IMPROVEMENTS IN THE ELECTRO-DEPOSITION OF TIN
Year: 1873

page_text: LETTERS PATENT to Thomas Fearn, of Birmingham, in the County of
Warwick, Electro-metallurgist, for the Invention of "IMPROVEMENTS
IN THE ELECTRO-DEPOSITION OF TIN."
Sealed the 13th June 1873, and dated the 7th April 1878.
PROVISIONAL SPECIFICATION left by the said Thomas Fearn at the
Office of the Commissioners of Patents, with his Petition, on the
7th April 1873.
I, THOMAS FEARN, of Birmingham, in the County of Warwick,
Electro-metallurgist, do hereby declare the nature of the said Invention
for "IMPROVEMENTS IN THE ELECTRO-DEPOSITION OF TIN," to be as follows:-
My Invention has for its object to effect the reduction or deposition
of tin by electricity with greater facility and certainty than can be done
by the processes at present in use for that purpose, so as to coat or
cover metals or metallic alloys with a coating of tin, and to produce
deposits of tin for other purposes.
My said Invention consists in the use of solutions from which to
effect the deposition of tin, made and used in the following manner :—

page_text: tin.
I prepare a solution of protochloride of tin by dissolving metallic tin in
hydrochloric acid, the solution containing by preference one ounce of
In every three ounces of the said solution I dissolve thirty pounds
of hydrate of potash or caustic potash in twenty gallons of water. I
dissolve thirty pounds of pyrophosphate of soda in sixty gallons of 5
water, and I dissolve thirty pounds of cyanide of potassium in twenty
gallons of water. I take two hundred fluid ounces of the solution of
protochloride of tin, and gently pour it into the twenty gallons of hydrate
of potash solution, stirring the liquids during the process of mixing
them with a glass rod. A precipitate is at first formed, which is soon 1
redissolved. Into the dissolution thus obtained I pour the twenty
gallons of cyanide of potassium solution, and lastly the sixty gallons of
pyrophosphate of soda solution is added. The whole after being well
stirred up is ready for use. Or I dissolve fifty-six pounds of muriate of
ammonia in sixty gallons of water, and I dissolve twenty pounds of
pyrophosphate of soda in forty gallons of water. I pour gently into the
solution of pyrophosphate of soda one hundred fluid ounces of the proto-
choride of tin solution. A white precipitate is at first produced, which
on stirring the liquid with a rod soon redissolves. I then mix the two
liquids together by pouring the muriate of ammonia solution into the
solution of pyrophosphate of soda to which the protochloride of tin solution
has been added. The liquid thus made is ready for immediate use.
The solution of tin thus prepared requires considerably less battery
power than a solution made as first described. Or I dissolve 150 pounds
of muriate of ammonia in one hundred gallons of water, and I pour
into this solution two hundred fluid ounces of the protochloride of tin
solution, and after the liquids have been well mixed by stirring the
solution is ready for use.
Or I dissolve four hundred ounces of tartrate
of potash in fifty gallons of water, and I dissolve twelve hundred ounces
of hydrate of potash in fifty gallons of water. I take six hundred fluid
ounces of the solution of protochloride of tin, and pour it slowly into
the solution of tartrate of potash. A bulky precipitate is immediately
produced. The hydrate of potash solution is then added. This quickly
redissolves the precipitate. Whilst the hydrate of potash solution is
being poured into the liquid containing the precipitate the whole should
be well agitated, and a clear liquid is the result.
When the first-described solution is employed I prefer to use a battery
power of or equal to two cells of Bunsen's battery, and to keep the
olution at or about a temperature of 70 degrees Fahrenheit.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent
filed by the said Thomas Fearn in the Great Seal Patent Office on
the 1st October 1878.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, THOMAS
FEARN, of Birmingham, in the County of Warwick, Electro-metallurgist,
send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her
Letters Patent, bearing date the Seventh day of April, in the year
of our Lord One thousand eight hundred and seventy-three, in the
thirty-sixth year of Her reign, did, for Herself, Her heirs and successors,
give and grant unto me, the said Thomas Fearn, Her special license
that I, the said Thomas Fearn, my executors, administrators, and
assigns, or such others as I, the said Thomas Fearn, my executors, admi-
nistrators, and assigns, should at any time agree with, and no others
from time to time and at all times thereafter during the term therein
expressed, should and lawfully might make, use, exercise, and vend,
within the United Kingdom of Great Britain and Ireland, the Channel
Islands, and Isle of Man, an Invention for "IMPROVEMENTS IN THE ELECTRO-
DEPOSITION OF TIN," upon the condition (amongst others) that I, the said
Thomas Fearn, my executors or administrators, by an instrument in

page_text: writing under my, or their, or one of their hands and seals, should par-
ticularly describe and ascertain the nature of the said Invention, and in
what manner the same was to be performed, and cause the same to be
filed in the Great Seal Patent Office within six calendar months next
and immediately after the date of the said Letters Patent.
NOW KNOW YE, that I, the said Thomas Fearn, do hereby declare
the nature of the said Invention, and in what manner the same is to be
performed, to be particularly described and ascertained in and by the
following statement thereof, that is to say :-
My Invention has for its object to effect the reduction or deposition
of tin by electricity with greater facility and certainty than can be done
by the processes at present in use for that purpose, so as to coat or cover
metals or metallic alloys with a coating of tin and to produce deposits of
tin for other purposes.
My said Invention consists in the use of solutions from which to
effect the deposition of tin, the said solutions being made and used in
the following manner :-I prepare a solution of protochloride of tin by
dissolving metallic tin in hydrochloric acid, the solution containing by
preference one ounce of tin in every three ounces of the said solution.
This solution may be made by dissolving tin in twice its weight of
hydrochloric acid, and adding water till for each ounce of tin dissolved
there shall be three ounces of the solution. I dissolve thirty pounds of
hydrate of potash or caustic potash in twenty gallons of water. I
dissolve thirty pounds of pyrophosphate of soda in sixty gallons of
water, and I dissolve thirty pounds of cyanide of potassium in twenty
gallons of water. I take two hundred fluid ounces of the solution of
protochloride of tin and gently pour it into the twenty gallons of hydrate
of potash solution, stirring the liquids with a glass rod during the
process of mixing them. A precipitate is at first formed which is soon
redissolved. Into the solution thus obtained I pour the twenty gallons
of cyanide of potassium solution, and lastly the sixty gallons of pyro-
phosphate of soda solution is added; the whole after being well stirred
up is ready for use. Or I dissolve fifty-six pounds of muriate of ammonia
in sixty gallons of water, and I dissolve twenty pounds of pyrophosphate
of soda in forty gallons of water. I pour gently into the solution of
pyrophosphate of soda one hundred fluid ounces of the protochloride of
tin solution; a white precipitate is at first produced, which on stirring

page_text: the liquid with a rod soon redissolves. I then mix the two liquids
together by pouring the muriate of ammonia solution into the solution
of pyrophosphate of soda, to which the protochloride of tin solution has
been added; the liquid thus made is ready for immediate use. The
solution of tin thus prepared requires considerably less battery power
than a solution made as first described. Or I dissolve one hundred and
fifty pounds of muriate of ammonia in one hundred gallons of water,
and I pour into this solution two hundred fluid ounces of the proto-
chloride of tin solution, and after the liquids have been well mixed by
stirring the solution is ready for use.
Or I dissolve four hundred ounces
of tartrate of potash in fifty gallons of water, and I dissolve twelve
hundred ounces of hydrate of potash in fifty gallons of water. I take
six hundred fluid ounces of the solution of protochloride of tin and pour
it slowly into the solution of tartrate of potash; a bulky precipitate is
immediately produced. The hydrate of potash solution is then added;
this quickly redissolves the precipitate. Whilst the hydrate of potash
solution is being poured into the liquid containing the precipitate the
whole should be well agitated, and a clear liquid is the result.
When the first-described solution is employed I prefer to use a battery
power of or equal to two cells of Bunsen's battery, and keep the solution
at or about a temperature of 70 degrees Fahrenheit.
When the second described solution is employed I prefer to use it at
a temperature of from 100 to 110 degrees Fahrenheit, and with a battery
power less than two cells of Bunsen's battery.
When the third described solution is employed I prefer to use it at a
temperature of about 70 degrees Fahrenheit.
The solution prepared as last described may be used cold.
The first and last described solutions yield deposits of considerable
thickness without the necessity for resorting to the process called scratch
brushing.
My improvements are applicable to the tinning of iron, copper, brass,
zinc, and other metals and alloys generally used in manufactures, as well
as to the electro-deposition of tin for other purposes.
In using the solutions herein-before described for the electro-deposition
5 of tin I employ electricity, obtained either from a galvanic battery or
from a magneto-electric machine, or from other source of electricity.

page_text: The process is conducted substantially in the same way as the process
for the electro-deposition of silver or copper, the bath in which the
articles are operated upon being made of one of the solutions herein-
before described and the anode being a sheet of tin.
Any one capable of conducting the electro-deposition of silver or a
copper, and acquainted with the general principles of electro-metallurgy,
will have no difficulty in conducting the electro-deposition of tin
according to my Invention, but as all baths or solutions used in the
electro-deposition of metals are liable to get out of order I will describe
the methods whereby the bath or solution may be best kept in order, and
I will also give such other practical information as will facilitate the
practice of my Invention.
As but few solutions of tin for electro-deposition are capable of
dissolving their anodes in quantity equal to the metal deposited it is
necessary to keep up an adequate supply of the said metal by adding
from time to time to the solution the oxide of the said metal or other
compound of the said metal capable of being dissolved by the solution
and otherwise suitable.
It is desirable to maintain the solution herein first described in as
caustic a condition as possible in order to obtain the best results. For
this purpose I boil it occasionally preferably in an iron vessel, and add
quicklime to it for the purpose of depriving it of carbonic acid, which
it may have absorbed from the atmosphere. It is then in a state to
receive a fresh supply of metal. After the liquid has cooled, and the
lime and carbonate of lime have fallen to the bottom of the vessel, the
clear liquid is syphoned or poured off, and that containing the lime
filtered. Protochloride of tin should then be added as long as the liquid
is capable of redissolving the precipitate which is formed in it. A little
of the hydrate of potash solution saturated with the protoxide or proto-
chloride of tin or of pyrophosphate of soda saturated with protochloride
of tin should be added to the solution as occasion may require. The
surfaces of the anodes used in this solution should be at least equal in
area to the surfaces of the articles in the bath to be coated.
When the second solution herein-before described requires a fresh
supply of metal, I take a hot and nearly saturated solution of pyro-
phosphate of soda and pour into it the protochloride of tin solution,
stirring the liquid well until it ceases to redissolve the precipitate, which

page_text: appears on adding the protochloride of tin. I add as much of this to
the solution which has been worked as occasion may require. The
surfaces of the anodes used with this solution should be equal in area to
the surfaces of the articles in the bath.
The third solution herein-before described does not require to be
renewed like the first and second solutions, as the anode dissolves freely
enough in the said third solution to maintain the said solution in a state
of saturation. Care must be taken in using the third solution to employ
no more battery power than is found necessary.
The surfaces of the anodes may be considerably less in area than the
surfaces of the articles which are receiving the deposit. Practice will
soon enable the workman to regulate properly the size of the anodes.
When the fourth solution herein-before described requires a fresh
addition of metal I add as much as may be necessary of the solution of
protochloride of tin and tartrate of potash. I pour this solution
cautiously into the old solution, stirring the mixture well with a rod.
The said protochloride of tin and tartrate of potash solution is added
until the liquid ceases to re-dissolve the precipitate formed; the
undissolved precipitate I dissolve by hydrate of potash and add the
solution to the bath.
The necessity for occasional additions of fresh metals to the solutions
is not peculiar to tinning solutions, as most of the solutions of gold,
copper, brass, and other metals require when they are alkaline frequent
additions of metal in order to maintain them in satisfactory working
order. It is advisable where a thick coating of tin is required to remove
the article or articles being coated from the solution whenever a
powdery deposit or exfoliation appears, and to brush the surface over
with an ordinary bristle brush, or with a scratch brush, and then replace
the article or articles in the bath for the reception of a further deposit.
When the articles have received a coating of tin of sufficient thickness
by the use of any of the solutions herein-before described, they should be
removed from the bath with the least possible delay and well rinsed in
water, after which they should be scratched brushed, well washed,
passed through hot water, and swung through the air, so as to remove
as much of the moisture as possible and finally dried in clean hot
sawdust.

page_text: In order to obtain the best results in depositing tin upon various
metals and alloys it is necessary that the surfaces of the metallic articles
should be entirely freed from grease. This is effected by boiling the
articles in a solution of common caustic potash, and in coating iron or
steel articles they should after having been boiled in caustic potash bei
passed through dilute sulphuric or dilute hydrochloric acid well rinsed
through water and quickly placed in the bath in connection with the
battery, so as to cause an almost instantaneous covering of tin over the
whole surface.
Cast-iron articles after having been properly pickled or cleaned by 1
acid, and before they are placed in the tinning solution should be coated
with a film of copper. This may be effected by employing the ordinary
cyanide of potassium bath or any of the other well known suitable
solutions of copper in connection with an electric current.
For tinning articles made of zinc I employ the solution herein first
described. Brass, copper, and zinc articles should be passed through
common aquafortis just before tinning in order to give them a clean and
proper surface for the reception of the tin deposit, but as this method of
treating metallic articles is well known I do not think it necessary to
describe it further.
Although I have herein-before described the relative proportions of
the several materials I employ in making solutions from which to effect
the electro-deposition of tin, which proportions in practice answer well,
and which I believe are the best proportions; yet I do not limit myself
thereto, as the relative proportions of the ingredients may be modified
within considerable limits without injuriously affecting the results
obtained.
Having now described the nature of my Invention, and the manner
in which the same is to be performed, I wish it to be understood that
I claim as my Invention of improvements in the electro-deposition of
tin,
First. The reduction or deposition of tin by electricity from a solution
or bath made by the admixture of solutions of protochloride of tin,
caustic potash, pyrophosphate of soda, and cyanide of potassium; the said
solution or bath being made and used substantially as herein-before
described

page_text: Secondly. The reduction or deposition of tin by electricity from a
solution or bath made by the admixture of solutions of protochloride
of tin, muriate of ammonia, and pyrophosphate of soda, the said solution
or bath being made and used substantially as herein-before described.
Thirdly. The reduction or deposition of tin by electricity from a
solution or bath made by the admixture of solutions of protochloride of
tin and muriate of ammonia, the said solution or bath being made and
used substantially as herein-before described.
Fourthly. The reduction or deposition of tin by electricity from a
solution or bath made by the admixture of solutions of protochloride of
tin, tartrate of potash, and caustic potash, the said solution or bath
being made and used substantially as herein-before described.
In witness whereof, I, the said Thomas Fearn, have hereunto set
my hand and seal, this Twenty-ninth day of September, in the
year of our Lord One thousand eight hundred and seventy-three.
Witness,
GEORGE SHAW.
THOMAS FEARN. (L.S.)