CERTAIN IMPROVEMENTS IN THE COVERING OR PLATING WITH SILVER VARIOUS, METALS AND METALLIC ALLOYS
Year: 1842

page_text: TO ALL TO WHOM THESE PRESENTS SHALL COME, I, EDMUND
TUCK, of the Haymarket, in the County of Middlesex, Silversmith, send
greeting.
.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her Letters
Patent under the Great Seal of the United Kingdom of Great Britain
and Ireland, bearing date at Westminster, the Fourth day of June, in the
fifth year of Her reign,. did,. for Herself, Her heirs and successors, give and
grant, unto me, the said Edmund Tuck, Her especial license, that I, the
said Edmund Tuck, my executors, administrators, and assigns, or such others as
I, the said Edmund Tuck, my executors, administrators and assigns, should at
any time agree with, and no others, from time to time and at all times during
the term of years therein. expressed, should, and lawfully might make, use,
exercise, and vend, within England, Wales, and the Town of Berwick-upon-
Tweed, my Invention of "CERTAIN IMPROVEMENTS IN THE COVERING OR PLATING
WITH SILVER VARIOUS, METALS AND METALLIC ALLOYS;" in which said Letters
Patent there is contained a proviso, obliging me, the said Edmund Tuck, by
an instrument in writing under my hand and seal, particularly to describe and
ascertain the nature of my said Invention, and in what manner the same is to
be performed, and to cause the same to be enrolled in Her Majesty's High
Court of Chancery within six calendar months next and immediately after the
date of the said recited Letters Patent, as in, and by the same, reference being
thereunto had; will more fully and at large appear.
NOW KNOW YE, that in compliance with the said proviso, I, the said
Edmund Tuck, do hereby declare the-nature of my-said-Invention, and in

page_text: what manner the same is to be performed, to be particularly described and
ascertained in and by the following statement, that is to say:-
My said Invention consists in the use and application of either of the two
carbonates of ammonia (namely, the sesquicarbonate and the bicarbonate) as
one of the ingredients in the mixtures or compounds employed for covering or
plating with silver various metals and metallic alloys by the action of electricity.
And I find that by the use of the said carbonates the silver so deposited, and
constituting such covering or plating, has not a crystalline character, and is
firmly adherent to the surface of the metal. Bicarbonate of ammonia may be
purchased of the manufacturing chemist, or may be prepared in various ways,
among others is the following:-Take any quantity of the solid carbonate of
ammonia of commerce, called sesquicarbonate of ammonia, reduce it to coarse
powder, and expose it to the air till it ceases to exhale or give off the pungent
odour characteristic of that salt. This change will take place under ordinary
circumstances in twenty-four hours, more or less, and the salt will have lost
from forty to about fifty-two per cent. of its original weight, and will now be
found to have become bicarbonate of ammonia, the composition of which is
one equivalent (or by weight about seventeen parts) of ammonia, two
equivalents (or by weight about forty-four parts of carbonic acid is one
equivalent, or by weight about nine parts) of water. The material of the articles
usually plated with silver is either copper or its alloys, and of these alloys,
especially that which is commonly called German silver. This latter consists
essentially of copper, nickel, and zinc, but the different manufacturers of this
alloy do not use precisely the same proportions of the said ingredients, nor are
these ingredients (especially the nickel) brought respectively to equal degrees
of purity; hence, the process of plating German silver requires certain
adjustments in the proportions of the substances used, and certain variations
in the manipulation in order to secure in all cases the best result; but these
adjustments and variations it is not possible to point out precisely, depending
as they do on the varying quality of the alloy. I have already stated that
bicarbonate of ammonia is one of the ingredients in the mixture or componnd
which I employ for plating, the other ingredient is a salt of silver; and I find
it advantageous to vary the salt of silver according to the nature of the metal
or alloy intended to be plated. For the common alloys of the so-called
German silver I use the compound or mixture of a solution of bicarbonate of
ammonia with the sulphate of silver; for plating on copper, or on good German
silver, I use the compound or mixture of bicarbonate of ammonia with cyanide
of silver; and I would observe, that though the latter compound may be used
to plate the common alloys of German silver, and the former compound to

page_text: plate copper or good German silver, the use of these respective compounds for
such
purposes s is not so advantageous, according to my experience, as those firstly
mentioned. Both these salts may be purchased of most manufacturing
chemists, or may be made in the following way :-To prepare the sulphate of
silver I take a cold saturated solution of the salt called nitrate of silver, and
add gradually to it strong sulphuric acid as long as any white precipitate comes
down, I then wash the precipitate with small portions of cold distilled water
till the excess of acid is got rid of, I then dry the powder at a gentle heat, and
it is now fit for use. The sulphate of silver thus prepared is composed of one
equivalent (by weight about forty parts) of sulphuric acid, and one equivalent
(by weight about one hundred and sixteen parts) of oxide of silver. The
cyanide of silver may be made by putting any convenient quantity of the yellow
salt, called prussiate of potash, or ferroprussiate of potash, or ferrocyanide of
potassium, into an earthen crucible, and exposing it to a low red heat for a
quarter of an hour; the black mass thus produced is to be digested in warm
distilled water, which, when passed clear through a filter, is a solution for the
most part of cyanide of potassium; to this is to be added gradually a cold
saturated solution of nitrate of silver as long as a white or greyish white pre-
cipitate comes down; this precipate, when washed in cold water and dried, is
cyanide of silver, and consists of one equivalent (by weight about one hundred
and eight parts) of silver, and one equivalent (by weight about twenty-six parts)
of cyanogen. The way of preparing the plating mixture or compound which
I have found to afford the best results, is to take one equivalent, that is,
seventy parts by weight of bicarbonate of ammonia, and either one equivalent,
that is, one hundred and fifty-six parts by weight) of sulphate of silver, or one
equivalent (that is, one hundred and thirty-four parts by weight) of cyanide of
silver. The bicarbonate of ammonia is to be dissolved in distilled water, and
the sulphate of cyanide of silver (whichever is made use of) is then to be
added, and the liquor is to be boiled till the salt of silver is entirely dissolved.
The strength of the solution, that is, the proportion of water, must be regulated
by the strength of the galvanic battery made use of. The strongest solution
that I have ever had occasion in coating bad German silver to employ was
composed of half an ounce of sulphate of silver and one hundred and seven
grains of bicarbonate of ammonia dissolved in one pint of water. The kind of
electricity whereby the plating mixtures above-mentioned are made to deposit
their silver on the metal or alloy to be plated is that which is produced by
means of a galvanic or voltaic battery, and of the various forms of such battery
which have been invented and published I prefer a modification of that which
is commonly known by the name of Daniell's constant battery, and of which a

page_text: figure and description are given in the four hundred and thirty-ninth page of a
book intituled "An Introduction to the Study of Chemical Philosophy, &c.;
by I. Frederick Daniel, F.R.S." The modification of this battery which I
employ is a rectangular trough of seasoned wood, the cavity of which is divided
longitudinally by a thin partition of porous wood into two cells, one of which
is twice as wide as the other. The wide cell is again subdivided by a longi-
tudinal partition into two equal cavities which have free communication with
each other, because the partition does not quite touch the two ends of the
trough. Of these two cavities the outer is to be filled with crystals of sulphate
of copper, and the inner one with a solution of sulphate of copper in water; a
plate of copper is also inserted in this cavity. The other cell is filled with
water, and a plate of zinc is also put in it. Near the above-mentioned trough or
battery is placed another trough, having no partition, and containing the
plating mixture or compound. The article to be' plated and a piece of zinc
are put into the plating mixture on opposite sides of the trough, the article to
be plated being connected by means of a strip of copper with the zinc plate of
the battery, and the piece of zinc being connected by a strip of copper with the
copper plate of the battery. The general proportion of the copper to the zinė
surface of the battery is as four of copper to one of zinc, but the proportion of
copper must be increased when operating on those metals or alloys that have
but a feeble affinity for silver. The article to be plated must first be made
quite clean. The method which I use for this purpose is to put it for two or
three hours in a cold solution of common carbonate of potash in water, then
to wash it in cold water, and afterwards dip it in pickle, which is a mixture of
aquafortis and water, the proper strength of which depends on the nature of
the metal or alloy of which the article is made. It is next to be washed and
dried and well rubbed with rottenstone in a rag or piece of leather. In
operating on German silver the qualitity of the alloy may be judged of by its
appearance when taken out of 'the pickle, the best kinds having a perfectly
white surface, the inferior kinds having a surface more or less dark coloured.
Immediately before immersing the article in the plating liquid I dip it into a
solution of common salt in which a little gum has been dissolved. The strength
of the battery must be such as to give a slow and even deposit of silver on the
surface of the metal or alloy to be plated. The usual time for obtaining a
satisfactory deposit is three or four days; a perfect coating; indeed, is obtained
in an hour, but the further length of time required depends on the intended
thickness of the plating.
:
Having now described the nature of my said Invention, and in what manner
the same is to be performed, according to the best of my present experience, 1

page_text: wish it to be understood that although I have given in this Specification of
my Invention a general description of the whole process of plating metals and
metallic alloys with silver as practised by me, yet I do not claim the exclusive
use of any of the several processes herein-before described, except so far as all
or any of them may be used in connection with or in aid of my said Invention,
which I declare to consist in the use of either of the two carbonates of
ammonia, namely, the sesquicarbonate and the bicarbonate as one of the
ingredients in the mixtures or compounds employed for covering or plating
with silver various metals and metallic alloys by the action of electricity.
In witness whereof, I have hereunto set my hand and seal, the Third day
of December, in the year of our Lord One thousand eight hundred
and forty-two.