AN IMPROVED PROCESS FOR PREPARING A CERTAIN MATERIAL FOR THE PURPOSE OF PAINTING
Year: 1846

page_text: TO ALL TO WHOM THESE PRESENTS SHALL COME, I, JAMES
MURDOCH, of Staple Inn, in the County of Middlesex, Mechanical Draughts-
man and Patent Agent, send greeting.
WHEREAS Her prescut most Excellent Majesty Queen Victoria, by Her
Royal Letters Patent under the Great Seal of Great Britain, bearing date at
Westminster, the Eleventh day of February, in the ninth year of Her reign,
did, for Herself, Her heirs and successors, give and grant unto me, the said
James Murdoch, my exors, admors, and assigns, Her especial licence, full
power, sole privilege and authority, that I, the said James Murdoch, my
exors, adñiors, and assigns, or such others as I, the said James Murdoch,
my exors, admors, 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
"AN IMPROVED PROCESS FOR PREPARING A CERTAIN MATERIAL FOR THE PURPOSE
OF PAINTING," communicated from abroad; in which said Letters l'atent is
contained a proviso that I, the said James Murdoch, shall cause a particular
description of the nature of my said Invention, and in what manner the same
is to be performed, to be inrolled in Her said Majesty's High Court of
Chancery within six calendar months next and immediately after the date
of the said in part 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 aforesaid proviso, I have
ascertained and set forth the nature of the said Invention, and the manner of
Price 8d1

page_text: carrying the same into effect, in and by the following description thereof,
reference being had to the Drawing hereunto annexed, and to the figures
and letters marked thereon.
The dangers attendant upon the use of white lead have led to many
attempts to discover a substance which might advantageously be employed as
a substitute for it. Amongst other substances proposed for the purpose is the
oxide of zinc, which has engaged the attention of many scientific and practical
men, more especially of Guiton de Morveau, of Courtois, and of Atkinson.
The insufficiency of the means hitherto proposed for producing and collecting
the oxide of zinc, and certain peculiar inconveniences attending its use in
painting, have prevented its employment to any considerable extent in the
arts, or for manufacturing purposes. The author of this communication, in
the course of his researches, has discovered certain processes which he
considers as completely obviating all the difficulties which have hitherto beset
the subject, and therefore as rendering equal service to humanity and the arts.
These processes, which constitute the Invention which forms the subject of
my Patent, may be ranged under two heads,-
First, the production of the oxide of zinc ; and,
Secondly, the collection of the oxide.
The methods hitherto ordinarily employed for obtaining the oxide of zinc
consist in charging a vessel, open at both ends, with zinc, or other materials
from which it may be obtained, and passing a current of air through this
vessel to inflame the metallic vapor, and to produce the oxide in the interior
of the vessel itself. The oxide is collected in the generating vessel, and in the
pipes which are connected with it. In producing the oxide in this way, only
the small portion of it which is driven into the tubes by the current of air is
collected in a pure state; the remaining and by far the most considerable
portion forms in a thick crust upon the bath of zinc, and is always very impure.
The process for which my Patent is granted differs essentially from this. It
consists,―
Firstly, in preventing the access of oxygen to the bath of zinc, or to the
materials furnishing the zinc; and this is effected by burning the metallic
vapor outside of the vessel in which it is generated.
Secondly, in causing the air charged with the oxide to pass through sieves
permeable to the air, but impermeable to the oxide.
Thirdly, in creating a strong current of air (by a blowing machine or any
other suitable means) through the chambers in which the oxide is produced
and collected, for the purpose of renewing the air, in order to facilitate the
production and collection. By this manner of proceeding the oxide of zinc is

page_text: obtained in a state of great purity and fineness, of a dazzling whiteness, and
requiring no expensive manipulations before it can be used, and there is little
or no less.
In order to render this process clearer, I shall now proceed to describe its
application, and for greater simplicity shall suppose that, only one retort
or generating vessel is employed. The establishment is composed of five
chambers, which I distinguish as follows:-First, the retort chamber;
second, the air chamber; third, the oxidating chamber; fourth, the collecting
chamber; fifth, the inspection chamber.
First, the retort chamber.-In this chamber is constructed the furnace, in
which is set the retort or generating vessel, and in this chamber are performed
the operations of charging and clearing the furnace and retort or generator.
The generator which receives.the zinc, or the material from which it is to be
obtained, may be in the form of a retort or other vessel suitable for the
purpose of distillation, made of earthenware, and capable of standing a white
heat. This vessel is provided with two or more apertures, one of them being
for the passage of the metallic vapour, and the other for the purpose of
charging and cleaning the retort, but the latter must be hermetically sealed
during the, distillation, in order to prevent the access of air to the interior.
In fitting this retort in the furnace the distilling aperture should open into
the oxidating chamber. The generator, being fitted into the furnace, is to be
charged with zinc, or with materials capable of furnishing zinc, in the same
way as takes place in treating the ores of zinc in the extraction of zinc by the
same method.
Second, the air chamber.-This chamber, which communicates with the
external air, is divided by sieves of cloth or wire gauze, which allows the air to
pass, but arrest all extraneous particles suspended in it, so that the air destined
to inflame the metallic vapors in the oxidating chamber enters the chamber in
a pure state.
Third, the oxidating chamber.-The distilling orifice of the retort, and the
aperture through which the purified air passes, both open into this chamber.
"The metallic vapor, on reaching the edge of the orifice of the retort, takes
fire by contact with the current of air, as gas issuing from a burner takes fire
on the application of a light. The white fumes resulting from this combustion
are the oxide of zinc, commonly known as the "flowers of zinc." The oxide
is formed more rapidly, and the combustion is more active and complete as
the temperature of the furnace is rendered more intense. As the formation
of the oxide proceeds a current of air, excited by a draft flue from the
collecting chamber, or by other suitable means, carries the oxide with it into
this latter chamber.

page_text: Fourth, the collecting chamber.-In order to promote a strong current of
air both in the air chamber and the oxidating chamber, a draught flue is
formed, leading from the collecting chamber into the chimney of the furnace,
or in lieu of this a pump or other mechanical means of causing a draught may
be employed. Sieves of cloth or wire gauze, of a texture more or less close,
are placed apart from each other before the opening of the draught flue,
exactly in the same manner and fulfilling the same office as those placed in
the air chamber, except that in the collecting chamber they are for the
purpose of collecting the oxide. The sieves should be shaken, either
constantly or at intervals, to detach the oxide, which would otherwise in the
course of time obstruct the current of air.
Fifth, inspection chamber.-In this chamber, and commanding the orifice
of the retort, are established two wickets or sinall apertures, one of which is
fitted with an eye piece of colored glass, to soften the glare of the inflamed
metal, and the other is fitted with a small door, through which to introduce
when requisite an instrument to clear the orifice of the retort if it should get
plugged up, but which wicket should be hermetically closed when the flowers
of zinc are required to be perfectly pure. At the commencement of the
operation care should be taken to close the orifice which opens into the
oxidating chamber, and to allow the first vapors (which are generally impure)
to pass offinto a separate chamber, as a compartment of the furnace chamber,
If this
for instance, so that they may be collected apart from the rest.
precaution be neglected there will be some risk of the product being deteriorated
in purity.
DESCRIPTION OF THE DRAWINGS.
Note, the same letters, where they occur in different figures, denote the
same parts in each. Figure 1 is a plan of the establishment; Figure 2 isa
section upon the line A, A; Figure 3, a section upon the line B, B;
Figure 4, a section upon the line C, C. D, retort chamber; E, air chamber;
F, oxidating chamber; G, collecting chamber; H, inspection chamber;
I, brickwork of the furnace; J, opening for charging and cleaning the retort,
which opening must be hermetically closed during the operation; K, retort or
generating vase; N, sieves permeable to air, but impermeable to the oxide;
L, flue of the furnace; M, draft flue; N1, N11, sieves permeable to the air,
and in a small degree to the oxide; O, orifice by which the purified air enters
the oxidating chamber; P, orifice by which the metallic vapors pass off;
Q, sieves permeable to the air, but not to the extraneous and impure particles
suspended in it; Q1, Q1, sieves permeable to the air, and slightly so to the
impurities suspended in it; R, door of the air chamber; S, opening by which

page_text: the oxide passes into the collecting chamber; T, door opening from the
inspection chamber into the oxidating chamber; U, air vent of the air
chamber, situated above the door R of the chamber; V, door of entrance for
shaking the cloths N, N¹, N11; X, fire grate.
Having thus fully and clearly set forth the nature of the Invention, and the
mode of carrying the same into effect, I proceed to state what are the particular
parts which are claimed. I claim,―
First, the manufacturing oxide of zinc without allowing the air to come in
contact with the bath of zinc, by causing the vapours of zinc to be burnt
outside of or after leaving the vessel in which they are generated.
Second, the causing the air to pass through sieves to free it from impurities,
and to cause it to deposit the oxide in the collecting chamber.
Third, the creating a strong draught or current of air through the air
chamber, oxidating chamber, and collecting chamber, by a draught chimney
ventilator or any other suitable means.
Fourth, the application of a current of air which has been purified by
passing through sieves to the collection of the flowers or oxide of zinc in the
process of obtaining zinc from the ores containing it, which oxide is now lost
during the melting of the metal.
In witness whereof, I, the said James Murdoch, have hereunto set my
hand and seal, this Eighth day of August, in the year of our Lord
One thousand eight hundred and forty-six.
JAMES (L.s.) MURDOCH.
AND BE IT REMEMBERED, that on the Eighth day of August, in the
year of our Lord 1846, the aforesaid James Murdoch came before our
said Lady the Queen in Her Chancery, and acknowledged the Specification
aforesaid, and all and every thing therein contained and specified, in form
above written. And also the Specification aforesaid was stamped according
to the tenor of the Statute made for that purpose.
Enrolled the Eighth day of August, in the year of our Lord One
thousand eight hundred and forty-six.