IMPROVEMENTS IN THE MANUFACTURE OF WHITE LEAD
Year: 1884

page_text: I HENRY JOHN BOLLMANN CONDY of Battersea in the County of Surrey do
hereby declare the nature of my Invention for "IMPROVEMENTS IN THE
MANUFACTURE OF WHITE LEAD" and in what manner the same is to be
performed, to be particularly described and ascertained in and by the following
statement:-
These improvements consist in certain modifications on the process described in
the Specification of a Patent granted to me on March 14th 1881 N° 1095 for
Improvements in the Manufacture of White Lead. Although the process described
in the Patent above named gives when carefully conducted results perfectly
satisfactory I find in practice the additions and modifications which I am about to
describe are of great consequence in rendering the process more certain in the
quality of its product and more valuable as a commercial inanufacture on the
practical scale by virtue of its offering greatly increased facility and economy in
production.
I would here remark that the chemical composition of white lead described in the
Specification of the herein recited Patent of the 7th October 1881 was through some
error in transcription designated as 3 Pb O 2 CO, whereas it should have been
2(PbO CO,) Pb O HỌ.
The results of numerous and repeated experiments on the larger scale have
induced me to qualify the recommendation contained in that Patent videlicet that
of employing a solution of tribasic acetate of lead and bicarbonate of soda in proper
proportion to precipitate nearly the whole of the lead, and further stating that I
preferred to employ "a slight excess of tribasic lead salt rather than find carbonate
of soda in excess." Though when carefully conducted, if the greatest nicety is
observed a satisfactory result is obtained, I find in practice the least variation from
the exact composition of the two substances is attended with the draw back that
the white. lead is liable to a slight uncertainty of tint after it is ground in oil,
whereas by the process hereinafter described, as a positive and reliable result can
be obtained as the white lead produced will be of a uniform white color, and not
liable to turn when ground in oil. Though my Patent hereinbefore recited was in
itself complete for the manufacture of white lead from oxide of lead it has since
occurred to me that a great object would be obtained in rendering the process more

page_text: valuable and more practical, if a method were devised worked out and described
for the manufacture of tri basic acetate of lead to be made entirely from metallic
lead by the action of acetic acid or neutral acetate of lead on metallic lead and not
to be dependent on the employment in anyway of previously manufactured oxide
of lead.
This portion of my Invention relating to the manufacture of tribasic acetate of
lead may be described as follows, videlicet I melt, and after skimming carefully,
feather the metallic lead by dropping it into water; I place this granulated lead
in wooden vessels or vats previously fitted with perforated false bottoms under
which are fixed taps for drawing the liquor off into other vats or tanks placed on a
lower level. Having filled with granulated lead the vessels fitted with the false
bottoms I fill up the interstices with a dilute acetic acid composed of one part (by
weight) of acid specific gravity 1-045 at 60 degrees Fahrenheit and 12 parts of
water, and after allowing the dilute acid to stand for two hours I draw it off
through the taps into the lower tanks.-This allows access of atmospheric air to
the lead which has the effect of heating the lead so that oxidation takes place.
After a time about three or four hours this oxidation begins to slacken, when I
pump up a second time the acid solution from the lower vat on to the granulated
lead and allow them to stand in contact for one hour,-I then again draw off into
the lower tank the liquid and again expose the metallic lead to atmospheric
oxidation allowing three or four hours for the latter operation and if the solution
of lead has not already attained the specific gravity of 1.040, at 60 degrees
Fahrenheit I again repass the liquor over the metallic lead partially oxidised until
it has attained that specific gravity when I place the dissolved lead with fresh
granulated lead and recommence the manufacture in the same way. I find this
operation succeeds much better on the large scale than on a laboratory scale.-In
vats containing upwards of one ton of lead the result is all that can be desired and
can be attained by passing the liquor from twice to three times over the metallic
lead partially oxidised.-A little practice enables the operator so to control the
process that he can obtain the solution of the desired specific gravity with perfect
ease.
This plan of manufacturing tribasic acetate of lead possesses the advantage of
producing that substance wholly or nearly wholly free from the impurities contained
in metallic lead such as copper and silver which are not taken up or soluble in the
presence of metallic lead. In consequence of the circumstance that foreign matter
is left almost untouched, I find it practicable to make white lead of a fine quality
from old lead such as lead piping, roofing, and worn out lead, generally which can
thus be utilized to greater advantage than in any other way.
Having obtained this solution of basic acetate of lead of the specific gravity of
1.040, at 60 degrees Fahrenheit I proceed as follows: videlicet:-To the solution
produced by each 60 pounds of acid and 750 pounds of water previously pumped
up into another vat or tank I add bicarbonate of soda in the proportion of
30 pounds for each 60 pounds by weight, of acid originally employed and agitate
the mixture. This will generally precipitate all the white lead, but it is necessary
to test the filtrate to ascertain the exact point when all the lead is thrown down.―
Sufficient bicarbonate of soda should be added to do this completely and it would
be better to use bicarbonate of soda in excess rather than leave any lead unpre-
cipitated, as by this means greater certainty is obtained in securing on the large
and practical scale a white lead capable of standing the effect of light and grinding
in oil without changing. The white lead after precipitation can be washed pressed
and dried in the usual way.
•
A variation may be made from the method described of making tribasic acetate
of lead videlicet this, That to each 60 pounds of acid and 750 pounds of water may
be added sufficient of the tribasic solution to make neutral acetate of lead with
which to recommence the manufacture of tribasic acetate of lead by the process
described. I am aware that vague reference has been made in chemical works to
the possibility of using metallic lead in the manufacture of sugar of lead, but such

page_text: references have been practically worthless as they contain no information of a
practical nature even for the manufacture of neutral acetate of lead and no process
at all has I believe ever been described for the manufacture of basic acetate of lead
from metallic lead acted on by acetic acid or acetate of lead.
Having now particularly described and ascertained the nature of, my said
Invention and in what manner the same is to be performed I declare that what
I claim is
The production with certainty of a white lead unaffected by grinding in oil
or exposure, by the employment of tribasic acetate of lead and bicarbonate of soda
in the manner as hereinbefore substantially described.
*
2. The manufacture of tribasic acetate of lead by the action of acetic acid or
acetate of lead on metallic lead in the manner as hereinbefore substantially
described.