US3449082A - Digestion cell and analyzing system containing same - Google Patents

Description

June 10, 1969 BAUMANN ETIAL 3,449,082

DIGESTION CELL AND ANALYZING SYSTEM CONTAINING SAME Filed Sept. 23, 1965 Sheet of 3 FIELl June 10,1969 A BA MAN E L 3,449,082

DIGESTION CELL AND ANALYZING SYSTEM CONTAINING SAME Filed Sept. 23, 1965 Sheet 2 of 3 June 10, 1969 BAUMANN ETAL 3,449,082

DIGESTION CELL AND ANALYZING SYSTEM CONTAINING SAME Sheet Filed Sept. 25, 1965 United States Patent 3,449,082 DIGESTION CELL AND ANALYZING SYSTEM CONTAINING SAME Arthur N. Baumann and Hugh H. Roberts, Lakeland, Fla., assignors to International Minerals & Chemical Corporation, a corporation of New York Filed Sept. 23, 1965, Ser. No. 489,708 Int. Cl. G01m 31/00; G01n 33/00 US. Cl. 23-253 Claims ABSTRACT OF THE DISCLOSURE A cylindrical cell for utilization in the digestion of solid materials by means of a solvent which comprises a plurality of solvent inlet orifices located intermediate the top and bottom of the cell and radially spaced apart from one another about the interior surface of the cell, arcuate bafile means positioned to downwardly direct liquid entering the interior of the cell through the inlet orifices, and liquid outlet means for removing digestion liquor from the cell at a level below the inlet orifices. The liquid outlet means includes a conduit having a portion thereof extending in an upward direction and being adapted to trap air therein during the filling of the cell with solvent. The digestion cell is useful in a system for determining the composition of solvent-digestible solid samples.

The present invention relates to an apparatus in which the digestion of solid materials efiiciently may be carried out, and more particularly to a digestion cell in which the digestion of solid materials by means of a solvent may be achieved for the purpose of determining the composition of the solid material. It will be understood that the terms digestion and solvent as employed herein are intended to refer to solubilization of solids by physical or chemical means and liquids which effect such solubilization, respectively. The invention further relates to a controlled system, including the digestion cell, and means adapted tomeasure the concentration of digestion liquor produced in the cell, for use in semi-continuous and continuous determinations of the composition of the starting solid material.

In commercial chemical processes employing solid reactant and the like streams, the economy of the overall system usually depends upon the movement of the solid streams and operation of equipment being as continuous as possible in order to utilize equipment capacity to the maximum. Often, in many of such operations the control of variables in the system depends vitally upon the actual composition of the solid raw material and intermediate and final product streams. In other areas of industry, such as mining, formulating, and the like, the particular composition of solid materials may be necessary to be known in order to determine whether such materials satisfactorily may be shipped and transported to customers, suppliers and the like to meet requisite minimum quality standards. Accordingly, devices which allow accurate, and also rapid, determination of the composition of solid materials are highly valuable and sought after commercial commodities.

Solid materials present initial problems in attempts to measure the composition thereof due to the fact that solids, unlike gases and liquids, are relatively nou-fiowable and diflicult to handle. Hence, composition measurement approaching a continuous level is extremely diflicult to attain. This difficulty is further aggravated by the fact that the actual composition, even for a particular batch of solid material, if it is not subjected to thorough mixing,

may vary greatly for different samples of the batch. Such factors, hence, have presented relatively serious difliculties in attempts to maintain, even semi-continuously, an accurate determination of moving solid streams, and particularly of solid materials, such as ores, which are complex mixtures having composition variations between different samples even when obtained from common natural sources.

Of the various techniques which have been suggested in the art for determining the composition of complex solid materials such as ores and the like, one method involves an initial digestion of a known quantity of a sample of the solid material by a solvent whereby it is more readily susceptible to handling and characterized by improved quality uniformity. While numerous embodiments of such techniques have been suggested, relatively few, however, have attained the desired continuity, efliciency, and accuracy of performance.

Accordingly, it is the primary object of the present invention to provide means advantageously adapted to be utilized in the eflicient and accurate determination of the composition of solid materials.

It is another object of the present invention to provide means adapted to provide a relatively continuous, efficient and economical determination of the composition of complex solid materials such as ores.

A further object of the present invention is to provide a digestion cell wherein samples of solid materials, the composition of which is desired to be determined, may be digested efiiciently.

It is a particular object of the present invention to provide a cell wherein samples of complex solid materials such as ores, and particularly phosphate rock, may be subjected to acid digesting to provide a resultant digestion liquid upon which measurements may be made which accurately reflect the actual composition of the starting solid material.

Another particular object of the present invention is to provide a system wherein the composition of different samples of complex solid materials such as phosphate rock accurately may be determined in a highly efficient and substantially continuous manner.

Broadly described, the present invention provides a cell for utilization in the digestion of solid materials which comprises a vertical, cylindrical housing closed at its bottom, means for introducing a Weighed amount of solids into said housing, means for introducing a metered amount of solvent into said housing, said solvent inlet means including a manifold extending around at least a portion of the periphery of the wall of said housing at a point intermediate the top and the bottom of said housing and communica-ting with the interior of said housing through a plurality of spaced orifices in said housing wall, which orifices extend through said housing Wall in a direction oblique to radii of said housing intersecting said orifices at the inner surface of said housing wall, arcuate baffle means positioned within said housing coaxial with said housing, said arcuate baffle means being positioned removed from and relative to said orifices to direct downwardly liquid entering said interior of said housing through said orifices, a plurality of spaced vertical bafile members within said housing, said vetrical bafile members being positioned adjacent said housing wall and intermediate the bottom of said housing and said orifices in said housing wall, means for agitating material in said housing, a first liquid outlet for removing samples of digestion liquor from said housing, and a second liquid outlet adapted to discharge by suction residual digestion liquor from said housing.

In the preferred embodiments of the digestion cell of the invention, the arcuate baflle means positioned within the cell housing is a cylindrical member which is coaxial with the housing wall and having its bottom edge extend slightly below the loci of the solvent inlet openings in the inner surface of the housing wall.

The invention will be more fully understood from the following description of the accompanying drawings of which:

FIGURE 1 is a schematic side view in section of an embodiment of a digestion cell of the present invention;

FIGURE 2 is a sectional view of the cell shown in FIG- URE 1 taken along line A-A';

FIGURE 3 is a schematic view partly in section of an example of a controlled measurement system of the present invention including a digestion cell; and

FIGURE 4 is a bar graph indicating a representative controlled sequence of operation of the elements of a typical measurement system of the present invention, exemplified by that shown in FIGURE 3.

With reference to the digestion cell shown in FIGURES 1 and 2, numeral 1 designates a vertical cylindrical housing closed at its bottom. The vertical walls of housing 1 are formed by a lower cylinder 3 and an upper cylinder 2 which is smaller in diameter and coaxial therewith. The lower end of cylinder 2 engages and is fixedly positioned within the upper extension of cylinder 3 to provide the housing with a wall inner surface free of horizontal projections whereby solid material introduced into the housing from above (as hereinafter described) falls to the housing bottom without encountering a surface on the housing wall inner surface upon which a portion of the solid material could collect and contribute utlimately to error in the desired measurement.

Housing 1 is closed at its top by a cover 4 which is operatively connected through a rod 31 fixedly attached thereto, to a means 30 adapted when actuated to cause cover 4 to move appropriately (back and forth horizontally) into positions wherein the top of housing 1 is opened to provide a solid material inlet to the housing and then closed, after a charge of solid is deposited in the housing. In the closed position as shown in FIGURE 1, cover 4 does not seat in an air-tight relationship with the top of housing 1.

Disposed above housing 1 is a means 35 for weighing solid material samples preliminary to their being charged to housing 1 for digestion. Solid weighing means 35 is adapted after accomplishing its desired weighing function and when appropriately actuated to deposit the weighed sample into solid inlet guide member 36 which extends downwardly to a position directly above the area of the top of the housing exposed when cover 4 is in an open position to provide the solid inlet.

Intermediate the top and bottom of housing 1 a recess 5 is provided in the outer surface of the housing wall. The recess extends circumferentially around the housing on the surface provided by cylinder 3 and in an area of the housing wall which is a region wherein cylinders 2 and 3 overlap. A ring member 6 is fixedly positioned around the periphery of the housing to cover recess 5 and thereby define with recess 5 an annular solvent inlet manifolds 7. A solvent feed inlet conduit 8 extends through ring member 6 and communicates with manifold 7. Manifold 7 communicates with the interior of housing 1 by means of a plurality of orifices defining solvent inlet nozzles radially spaced apart from one another about the periphery of lower cylinder 3. Orifices 10 extend from manifold 7 through. the housing wall in a horizontal or downwardly slanted direction which is oblique to radii of the housing which intersect said orifices at the interior surface of the housing wall. The radial spacing between orifices 10 preferably is uniform with from 2 to about 12 orifice openings being provided. As shown in FIGURE 2 each of the orifices 10 extends through the housing wall in a direction which allows solvent to be passed therethrough from manifold 7 and introduced into the housing in a stream which is essentially non-interfering with solvent introduced through another orifice nozzle in the series.

In the overlapping region of cylinders 2 and 3, the outer surface of cylinder 2 is recessed and cut away adjacent the inner surface of cylinder 3 to provide at the lower end of cylinder 2 an arcuate extension member 9 which is located opposite to the openings of orifices 10a The bottom edge of extension member 9 extends downwardly below the loci of the openings of orifices 10 into the interior of the housing whereby arcuate extension 9 defines a cylindrical bafiie means supported in and coaxial with housing 1 which directs downwardly solvent introduced into the housing by means of the inlet system provided by manifold 7 and orifices 10.

Positioned within housing 1 intermediate the bottom thereof and orifices 10, is a plurality of vertical bafile members 11. As shown in FIGURE 2, vertical baffie members 11 preferably refine planar surfaces and are positioned in a radially spaced relation from one another around the inner perimeter of the housing. The number of vertical bafile members preferably equals the number or orifices 10 with at least one baffie member being positioned between each pair of adjacent orifices and preferably more closely disposed to the orifice of such pair which directs solvent into the housing in a substantially tangential direction toward it.

A first digestion liquid outlet 12 is positioned adjacent the bottom of housing 1 communicating with the interior thereof. Outlet means 12 extends out of housing 1 in an upward direction and is adapted, such as being provided with a bend in the extension thereof, to trap air in the conduit provided thereby during the filling of the housing with liquid, as described hereinafter. A second digestion liquid outlet 13 from housing 1 is provided near the bottom of the housing and preferably removed from outlet 12 by an angular displacement of about 180. Outlet 13 is a conduit which extends downwardly into the interior of the housing and terminates closely adjacent the housing bottom whereby residual fluid may be removed from the housing by suction imposed by applying a vacuum through conduit 13. An impeller 14 for agitating liquid in the housing is located in the bottom of housing 1. Impeller 14 is adapted to be driven by a driving means 15.

With respect to the controlled over-all system shown in FIGURE 3, numerals appearing therein also employed in FIGURES 1 and 2 identify like elements. In FIGURE 3, numeral 16 designates a pump in solvent inlet conduit 8 for charging continuously to housing 1 a metered amount of solvent from a constant level reservoir (not shown). A vacuum pump 17 communicates with a waste digestion liquid reservoir 18 and via reservoir 18 and a valve 61 with outlet conduit 13 from the housing. A U-tube communicates at one leg 71 with liquid outlet conduit 12 from housing 1. A valve 62 is provided in conduit 12 to control the flow of digestion liquid from housing 1 to U-tube 70. U-tube 70' preferably is positioned at an elevation below housing 1 whereby digestion liquid flows from the housing to the U-tube by gravity. Leg 71 of the U-tube contains a body of filter material 73 which removes solid suspended material and the like from digestion liquid in U-tube 70. Leg 72 of U-tube 70- is provided with a liquid overflow outlet through which excess liquid may be withdrawn and removed to a waste reservoir (not shown).

A reservoir means 40 communicates with leg 71 of U-tube 70 via a conduit 74 containing a continuously operating pump 76. Reservoir 40 is provided with an overflow outlet conduit 43 which suitably may lead to a waste reservoir (not shown).

A probe conduit 52 of a digestion liquid sample analyzing means 50 such as a colormeter, spectrophotometer, and the like, is operatively connected to a probe positioning means 51. When appropriately actuated, probe positioning means 51 raises or lowers probe 52 into liquid present in reservoir 40.

A system control means 90 is operatively connected to each solid material weighing means 35, cover positioning means 30, impeller driving means 15, valve 61 in conduit 13, valve 62 in conduit 12, and probe positioning means 51.

In operation the system shown in FIGURE 3 cooperates as follows, the description being given with further reference to FIGURE 4:

As shown in FIGURE 4, solvent for the digestion of a solid material sample is continuously charged to housing 1 throughout a cycle of the systems operation. In the solvent addition, pump 16 continuously feeds a uniform supply of solvent into housing 1 via manifold 7 and orifices 10. Due to the relative directions and positioning of the orifices the solvent enters the housing in a plurality of non-interfering tangential streams and encounters the arcuate surafce of arcuate extension member 9 whereby the solvent is directed and bafiled downwardly in a smooth initially spiraling path toward the bottom of the housing, and splashing of solvent feed which is detrimental to the systems overall accuracy is essentially eliminated.

Preliminary to the initiation of the actual cycle (during a previous cycle) in which a given sample of solid material is digested and measured as to composition, the sample is accurately weighed by weighing means 35. At the start of the actual cycle, means 30. is actuated by control device 90 to open cover 4 of the housing. After a relatively short period of charging solvent to the housing, control element 90 actuates a release mechanism provided in weighing means 35 whereby the weighed solid sample is deposited through the open top of the housing. Control element 90 then again actuates cover positioning means 30 and cover 4 is returned to a closed position. By virtue of the overlapping design of cylinders 2 and 3 which define the walls of the housing and of the tangential directioning of orifices 10 into the protected annular area defined by arcuate baffle member 9, the solid sample deposited in the housing is bafiied and guided as it falls to the housing bottom so not to contact and interfere with solvent inlet streams and splashing further is avoided.

At the beginning of the cycle the housing is empty and valves 61 and 62 are closed. The continuous feeding of solvent to the housing causes the solvent to build up therein. The rising liquid level in the housing traps air in conduit 12 and causes an air bubble to form there.

The solid sample deposited in the housing is digested by the continuously introduced solvent with the resultant mixture initially being unagitated. When the level of liquid in the housing reaches a predetermined height, driving means for impeller 14 is actuated by control element 90 whereby agitation of the digestion mass in the housing is commenced. Vertical baflle members 11 aid in achieving eflicient mixing of the agitated solid and solvent and are effective in maintaining splashing of the agitated medium at a minimum. The vertical baflle members 11 further aid in eliminating splashing of solvent feed streams being introduced tangentially from above through orifices 10 since the solvent feed streams are guided downwardly by the planar verticalbaflles.

After a timed interval during which the weighed unknown solid sample has had an opportunity to become completely digested by solvent, valve 62 in liquid outlet conduit 12 is actuated and opened by control element 90 and digestion liquid passes, in this case by gravity, to U-tube 70 which functions as an initial digestion liquid retention reservoir. Due to the presence of the air bubble trapped in outlet conduit 12 during the housing filling phase, digestion liquor withdrawn from the housing is essentially precluded from directly mixing at an interface with liquor present in U-tube 70 from the previous cycle. The air bubble also aids the fresh liquor sample to flush the prior cycle liquor from the system, the predomi nant proportion of the flushed liquid passing out through overflow conduit 75.

After removal of a suflicient amount of the digestion liquor from the housing to complete the flushing out of U-tube 70, valve 62 is closed by control element which simultaneously actuates valve 61 in liquid outlet line 13 to open it and allow the remainder of the digestion liquor in the housing to be evacuated and passed to reservoir 18 under the suction provided by vacuum means 17. During the later stages of the evacuation of the excess digestion liquor from the housing, driving means 15 of impeller 14 is inactivated by control element 90-. The continuous introduction of fresh solvent into the housing aids in the flushing out of residual digestion liquid.

At the termination of the evacuation of the housing, the portion of the measurement operation involving the digestion cell proper is repeated beginning with the opening of cover 4 and the addition to the housing of an additional solid sample which has been weighed during the preceding cycle.

The digestion liquor sample passed to U-tube 70 is treated therein by filter medium 73 to remove suspended solids, Liquor is continuously withdrawn from U-tube 70 and passed by pump 76 via conduit 74 to degassifying reservoir 40. The overflow outlet leg 43 in reservoir 40 allows the maintenance of a constant level of liquid in reservoir 40'. The continuous pumping of liquid through conduit 74 and reservoir 40 has the result that this portion of the system is continuously flushed out and mixing of liquor samples from succeeding cycles is essentially precluded.

The end of conduit 74 at reservoir 40 extends upwardly into reservoir 40 to a height above the level therein at which overflow conduit 43 is positioned so that digestion liquid charged to reservoir 40' via conduit 74 opened to the atmosphere and is degassified, i.e., freed of gas bubbles, as it enters. At several timed intervals throughout the cycle, analysis probe element 52 is lowered into and raised out of degassifying reservoir 40 by the actuation of probe positioning means 51 by control element 90. Probe 52 thereby obtains several digestion liquid sample increments which are passed to analyzer 50 during each cycle. The movement of probe element 52 is controlled by positioning element 51 such that it is lowered rapidly into reservoir 40 to pick up a liquid sample increment and then raised slowly out of the constant level of liquid whereby loss of liquid sample through erratic motion is minimized. In analyzer 50 the sample increments are subjected to composition analysis by any suitable technique, usually involving comparison with a standard solution, by colorimetry, spectrophotometry, and the like.

By means of the design of the digestion cell of the invention and the controlled measurement system in which it is utilized as described above, composition determinations on unknown solid samples efiiciently and accurately may be carried out in even an essentially continuous manner. For example, the controlled measurement system described above was utilized to measure the composition of unknown samples of standard phosphate rock. Hydrochloric acid was used as the digestion solvent, and the control system was set to three minute cycles for each sample weighing with duplicate readings by the analyzer, a commercial colorimeter, being made in each cycle, It was determined in the runs that the phosphate rock was 74.4% BPL. Standard laboratory analysis revealed the rock samples to be 74.5% BPL. The accuracy obtained expressed as the standard deviation for each reading was sigma :0-.47. The distribution of this sigma value between the various unit operations of the system was digestion and weighing $0.15 BPL, colorimetric analysis i0.23% BPL, and instrument variations :0.09% BPL.

Other variations and modifications of the digestion cell and measurement system disclosed hereinabove which do not deviate from the spirit and scope of the invention will be apparent to those skilled in the art. It is to be '7 understood that it is intended that the invention be limited only by the scope of the appended claims.

We claim:

1. A cell for utilization in the digestion of solid materials, which comprises a vertical, cylindrical housing closed at its bottom, means for introducing solids into said housing, solvent inlet means for introducing a solvent into said housing, said solvent inlet means including a plurality of solvent inlet orifices located intermediate the top and bottom of said housing and radially spaced apart from one another about the interior surface of said housing, arcuate baffle means positioned within said housing coaxially with said housing, said arcuate bafile means being positioned removed from and relative to said orifices to downwardly direct liquid entering said housing through said orifices, means for agitating material in said housing, and liquid outlet means for removing digestion liquor from said housing at a level below said orifices.

2. The cell according to claim 1 including a plurality of spaced vertical baffle members positioned within said housing adjacent said housing wall and intermediate the bottom of said housing and said orifices.

3. The cell according to claim 1 wherein said orifices are positioned so as to introduce solvent into said housing in streams that are oblique to radii of said housing intersecting the respective orifices at the interior surface of said housing.

4 The cell according to claim 3 wherein said arcuate bafiie means is a cylindrical member coaxial with said housing and having the bottom edge thereof terminating at a point below and adjacent the loci of said orifices.

5. The cell according to claim 4 wherein the walls of said housing are defined by two coaxial cylinders of different diameters in overlapping engagement at their ends with the smaller diameter cylinder defining the upper portion of the housing wall, and the lower end of said smaller diameter cylinder is recessed from the inner surface of the upper end of the larger diameter cylinder to define, by the cylindrically shaped extension provided thereby, said arcuate baffle means.

6. The cell according to claim 5 wherein about 2 to 12 of said orifices are uniformly spaced apart in said housing wall and are adapted to introduce solvent into said housing in essentiall non-interfering streams.

7. The cell according to claim 6 wherein said solvent inlet means includes a manifold extending around at least a portion of the periphery of said housing and communicating with the interior of said housing through said orifices.

8. The cell according to claim 1 wherein said liquid outlet means includes a conduit having an upwardly directed portion adapted to trap air therein during the filling of said housing with solvent.

9. The cell according to claim 8 wherein about 2 to 12 of said orifices are uniformly spaced apart in said housing wall and are adapted to introduce solvent into said housing in essentially non-interfering streams that are oblique to radii of said housing intersecting the respective orifices at the interior surface of said housing; the walls of said housing are defined by two coaxial cylinders of different diameters in overlapping engagement at their ends with the smaller diameter cylinder defining the upper portion of the housing wall, the lower end of said smaller diameter cylinder being recessed from the inner surface of the upper end of the larger diameter cylinder to define, by the cylindrically-shaped extension provided thereby, said arcuate baffle means; said arcuate baffie means has the bottom edge thereof terminating at a point below and adjacent the loci of said orifices; a plurality of spaced vertical baffle members are positioned within said housing adjacent said housing wall and intermediate the bottom of said housing and said orifices; and said liquid outlet means comprises a first liquid outlet means including said conduit for removing samples of digestion liquor from said housing and a second liquid outlet means for removing residual digestion liquor from said housing.

10. A system for measuring the composition of a plurality of solvent-digestible solid samples by a technique wherein each of said solid samples is measured in a separate cycle of said systems operation, which comprises the cell, first liquid outlet means, and conduit according to claim 8, said first liquid outlet means and conduit being for withdrawing samples of digestion liquor from said housing in each cycle of said systems operation, and a second liquid outlet means for removing residual digestion liquor from said housing at the end of each cycle of said systems operation; means for weighing each solid sample for introduction into said housing; means for delivering a metered continuous stream of solvent to said solvent inlet means; means for analyzing digestion liquor samples; and means communicating with said conduit for delivering digestion liquor samples to said analyzing means, whereby the air trapped in the upwardly directed portion of said conduit during the filling of said housing with solvent serves to maintain each digestion liquor sample essentially unmixed with digestion liquor samples withdrawn from said housing and analyzed in another cycle of said systems operation.

11. The system according to claim 10 wherein about 2 to 12 of said orifices are uniformly spaced apart in said housing wall and are adapted to introduce solvent into said housing in essentially non-interfering streams that are oblique to radii of said housing intersecting the re spective orifices at the interior surface of said housing; the walls of said housing are defined by two coaxial cylinders of different diameters in overlapping engagement at their ends with the smaller diameter cylinder defining the upper portion of the housing wall, the lower end of said smaller diameter cylinder being recessed from the inner surface of the upper end of the larger diameter cylinder to define, by the cylindrically-shaped extension provided thereby, said arcuate bafile means; said arcuate baffle means has the bottom edge thereof terminating at a point below and adjacent the loci of said orifices; and a plurality of spaced vertical bafile members are positioned within said housing adjacent said housing wall and intermediate the bottom of said housing and said orifices.

12. The system according to claim 10 wherein said digestion liquor sample delivering means includes a digestion liquor sample reservoir for supplying increments of digestion liquor samples to said analyzing means, said reservoir being adapted to be flushed by each digestion liquor sample so that said reservoir is flushed substantially free of digestion liquor initially present therein.

13. The system according to claim 12 including control element means operatively connected in said system to coordinate in a timed sequence the introduction of solid samples into said cell holding, the withdrawal of digestion liquor samples from said cell housing, the evacuation residual digestion liquor from said cell housing, and the analysis by said analyzing means of increments of withdrawn digestion liquor samples.

14. The sysetm according to claim 13 wherein said digestion liquor sample delivering means includes means to degassify digestion liquor samples preliminary to their being analyzed by said analyzing means.

15. The system according to claim 14 wherein about 2 to 12 of said orifices are uniformly spaced apart in said housing wall and are adapted to introduce solvent into said housing in essentially non-interfering streams that are oblique to radii of said housing intersecting the respective orifices at the interior surfaces of said housing; the walls of said housing are defined by two coaxial cylinders of different diameters in overlapping engagement at their ends with the smaller diameter cylinder defining the upper portion of the housing wall, the lower end of said smaller diameter cylinder being recessed from the inner surface of the upper end of the larger diameter cylinder to define, by the cylindrically-shaped extension provided thereby, said arcuate baffie means; said arcuate baflie means has the bottom edge thereof terminating at a point below and adjacent the loci of said orifices; and a plurality of spaced vertical bafi le members are positioned within said housing adjacent said housing wall and intermediate the bottom of said housing and said orifices.

References Cited UNITED STATES PATENTS 5/1953 Carr 23-271 9/1960 Claudy 23253 3/1966 Ferrari 23-230 5 MORRIS O. WOLK, Primary Examiner.

ELLIOTT A. KATZ, Assistant Examiner.

U.S. C1. X.R.

" UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 1M9, 082 Dated June l0, 1969 Inventoflg) Arthur N. Baumann and Hugh H. Roberts It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

T Column 4, line l8,"re1ine" should be define Column 5, line 17, "surafce" should be surface Column 8, line E L, "holding" should be housing Column 8, line 56, after "tion" and before "residual" of should be inserted; Column 8, line 59, "sysetm" should be system SIGNED AND 8 EM. E D MAR 1 7 1970 Anew Edward M. Fletcher, In Attesting Officer gfii s ifibei m nfi

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