Vol. XIV MARCH, 1927 No. 3
The older platers who have had years
of experience handling men and are quite up on modern production methods can
absorb their fill of chemical science and profit thereby. It will eliminate
the guess work and cut and fit methods of maintaining solutions.
On the other hand guess work and
rule of thumb practice have no part in modern production methods. The plater
is manager of an important department and must know how to manage a working
force, also have mechanical ability to develop short cuts to greater efficiency.
So then the young man fitting himself for a plating foremans job, should
not be misled into thinking that a job knowledge of metal disposition is the
all essential thing needed. The plater is also a foreman among other foremen
of the plant, a leader of his men and holds a strategic position between the
management and the men.
SILVER CYANIDE PLATING SOLUTION
F. H. Nordman
The fundamental reactions in
silver plating solutions when subjected to electrolysis are comparatively simple.
The double potassium silver salt in solution is ionized according to the equation:
KAg(CN)2 = K+ + Ag(CN)2-
This primary ionization is undoubtedly
accompanied by a secondary slight ionization of Ag(CN)2-.
Ag(CN)2- = Ag+ + 2 CN- (2)
The entire ionization reaction may
then be stated:
KAg(CN)2 = K+ + Ag+ + 2(CN)- (3)
The free cyanide is ionized according
to the following reaction:
KCN = K+ + CN-
On electrolysis the selective neutralization
of the positive ions present is dependent upon the voltage impressed. That ion
which is most easily neutralized will be deposited and will continue to be deposited
as long as any of that type ion remains, provided the voltage impressed is such
as to allow a selective neutralization of charge. Any voltage impressed that
is sufficiently high as to allow the neutralization of the most difficult neutralizable
ion will likewise effect the deposition of the two metals simultaneously. In
the case of silver cyanide plating solutions, it is probable that the silver
ion is the most easily neutralized and therefore one would expect the deposition
of the silver molecule at the cathode without any change in the potassium ion
present. At the cathode then the reaction is as follows:
Ag+ + (-) = Ag
At the anode, which in silver plating
is silver, the CN- is neutralized by a positive charge.
2(CN)- + 2(+) = 2(CN)
The metallic silver anode is attacked
by the liberated (CN) radical resulting in the formation of Ag(CN)2.
Ag + 2(CN) = Ag(CN)2
This compound is immediately ionized
according to reaction (2), and the cycle of electrolysis repeats itself.
It would be well to consider here the first objection to the use of sodium cyanide
in place of potassium cyanide, namely, that of causing increased spotting-out
and difficulties in burnishing. Although the question of spotting-out has not
been systematically investigated, the general opinion is that this phenomenon
may be attributed to the occlusion of cyanide in the pores of the plate. With
inefficient washing these cyanides remain in the pores, and being deliquescent
attract moisture and corrode the base metal. If spotting out is more pronounced
with the use of sodium cyanide, the most logical conclusion is that the deposits
from sodium cyanide baths possess a physical structure different from deposits
obtained from potassium cyanide baths.
The factors that ultimately affect
the type of deposit obtained may be classified as follows:
1. Current density.
3. Metallic ion concentration.
4. Type of metal deposited on.
5. Presence of colloids, etc.
If the current density, temperature,
base metal, and type of solution are maintained constant, the only difference
in the physical structure of the deposit would seem to be due to different metallic
ion concentrations in the two solutions. The metallic ion concentration of baths
of this type has never, to the writers knowledge, been determined. An
examination of the deposits from a bath made from C. P. sodium cyanide and one
made from C. P. potassium cyanide should show if there exists a difference in
the metallic ion concentration, at least to the degree that affects commercial
Inasmuch as commercial cyanides are
not, in general, exceptionally pure, especially sodium cyanide, the effect on
the character of the deposit of such impurities as chlorides, hydroxides and
carbonates should be considered. Chlorides are often added to sodium cyanide
to decrease the total cyanogen content to one hundred per cent potassium cyanide
equivalent; hydroxides may be present from the original preparation; carbonates
are formed as a decomposition product of cyanides exposed to air. An examination
of the fundamental reactions, previously given, seems to indicate that, under
given conditions of electrolysis there should be no difference in the type of
deposit obtained in the presence or absence of these impurities. The only minor
reaction that might take place would be between these salts and metallic silver;
it is doubtful whether this is sufficiently great to affect the character of
the deposit. Frary and Porter (2) investigated the effect of potassium chloride
and potassium hydroxide on the simple potential of various metals used as cathodes.
No appreciable different results were obtained in the presence of potassium
chloride and potassium hydroxide. One would therefore expect no adverse effect
on the type or adhesion of the deposit.
A theoretical examination of the
fundamental reactions of electrolysis, previously stated, shows that regeneration
of the bath should be unnecessary, since there occurs only dissolution and deposition
of the silver. However, this is not the case. Decomposition of the free cyanide
occurs with the formation of carbonates, formates, ammonia, etc. But little
investigation as to the products and reactions of decomposition has been attempted,
so that the reactions themselves are very little known. Theoretically, the three
factors that may account for the decomposition of the solution are as follows:
2. Presence of air.
A resume of the literature shows
that very little has been done to determine the proportion of decomposition
that may be due to each of the above factors. Provided that these factors are
equal in magnitude in the case of baths made from potassium cyanide and sodium
cyanide, the rate of decomposition in each case would in all probability be
The reactions of hydrolysis may be
briefly stated as follows:
1. The potassium cyanide is hydrolyzed
in neutral solution.
KCN + H2O = KOH + HCN
2. The hydrocyanic acid in the presence
of an alkali and water breaks up, forming ammonia and formic acid.
HCN + 2 H2O = H2CO + NH3
3. In the presence of an alkali,
the formate of the alkali is formed.
KOH + H2CO2 = HCOOK + H2O
The above reactions may be represented
by a single equation which shows the hydrolysis of potassium cyanide.
KCN + 2 H2O = HCOOK + NH3
Worley and Brown (3) investigated
the hydrolysis of sodium cyanide in connection with the dissolution of gold
and found that at 20°C the value of the hydrolysis constant multiplied by
104 was equal to 0.27. To the writers knowledge, no work has been done
on the hydrolysis of potassium cyanide solutions at ordinary temperatures. There
is, therefore, no data available on which to base a determination of the different
amounts of hydrolysis of free sodium and potassium cyanides in cyanide plating
The presence of such impurities as
chlorides and carbonates should have no effect on the extent of hydrolysis.
Hydroxides would decrease it due to the common ion effect.
Many practical discussions on electroplating
note that the formation of the carbonates in silver cyanide plating solutions
is probably due to the absorption of carbon dioxide from the air. Jordis and
Stramer (4) noted that a silver cyanide plating bath, when not being used, increased
in carbonate content on standing in contact with air. A number of authorities
on general chemistry mention the fact that when moist air comes in contact with
potassium cyanide, potassium carbonate is formed and hydrocyanic acid gas is
liberated. One would, therefore, conclude that in the presence of air, the plating
solution would take up carbon dioxide, with the subsequent removal of two molecules
of potassium cyanide for the formation of one molecule of carbonate.
2 KCN + H2CO3 = 2 HCN + K2CO3
Atmospheric air might have an oxidizing
action on potassium cyanide, forming potassium cyanate, and this on hydrolysis
would yield potassium and ammonium carbonates.
2 KCN + O2 = 2 KCNO
2 KCNO + 4 H2O = (NH4)2CO3 + K2CO3
Thus for every two molecules of cyanide
decomposed there should be formed two molecules of carbonate.
The effect of impurities such as chlorides, carbonates, and hydroxides on the
decomposition of cyanide due to the presence of air may now be noted. Theoretically
there is no apparent reason why chlorides should have an effect on the rate
of decomposition. Hydroxides might aid in the absorption of the carbon dioxide
from the air, giving an increase in carbonic content, without the same proportional
increase in the decomposition of the cyanide.
2 KOH + H2CO3 = K2CO3 + H2O
The presence of carbonates should
have no decided effect on the decomposition of the cyanide.
Jordis and Stramer (4) also noted that the decomposition of the free cyanide
in a silver- cyanide plating solution was greater when the solution was being
electrolyzed than when it was idle. Just why this decomposition would be different
in a bath in use is not at once apparent. The reactions of electrolysis have
been previously stated. Theoretically, there seems to be no explanation of why
the decomposition should increase on electrolysis. However, when the mechanical
details of electrolysis are investigated, the loss of KCN may be accounted for.
For instance, the silver anode is hung on an iron wire, which extends into the
solution. There is therefore every possibility of the liberation of the (CN)2
radical where it cannot attack the silver; it perhaps does not attack iron,
so that it is liberated. It might combine with any base present to form the
cyanide and the cyanate according to the equation:
(CN)2 + 2 KOH = KCN + KCNO + H2O
The cyanate might then be hydrolyzed,
according to the reactions given above, to produce ammonium and potassium carbonates.
This decomposition would not decrease the free cyanide content; it would however
result in the format on of carbonates at the expense of the decrease in the
combined cyanide present.
Then, too, if the voltage was such as to cause the neutralization of a potassium
ion simultaneously with the deposition of silver, the effect would be the electrolysis
of potassium cyanide.
K Ag (CN)2 = K+ + Ag+ + 2(CN)-
KCN = K+ + CN-
The potassium, liberated at the cathode,
would combine with the water present to form potassium hydroxide and hydrogen.
2K+ + 2H2O = 2KOH + H2
The (CN) liberated at the anode would
attack the anode according to the reactions previously given. Such a series
of reactions would result in the decomposition of free cyanide with the subsequent
formation of a molecule of potassium hydroxide.
The presence of such impurities as
hydroxides, carbonates and chlorides would tend to cause an oxidation reaction,
similar to that caused by potassium cyanide provided the deposition voltage
of the chloride, hydroxyl and carbonate ions was reached. Jordis and Stramer
(4) noted that the formation of carbonates was greater when the cyanide plating
solution contained chlorides than when it was free from chlorides. This can
only be accounted for by assuming that such a voltage was being used that the
deposition voltage of the chloride ion was reached. The oxidation reactions
discussed above would then account for the increase in carbonate formation.
A consideration of the above reactions
when comparing plating solutions made from sodium cyanide and potassium cyanide
shows that there are few reasons why there should be any difference in the rates
of decomposition. It may be noted here that sodium carbonate is much less soluble
than is potassium carbonate, a fact that might have an influence on the reactions
of carbon dioxide of the aid on the solution. On the equilibrium between carbonates
and cyanides; also, (To be continued)
Our meetings that have recently been
held in the Down Town Branch Y. M. C. A., Pittsburgh, have been very well attended,
and much more interest is being shown by the members, and we all hope the good
work continues. Last Saturday night we had a record number present and several
questions came up for discussion, several members came with a sample of their
nickel solutions, for testing for pH with the Double Wedge Comparator, and the
range ran clear from one end of the scale to the other, and each member said
that his OWN solution was right to standard and could not be improved Upon.
Next meeting it is hoped the members will remember to bring more samples, when
test will be made with the LaMotte Ion Comparator, when the results will be
checked. The question of Saw Dust was brought up, and we found that none of
the platers in the district were using this material for drying; other methods,
such as hot air, ovens and other mechanical methods were the rule. One of the
members had samples of copper, brass and nickel work to pass around, but would
not answer any questions as to how the finish was obtained, just saying, match
the work if you can, and make your samples better if possible, when at a later
date a discussion will be had upon the various finishes and the methods used.
This is, to my mind, a good way to see just what the platers will and can do,
and ought to pave the way for some good talks later.
Hooray: Coming to 1927 Convention
Toledo, Ohio, the city selected for
this years convention of the National Electro-Platers Association, to
be held June 29 and 30 and July 1 and 2, is known as the Gateway City to the
The city located on Maumee Bay and
at the hand of picturesque and historical Maumee Valley, together with many
beautiful parks and drives, make it an ideal and interesting city for the visitors.
In the summer months palatial steamers give the visitor an opportunity for a
refreshing ride on Lake Erie visiting historical Put-In-Bay and other interesting
Toledos Museum of Art has become
an art center of international reputation. Its collections of paintings, Egyptian
antiques and glassware are world famous.
One of Toledos accomplishments
and one in which they are justly proud of are the many beautiful schools.
Toledo has thirteen parks, three public golf courses and in addition seven private
golf courses and five yacht and canoe clubs, affording a diversion of recreation
for its visitors.
Toledo is internationally known for
its wonderful railroad transportation facilities with seventeen main lines and
seven branch lines reaching out to all sections of the country, 116 express
trains enter and leave Toledo daily. In addition to the railroad transportation
the large lake freighters are arriving and leaving constantly during lake shipping
season. Toledo is the soft coal port of the United States, over fourteen million
tons of coal were shipped from Toledo ports last year.
Toledo has in the neighborhood of
700 factories of a diversified nature producing over 1,200 different articles.
Situated in the center of a thickly populated district with ready transportation
to a number of the nations leading cities the question of distribution
does not trouble Toledo manufacturers.
Toledo is the largest childrens
vehicle manufacturing center in the country. The Gendron Wheel, American Wheel
and Toledo Metal Wheel, manufacturers of the various kinds of childrens
vehicles, are among the foremost manufacturing concerns in the city.
One of the outstanding features assuring
amicable working conditions is a matter of home ownership. Practically 50 per
cent of Toledos population own their own home, which tends to make a more
satisfactory condition to the life of a city.
Regular monthly meeting of the Detroit
Branch held March 4th, at the Detroit Testing Laboratory, with President J.
Flanagan in the chair and a good attendance.
One applicant was elected to active
membership. Also received one member from Cleveland Branch and transferred one
to the Chicago Branch.
General discussion was regarding
a chemical class, the committee having reported they would have an answer as
to whether the Cass Tech. would be available for us on about Monday next, when
a report would be had from the Board of Education. It was decided that as soon
as the committee received an answer, if favorable, the Secretary should send
out notices to all the members and definite steps taken at a special meeting
to express their views.
Mr. Barber, one of the oldest members
of the society from Bridgeport Branch, gave a most enjoyable talk. His subject
being, The Use of the Amp meter as a Means of Determining the Weight of Deposit
Dayton Branch held its monthly meeting
March 5th at Y. M. C. A. building. We had a fine gathering of the members.
The speaker of the evening was C.
E. Vanderan of Westinghouse Electric Manufacturing Co.. at Mansfield, Ohio,
who gave us a lecture on Chrome Plating as it is done in production, also exhibited
samples of this work, which was best we have seen, and the lecture sure was
instructive and very well handled by Van, who has the knack of bringing out
the smallest details of these explanations and it sure is a pleasure to have
him with us, and any Dayton members who were not there sure missed a real treat
and we hope Van will call again soon and make his visits many.
The question box was full and many
topics were discussed and we adjourned at a late hour.
Newark Branch held its business meeting
on Friday evening, February 18, 1927, with twenty-one members present. President
Geo. Onksen presiding.
Minutes were approved as read. One
application for associate membership was voted to take the usual course. Banquet
committee report progress on our banquet, which will be held on April 30th.
Librarian Calabrese reported that
he was quite sure he will secure a paper to be read at the Toledo convention.
Regular monthly meeting, Chicago
Branch, held March 12, 1927, at the Atlantic Hotel.
The meeting was called to order with
President Jacob Hay presiding, and a very good attendance.
President Hay called the attention
of the members to the joint meeting of the American Chemical Society and the
American Electro Platers Society, same to be held at the City Club, 315
Plymouth Court, Friday, March 25, 1927, at which Dr. Wm. Blum will speak on
Research on Electro Plating Solutions.
Mr. Oscar E. Servis, our librarian,
called upon the members for papers for the Toledo convention and was promised
a few; he also called attention to the Research Fund Drive.
The Booster Committee for the coming
convention reported that there would be a good attendance from Chicago.
The balance of the evening was given
over to our Librarian, who found the following questions:
Question 1.Wanted information
on ball burnishing iron and steel. What is a good soap or other agent to use
for the burnishing operation?
Answer 1.Lux Soap Chips was
recommended as a good soap, same to be followed by a 10 per cent muriatic acid
dip before work is plated.
Question 2.Is there any other
bright dip other than acid dip on sheet brass ?
Answer 2.A dip made up of 10
ounces of potassium bichromate, sulphuric acid 3 to 4 ounces, water 1 gallon.
Temperature 175 or more was given.
Question 3.How can aluminum
sheets be etched so as to produce a fairly rough surface?
Answer 3.Muriatic acid with
a small addition of chloride of iron.
Answer 4.Nickel cyanide, lead
carbonate cut down with caustic soda, liver of sulphur and hypo was suggested.
Answer 5.It was stated that
it cannot be done.
Question 6.How can spotting
out on sheet brass copper plated and oxidized with liver of sulphur for statuary
Answer 6.Acid copper plate
followed by a black nickel made up as follows: 8 ounces single nickel salt,
2 ounces sulpho cyanide, 3/4 ounce zinc sulphate, 1/2 ounce sal ammoniac.
Question 7.What is the proper
way of introducing chromium sulphate into chromic acid when preparing a new
Answer 7.Will anyone answer