A New or Improved Process for Manufacturing Bleaching Powder and Caustic Soda.
Year: 1890

page_text: Date of Application, 23rd May, 1890-Accepted, 28th June, 1890
COMPLETE SPECIFICATION.
A New or Improved Process for Manufacturing Bleaching Powder
and Caustic Soda.
We, JOHN DoWNER PENNOCK and JOSEPH ALBERT BRADBURN, of Syracuse,
Onondaga County, State of New York, United States of America, Chemists, do
hereby declare the nature of our invention and in what manner the same is to be
performed, to be particularly described and ascertained in and by the following
statement:-
Our invention relates to the process for manufacturing bleaching powder and
caustic soda, in which common salt is used as a base for the several reactions.
Our object is to simplify the process and reduce the cost of production.
Our process consists in the new and novel method described as follows and'
specifically set forth in the claims annexed.
Into a still constructed of stone and provided with suitable tubes for heating,
we introduce salt and add a sufficient amount of nitric acid to transform it into
nitrate of soda.
Upon applying a gentle heat the decomposition begins and a nitrate of soda is
rapidly formed.
As the nitrate of soda is extremely soluble in a hot solution the operation is so
conducted that the solution of nitrate of soda in the still is saturated at the boiling
temperature.
The solution is then run out from the still and cooled.
Owing to the great difference in the solubility of nitrate of soda in hot and cold
solutions a great mass of the salt is deposited on cooling. Over half of the quantity
of nitrate of soda in solution at 110 to 120 C. is deposited on cooling the solution
down to 20 C.
The crystals obtained by this cooling are separated from the mother liquid
which together with more salt and nitric acid is again sent to a still and the
operations repeated.
The gases resulting from the reaction in the still, composed principally of
nitrosyl chloride and chlorine, pass into a vessel containing nitric acid and manganese
dioxide in suspension where nitrate of manganese is formed and chlorine is given off.
The chlorine evolved passes through a washer and then into a bleaching powder
apparatus.
A very great superiority of our process over others is that all of the chlorine
combined with the sodium in salt is obtained in the form of bleaching powder, and
that the gas passing to the bleaching powder chamber is pure chlorine gas thus
avoiding the weak and impure chlorine obtained in all of the magnesia processes and
avoiding the loss of two thirds of the chlorine which is incurred in the Weldon
process.
The crystals of nitrate of soda obtained by cooling the nitrate of soda solution
coming from the still are mixed with two or three times their own weight of oxide
of iron.
The mixture is then heated to a red heat in a current of air in a cylindrical
furnace.
The nitrate of soda is completely decomposed and the gases evolved with the excess
of air are passed over an oxidising substance such as manganese dioxide, a manganite,
a manganate or a permanganate of the alkalies or of the alkaline earths.
The nitrate of manganese liquor mentioned above is heated and evaporated to
a plastic consistency by the hot gases coming from the decomposition of the nitrate
of soda.
1

page_text: The nitrous gases coming from the decomposition of nitrate of soda and nitrate of
manganese finally pass after treatment with air and steam into the usual apparatus for
condensation of nitric acid.
Nitrate of manganese evaporated to the plastic condition mentioned above contains
about 90% Mn - 0 2.
It will thus be seen that both the nitric acid and manganese are recovered.
The mixture of iron oxide and soda is taken from the furnace and lixiviated.
If the heat has not been carried too high, the mixture is in good condition for
lixiviation.
If lixiviated with hot water a caustic liquor of 30° Be. to 40° Be. may be obtained
practically free from carbonate of soda so that when this liquor is evaporated and
made into caustic soda, an extremely high test of caustic soda may be obtained.
Having now particularly described and ascertained the nature of our said inven-
tion and in what manner the same is to be performed we declare that what we
claim is :-
The herein described process for the manufacture of bleaching powder (chloride
of lime) and caustic soda consisting of the following steps:
First Treating salt in a still heated by steain or its equivalent, with nitric
acid, and
Second: By passing the resulting gases nitrosyl chloride and chlorine, through
a vessel containing nitric acid and manganese dioxide the gas chlorine resulting
being passed through a washer and then to the bleaching powder chamber: and
Third: The recovery of the nitric acid in the nitrate of soda by furnacing with
oxide of iron, and the lixiviation of the mixture to produce caustic soda; and the
recovery of nitric acid from the nitrate of manganese by heat; leaving Mn - 02
which is used over again.
Dated this 23rd day of May 1890.
HERBERT & Co.,
18, Buckingham Street, Strand, W.C., London, Agents to Applicants.