US1611401A - Process for the manufacture of sodium bicarbonate and the production of nitrogen - Google Patents

Description

,Dec. 21 1926. r 1,611,401

ARNOLD E. E. v PROCESS FOR THE MANUFACTURE OF SODIUM BICARBONATE AND THE v PRODUCTION OF NITROGEN 1 Filed Oct. 2]. 1924 aLoyJEa GHSOMETER 45' ens TURBINE COMPRESSOR Patented Dec. 21, 1926.

UNITED STATES tens-i PATENT OFFECEW EDWA RD E. ARNOLD, OF COVENTRY, RI-IODE ISLAND, ASSIGNOR' TO NITROGEN CORPORATION,

ISLAND.

OF PROVIDENCE, RHODE ISLAND, A CORPORATION OF RIC-KOBE rnoonss FOR THE MANUFACTURE or sonIuM BIGARBONATE AND TH rnonucrron or mctnoenn.

7 Application filed Octobcr 21, 1924. Serial No. 744,922.

' This invention relates to an improved process for the manufacture of sodium bicarbonate and the roduction of nitrogen, which is particular y applicable for use in connection with the manufacture of iron and steel, but is not limited to this application as it can be applied to any industry where large qluantities of carbonaceous fuel is used in c ose proximity to a salt supply.

In the manufacture of iron and steel from the ores in accordance with present methods of Operation, the ores are first smelted in a blast furnace to obtain crude iron which may be further treated by various methods, such, for example, as by purification with an air blast in a Bessemer converter, to remove a ,suitableiportion of the carbon and form steel. It is the practice in carrying out the above process 'toplace the ore together with coal or coke and a suitable flux in theblast fur- [nace and after igniting the mass at the base, force a blast of air therethrough to reduce the ore and obtain the same in a molten form while the air forced into the base of the furnace is' changed in part to {forma gaseous mixture which is withdrawn from the top thereof and utilized as a "fuel in stoves or gas engines whereby "the unconsumed heating elements of the gases may be utilized most completely.

The composition of the gases as they emer e through a suitable pipe at the top of thebTast furnace is represented as made up of the following constituents in approximately the proportions indicated, although it is to be understood that these proportions vary at different times under different con.- ditions and varying methods of operation; nitrogen 60%, carbon dioxid 15%, carbon monoxid 23% and hydrogen 2%. The bases issuing from the furnace may be {treated to remove dust and certain foreign} materials before being conducted to stoves, gas engines or other suitable furnaces where they, are

burned with the addition of a sufficient quantity of air to furnish the requi ite oxygen for combining with the carbon monoxid and hydrogen content of the gases whereby the tion also compre heat energy of the gases may be conserved and used. It will be seen from the above that if a proper quantity of air is burned with the gases to provide o Xygen for the complete combustion of the carbon lilOIlOI'ilil.

and hydrogen content thereof the resulting gases emerging from the "stoves or heaters Willbe composed of approximately 23 or percent of carbon dioxid while the remain ing 76 01 77% will be practically all nitro gen mixed with a small amount of water vapor. 1

It is the main object of the present inven tion to utilize the gas mixture thus obtained for the formation of sodium bicarbonate and at the same time eliminate the carbon dioxid from the mixture vto provide a convenient means for obtaining substantially purenitrogen gas in large quantities. The nitrogen thus obtained may be advantageously employed in various processes for the fixation of nitrogen and I may employ it for this purpose as an additional step of the present process. As illustrative of one method by which the nitrogen thus produced may be employed in thefixation of nitrogen I have shown and described its use in a Bessemer converter or like appliance where in the nitrogen acts upon carbon in the presence of the molten metal to produce carbon nitrogen compounds. It is to be understood, however, that this particular manner of utilizing the nitrogen in the formation of nitrogen compounds is merely illustrative of one method of o oration and that my inven hends the use of the nitrogen produced in forming alkali metal ,cyanids, ammonia or other nitrogen compounds either by treating an alkali carbonate, carbide or' cases, the nitrogen thus obtained being couveniently located for use in the Bessemer converter of the iron works for purifying the molten iron with formation of cyanogen compounds as described in U. S. Patent No. 1,505,281 by Adriaan Nagelvoort, dated Aug. 19, 1924, or for forming nitrogen compounds by any other suitable method such, for example, as those described in US. Patents 1,091,425, 1,120,682, and 1,174,944. r

The ammonia soda process for the manufacture of sodium bicarbonate as at present carried out comprises the contactingof a gas mixture containing approxin'iately 40% carbon dioxid and 60% nitrogen (or other inert gas) with an ammoniated brine solution in carbonating' towers which results in a reaction between the carbon dioxid content of the gaseous mixture and the sodium chldride of the solution to form sodium bicarbonate and ammonia chloride. The sodium bicarbonate is commonly conyerted to the normal salt by heating as is wellknown in the art.

It is the present practice in the operation of the ammonia soda process to calcine all or part of the sodium bicarl'ionate' i'orn'ied according to the following equation QJaHCO, t-heat:Na CO,+H O+CO whereby additional carbon dioxid is obtained which is used to enrich the normal gas mixture as above described whereby under certain conditions the rcactingeas mixture may eventually contain as high as 60124570 of carbon dioxid even though the normal gas as received from the' kilns and as u: ed at. the beginning ot the operat on contains as low as 35% carbon dioxid. H is alsothe practice in the nnuuifacture of sodium bicarbonate by the ammonia soda process as now employed to pass the gases into the carbonating towers and forcethe same thercthroug'h against the normal bydrostatic pressure prevailing in the towers which varies from 30 to tidpounds per square inch, depending upon the height ot' the towers. a d v From the aboveitwillbe seen that the proportion otcarbon dioxid in the gases as now generally used in the ammonia soda process is normally approximately 40%, which percentage is increased by enrichbment to possibly as high as 60%75 o. In

the waste gases obtained from blast furnaces after combustion of the carbon monoxid and hydrogen content thereof the carbon dioxid content would be normally 2070-2470 nib-h may be increased by enrichment-as the usual practice to from 40% to 6071: '3! will. be understood from the above that the term normal. carbon dioxid content of the gaseous mixture and equivalent expressions as used herein refer to the carbon dioxid content of the gas employed for lr1ning sodium bicarbonate before such gas has been enriched by the addition of carbon dioxid obtained by calcining the bicarbonate or from any other source.

I find that sodium bicarbonate can be readily produced by means oi a lean e'as mixture containing normally as low as 2- 1-% carbon dioxid, such as is obtained by burning; the waste blast furnace gases in a sutl icient quantity of air to combine with the carbon monoxid and hydrogen content thereof. In order to effect the formation of sodium bicarbonate with a lean gas mixture containing, for example, QOib-Q LQ; carbon diosid I propose to increase the pres sure upon the gaseous mixture before passing it into the :arbonating towers over that ordinarily employed by placing the same under a pressure of from to 60 pounds per square inch inaddition to the hydrostatic pressure in the carbonating towers. That is, the normal hydrostatic pressure in the carbonating towers under prcf'ent opcrating conditions being from 30 to 60 pounds per square inch] I propose to practically double this pressure in order that when operating with a normal gas of 20% to :3--,t= carbon dioxid the volume concentration of the carbon di-oxid will be equivalent under the increased pressure to that of a normal gas of 40% to carbon dioxid such as is now generally used in the manufacture of sodium bicarbonate. In specify i no the pressures which I propose to employ i addition to the ordinary hydrostatic pressure otthe carbonating towers it is to be understood that the present process is not to'be restricted to the use of the exact pressures indicated above but that the pre:-1sures above noted are given as illustrative only. and that the same maybe varied somewhat dependent upon conditions of operation, such, for exan'iple, as that in operating: with towers of such height as would provide a hydrostatic pressure 01"" 30 pounds per square inch it might be found desirable to use an additional pressure of as high as pound per square inchi'n order that the totallp'res sure upon the gas entering the towers be as high asltlO pounds per square inch, as I have found that a lean gas mixture, containing from 20% to 24%":earbon dioxid produces sodium bicarbonate efficiently and of a erzulesuitable for the usual mmmercial uses when operatine under a total pressure (including the hydrostatic pressure in the towers) of from 90 tollO pounds per square inch. In other words I proper to use such pressure in addition to the normal hydrostatic pressure in the towers as will give a weight of carbon dioxid per unit vohune in the cou'ipressed gas which is substantially the same as the weight of carbon dioxid per unit volume now used in the most efficient practice. But I donot wish to limitmyself thus plac t. the exact pressures specified above as.

ploy a-gas mixture, relativelylean in carbon di'oxid such as normally contains approximately 20%24% of carbon dioxid,:md in order to facilitate the use of such gas mixture and insure the formation of sodium bicarbonate crystals of suitable size I place the gaseous mixture under a pressure substantially in excess of that necessary for,

overcoming the hydrostatic pressure in tin carbonatin towers. When the gases are under an er-normal pressure b fore being a'dmitteii to the ca'rbonating towers I pression utbefore their admission to the towers in order that the partial expansion of the gases in the carbonating towers will act most eiiiciently to cool the towers. It will, be understood in this'connection that the relatively large nitrogencontent of the gaseous'mixture which I propose to employ will be compressed equally with the carbon dioxid content and-that the nitrogen content of the mixture while chemically inactive in the ammonia-soda reaction will, by its expansion in the earbonating towers, partic1- pate in the cooling action.

i i izile the gases may be permitted to expandeoge'iewhat in the'car onating towers in order to efi'ect a cooling action counterbalancing to a certain extent the heat of reaction, I propose to maintain the carbonating towers under a considerable pressure in orde' to prevent a too rapid passage of the gas iherethrough with consequent loss by reason of incomplete contact with the am-' moniated brine, and prefer to passthe exit gas from the carbonating tower through a low pressure turbine to recover a portion of the power used in the initial compression of the gases. I

It has been the ractice heretofore to add the carbon dioxigiilobtained from thei calcination of the ium bicarbonate to the normal gas for the purpose of enriching the sameby increasing the percentage of carbon dioxid therein and this practice may be followed in carrying out the process described herein or I may employ a series of carbonating towers and pass the gases rich in carbon dioxid, obtained by calcining the bicarbonate, through a tower, containing prefer to cool the same after com-' freshly prepared ammoniatedbrine to fix a certain proportion of the ammonia in the form of ammonium carbonate and then pass the normal lean gas therethrough, thus preventing undue loss of gaseous ammonia which would be more freely taken up by the .large proportion of inert gas in the lean mixture.

The gas rich in carbon dioxid as obtained from calcining the sodium bicarbonate may I be passedthrough a carbonating tower which is not under pressure, thereby avoiding the v I additional cost of compressing this rich gas to pressures in excess of the normal hydrostatic pressure in the carbonating towers. The partially carbonated ammoniated brine may then be passed into a carbonating tower which is under pressure and the lean gas mixtpre passed therethrough under. a pressure in excess of the hydrostatic pressure in the tower as above described.

The gas remaining after the elimination of the carbon dioxid from the "mixture in ,the carbonating towers consists almost entirely offinitrogen and this process affords the most economical means devised up to this time for producing large quantities of pure nitrogen for nitrogen fixation purposes. This results by reason of the enormous quantities of air employed in the operation of the modern blast. furnace as well as from the relatively large proportion of nitrogen in the gases as they come from the, stoves atter the combustion of the carbon monoxid and hydrogen.

A large quantity of substantially pure ni' trogen is thus rendered available for use by any desired fixation gen compounds may e readily formed, and the cost of thenitrogen is made relatively low by reason of the fact that it is obtained from what are ordinarily waste products of. the iron works. The process also possesses.

the added advantage of producing sodium bicarbonate in large quantities and ate relatively low price as an incident to the elimis nation of carbon dioxid from the nitrogen.

Iri'- the drawings annexed hereto there is. shown a diagrammatic arrangement of one. form of apparatus which may be employed. in carrying out the .process although it is to be understood that various different arrangements of the elementsmay be employed, and certain modifications of the same me be used as will be apparent to those skilled in the art r a I Referring to the drawings 1 designates a supply pipe for conducting-the exit gases from the'blast furnace to-a' blower 2, it being understood that any desired arrangement of. dust; receptacles and scrubbers may.

be interposedbetween the blast furnace and rocess whereby nitromove before burning the gases. 3 designates an air pipe through which air may be forced into the stoves or gas engines 5 by means of a suitable blower (not shown) in sullicient quantity to furnish a supply of oxygen for combining with the carbon monoxid and hydrogen content of the gases to secure complete combustion of these gases. From the blower 2 the gases from the blast furnace are forced through a pipe at into the stores or heaters 5 where they are mixed with the air entering through the pipe 3 which provides the necessary oxygen for their combustion. The flow of air is preferably so regulated as to supply an amount of oxygen just sutficient to combine with the carbon monoxid and hydrogen to term carbon dioxid and water vapor respectively.

While the stoves'or heaters 5 are shown as embodied in a single structure it-is to be understood that there may be any desired number of such heat engines and that the .terms stoves, heaters etc. as a ilied thereto covers not only the usual direct burning gas heaters but also gas engines of any type which may be suitable and adapted for use in this connection.

From the stoves or gas burners 5 the gases pass through a pipe 6 to a scrubber 7 through which they may be passed for the purpose of cooling the gaseous mixture and removing any dust or other extraneous matter which may have been taken up in the gas burners. A gasometer 8 is shown as connected with the scrubber 7 by means of a connecting pipe 9 in orderthat a suitable supply of gases from the burner may be stored for use in the manufacture oi sodium bicarbonate-or for diverting the gaseous mixture from one to another ot a series of carbonating towers 10 as may be desired in operation.

It is to be understood that a series of gasometers S'may be employed instead of one only as shown in the drawings, the number being dependent upon the capacity as well as the volume of gases received from the gas burners and the number and capacity of the oarbonating towers employed. The carbonating towers 10 as Well as the gasometers 8 may be arrziinged in series as the rate of flow at the gases through the carbonating towers 'ill ordinarily be somewhat slower than the rate of flow of the gases through the gas burners. In the present instance there has been shown a single gasomcter 8 and a single curbonating tower 10 connected to the gasometer by a pipe 1 through a compressor 8', this showing of the arrangement of theparts by means of a single unit each being for the purpose of sin'1pli'l' \'ing the arrangement of parts in the drawings, but it is tobe understood that the invention com- .prehends the use of a plurality of gasome ing pipes as permit the drawing of the gases from any one or more of the gasometers and their delivery to any one or more of the carbonating towers either singly or in series as circumstances may require or conditions of operation render expedient. While the blower 2 is shown for forcing the gases into the gasometer 8 from whence they may to the carbonating tower 10 by reason. of the pre sure normally exerted thereupon by the gasometer cover it is to be understood that I may employ any suitable number of compressors 8 for forcing the gases from the gason'ieter 8 through the v carbonating tower 10 or for COIHPI'QSSlDg the gases to a suitable degree before their entry into the carbonating tower.

In this connection .it may be stated that in placing the gases from the gasometers 8 under compression in excess otv that required to overcome the hydrostatic pressure inthe carbonating towers Ipropose to install one or more Compressors 8 between the gasoline-- ters 8 and the carlnniating towers as well as suitable cooling coils or other similar devices for cooling the gases after compression and before admission into the carbonating towers. 1' also place -a suitable gas turbine 12' between each carbonating tower 10 which is being operated under pressure in excess of the normal hydrostatic pressure of the tower whereby the gas leaving the carbonating tower under pressure will escape through the turbine in passing from the carbonating tower 10 to the gasometer 13, thus making it possible to recover a portion of the power used in compressing the gas. (bile for purposes of illustration a single gasometer LEis shown as receiving the gases from the earbonating tower or towers through the pipe 12 it is to be understood that the invention comprcl'iends the use of a-plurality of gasometers for this purpose, especially as it may be desirable in practice to store gases from the carbonating towers for a longer or shorter period of time before utilizing the same in the fixation of nitrogen or for other purposes. When the gases (consisting principally of nitrogen) emerging from the carbonating tower or towers are used for the fixation of nitrogen either by the particular method shown herein or in any other suitable or desiredmanner it will probably he found desirable to employ a plurality of gason'ieters 13, each of which may advantageously be located in proximity to a single nitrogen fixation unit, or the several gasome tors 1:3 may be so interconnected with one or more nitrogen fixation units that the gases may be drawn from any one 0111'101'8 of said gasometers and fed to any one or more of the nitrogen fixation units. In conducting the gases irom the gasometer or gasometers 13 to the nitrogen fixation units it is regarded as desirable to mterpose one or more the fans or blowers employed being depend-- ent upon the number and capacity of the gasomcters as well as the number and ca pacity of the nitrogen fixationunits being operated and the arrangement otthe con-' nections for placing the units in communi cation with the gasometers. In the presentinstance a single blower115 is shown which is adapted to draw the gases from the gasometer 13 through the pipe 16 to the nitrogen fixation unit 17. The nitrogen fixation unit. illustrated diagrammatically herewith comprises a Bessemer converter, or modified Bessemer converter 18, provided with trunnions 19 mounted in bearings 20 carried by supporting standards 21. The pipe 16 con;-

municates through one of the trunnions 1'9 with the tuyeres in the base of the converter after a manner well-known'in theart whereby the-gases may be forced through the tuyercs to pass through the molten metal in the converter after the manner described in United States Patent No."

An air pipe 24 communicates through the other trunnion 19 with the tuycres' at the base of the converter in a similar manner and in the operation of the nitrogen fixation unit. shown it is proposed to first force a current of air from the pipe 2 1 through. a mass of molten metal in the converter 18 by means of a blower (not shown) until the silicon, content of the metal in the converter is substantially eliminated, and then discontinue the current of air through the pipe 24 andimmediately pass a current of the'nitrogen gas from the pipe 16 through the molten metal in the converter 18 to remove the can hon content of the molten metal and at the same time effect aunion of the carbon and nitrogen in the presence of the heated metal acting to promote the reaction and to form cyanogen compounds which may be recovered and conducted by suitable means-to a vreceptacle where they may be cooled and freed. from impurities or converted into other forms. lVhen necessary or desirable an alkali, alkali compound or other strongly l'wasic element may be introduced. into the molten metal contained in the-converter during the passage of nitrogen gas therethrough or previous to the introduction of the nitrogen, and the basic element may be introduced into the metal in any desired manner such as that described in the copending application mentionedabove. While the i'iitrogcn fixat on unit illustrated herewith has been tute for the nitrogen fixation unit herein doscribed anyother suitable form of nitrogen fixation apparatus employing any other suitable process or mode of operation, such, for example, as those described and claimed in U. S. patents to Bucher 1,091,425, 1,120,682 or 1,1743%. j t y While I have shown diagrammatically one arrangement of apparatus capable of being utilized in carrying out the present'inven tion it is to be understood that the form and arrangement of the apparatus illustrated herewith is shown solely for the purpose of illustration and that various modifications may be made therein both with respect tothe arrangement of the parts. as Well as in the form and method of connecting the elements Without departing from the intended scope of the present invention.

It is also to be understood that certain or all of the elements shown may be multiplied if desired and various details of refinement introduced-in the manner of connecting the parts as well as in the provision of suitable and adequate means forsecuring a proper flow of the gases therethrough while within the scope of the present invention and the claims ap-pended hereto.

From the above it will be understood that have provided a simple and readily operable method and means for obtaining large quantities of substantially pure nitrogen capable of use for the fixation of nitrogen in quantities adapted to make ossible large scale productioncf nitrogen xation products, such as has heretofore been impractical" by reason of the comparatively limited quantities of ,nitrogen ,which' have been made available lb processes previously used, as

well as this ligh cost of producing the same.

It will be seen moreoverthat my improved process comprehends the production, as an incident tothe purification of the nitrogen obtained, of large quantities of sodium bicarbonate at a cost substantiall below that at which the same can be pr need by the methods employed at the present time.

This apphcationis a continuation in part of my application Serial Number 653,739, filed July 25, 1923. 1

What I claim is 1 1. The process for obtainm sodium bicarbonate and nitrogen whic comprises,

burning waste blast furnace gases in air to convert the carbon monoxid and hydrogen content thereof to carbon dioxid and water with proportionate increase in the nitrogen content, compressing the gaseous mixture thus formed and passing it into contact with ammoniated brine while under a pressure considerably in excess of the hydrostatic pressure exerted by the ammoniated brine.

2. The process for treating waste blast furnace gases which comprises, burning the gases in. a quantity of air sufiicient to oxidize the combustible elements thereof thereby forming a gas mixture containing less than 30 per cent of carbon dioxid, washing the gaseous mixture thus l ormed to remove impurities therciroi'n, compressmg the gases and passing them into contact with aminoniatcd brine while under a pressure considerably in excess of the hydrostatic pressure exerted by the ammoniated brine to remove the carbon dioxid component of the gases with formation of sodium bicarbonate.

3. The process for treating waste blast furnace gases which comprises, burning the gases in a quantity of air sutticient to convert the carbon monoxide content thereof to carbon dioxid and form a mixture containing less than 30 per cent of carbon dioxid, washing the gaseous mixture thus formed to remove impurities therefrom, compressing the gaseous mixture, cooling the said gases atter compression and passing them into contact with ammoniated brine while under a pressure considerably in excess of the hydrostatic pressure exerted by the ammoniated brine to remove the carbon dioxid content oi the gases with formation of sodium bicarbonate.

4. The process of forming sodium bicarbonate and nitrogen which comprises, treating an ammoniated brine solution with a gaseous mixture of carbon dioxid and nitro gen which normally contains less than 30 per cent of carbon dioxid by first placing the gaseous mixture under a pressure considerably in excess of the hydrostatic pressure exerted by the ammoniated brine and passing it upwardly through the ammoniated brine while under such excess pressure to form sodium bicarbonate and separate the carbon dioxid from the nitrogen.

5. The process of obtaining sodium bicarbonate and nitrogen which comprises, treating an ammoniated brine solution with a gaseous mixture of carbon dioxid and nitrogen normally containing less than 30 per cent carbon dioxid by admitting the said gaseous mixture to the carbonating towers of an ammonia soda apparatus under a pressure considerably in excess of the hydrostatic pres sure exerted by the solution in the carbonating towers, whereby the carbon dioxid con tent of the gaseous mixture will substantially completely combine with the solution to form sodium bicarbonate while at the same time a portion of the exothermic heat of reaction will be counteracted by the expanding gaseous mixture.

6. The process of obtaining sodium bicar bonate and nitrogen which comprises, forming a gaseous mixture of carbon dioxid and nitrogen containing less than 30 per cent of carbon dioxid by volume, compressing said gaseous mixture, treating an ammoniated brine solution with said gascous'mixture by admitting said gaseous mixture to the carbonating towers of an ammonia-soda apparatus While under a pressure considerably in excess of the hydrostatic pressure exerted by the solution in the carbonating towers whereby the carbon dioxid content of the gaseous mixture will substantially completely combine with the solution to form sodium bicarbonate thus separating the carbon dioxid content of the gases from the nitrogen, and recovering the nitrogen gas from the carbonating towers.

7. The process of obtaining sodium bicarbonate and nitrogen which comprises, treating an ammoniated brine solution in carbon nating towers with a gaseous mixture of carbon dioxid and nitrogen which normally contains less than 30 per cent of carbon dioxid, by first placing the gaseous mixture under a pressure, in addition to the normal by" drostatic pressure in the carbonating towers, sufficient to give a weight of carbon dioxid per unit volume of the compressed gas substantially the equivalent of the weight of carbon dioxid per unit volume of carbon dioxid in gas normally containing approx- 'imately 40 per cent carbon dioxid, and passing the compressed gas upwardly through the ammoniated brine while under pressure to form sodium bicarbonate and separate the carbon dioxid from the nitrogen.

8. The process of obtaining sodium bicarbonate and nitrogen which comprises, treating an ammoniated brine solution in carbonating towers with a gaseous mixture of carbon dioxid and nitrogen which normally contains less than 30 per cent of carbon dioxid by forcing the gaseous mixture into the carbonating towers under a pressure of approximately double the hydrostatic pressure at the base of the towers to form sodium bicarbonate and separate the carbon dioxid from the nitrogen.

9. The process of obtaining sodium bicarbonate and nitrogen which comprises, first treating an ammoniated brine solution in carbonating towers with a gaseous mixture containing over of carbon dioxid, and then passing a gaseous mixture of carbon dioxid and nitrogen which normally contains less than 30 per cent of carbon dioxid through the carbonating towers and into contact with the ammoniated brine which has previously been treated with the gaseous mixture containing over 70 per cent of car bon dioxid under a pressure considerably in excess of the hydrostatic pressure in the can bonating towers to form sodium bicarbonate and separate the carbon dioxid from the nitroge 10. The process of obtaining sodium bicarbonate and nitrogen which comprises, treating an ammoniated brine solution in carbonating towers with a gaseous mixture of carbon dioxid and nitrogen, the said mixture containing less than 30% of carbon dioxid by volume, by forcing the gaseous mixnae ture into the carbonating towers under a pressure considerably in excess of the hydrostatic pressure at the base of the towers, and passing the said gaseous mixture through the 5 ammoniated brine while maintaining such pressure upon the carbonating towers as will insure the contacting of the carbon dioxid with the ammoniated brine while under a pressure considerably in excess of normal atmospheric pressure.

In testimony whereof I have affixed my signature.

EDWARD E ARNOLD.

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