromium plated brass were cleaned, dipped in 10% hydrochloric acid to activate and then quickly, to forestall reformation of oxide, transferred into a nickel plating bath with the current on. The’ nickel did not peel when the experiment was properly performed even after a second coat of chromium was applied.

Chromium on Various Metals

Electro-deposited chromium, being passive, acts like a noble metal. When plated upon any common metal, it offers no electrochemical protection to the base metal, as do zinc and cadmium; if anything it would tend to accelerate the corrosion of the underlying metal, because of its lower potential. Whatever protection chromium does afford against corrosion is due simply to the fact that it is on top. Its efficiency in this respect is clearly dependent upon its continuity, and unfortunately chromium deposits are particularly discontinuous. Grant and Grant (Notes on Hardness and Structure of Deposited Chromium, Vol. 53, American Electro-chemical Society.) have demonstrated that a heavy deposit of chromium is covered by a network of cracks which occasionally are open down to the base metal. Baker and Pinner, followed up the above mentioned paper by showing that lighter, commercially practical deposits are discontinuous also by reason of a system of numerous fine cracks which are found over the entire plated surface These cracks, they found, decrease in size as the thickness of deposit increases up to the thickness obtained by means of 500 ampere minutes per square foot, after which the number and size of cracks reaching through the plate gradually increase with thickness.

Since a chromium plate is at best imperfect and offers no electro-chemical protection to the base metal, it is to be expected that a chromium plate will be of no more value in preventing corrosion in any medium corrosive to the base metal than is a leaky roof in preventing the entrance of rain. The conclusion was borne out by the results obtained when chromium plated copper (pure), nickel, mild steel and brass specimens were immersed in various solutions. Where the action of the corrosive solution on the base metal was rapid, the chromium deposit soon flaked off. In cases where the action of the solution upon the base metal was slow there was no flaking of chromium in the time allowed for the tests, although corrosion products were observed in the solution or on the specimen. It is probable that the local couple action between the deposit and the base metal is of importance in this latter case.

All specimens used in these tests were plated in Bureau of Standards solution: 33 ounces per gallon of chromic acid, 33 ounces of sulphate as sulphuric acid, low trivalent chromium, and about 1 ounce per gallon of iron, which was the result of tank and heating coil corrosion The time of plating was 7 minutes, the current density 100 amperes per square foot, and the temperature 113 degrees F.

Unless otherwise specified all tests lasted 10 days and were conducted at room temperature.
(The corrosion test results are summarized in Table II )

Judging the results obtained above with a few possible corrosive agents it certainly behooves one to proceed with caution when the use of chromium plated metal is to be considered in connection with liquids. Thorough tests should be made before chromium plated ware is accepted for any such purpose.

Out-of-door exposure, which is probably the most common and therefore the most important type of exposure, remains to be considered. Chromium plated copper and chromium plated nickel are easily disposed of, since both resist atmospheric corrosion satisfactorily.

Chromium plated steel is not durable out of doors. Grant and Grant, in a paper already cited, submit micro-photographs to demonstrate how rust, which begins at the bottom of the cracks or pores in the plate and creeps under the chromium, loosens a small fragment of chromium so that it finally flakes. Baker and Pinner and Ollard and others have worked with interposed plates of various metals seeking a combination of deposits that will most completely protect the base metal from attack.

Chromium plated brass does not resist atmospheric corrosion, as many platers have found. Very little has been said on this phase of the subject, however; to our knowledge no explanation has been offered and therefore the attention of this section of the paper is centered thereon

Nickel, copper and brass tarnish when exposed to air, but do not corrode as does steel. Chromium plated nickel and copper are durable in air but chromium plated brass is not. It is at once apparent that some unaccounted for reaction takes place loosening the bond between the brass and the chromium. High copper brasses, apparently, are not susceptible to this form of corrosion.

The explanation, it is believed, lies in a paper by Ralph Abrams, entitled “Dezincification of Brass.” Briefly, according to Abrams, dezincification of brass is the dissolving of brass as a whole, the holding of the dissolved copper in contact with the brass by a membrane, and the subsequent redeposition of copper by immersion. Abrams used wood, paper or cloth as a membrane; in the case in question the chromium plate serves both as the container for the corrosive solution that has found its way down through the cracks in the chromium to the brass underneath, and as the membrane to hold the copper salts formed by corrosion in contact with the brass. Just as described by Grant and Grant in the case of steel, corrosion, or, in this case dezincification, starts at the bottom of a pore and spreads gradually under the deposit. In most cases the redeposited copper is loose and granular and offers no bond to the chromium to replace the one destroyed. In consequence platelets of chromium flake off as the dezincification progresses. High brasses and bronzes of 90% copper or over and nickel silver do not dezincify (A Furtler Study of the Dezincification of Brass, Cleveland F. Nixon, Vol. 46), and therefore chromium plate does not peel from these materials. Further, the nature of surface, be it cast or rolled or filed or fractured, or polished (referring to the same paper) has been found to determine sometimes whether or not dezincification takes place. These later qualifying statements will explain the discrepancy in results thus far reported by others on this subject.

A number of specimens of brass exposed (1) out of doors and (2) in a salt spray box on which the chromium plate failed were examined under a- binocular microscope. When loose chromium was flicked off with a needle, granular copper was clearly discernible under the glass and the reddish color apparent to the naked eye. Referring back to Table II it is seen that chromium brass in sodium chloride, in zinc chloride, in sodium nitrate and in sodium sulphate are classed as apparently unattacked during period of test. If the dezincification idea is right, some dezincification should have taken place. Experiments were checked and dezincification was found.

It is logical to infer that dezincification would take place under other deposits than chromium, since it-is the membrane that is essential and its nature incidental. Nickel plated brass specimens immersed in cuprous chloride solution, alum solution, and sodium chloride solution were examined after one day’s immersion. Quite large deposits of copper crystals were found under the pores in the nickel in specimens immersed in the first two solutions, especially near the edges, and to a lesser degree on the specimen in the salt solution. The copper was definitely crystalline and fairly well bonded to the nickel. Only a few blisters in- the nickel were observed.

Experience has shown that an intermediate plate of nickel between brass and chromium prevents the disintegration of the deposit, but an extra plating operation and polishing operation necessarily increase the cost of refinishing. In order to learn whether or not a strike deposit of bright nickel or copper between chromium and brass would serve to prevent failure of deposit, a large number of out of door exposure tests and salt spray tests have been run. It was found that while a true strike was inadequate, a two or three minute bright plate of copper or nickel just prior to chromium plating was sufficient to secure a reasonably durable plate. Specimens plated in this manner did not shed chromium at the end of two months exposure out of doors. The surface of those specimens, however, especially those having an intermediate copper strike, became covered with a dark tarnish-like stain which was easily removed by buffing. Specimens plated with .001” or .002”, of nickel before the chromium did not stain in this manner and so may be considered better.

It is possible that the intermediate plate may be eliminated entirely by using a brass containing less than 0.370 of arsenic or brass containing a low percentage of nickel (Nixon, in paper referred to above) These brasses were found to resist dezincification to a marked extent; if the flaking of chromium is due to dezincification such alloys should be useful.

Summary

Chromium plate is passive because of a film of oxide which rapidly forms when active chromium is exposed to air The presence of this film explains the peculiar surface properties of chromium, among which is one of particular interest to platers, the property of shedding all other plates deposited on it but chromium. Chromium sticks to chromium because chromic acid dissolves the film of oxide; other metals will stick if the chromium is first dipped in 10% hydrochloric acid and then immediately into a plating solution, closing the circuit as the work enters the solution.

Deposited chromium flakes off when the specimen is immersed in a solution definitely corrosive to the base metals. When the corrosive medium but slowly attacks the base metals the chromium deposit may not flake off but corrosion of the base metal will proceed slowly. In cases, then, where the corrosive medium is known to attack the base metal the use of chromium plate, at least without intermediate deposits, is to be avoided. In doubtful cases thorough tests should be made before chromium plating is adopted.

The flaking of chromium from brass is considered to be due to dezincification of the brass. An intermediate plate or possibly the introduction of some substance such as arsenic to prevent the dezincification of the brass is necessary. Where the cost of a regular nickel- plate under the chromium is prohibitive a two or three minute strike of bright nickel or copper will serve the purpose.

Acknowledgment is due to John Camenisch, Herman Steinmayer and Bryan Chasteen, of the Western Clock Company Research Laboratory, who performed most of the experiments upon which this paper is based.
(Applause.)

CHAIRMAN VAN DERAU: Mr. Reinhardt will be glad to answer any questions you see fit to ask him regarding this paper. Are there any questions ?

MR. W. L. PINNER: The paper referred to a two or three minute bright plate of nickel over copper or brass before chromium plating. Has Mr. Reinhardt any idea as to the actual number of ampere minutes or the thickness of the bright nickel deposit?

MR. REINHARDT: The thickness was between one and two hundred thousandths. As to the ampere minutes, I don’t know.

MR. HOGABOOM: Mr. Nixon brings out a very interesting point, and I am wondering whether we can accept it as given. It will probably require, as Mr. Nixon would probably agree, some further investigation. I am wondering whether dezincification is really the answer to the hair line cracks which develop upon chromium deposited directly upon brass. If you will deposit chromium directly upon a die cast zinc base, die cast metal, you will get hair line cracks, and there can be no dezincification there. It is my opinion (I may be in error) that the brass going into a chromium solution is etched and the entire crystalline boundaries are etched, and you get inter-crystalline attack, and that is what you get, a bridging over, then, and you get an attack of that crystal of an etch, you get a point down, and then the deposit would try to bridge over, and not completely bridging over, on exposure to atmospheric or to electrolytic action, would crack. On examination of a number of pieces that had shown hair line cracks, and from the fact that dezincification occurs all over a whole surface, rather than in the boundaries of grains or the inter-crystalline structures of the metal, it is more reasonable to suppose that there is a solution of the material that is in between the crystals. It was formerly called Beilby’s cement, but now they call it an amorphous metal holding the crystals together. If you examine under a high powered microscope you will find the grain boundaries are very definitely defined through those grain cracks. It has been found that brass, having a high copper content, or a low zinc content, if worked, cold worked, has strains in it, that where the metal is cold worked that hair line cracks will develop, showing an indication of those strains that there may be an inter-crystalline attack by the chromic acid.

MR. REINHARDT: I would like to say a word about that. I think Mr. Hogaboom is right. We did not feel that the hair line cracks that appear in chromium are due to the dezincification, but rather the fact that they flake off. I mean it explains the mechanism of the flaking off of the chromium specimens we have examined under the microscope. Chromium will develop hair line cracks on any metal if it is heavy enough. That point is clear. So dezincification has nothing to do with the cracks, but rather it is the lifting off of the flakes.

This experiment of Mr. Evans is quite interesting. I just want to go into that a minute. He took a small piece, about a half a square inch of iron, and actually leached out all the iron on the inside and had this film around the iron left, so you could actually hold it up and look in it and see all the surface that was there originally.

MR. HOGABOOM: Mr. Reinhardt spoke of Dr. Evans’ work. Personally, I think that every plater in this room ought to read Dr. Evans’ paper. I think it is one of the most interesting papers that I have had the pleasure of reading in a long time, and to my mind it explained some of the difficulties that have been experienced with cold rolled steel. You that have plated cold rolled steel know that you have had some that would plate beautifully. Others, cleaned and handled in identically the same way, would blister or peel. That is mostly true on highly burnished steel. You have pickled it and found a deposit that you could rub your finger on and called it carbon, stating, as I have myself, that they probably put oil on it in the rolling, and then when they came to anneal it that oil is carbonized and therefore that carbonized surface was what caused the trouble. It is my opinion, which must be substan-tiated by data, that in the rolling of highly burnished stock they use less lubrication, and there is greater friction, due to trying to get the very dense structure and the highly burnished top. That friction causes oxidation. I have taken Dr. Evans’ one twentieth molar nitrate of copper and put it on a little burnished stock and it has taken two hours before I would get a precipitation of copper, and during those two hours adding a glass rod of fresh solution directly upon the spot. If I were to electrolytic pickle that, and, as Dr. Graham said last night, put hydrogen on so as to reduce that oxide, use cathodic pickling, I could immediately get a copper spot. Collecting a number of samples of cold rolled steel, I got everything from an immediate precipitation of the copper to two hours, according to the stock. So it is only opinion that Dr. Evans has explained a difficulty that has been experienced by platers with rolled steel and it is not a carbonized surface, but an oxidized surface, caused by the friction or the heat of the friction, due to rolling.

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THE BENT CATHODE TEST FOR CHROMIUM PLATING
AND SOME OBSERVATIONS ON CHROMIUM PLATING

W. L. Pinner & E. M. Baler

At the time that the subject of the bent cathode test was presented at the American Electro-Chemical Society meeting, at Toronto, our attention was called to the fact that Mr. Sizelove had previously conducted some experiments and presented the results of those experiments before you, using a cathode bent at right angles such as we have used. I therefore want to make acknowledgments to Mr. Sizelove as having preceded us in the use of a bent cathode for the study of the sulphate effect in chromium plating baths. I think that all of you who are doing chromium plating will agree with me that there are many factors outside of the chromium plating bath itself which will give a defective deposit of chromium. For instance, a gray deposit of chromium may be traced, or a gray appearing deposit may be traced as far back as the grinding department—in a base metal which has not been sufficiently ground. So that after chromium plating the scratches are so magnified that the inspector who is supposed to know chromium has rejected it as gray or burnt chromium. Gray deposits may also be due to burnt nickel which has been insufficiently buffed, or good nickel which is insufficiently buffed. It may also be due to smears or finger marks. And a great deal of gray chromium may be traced to the cleaner line used for cleaning the nickel preceding the chromium operation. Finally, coming to the chromium plating bath itself, an anode making poor contact or an anode which is partly insulated with a covering of lead chromate, may cause gray chromium. And the solution temperature, current density, or the solution composition may give a gray appearing deposit of chromium.

The same line of thought may apply to other defective deposits such as colored spots, or non-covering, poor throwing power. I wonder, however, how many of you when a defective deposit of chromium was obtained, have been able to say to your entire satisfaction, and what is better, to the satisfaction of your General Manager, that these defective deposits are absolutely due to a condition in the chromium plating bath, or they are due to some thing: else. I wonder further how many of you have been sure at any time that you have been operating your chromium plating bath at its best condition as far as the bath composition itself is concerned.

These questions and many others can be answered by the bent cathode test. The bent cathode test, which can be conducted in about five minutes, and requires no knowledge of chemistry, is-a plating-test carried on a small scale. In it, we take a small sized sample of the main bath which may be giving trouble. In our case we use something around a half a pint of the solution. This solution is so small that we are sure we have got a uniform temperature throughout it. For our cathode, we use a piece of sheet copper, one inch wide, 2” long, the surface characteristics of which we know, and the type of deposit we recognize as being due to its particular condition in the bath. For our anode, we use a freshly clean piece of sheet lead which is so small that we can see whether it is dirty or not, and we know it is making contact.

Now, in order to better give you the method of applying the bent cathode test, let us assume that we are operating a chromium plating process, and from that we are obtaining a defective deposit of chromium; let us assume that we have carefully prepared an article or a rack of articles for chromium plating. We feel that these are buffed correctly, and they have been cleaned correctly for chromium plating. We feel quite sure that the temperature in our chromium plating bath is correct and uniform, and we feel quite sure that we will apply to this article or rack of articles the correct cathode current density. Let us then plate this article for whatever time we like, also being sure our anodes are clean, and making contact, and upon removing the article we find we have obtained a defective deposit of chromium. It may be burnt, or it may not- be completely covered, or it may have a colored spot on it. Now, since all other conditions were believed to be correct, then about the only thing that can be incorrect is the solution composition itself, and the only principal thing that might affect the solution composition, in my opinion, is the chromic acid concentration and the sulphuric acid concentration. So let us study and see if the proper relation exists between the chromic acid concentration and the sulphuric acid concentration by taking a sample of the bath for our plating test.

Now the important thing is to use in our plating test the same temperature and the same cathode current density that we use in the main bath. Then, if our bath is at all at or near the operable range, we will get a cathode that resembles one of these that I have’ on this card (Shows card of bent cathodes.) I will pass these around after a bit. These cathodes, which incidentally were bent at right angles, one inch from the end, and the bent end protruding towards the anode, were plated in a bath containing 64 ounces per gallon of chromic acid and starting off with practically zero sulphate, and increasing the sulphate until we obtained so much that our throwing power decreased to a marked extent. We find that as we start out we obtain only a coloring effect on these cathodes; no chromium is obtained. As we increase the sulphate, we commence getting chromium in the high current density area, which is on the protruding bent section, which extends toward the anode. The amount of chromium on the cathode then increases in extent, and the coloring decreases until finally we get practically a completely covered piece, except that down in the very low current density area, which is in the corner of the bend, there is obtained a bare, mottled appearing space with the copper showing through As we increase sulphate further, we get full coverage on the cathode. Then we increase our sulphate to a still higher degree, keeping our temperature and current density constant, of course, and again our low current density area is affected and we get this time what when straightened out appears to be a perfectly shaped ellipse of bare spot of copper, and that bare spot then spreads and increases until we only get chromium on the very high current density area at the tip of the bent section again; and if we had increased our sulphuric acid content further we would have only gotten a very nicely cleaned piece of copper.

Slide No. 1. This shows a diagramatic sketch of the equipment we use for controlling our chromium plating baths. We have on the outside a water bath which we contain in a half gallon crock. This is heated by a steam coil, a closed steam coil, and we have a thermometer suspended in the water bath for the control of the temperature there. Then, seated on a pedestal, which is not shown, is our glass container, an ordinary 250 cubic centimeter beaker, which is about 234” in diameter and 3” high, which contains the chromium plating solution, which is heated up to the proper temperature by the water bath, and .we have a thermometer in the chromium plating bath itself, so as to be sure of the temperature there. This slide also shows our cathode with its bent section protruding toward the anode, which is a piece of sheet lead at the opposite side, and with its sides parallel to the main side of the cathode. Across the set-up we have a voltmeter for reading the voltage and our current coming in from the generator through these bus bars, is properly controlled with a rheostat and with an ammeter in the circuit.

Now I might suggest that this set-up and this particular bent cathode is specific. It was built for the control of a chromium plating bath for the production of bumper bars. With it we get a fairly wide plating range. Now if you are plating some object which has a more complicated shape, and requires a more rigid control of the bath than a bumper bar, you may have to change the shape of the bent cathode Perhaps you would have to bend it further up, at a more acute angle, or you might use a cylinder and say arbitrarily that “I shall have to plate so far into that cylinder in order that my bath will have enough throwing power to do the job for me.”

Now, having determined that the bent cathode test was sufficient for control of the bath which we were using, which was the Bureau of Standards original bath containing 33 ounces of chromic acid, we decided to see if this method of testing was applicable to other baths containing different amounts of chromic acid and containing also trivalent chromium and iron which frequently are met with by intent or otherwise, in chromium plating baths. As a result of that study, we believe that the sulphuric acid/chromic acid ratio can not be defined or set without defining the particular temperature or the particular current density which is being used, or, conversely, if you wish to keep as many of your variables constant as possible in your process and decide to keep your current density and your temperature constant, then it will be necessary to have a particular ratio for each bath which you use.

Slide No. 2. This slide shows the sulphate ratio and the way it changes with varying amounts of chromic acid. I might say, that first these points and the line drawn through them (pointing to diagram) represent the bounding lines of that range in which the best cathodes were obtained for each series which we ran, which series was run the same as the one which I have shown you. We see that for a bath .2 molar in chromic acid, that the ratio of chromic acid to sulphate is at this, which we have marked as 60. Now that 60 means this. In chemists’ nomenclature, it is the -chromic acid molarity divided by the sulphate molarity; or, to the plater, the weight ratio would be just twice that. In other words, for this bath, the center of the plating range would lie where there are 120 parts of chromic acid to every one part of sulphuric acid.

Now, while we do not consider these lines to be perfectly definite, we do believe that the center of the range included between these lines is definite and that therefore the center of the range for a bath .2 molar in chromic acid requires that ratio at the particular temperature and current density we were using A bath .4 molar requires two-thirds of that ratio at the same temperature and current density. Further, at the temperature and current density which we were using, which was 118 degrees F., and 150 amperes per square foot, we see that of all the chromium plating baths, a bath just about .2/ molar in chromic acid that is 33 ounces per gallon, has about the widest plating range and the ratio there agrees very well with the other findings in being approximately 50 to 1 or 100 to 1 by weight. Therefore this shows the value in one way of the bent cathode test over a pure chemical analysis, because if one starts out and keeps his temperature and current density constant and says that ”My chromic acid to my sulphate will always be 50 to 1,” if his bath should go from .4 molar up to .2 molar, he is going to be out here (pointing to 30), which is certainly not the center of the plating range that is best for him, as found by us.

Slide No. 3. This shows the effect on the sulphate ratio of vary the trivalent chromium, keeping everything else constant, increases, no trivalent chromium, and again we have our 50 to 1 ratio. As the trivalent chromium, keeping everything else constant, increases, we find that there is a slight increase in the required sulphate ratio as we go up.

Now I might say that while the plating range for .4 molar trivalent chromium is as wide, or maybe wider than the-plating range for over here (pointing) it does not mean it plates the same These lines include the range in which the best deposits were obtained, though that doesn’t necessarily mean fully covered deposits. As a matter of fact, when we got out to molar trivalent chromium, we couldn’t plot a point because we couldn’t obtain a condition at the temperature and current density we were working in which we got a deposit of chromium, and as a matter of fact the throwing power of the bath seemed to decrease steadily as trivalent chromium increased

Slide No. 4. This shows the effect on the sulphate ratio of increasing amounts of iron in a chromium plating bath, keeping everything else constant and having no trivalent chromium Again we start off with our pure bath with the 50 to 1 ratio in the center of the plating range, and, peculiarly, the sulphate ratio seems to increase at the beginning up to about 6 grams per liter of iron, and then to decrease Further than that, the plating range (and this was a good plating range) is wider in a bath containing 6 grams per liter of iron than it is with no iron As you get past six grams per liter of iron, however, the plating range very markedly contracts, the throwing power decreases, the resistance of the bath goes up enormously, and the sulphate ratio changes back to a down grade again

I find that we are rather late correcting our plating bath which was giving us defective deposits We will correct it now As we make our bent cathode tests on this sample of the bath which was giving us a defective deposit, suppose we should find that we obtain a cathode such as one of these in the upper row on the card, where we have a color deposit of chromium. Personally, I have run about one thousand of these things, and I would immediately recognize that as being low sulphate. So we start out and add a small known quantity of sulphuric acid to our plating bath until the required appearing deposit is obtained. We add an equivalent amount, then, of sulphuric acid, which we can compute, to the main bath. Suppose we obtain a deposit showing this elliptically shaped bare spot in the corner, and we know that our sulphuric acid content is high. We then add some barium salt to precipitate the sulphate, or, better yet, add chromic acid to reduce the sulphate ratio until we reach the required appearing cathode. Then we add an equivalent amount to the main bath.

Now suppose, when we run our bent cathode test that we get a good deposit of chromium. Then we can forget about our plating bath; it is right, and there is something else wrong that was giving us the defective deposit of chromium, and we go to work on that.

Suppose, again, that we get a poor appearing bent cathode, and’ we try to correct it with our sulphuric acid and we find that no correction in any direction will give us the desired deposit? Then we know that we shall have to change, if we want to get our bath back to its best condition, we shall have to change some one of our other standard conditions of temperature or current density. This can best be done with the bent cathode apparatus; and we may find even that practically no temperature or current density combination will give us the desired result, in which case we come to the conclusion that we have a bath which may be like the one I showed you that has so much trivalent chromium or so much iron in it that the throwing power and the plating range is practically nil.

Now I want to pass this card around, and you will note that I have marked on here, under each cathode, the molar ratio and the weight ratio. That refers to this chromic acid/sulphuric acid ratio which I have discussed The weight ratio is the direct weight ratio between ounces per gallon of chromic acid and ounces per gallon of sulphate

In conclusion, I might say that at the General Spring Bumper Corporation we have used the bent cathode test about thirteen months on the control of three 800 gallon chromium plating baths through which we have run an average production of about one million and a quarter square feet a month. During this time we have made sulphuric acid analyses, but purely as a matter of record We have controlled our bath in spite of the sulphuric acid analyses by the bent cathode test, and during that time we have reduced our amount of rejected materials from 8% to less than 2% and we attribute a large part of this reduced amount of rejections to the bent cathode test. I thank you. (Applause )

CHAIRMAN VAN DERAU: Any questions on this paper?

MR. MUSICK: In making those bent cathode tests, what ratio .of anode surface to cathode do you use?

MR. PINNER: We didn’t try to get any particular ratio between-anode and cathode surface. It happens that.we used about the ratio that we are using in our main bath. However (this is a personal opinion of .mine which I would like to be checked up on), I don’t think that it makes any difference in the bent cathode test what size anode or what position the anode occupies. Surely, if we change the size of the anode or its position in the test we will get a different type of deposit; but I think that even then that we could choose the cathodes from the same bath as being the best ones as we would choose from any other bath; that is, as we would choose with any other anode.

DR. WM. BLUM: I want to comment on this paper just briefly, because we are going to refer to the same subject in the talk of Mr. Farber’s tonight; but I just want to express the opinion first of all that as a means of control’ of factory control, to keep within certain favorable conditions of operation, I thoroughly agree with Mr. Pinner and Professor Baker that it serves its purpose, so that it is not any question of the value from that standpoint. I do question, in all frankness (I have discussed this with them, so this is not the first time they know we differ)— do question as to whether in the form they used it, it serves as a means of research to define the best conditions of operation quite so closely as their slides and curves would indicate. It so happens, as you look at this card, that you will see- that there are a number of the specimens which are completely covered, and therefore so far as the degree of coverage is concerned, you can not distinguish between whether one ratio or another is slightly different it is better In other words, this simply indicates the range of composition within which a satisfactory deposit can be obtained. I don’t believe that it fixes the exact composition or the exact center of that range quite as closely as the authors might indicate. I simply mention that because I believe, as we will explain this evening, that some of our conclusions, not as to the value of the bent cathode, but of the results we get with it, are somewhat different from theirs, simply indicating that it is not as quantitative as might appear from the data that was shown on the slides.

MR. PINNER: Regarding Dr. Blum’s remarks, which are quite well brought up, as Dr. Blum told you, we had previously discussed this, and that was one of the reasons that I suggested this test was a specific test for the control of a bath for plating bumper bars and that we can work anywhere within the range shown on the panels which are being passed around; but that if you have a more complicated shape to plate than a bumper bar, that you should have to possibly change the shape of the bent cathode in order to control your bath more closely.

MR. McGUIRE: I would like to ask in what form trivalent chromium is added.

MR. PINNER: The trivalent chromium was manufactured and analyzed We first started out and produced trivalent chromium by means of introducing chromium carbonate into the bath, and found we could get-only a limited amount. So in order to get up as high as .5 molar, we had to reduce the bath with alcohol. Now I don’t know whether this alcohol had any effect or not, but I don’t think any of it existed as such after being in chromic acid for a short while. After reducing the bath with alcohol, it was analyzed for by the approved methods for trivalent chromium.

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FACTS FROM ”OLD TIMER”

In no other branch of engineering is so much expected of the materials used as there is in electroplating. In mechanical engineering exactness of detail is demanded—tolerances are definitely stated. In electrical work a strict adherence is maintained to carefully worked out formulas. In chemistry, and especially in analytical work, solutions and compounds are made the component parts of which have been weighed on balances that are sensitive to at least a tenth of a milligram.

In electroplating some chemicals are weighed on a hundred weight scale, or the weight guessed at, thrown into some water the quantity of which may be ”near enough” to what it should be, stirred with a stick and it becomes a plating solution. Electrical connections are made, and how? What is the optimum number of amperes that can be used for a gallon of a nickel solution, of any solution? Some anodes are hung in the tank. What is the surface area of the anodes? Who knows? The work to be plated is hung on racks or strung on wires and put into the solution. The current is turned on—and, what is expected ? A definite thickness of deposit- all over the article regardless of its shape or size. This must be accomplished, in this record breaking era, in a space of time that will break all of Faraday’s records. The character of the deposit must be such that it requires just passing over a coloring buff or if the plater knows his business no buffing at all When buffing is to be done the deposit must be such that it cannot be cut through by a buff running at the ”burning point” speed and with a composition that should be used on cast iron. It must now stand up in a salt spray test for an indefinite period and be capable of maintaining its lustre and protective value after having been-; dragged through several miles of road that have been ”flooded” with calcium chloride. These requirements are the test of the ability of the foreman plater but above all the final approval is withheld until the costs have been pared to a figure that looks like a zero. If this class of work is not produced at the required cost ”A Warning” is sounded that better plating must be had or the whole electroplating industry will be like Model X—discontinued.

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PAPER ON CHROMIUM SOLUTION UPKEEP

By R. M. Goodsell, Milwaukee Branch (Reprinted at Request of Los Angeles Branch)

Very little has been written on the upkeep or maintenance of a Chromium plating bath.

The writer has a very simple method, which will apply to any chromic acid bath, which does not require analysis, but only by observation of the chromium deposit.

Poor throwing power is due to either too much sulphate, too high temperature, or, poor contact.

Be sure that all connections are good, and that the temperature of the solution does not rise above 115 degrees F. Temperatures between 110 degrees F. and 115 degrees F. give a good bright deposit, and a good throwing power.

The sulphate content is the most important factor of your throwing power. Thirty-two ounces per gallon chromic acid, sulphate conservation, one-third ounce per gallon of water. This solution can be maintained indefinitely by carefully observing the deposit.

To test for sulphate take out one gallon of solution, heat up to proper temperature, and connect up for plating. Add 1 CC of sulphuric acid. If throwing power increases, add another CC, and keep adding until throwing power is at its highest point of efficiency. If you have used three CC to one gallon, and your tank holds 350 gallons of solution, it will take 1050 CC of sulphuric to bring up the bath.

On the other hand if by adding one CC of sulphuric acid, to the one gallon of solution, the throwing power decreases, it shows that the sulphate is too high. Barium Carbonate is used for decreasing the sulphate.

Proceed as before by adding one-fourth ounce Barium Carbonate.

If throwing power increases add another one-fourth, and keep adding until throwing power is at the highest efficiency. If one-half Barium Carbonate is added and the Chrome bath holds 350 gallons of solution it takes eleven pounds of Barium Carbonate to reduce the sulphate to the proper proportions. When the sulphate is high, and you are plating Chrome over nickel, spots of nickel will show Where the Chrome does not cover, and there spots remain bright. If sulphate is low these spots Oxidize or stain, and has a dull rainbow color.

It is not necessary to throw out your Chromium Bath if you use the above methods.

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COOKING IN METAL POTS

Except there he the grossest carelessness, there is no danger in cooking soups, meats, vegetables, and fruits, or in making marmalade, pickles and preserves in metallic cooking utensils. It is true that some of the metal Foes into solution, that the food ”eats” the utensil to some extent. It is also true that the heavy metals are poisonous, mercury and arsenic highly so and iron slightly so and the others in between. However, the amount of metal which is dissolved from the utensil in the process of cooking is so very small that the food which dissolves it is wholesome. This applies to copper kettles, tin coffee pots, iron pans and every other kind and variety of cooking utensil.

* * * *

Dr. E. E. Smith has recently published a book in which he gives the results of his studies of foods cooked in aluminum kitchenware. He quotes the opinions of many others in this country and Europe based on all kinds of chemical analyses. Examinations were made of many foods cooked in such kettles, pots and pans. There were meats and vegetables, milk, both sweet and sour pickles, and other objects soaked in vinegar; fruits, sweet and sour, alkalis and carbonated mineral waters.

It was found that in every case the contents had absorbed some aluminum from the kettle. These analyses were supplemented by Very careful weighing of the pots before and after, and examination of their surfaces with magnifying glasses to discover evidence that the food had absorbed some of the metal. It was found that some aluminum had gone from the pan into the pickle or other food. But in no instance had the food taken up a harmful amount of the metal.

* * * *

Analysis of uncooked food for aluminum showed that we get some of this metal in whatever we eat, cooked or uncooked. The amount absorbed from the pot in cooking is trivial compared with the amount the food naturally contains.

The country is being flooded with propaganda which sets forth that cancer is caused by eating foods cooked in aluminum vessels. There is no suggestion of scientific proof of this anywhere in the literature.

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A. E. S. PAGE
"Assembled Expert Scraps With and Without Significance"

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Find Substitute for Platinum

New York, Sept. 8.—(A.P. )—Discovery of a metal that, while red hot is stronger than steel, was announced today by the Westinghouse Electric & Manufacturing Company. The, new alloy can be used in the moving parts of internal combustion engines and in other extremely hot places.

Konel is the alloy’s name, and it is made of cobalt, nickel and ferrotitanium. The name is a combination of cobalt and nickel. It was made originally to fill the need of radio for a cheaper substitute for $180 an ounce platinum for filaments.

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A Little Trust

A little bit of sunshine, a little bit of rain,
A little snow and winds that blow—and spring is here again.
The summer days are ending, the nights are grow chill;
But roses rare will bloom as fair again—I know they will!
A little bit of sorrow, a little bit of grief, A summer’s day that slips away, and then the falling leaf,
Aye, God has made the seasons, yet God will bring us through,
And we shall learn God’s gifts return some day— I know they do!
A little bit of trouble, a little bit of wrong,
But let us smile a little while —it never is for long.
Oh, have the faith of springtime, oh, have a little trust,
And tears will end and things will mend some day—I know they must!

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SCIENCE SPLITS HYDROGEN GAS AT CONVENTION

So Now “Books Must Be Rewritten”

Minneapolis, Minn., Sept. 10. (A. P.)—The greatest scientific discovery of 1929, splitting of a supposedly indivisible element, hydrogen gas, in two substances, was demonstrated to the American Chemical Society today.

Dr. K. F. Bohnhoeffer, a shy, blonde young German, who was a 17 year old infantryman in front line trenches at the close of the World War, is the discoverer.

Dramatically he set his proof before the eyes of the chemists in a spot of light upon the wall of a University of Minnesota lecture room. Like a moving finger it wrote the forecast of a revolution in physical chemistry This revolution was described enthusiastically by an older man, the chairman of the session, Dr. Hugh S. Taylor of Princeton University.

”It is the greatest scientific discovery of 1929 in physical chemistry,” he said. ”It is the first tangible proof of existence in supposedly indivisible molecules of what we may call a different kind of molecule. It is the first proof of something forecast mathematically by the new wave-mechanics. It means that our text-books on physical chemistry will have to be rewritten.”

Dr. Bohnhoeffer passed some ordinary hydrogen gas over charcoal chilled to the intense cold of liquid air. This process converted it into the new form which he called parahydrogen.

He pumped this parahydrogen over a hot wire where it interfered with the flow of heat through the wire. This heat flow was indicated by a spot of light on the wall. Next he converted some parahydrogen back into ordinary hydrogen, and when it passed over the wire, the spot of light changed its position. This demonstrated, he said, that the two hydrogen gases are; different physically, one making the heat flow faster than the other.

The two also have different boiling and different freezing points, but Dr. Bohnhoeffer said he has not found any difference in their chemical effects.

The discovery has no present commercial use, but the new world in chemistry which it seems to open is important. For one thing, hydrogen is one of the elements much used in the new synthetic chemistry, which changes petroleum into coal and coal into gasoline. For another, the cracking is one of the first proofs of a long held theory that atoms somewhat resemble small solar systems, in which electrons, instead of worlds, spin around a central nucleus.

Dr. Bohnhoeffer said he found that parahydrogen is formed by electrons spinning in opposite directions, and that they both spin in the same direction to make the opposite form, which he calls orthohydrogen. Theoretically the spin makes them into tiny magnets, thereby accounting for their sticking together to form a tangible substance.

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Cleveland, O., Sept. 10.— (A. P.)—A prediction that metallurgists will learn the secrets of controlling atmospheres, which will revolutionize the steel industry, was made before the National Metals Congress here today by Robert G. Guthrie of Chicago, vice-president of the American Society for Steel Treating.

Tremendous possibilities have been opened up by the development of furnaces designed to control atmospheres, opening the way for treating steel with economy and speed far surpassing present methods, Guthrie said.

A vast amount of research still faces metallurgists, but eventually there will be a great number of new gases brought into use. When that time is reached, it may be possible to go even further than surface treatment of steels and change the inner structure through treatment at low temperatures with gases, Guthrie predicted.

Greater understanding of the affinities of gases and metals will open up new resources in the future, he said.

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Idiotorials
They won’t let the prisoners gamble in Sing Sing. They don’t want to give a place a bad name.

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Buttered Toasts
Here’s to the good old fashioned girl who never lives beyond her alimony.

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Take It Or Leave It
Samson wasn’t a song and dance artist, but he brought down the house.

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Financial Note
It’s easy nowadays for a man to earn an honest living. He doesn’t have much competition.

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Health Hint
It’s against law to sell stale eggs unless the eggs were laid before the law was passed.

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Asaps Fables
Once upon a time there was a clerk who never kept his eye on the clock. He bought himself a wrist watch.

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Among the Illiterati
You can buy Shakespeare by the volume, but they sell Bacon by the pound.