Improvements in the Method of Producing Chloride of Lead.
Year: 1889

page_text: Date of Application, 15th Oct.. 1889-Accepted, 9th Aug., 1890
COMPLETE SPECIFICATION.
Improvements in the Method of Producing Chloride of Lead.
I, WALDRON SHAPLEIGH, a citizen of the United States, residing at Camden, in
the County of Camden, and State of New Jersey, Chemist, do hereby declare the
nature of my invention for IMPROVEMENTS IN THE METHOD OF PRODUCING CHLORIDE
OF LEAD and in what manner the same is to be performed to be particularly described
and ascertained in and by the following statements :-
Heretofore chloride of lead has generally been made by dissolving granulated lead.
obtained by dropping a mass of molten lead, from a height into a vessel of water in
dilute nitric acid, thereby forming lead nitrate, which is held in solution by the
liquor. The solution of lead nitrate being then drawn off and hydrochloric acid
added thereto in a quantity sufficient to react upon the solution of lead nitrate. By
this reaction the chlorine unites with the lead to form chloride of lead, a white
crystalline precipitate, which settles rapidly in the bottom of the vessel and the
liberated nitric acid together with a greater or less quantity of free hydrochloric acid
which may have been added in excess of the quantity required to precipitate the
lead nitrate being held in the superincumbent liquor, the latter is then drawn off
into a suitable vessel and preserved for use in dissolving a fresh charge of granulated
lead. The chloride of lead is then removed and washed with a small quantity of
cold water, in which it is but slightly soluble, for use.
The above described method of making chloride of lead possesses several serious
disadvantages, for example, the granulation of the lead by dropping the molten
metal from a height into water produces a powder consisting of grains or granules
of irregular size and of leaf-like shape having a thick mass of metal similar to a shot
at the centre thereof. Such grains or granules are slowly and imperfectly dissolved
even in a solution of pure nitric acid, therefore, if the nitric acid be not pure but
contains hydrochloric acid, as is frequently the case when nitric acid has been
previously used in the manufacture of the chloride of lead, the granules or grains
of metallic lead when introduced into such liquor before they entirely dissolve in the
nitric acid are attacked by the hydrochloric acid, thereby becoming coated with
chloride of lead, which coating prevents further action of the nitric acid, and collects
forming a mass of insoluble matter. This mass of materia! composed of lead
granules coated with chloride of lead is removed from the vessel as a residue to be
reduced to a metallic state by a smelting operation. The latter process is not only
difficult but also expensive, and occasions a loss of the hydrochloric acid.
The action of an aqueous solution of nitric acid upon metallic lead powder in a
vessel of a construction such as has been usually used for this purpose causes
first the deoxidation of a portion of the nitric acid which is estimated at about
25 per cent., the metal being oxidized and the oxide so formed is dissolved by the
rest of the nitric acid forming lead nitrate, while the deoxidized nitric acid which
becomes nitric oxide passes off from the liquor now heated by the above described
chemical action into the air, from the latter the nitric oxide absorbs oxygen, thereby
forming nitric peroxide, a dense, irritating, offensive and poisonous orange colored
gas. In the conduct of the above described method not only is a considerable
quantity of nitric acid wasted or lost, but also the health of the workmen is
impaired by the fumes of nitric peroxide rising from the surface of the hot liquor.
The principal objects of my invention are to obviate the above mentioned serious
results heretofore obtained and to manufacture chloride of lead by dissolving
metallic lead powder in an aqueous solution of nitric acid and to precipitate the lead
chloride therefrom, by the addition of hydrochloric acid to hasten and finally attain
a more perfect dissolution of the lead powder by its union with the nitric acid and

page_text: to counteract the formation of nitric peroxide fumes and consequent injury to the
health of the workmen and to avoid the unnecessary loss of the nitric acid.
My invention consists in introducing a blast or stream of air into an aqueous
solution of nitric acid, while powdered or pulverized lead is being added thereto and
chemical action is going on for the ultimate manufacture as a finished product of
chloride of lead.
My invention further consists in adding to an aqueous solution of nitric acid and
an excess of hydrochloric acid previously added but not uniting with lead nitrate
to form as a finished product chloride of load, a solution of lead nitrate before using
such aqueous solution to dissolve a fresh charge of pulverized lead and introducing
a blast or stream of air into the aqueous solution of nitric acid after it has been freed
of the excess of hydrochloric acid and while the pulverized lead is being added to
said aqueous solution and chemical action is going on.
My invention further consists in introducing into the mixture containing hydro-
chloric and nitric acids while the hydrochloric acid of said mixture is being used
for decomposing the lead nitrate, a blast or stream of air to oxidize the acids freed
from the salts of lead containing less oxygen than the nitrate of lead.
To carry my invention into effect I mix in a suitable vessel nitric acid with water.
I have obtained in practice good results by mixing one part of nitric acid with
about five parts of water, however, as the water is added to the solution for the
purpose of preventing the lead nitrate from assuming a crystallized form, when the
acidity of the liquor is neutralized, the above proportion of 1 part of acid to about
5 parts of water may be varied and will largely depend upon the temperature of the
liquor. Into this aqueous solution of nitric acid I slowly introduce finely powdered
lead and during the introduction of the powdered lead a strong blast or stream of
air is forced into and through the liquor. The mechanical action of the blast or
stream of air is to agitate and cool the liquor. The chemical action which ensues is
as follows: First, a portion of the nitric acid is deoxidized by the lead and the metal
is oxidized, and the oxide so formed is dissolved by the rest of the nitric acid forming
lead nitrate, while the nitric oxide compounds liberated by the action of the nitric
acid in oxidizing the lead while in the nascent state, unite with the oxygen of the
incoming air to form compounds containing nitric acid, which are dissolved in the
liquor before escaping therefrom into the atmosphere. When a sufficient quantity of
lead powder has been introduced to unite with the free nitric acid the introduction of
the lead powder is stopped, the blast of air is turned off, and the resulting solution
of lead nitrate drawn off into vessels, a small quantity into one and the remainder into
another or preferably only a portion of said solution is drawn off and a small quantity
retained in said vessel. This small quantity of the solution of lead nitrate is saved
use to be hereinafter explained, and to the larger quantity of the liquor is
added sufficient hydrochloric acid to react upon the lead nitrate to decompose the
latter and unite with the lead to form chloride of lead, a white crystalline precipitate,
which collects in the bottom of the vessel while at the same time is set free the nitric
acid which remains in solution in the liquor. It is however, very difficult to add
the exact quantity of hydrochloric acid necessary to unite with the lead, and in
practice, this acid is often added in excess, in such cases the solution will contain not
only nitric acid but also a certain percentage of free hydrochloric acid. To remove
this free acid and to render the solution of nitric acid. fit for use in the reduction of
a fresh charge of powdered lead the liquor is drawn off into the first mentioned
vessel by means of suitable apparatus and mixed with the small quantity of lead
nitrate saved therein as above described, whereby the lead is attacked by the hydro-
chloric acid and precipitated from the solution as chloride of lead, thereby freeing
the solution from hydrochloric acid. At the same time that the chemical reaction is
taking place between the above mentioned solution of lead nitrate, nitric acid and
free hydrochloric acid in the first mentioned vessel, a blast or stream of air may be
again introduced therein, whereby the liquor will be mechanically agitated and
cooled. The liquor after being freed of hydrochloric acid may be used to dissolve
for a

page_text: fresh charges of lead and the process may be repeated until the nitric acid becomes
so impregnated with foreign impurities as to render its use no longer economical.
The chloride of lead is then removed and washed with a small quantity of cold
water in which it is but slightly soluble, for use.
In the accompanying drawing is illustrated in vertical longitudinal section a form
of apparatus which has been found practically efficient for the conduct of the above
described process.
The horizontal shelves or floors A, A¹ and A³, are arranged in tiers and constitute
the frame-work upon which the apparatus rests. Upon the shelf A, is placed a tank B,
provided with a spigot 2, and into which tank is introduced an agitator or perforated
coiled pipe D, leading from the blower C, and provided with a valve-cock c. The
vessel F, is supported upon the shelf A¹, beneath the spigot 2. Upon the shelf A¹ is
also placed a filter G, provided with a blanket g and a drip cup g¹. The container H¹,
enclosed in an air tight casing H2, is placed upon the shelf A². A syphon I, provided
with a valve-cock A, extends from near the bottom of the tank F, through the air tight
casing H2. The pipe H³, provided with a spigot h, extends upwards from near the
bottom of the container H, through the air tight casing H2, in such manner as to
permit of a discharge being made into the tank B.
The method of making chloride of lead according to my invention may be carried
out by means of the above described apparatus as follows:
The spigot 2, and all the valves being closed, nitric acid is mixed with water in the
proportion of say, one part of acid to five parts of water, more or less in the tank B,
and then the valve-cock c, in the pipe d, is opened and air forced by the blower C,
through the agitator D, at the same time that a blast of air is admitted finely powdered
lead is slowly introduced into the liquor until all the nitric acid is taken up in the
form of nitrate of lead, when this is obtained the valve c, is closed and the solution is
drawn off through the spigot 12, into the tank F, taking care, however, to retain a
small quantity of the liquor in the tank B, for future use. To the liquor in the tank F,
is gradually added hydrochloric acid which causes chloride of lead to be precipitated
from the solution of lead nitrate in the form of a white crystalline powder which
settles on the bottom of the vessel F, and the superincumbent liquor containing nitric
acid and hydrochloric acid is drawn off through the syphon I, into the vessel H³.
The chloride of lead is collected and removed from the vessel F, and placed upon
the blanket g, where it is washed and the water passing off into the drip
receptacle g¹.
In order to repeat the process the valve c, and spigot 62 are closed, the solution
containing nitric acid and hydrochloric acid is drawn off from the vessel F, by means
of the siphon I, into the container H', and then by means of the blower C, air is
forced into the container H', through the pipe H, thereby causing the liquor to rise
from the container H₁, through the pipe H³, and to be discharged into the vessel B,
where it not only mixes with the lead nitrate previously retained therein, but also
forms chloride of lead and free nitric acid, the latter remaining in solution and the
former falling to the bottom of the vessel and may be saved and washed for use. At
the same time that the chemical reaction is taking place between the solution of lead
nitrate previously retained in the vessel B, and the nitric and free hydrochloric
acids, a blast or stream of air may be introduced by means of the blower C,
through the pipe d and agitator D, to mechanically agitate and cool the mass or liquor
in said vessel B. It being understood that the nitric and hydrochloric acids are
admitted from the vessel H, into the vessel B, through the pipe H³, by means of the
blower C, and pipe H, as above described.
It is obvious that the liquor from the vessel H, may be drawn off into another
vessel and there treated with the solution of lead nitrate instead of treating it in the
vessel B. The nitric acid thus freed from hydrochloric acid may be used to dissolve
a fresh charge of lead in repeating the above process, until it becomes so charged
with foreign or extraneous impurities that its use is no longer practical or
economical.

page_text: Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is
1. In the manufacture of chloride of lead, introducing a blast of air into an
aqueous solution of nitric acid during the admission of finely divided lead thereto and
while the solution is undergoing chemical action, substantially as and for the purposes
set forth.
2. In the method of making chloride of lead, adding to a solution of lead nitrate
hydrochloric and nitric acids and then introducing a blast of air into the same while
the chemical reaction is taking place between said lead nitrate and hydrochloric acid,
substantially as and for the purposes set forth.
3. In the method of making chloride of lead, precipitating the lead from a solution
of lead nitrate in the form of lead chloride by the addition of hydrochloric acid, then
introducing a blast of air into said solution during the re-action to oxidize the lower
oxides of nitrogen given off during the re-action and then adding lead nitrate thereto
to remove the excess of hydrochloric acid, substantially as and for the purposes
described.
Dated at Philadelphia. Pa.. this 23rd day of August A.D. 1889.
WALDRON SHAPLEIGH.
Witnesses:
GEORGE WASHINGTON REED.
JOHN WALTER DOUGLASS.
W. P. Thompson & Boult,
Agents for the Applicant.