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MONTHLY REVIEW

American Electroplaters Society Publication and Editorial Office
3040 Diversey Ave., Chicago

VOL. XIV AUGUST, 1927 No. 8


EDITORIAL

PRESIDENT MESLE: I have a few notes here but I would like to say that the first thing that comes to mind is that I would like to start some kind of a revolt against the type of clothing men have to wear. In other words, I would like to take off my collar and coat. We should take a lesson from the ladies; they have learned to get along with fewer clothes, and I tell you this is a hardship on the men this afternoon.

Now, I presume the shorter we make the speech the better it will be liked. You know some one has said that anybody who tries to talk in public has to stand up to be heard and sit down to be liked. That is rather a difficult problem but we will try not to talk too long, we have made notes since coming here.

Of course, we could spend a half hour telling about the aims of the Society, but we know what those aims are. They remain the same. Of course, the goal has not yet been reached, we are not perfect. I did hear about one fellow who, it is said, said to another: “I never made but one mistake in my life.”

“What was that?”

“Once I thought I was wrong, and I found out afterwards I was not.”

The Society has not reached that state of perfection yet, but we come to these conventions, and, of course, as Mr. Proctor has suggested, every convention we attend should be the best ever.
That is a step in the right direction because it means progress, and every convention ought to learn from the experience of the past and see if they can’t go them one better. Of course, we are hoping this convention will be the best ever.

Now, we come here for two or three different reasons and perhaps for only one of those two or three. We come here for the social advantages. I mean the opportunity to mingle with fellow members of the organization and have a good, sociable time. We come here also as a sort of vacation trip which has to do with our physical or our recreational opportunities, and we also come here for educational purposes.

I am sure that the program the committees have arranged is going to take care of each of these particular lines of activity, and I hope that all of us will in some way participate in the social or recreational, and not forget the educational part of the convention program.

We can always draw lessons from those who are prominent in world events, and Mr. Proctor’s reference to Lindbergh suggested a few thoughts to me. We have some folks from St. Louis here, by the way, who feel quite proud of the achievements of Lindbergh. He is referred to by some as Lucky Lindy. That suggests that his trip across the Atlantic had the element of chance in it. I just want to suggest a few things in connection with that trip.

In the first place, I believe that Lindbergh used the best motor that our knowledge and skill was able to produce up to that time. Further, I think he had the best type of equipment, the best kind of charts, the best kind of skill, and we can combine all those with the courage necessary, that will not let us hesitate on entering upon a new venture. Then we have some of the elements of success, and so we suggest that every member of the Organization take these lessons from Lindbergh and see if we can’t apply some of the essential things that were not elements of luck but elements of using the best that there is in each line to accomplish the end in view.

You know we can get other lessons from Lindbergh, as well. You know he didn’t require very much, shall we say, outside stimulation to keep him awake or keep him on the job, and I think that is a lesson we can apply especially while here at the convention. (Applause.) I want to see every body get all they can out of the convention, and not feel it is necessary to over-stimulate themselves in order to get the full benefit of a convention of this type. I trust we shall just take this lesson and in that way be able to do the outstanding thing.

I am certainly glad to see so many here, and I hope that the number will increase and that the interest in every session will be gratifying, that each one of us will assume some responsibility toward making this convention a success along with the work already done by the committee. I guess perhaps I have said enough.

At this time I want to vary from the program for a moment. We have among us Dr. Bartley, of England, and I am sure that if the committee had known he was going to be here they would have had him on the program, and’ at this time we are going to call on Dr. Bartley for just greetings from England.


PROGRESS REPORT

Research on Electrodeposition, Bureau of Standards, July 1, 1926 to June 30, 1927
by William Blum

(Presented to Annual Meeting of American Electroplaters’ Society, June 30, 1927.)

1. Chromium Plating. A large part of the work of the section during the year has been devoted to chromium plating, in which great interest has been shown by platers and manufacturers. A detailed study of the conditions for chromium plating, including the bath composition, temperature and current density, and their effects on the efficiency, type of deposit, and throwing power, was made by H. E. Haring and W. P. Barrows. The results have just been published in detail in Bureau of Standards Technologic Paper 346, a copy of which may be obtained only by sending 15 cents to the Superintendent of Documents, Washington, D. C. The important conclusions and recommendations will be reported to this convention and also published in the Monthly Review.

The results of these studies have been confirmed at the Bureau of Engraving and Printing, and have improved and simplified their procedure. As a result, chromium plating is being applied to both currency and stamp plates, with marked success.

Other Government departments have also considered or adopted chromium plating. The Government Printing Office is using it on electrotypes for long runs. The U. S. Mint in Philadelphia is soon to install a plant for chromium plating dies, collars and plaques. The War Department, the Coast Survey, the Advisory Committee on Aeronautics and other bureaus have submitted materials to the Bureau of Standards for chromium plating. In addition various devices such as gages and reflectors have been chromium plated for other divisions of the bureau for purposes of research and testing. From all of these experiences valuable information has been obtained regarding the methods of chromium plating, and its value in service under various conditions.

In response to numerous inquiries on this subject many copies of Letter Circular 177 were sent out. During the year about two hundred persons visited the bureau to confer on plating problems, chiefly related to chromium plating. Talks were given in several cities to branches of the Electroplaters’ Society and other technical organizations. Owing to the limited funds available for travel, the expenses of most of such trips were paid by the organizations requesting them.

2. Iron Deposition. In cooperation with C. T. Thomas of the Bureau of Engraving and Printing, experiments have been made by M. R. Thompson and R. O. Hull on the deposition of iron, with special reference to the production of very thick deposits. Some time will be required before the applicability of this process can be determined. When completed, the results will be published.

3. Protective Value of Nickel Plating. Further observations on the samples described in a previous report, showed that much better protection is obtained from coatings which include a copper layer, than from those consisting only of nickel. The value of nickel plating on steel depends mostly on its freedom from porosity.

4. Spotting Out. In January, 1927, W. P. Barrows started work as a Research Associate, with his salary and expenses paid from the Research Fund of the American Electroplaters’ Society. Since that time he has been engaged in a study of “spotting out,” on which a progress report will be made to this convention. The interest and support for this work from both platers and manufacturers has been very gratifying. In planning and conducting this investigation we have kept in close touch with the Officers and Research Committee of the American Electroplaters’ Society, and with numerous manufacturers, from all of whom we have received valuable information and advice.

5. Electrotyping. The International Association of Electrotypers has continued to employ J. H. Winkler as Research Associate at the bureau. The principal subject studied this year was graphite. From the tests made both in the laboratory and in several electrotyping plants, it is hoped that the properties of graphite suitable for electrotyping can be defined and specified.

6. Corrosion Testing. The procedure for measuring polarization developed at the bureau by H. E. Haring, was adapted to a study of electrolytic methods of testing the corrosion resistance of metals, on which a paper was published by W. Blum and H. S. Rawdon. While this work has no direct relation to electroplating, it may have a bearing on the choice of metals to be applied by plating for any specific purpose.

7. Future Plans. In view of the importance of cyanide plating solutions, we expect to undertake their study as soon as possible. Certain problems such as methods of analysis, including the determination and control of “free cyanide” will first be undertaken, as such knowledge is essential for any exhaustive study of the actual plating solutions and conditions.

Some further work will be conducted on chromium plating, and especially its application and value for specific purposes. Even though most of such applications will be considered with special reference to needs of Government departments, the information and experience gained will also assist platers and manufacturers.

The study of spotting out will be continued until definite and it is hoped useful, information is obtained. Whenever the Research Fund warrants, another plating problem can be undertaken by an additional Research Associate. We will confer with your Research Committee regarding such plans.

As in the past we have endeavored to make our results directly useful by publishing them in the Monthly Review and other journals and in printed and mimeographed Government publications; and by visiting plants and meetings of platers and manufacturers. Even with such close and cordial contacts, it is still difficult for us to know whether the results of our researches are directly applicable in industry, or whether they require adaptation for specific purposes, or possibly more extensive laboratory studies.

Platers and manufacturers will therefore render a valuable service by informing us of their experiences with any solutions suggested by us, and especially stating in as much detail as possible, what difficulties may have been encountered with them. In that way only can the research work be so conducted as to render the greatest return to the plating industry, and through it to the general public by whom the bureau is supported.


CHROMIUM PLATING1

H. E. Haring2 and W. P. Barrows3

1 Published by permission of the Director of the Bureau of Standards, Department of Commerce, Washington, D. C.
2 Associate Chemist.
3 Formerly Asst. Chemist, now Research Associate.

I. Introduction
This short paper is a summary including the principal conclusions of an extensive research on chromium plating, the details of which are published in Bureau of Standards Technologic Paper No. 346, copies of which can be obtained only by sending 15 cents to the Superintendent of Documents, Washington, D. C.

II. Composition of Baths
Practically all of the baths used or proposed for chromium plating contain chromic acid as the principal constituent, with small amounts of one or more other substances. These baths are chiefly of three types:

1. The “acid” bath, containing only chromic acid and sulfuric acid, which was proposed by Carveth and Curry in 1905.

2. The “neutral” bath, containing chromic acid and chromium sulfate, which was described by Sargent in 1920.

3. The “basic” bath, containing chromic acid, chromium sulfate, and “chromium chromate” formed by adding a basic material like chromium carbonate to Sargent’s solution. This was described by Haring in 1925 and formerly used at the U. S. Bureau of Engraving and Printing.

It was found that, strictly speaking, all of these baths are strongly acid, on account of the large amount of free chromic acid present. The difference between them is that (1) contains no base to neutralize the sulfuric acid; (2) contains just enough base to neutralize the sulfuric acid; and (3) contains enough base to neutralize a part of the chromic acid also.

It was found that all three types of solution have just the same cathode efficiency for a given content of sulfate, regardless of whether the latter was added as sulfuric acid, or as sulfate of chromium, sodium, ammonium, potassium, aluminum, magnesium or iron. The highest efficiency is obtained when the content of sulfate (actual SO4) is about one per cent of the chromic acid present. Thus in a solution containing 250 g/L (33.5 oz/gal.) of chromic acid, the best sulfate content is 2.5 g/L or 0.33 oz/gal., which corresponds to this same concentration of sulfuric acid, or to 3.3 g/L or 0.44 oz/gal. of (pure) chromic sulfate.

Similarly it was found that the cathode polarization and conductivity of these three types of solution are identical. Therefore the throwing power, vhich depends on these two factors and the cathode efficiency, is the same in all three solutions. The deposits produced in them under given conditions are also identical.

It is evident then that the success of chromium plating with any of these types of solution does not depend upon any improvement that has been made in their composition, but simply upon greater care in their operation.

The only essential constituents of a chromium plating bath are chromic acid and any acid or salt that will not be decomposed or precipitated by the chromic acid. Sulfates are cheap and as even the purest chromic acid always contains a little sulfate or sulfuric acid, it is the most logical substance to use. Sulfuric acid is the best form in which to add the sulfate ion, as it is easily obtained pure, and can readily be weighed or measured. Chromium sulfate is equally satisfactory to use, but as its composition is uncertain it must be analyzed to learn how much to add.

The chromic acid should not contain more than 0.5 per cent of SO4, whether present as sulfuric acid or a sulfate. So-called 98 per cent chromic acid, which generally contains over 97 per cent of CrO3 and less than 0.5 per cent of SO4, is satisfactory. The exact content of SO4 should be known, so the necessary additional amount may be introduced. It should not contain any appreciable amount of insoluble matter.

As the sulfate is removed only by mechanical losses such as drag out and spray, and the chromic acid is also used up in depositing the chromium, it is necessary to add less than one per cent as much sulfuric acid as chromic acid in replenishing the bath. The exact proportion required varies according to conditions, but in some cases about one part of sulfuric acid to two hundred of chromic acid must be used in making the additions. Suitable formulas for making up new baths are as follows:

 
Pure Chemicals Concentrations
(1) Constituents
g/L
oz/gal
Chromic acid
250
33
Sulfuric acid or
2.5
0.33
(2) Chromic acid
250
33
Chromium sulfate
3.3
0.44

If however the chromic acid contains for example 0.5 per cent of SO4; and the chromium sulfate contains only 70 per cent of Cr2(SO4)3, it would be necessary to use:

 
Impure Chemicals
g/L
oz/gal.
(1) Chromic acid
250
33
Sulfuric acid or
1.25
0.17
(2) Chromic acid
250
33
Chromium sulfate
2.4
0.32

This illustrates the importance of knowing the purity of the materials used, as otherwise the solutions will not have the best composition.

If the original composition is correct, and no large amount of chromium chromate forms in the bath, the composition can be controlled approximately from the density of the solution, according to Table 1.

TABLE 1
Concentration of Chromic Acid Solutions
 
Content of Chromic Acid
Specific Gravity
g/L
oz/gal.
1.07
100
13.4
1.08
114
15.3
1.09
129
17.3
1.10
143
19.1
1.11
157
21.0
1.12
171
22.9
1.13
185
24.8
1.14
200
26.8
1.15
215
28.8
1.16
229
30.6
1.17
243
32.6
1.18
257
34.4
1.19
272
36.4
1.20
288
38.6
1.21
301
40.3
1.22
316
42.3
1.23
330
44.2
1.24
345
46.2
1.25
360
48.2
1.26
375
50.2

The solution must however be analyzed occasionally to keep the right ratio of chromic acid to sulfuric acid. Details of the methods of analysis (which are rather involved) are contained in B. S. Technologic Paper 346.

It will be noted that the formulas just suggested contain no chromium chromate or substances added to form it. Actually, under most conditions some chromium chromate forms in the solution, to which it gives a dark color. It is however not only unnecessary, but actually undesirable. This is because when it forms, part of the chromic acid is used up, and the conductivity of the solution is decreased. Hence in solutions that have been operated under conditions that I produce a large amount of chromium chromate it is often impossible to get the desired current density with the voltage that is available.

The reason that in the earlier work at the Bureau, the addition of chromium carbonate was found to be beneficial, was that it contained as an impurity just enough sulfate to make up for the lack of sulfate in the impure chromium sulfate used. In consequence the baths then used at the Bureau of Engraving and Printing gave good deposits, not on account of the chromium carbonate, but in spite of it. Since then, baths made up from only chromic acid and sulfuric acid have given good results, both when freshly prepared and after long periods of operation.

III. Anodes
The composition and size of the anodes determine largely whether this undesirable chromium chromate forms in the bath. It is least likely to form if lead anodes, of the largest feasible size, are used. Chromium chromate accumulates rapidly if iron anodes of any size are used, and still more rapidly if chromium anodes are employed.

IV. Operating Conditions
The favorable temperature and current density for producing a bright deposit of chromium depend not only on one another, but also on the bath composition and the composition and structure of the cathode to be plated. For a bath containing 33 oz/gal. of chromic acid and 0.33 oz/gal. of sulfuric acid, most metals can be plated with bright chromium, at temperatures from 95 to 130°F, at an appropriate current density. The best current density to use in each case is the average of the limits between which bright deposits can be obtained. These limits differ with different metals, being widest for copper and brass, which are therefore most readily plated. Thus it is possible to plate satisfactorily a brass or copper article of such shape that the current density on one part is five times that on another part; this cannot be done on a steel article if the maximum current density is more than about two and one-half times the minimum. It is hence desirable, whenever possible, to copper plate articles before chromium plating them.

Typical operating data are listed in Table 2, which may serve as a guide in selecting conditions for plating any article. In general, better results are obtained, and in a shorter time, by using the higher temperatures and corresponding current densities given in Table 2.

TABLE 2
Operating Conditions for a Bath Containing 250 g/L (33 oz/gal.) of Chromic Acid
and 2.5 g/L (0.33 oz/gal.) of Sulfuric Acid
Cathode Material
Bath Temp. °F
Ratio of limiting current densities
Best Average Current Density Amp/sq.ft.
Average Cathode Efficiency per cent
Time required to deposit av. thickness of 0.0002" (minutes)
Steel or nickel plated surface
95
2.5
35
7
255
104
2.5
60
10
96
113
2.6
100
12
50
122
2.7
150
13
30
131
2.6
200
14
21
Surface of nickel electrotype
95
3.2
55
9
116
104
3.2
100
12
50
113
2.7
145
14
29
122
2.4
205
15
19
Copper or brass
95
2.6
70
11
76
104
3.1
100
13
44
113
4.7
185
15
21
122
5.0
230
17
15

The throwing power in chromium plating is poor (always negative) especially because the cathode efficiency is very low at low current densities, such as exist in depressions. No means was found for improving this throwing power by changes in the solution. By proper choice of operating conditions, using fairly high temperatures and current densities, the throwing power can be slightly improved. In many cases, however, complete covering can be obtained only by ingenious arrangements of the anodes, cathodes and racks, so as to get the most nearly uniform current density.

In plating copper and brass, the cathodes must be connected before they are introduced into the bath. This is not necessary with steel and nickel, though it somewhat improves the throwing power. Still further improvement can be made on steel and nickel by making them anodes for one or two minutes, and then reversing the current to make them cathodes, without removing the articles from the bath.

V. Equipment and Costs
The tanks may be constructed of stoneware, iron, or lead coated iron. They should be provided with coils for heating or cooling the bath. These may be in the plating tank or in a surrounding outer iron or lead-lined tank filled with water.

Very good ventilation should be provided to carry off the spray, which is injurious to the nose. This can be conveniently done by locating a suction flue with a slot, so the gases and spray are drawn across the surface of the bath. As the mixture of hydrogen and oxygen is explosive, the bath should not be covered to confine the gases.

In some cases it is possible to do chromium plating with six volts, but in general, especially with high current densities, it requires from eight to ten volts at the tank. The total electrical energy required to deposit 0.0002” of chromium costs about three cents per square foot, as compared with about one-tenth cent for nickel. The actual cost of the chromium in the form of chromic acid is not much more than that of nickel as nickel anodes.

The labor cost, especially at first, will likely be higher for chromium plating than for the same thickness of nickel, as greater attention is required, and more experimenting may be needed. If a bright chromium deposit is produced the cost of subsequent buffing may be less than for nickel.

VI. Conclusion
It is evident that chromium plating will always require more care and attention than other plating, especially when the articles are of varied or irregular shapes. With experience, however, together with occasional advice and assistance from a chemist, there is no reason why a progressive plater should not be able to get good results on all articles that are adapted to chromium plating.

The authors desire to express their appreciation to William Blum for his interest in this investigation and to T. F. Slattery and C. T. Thomas for their co-operation in confirming on a large scale, the conclusions drawn from the laboratory experiments.


A SHORT TALK ON BRONZE PLATING

By Chas. Stopper, Chicago Branch

I will endeavor to put before you in a brief way my personal experience in bronze plating, outlining a few of the successes and failures,

There are many formulas on bronze solutions and a great deal has been written on the making and operating of them. Every plater seems to have different dope to get certain results and I for one have tried a good many of them without results. I found that the fewer chemicals you use the less trouble you have operating same.

All platers know that bronze solutions consist of Carbonate of Copper, Carbonate of Zinc, Cyanide and water. The big problem in operating a bronze solution is in maintaining the color which is done by raising or lowering temperature, also by your current or rheostat. The main factor in a bronze solution is Copper Cyanide and your Anodes. By using heat and replenishing the solution with copper and Cyanide I am able to keep the desired color without the use of very much zinc.

In most cases where the solution is plating to red, add just a small amount of zinc to bring back the right color.

Copper forms the body and keeps the solution in plating a uniform color. When solution plates streaky in most cases it indicates too much zinc. This may be overcome by adding more copper. Sometimes a hard scum forms on Anodes which means not enough free Cyanide. Anodes should be free from scum with the exception of a light brown Oxide when in use.

I am operating about 800 gallons of bronze solution at our plant and have had very little trouble in the past sixteen years that it has been in use. A bronze solution registering from 15 to 20 degrees Beaumea gives the best results.

My method of making a bronze solution is as follows:
I make up a standard copper solution standing about 12 degrees Beaumea then add zinc until desired color is obtained.


UNITED STATES GOVERNMENT MASTER SPECIFICATION FOR TABLEWARE, SILVER PLATED

Federal Specifications Board Specification No. 411

This specification was officially promulgated by the Federal Specifications Board on May 22, 1926, for the use of the Departments and Independent Establishments of the Government in the purchase of silver plated tableware.

The latest date on which the technical requirements of this specification shall become mandatory for all Departments and Independent Establishments of the Government, is August 23, 1926. They may be put into effect, however, at any earlier date, after promulgation.

I. GENERAL SPECIFICATIONS
There are no general specifications applicable to this specification.

II. GRADES AND CLASSES
1. Silver plated tableware covered by this specification shall be of a grade equal to that required for high class hotel and restaurant service.
2. Silverware of this grade shall be divided into the following classes:
Class I a—Flatware for frequent use.
Class I b—Flatware for occasional use.
Class II a—Hollow ware for frequent use.
Class II b—Hollow ware for occasional use.

III. MATERIAL AND WORKMANSHIP
1. Base Metal Composition
(a) Unless white metal is specified, the base metal of bodies, spouts and handles shall consist of “ 18% nickel brass” (also known as “nickel silver” or “German silver”), except that the base metal of articles manufactured by spinning shall be of “15%” nickel brass. Tips and other small parts shall consist of “12%” nickel brass. For each of these alloys a minus tolerance of 1% of nickel will be permitted.

(b) When “white metal” (Britannia) is specified, it shall be a tin-base alloy with not less than 80% of tin by weight.

(c) The blades of knives shall be of high grade cutlery steel properly heat treated.

(d) When “corrosion resistant steel” knife blades are specified, the bidder shall furnish samples or information regarding the metal to be supplied.

(e) On hollow handle knives the handles shall be of 18% nickel brass. On solid handle knives, the handle shall be of steel.

(f) All soldering on hollow ware shall be with hard or silver solder.

(g) Shells of hollow handle cutlery shall be silver soldered. Blades and tines may be soldered into the handles with soft solder.

(h) Where non-conducting handles are specified, they shall consist of or be provided with insulators consisting of wood, fiber or other approved composition.

2. Base Metal Gage
(a) Flatware—The blanks for flat ware shall weigh not less than the following amounts:

 
Avoir. oz./doz.
Demitasse spoons
3
Tea spoons
11
Dessert spoons
18
Soup spoons
18
Table spoons
24
Dinner forks
24
Dessert forks
18

Bidders shall state in their bids the weight of blanks for other pieces of flatware.

(b) Hollow Ware—The gage of the metal used for each piece of hollow ware shall be such as will provide the strength and durability required for the service for which the particular piece is intended.

3. Finish
(a) Flatware—Unless otherwise specified, flatware shall have the “Butler” (dull) finish except for the bowls, tines and plated blades, which shall be burnished, and left bright.

(b) Hollow Ware—Unless otherwise specified, hollow ware shall have the “Butler” (dull) finish.

IV. GENERAL REQUIREMENTS
1. The size, shape, design and insignia of each article will be shown by appropriate drawings or samples, to be furnished by the purchasing officer.

2. The amount of silver to be applied to each article will be specified by weight. In general, this weight will represent approximately for each class, the average thickness corresponding to Table 1.

Table 1
Approximate Average Thickness and Weight of Silver
Class—
Average Thickness
Inches
Weight of Silver
dwt./sq.ft.
I a and II a Flatware and hollow ware
0.0008
12.8
I b and II b Flatware and hollow ware
0.0006
9.6

3. The back of the bowls of spoons and tines of forks in class I a shall have on the middle line of the bearing surface a coating of silver not less than 0.0012 inches thick at the thickest point.

4. On flatware and hollow ware, a minus tolerance of 15% of the specified weight of silver shall be permitted on individual samples, and of 5 per cent on the average of three or more samples of the same lot or shipment.

V. DETAIL REQUIREMENTS
1. The four classes of tableware included in this specification cover the following articles:
Class I a—Flatware for frequent use—
Forks: dessert, dinner.
Knives: tea, dessert, dinner.
Spoons: dessert, soup, tea, table.
Class I b—Flatware for occasional use—
All articles of flatware not listed in Class I a.
Class II a—Hollow ware for frequent use—
Boats: gravy.
Bowls: ice, salad, sugar.
Dishes and Covers: chafing, butter, fish, fruit, meat, vegetable.
Pitchers: cream, ice, water.
Pots: chocolate, coffee, tea.
Scrapers: crumb.
Shakers: salt, pepper.
Trays.
Tureens: soup.
Waiters.
Class II b—Hollow ware for occasional use—
All articles of hollow ware not listed in Class II a.

2. The actual weight of silver required for flatware of class T shall be as shown in Table 2.

Table 2
Article—
Approx. area sq. in.
Required weight of silver tr. oz/gross
Forks—dessert
9
8
Forks—dinner
11
10
Knives—tea H.H
10
6
Knives—dessert H.H
15
10
Knives—dinner H.H
19
12
Knives—dinner H.H. (handle only)
9
6
Knives—dinner S.H.
17
10
Knives—dinner S.H. (handle only)
7
5
Spoons—dessert
13
Spoons—soup
14
9
Spoons—tea
9
6
Spoons—table
17
12

VI. METHOD OF INSPECTION AND TEST
1. Sampling.
(a) On flatware or hollow ware, one piece may be tested for each gross or less of that article or class purchased. If this sample fails to have within 15 per cent of the specified weight of silver, two more samples shall be selected at random. Unless the average of the three samples tested shall have within 5 per cent of the specified weight of silver, the shipment will be rejected.

(b) The purchaser will pay for all samples tested upon accepted deliveries, but not for any samples tested on rejected deliveries. All rejected samples of hollow ware shall be returned to the contractor.

2. Determination of the Weight of Silver.
(a) On Nickel Brass—The articles are thoroughly cleaned from grease by washing with alcohol or an alkaline solution, and are then dried and weighed. They are then introduced into a suitably sized vessel containing a mixture of nineteen parts by volume of C. P. concentrated sulphuric acid (sp. gr. 1.84) and 1 part by volume of C. P. concentrated nitric acid (sp. gr. 1.42) vhich mixture has been heated (e.g. on a sand bath) to 80°C. (176°F.). (The stripping bath should be kept covered when not in use, to prevent absorption of water. ) The articles are kept in the solution until all the silver is dissolved as indicated 1` the production of a dark color over the entire surface. They arc then thoroughly rinsed, dried and reweighed, and the loss in weight is calculated as silver.

grams X 0.0322 = troy oz.
grams X 0.644 = dwt.

(b) On steel and white metal—The articles are cleaned, dried and weighed as before, and are then hung as anodes in a solution containing 30 g/L (4 oz/gal.) of sodium cyanide, in which an iron or silver cathode is suspended. A potential of 3 to 4 volts is applied and the articles are shaken or the solution is agitated until all the silver has dissolved. The articles are then rinsed, dried and weighed, and the loss in weight is considered as silver.

(c) Alternate method: The purchaser may require the contractor to give notice as to when the material is to be plated, so that the purchaser may send an inspector to the factory at that time. The inspector shall then weigh one or more pieces from each gross or one hundred pieces before plating and after plating and finishing, to determine whether the specified amount of silver is present.

(d) Umpire method: In case of disagreement upon the results by the methods in (a), (b) or (c), three additional samples shall be tested by the following method. The article is treated with nitric acid (sp. gr. 1.2, prepared by mixing equal volumes of water and concentrated nitric acid) until all the silver is dissolved. The solution is evaporated to dryness on a steam bath, treated with a few drops of nitric acid, taken up in water, filtered if necessary and diluted to a definite volume. An aliquot portion containing about 0.5 g of silver is then precipitated with hydrochloric acid and the silver chloride is filtered on a Gooch crucible, washed with dilute nitric acid, dried and weighed. Weight of silver chloride X 0.753 = silver.

3. Determination of the Thickness of Silver. On the back of the bowls of spoons and tines of forks of class I a, the maximum thickness of silver will be determined by microscopic examination of the cross section. This is conducted by first plating that portion of the spoon or fork with copper from an acid copper sulphate solution, to a thickness of at least 0.01”. The bowl of the spoon, or the body of the fork is then cut with a fine saw along the center axis, and the surface is carefully polished on a plane perpendicular to the surface of the spoon or fork at the point of contact until all saw marks and polishing scratches are obliterated. The thickness of the silver coating on the back of the spoon or fork, at the point where it would normally rest on a plane surface, is then measured with a suitable microscope and scale. The thickness of silver on that part at the thickest point shall be not less than 0.0012”.

VII. PACKING AND MARKING
1. Packing—All articles shall be packed in accordance with best commercial practice and in such manner as to prevent injury during shipment.

2. Marking—All articles shall bear the manufacturer’s name or trade-mark. Containers shall be plainly marked with the name of the contractor, the exact name of the material and the net contents. Packing boxes shall be marked with the contract order number.


VIII. NOTES
1. Method of Measuring Areas and Specifying Weights of Silver.
(a) For all articles for which the required amount of silver has not been previously specified, the specifying or purchasing officer will estimate the total area of the particular piece, and compute the amount of silver to be applied to produce the average thickness indicated in Table 1.

(b) Measurement of Areas—It is not possible by any simple methods to measure the area of irregularly shaped articles with high precision. By making a few measurements and the following arbitrary assumptions, however, the area can usually be estimated within a probable accuracy of 10 per cent.

(1) Flat or nearly flat surfaces such as the handles of spoons and forks, blades of knives, etc., may be considered as rectangles, with a length equal to the maximum length (measured with a flexible scale) and a width equal to the average of the maximum and minimum widths. The area on the two sides is therefore equal to the length multiplied by the sum of the minimum and maximum widths. Thus, if the length of the handle of a teaspoon is 4.0”, the maximum width 0.75” and the minimum width 0.20”, the total area of the handle may be considered as 4.0 (0.75+0.20) =3.80 sq. in. (In this calculation it is assumed that the error involved in omitting the thickness of the handle usually about balances the error involved by the assumption that the average width is the mean of the minimum and maximum widths.)

(2) For surfaces which approach a cylinder or cone (e. g., a knife handle or the body of a pitcher), the area may be estimated by multiplying the length by the average circumference, e. g. the mean of the minimum and maximum circumferences, as measured with a string or flexible scale. Thus, if a knife handle is 4.5” long, the maximum circumference 2.75 and the minimum 1.55”, the area is assumed to be

 
(1.55 + 2.75)
 
4.5
——————
= 9.7 sq. in.
 
2
 

(3) For ovoid or elliptical surfaces, such as the bowls of spoons, dishes, etc., it has been found by a series of measurements and approximations, that the area on each side is approximately equal to that of an ellipse, the two axes of which are equal, respectively, to the extreme length and width of the bowl. (These measurements may be made on the outside of the bowl with a flexible scale). Thus, if the extreme length of the bowl of a teaspoon is equal to 2.20”, and the extreme width 1.44”, the area on each side is equal to.

 
(2.20 X 1.44)
 
3.14 X
—————
= 2.49”
 
4
 

A simple formula for the area on the two sides of the bowl is therefore a =

 
p lw
a =
————
 
2

where a = total area of bowl
π = 3.14
1 = extreme length
w = extreme width

The total area of the teaspoon considered in this paragraph is 4.98 (bowl)+3.80 (handle) = 8.8 sq. in. or for practical purposes 9 sq. in.

(c) Relation Between the Area and the \\’eight and Average Thickness of the Deposit.

For such computations the following factors may be employed:
(1) Specific gravity of silver = 10.5.
(2) A silver coating 0.001 “ in thickness, weighs 0.80 troy oz./sq. ft., or 16 dwt./sq. ft., or 0.11 dwt./sq. in.
(3) Dwt./doz. X 0.6 = troy oz./gross.
(4) Average thickness in inches X 800 = troy oz./sq. ft.
(5) Average thickness in inches X 16000 = dwt./sq. ft.
(6) Area of a piece in square inches—number of square feet per gross.
(7) Examples.
If it is found that the area of a salad fork (Class lb) is 13 sq. in., the weight of silver per gross required to produce an average thickness of 0.0006” may be computed as follows:

1 sq. ft. of deposit 0.0006” thick weighs 0.0006 X 16000 = 9.6 dwt./sq. ft.
If the area of the piece is 13 sq. in., the area of a gross will be 13 sq. ft.
Therefore it will require for a gross,
13 X 9.6 = 125 dwt. or

125
 
————
= 6.25 tr. oz. of silver,
20
 

or for practical purposes 6 tr. oz./gross.

If a 16” meat dish (Class IIa) is found to have an area of 324 sq. in., the weight of silver required per piece to produce an average thickness of 0.0008” may be computed as follows:
1 sq. ft. of silver 0.0008” thick weighs 0.0008 X 16000 = 12.8 dwt./sq. ft.
The area of the dish is

324
 
————
— 2.25 sq. ft.
144
 

Therefore, it will require 2.25 X 12.8 = 28.8 dwt. or for practical purposes 30 dwt. of silver per piece.

 

 


 



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