Treating Cotton with Volatile
and Toxic Chemicals LUCIEN H. GREATHOUSE, CHESTER H. HAYDEL,
AND
HERMANN J. JANSSEN
Southern Regional Research Laboratory, New Orleans, La.
INCRESSINC: to
research attention has been directed in recent years to chemical modifications to impart improved or new properties cotton and a t the same time retain essential physical properties of the native fiber when spun and woven into fabrics. Thus many modifications and treatments have been studied to improve resistance to rotting, heat, and weathering and to improve laundering and dyeing characteristics. M.any of the treatments require the use and handling of chemically active agents such as acetic anhydride in glacial acetic acid with which perchloric acid is used as a catalyst for partial acetylation (Z), monoethylamine for decrystallization ( 4 ) , and acrylonitrile for addition of cyanoethyl group ( 3 ) . Many of the chemicals that are or may be used form explosive mixtures with air. They are toxic or a t least severely irritating to the eyes, nose, and throat. Some are skin vesicants. A pilot plant has been designed, built, and tested for treating cotton fiber, yarn, and fabric with volatile and toxic reagents in sufficient quantities for product evaluation and to provide an indication of the feasibility of the treating process for industrial use. To date the pilot plant has been used successfully for treating cotton with ethylamine and acrylonitrile. Versatility and ease of control are service requirements of desirable unit
.
'
The elements that determined the design of the new unit were the operating conditions t h a t must be controlled within ranges predetermined b y laboratory experiments and adverse conditions that must be avoided. It is desirable to handle as many reagents as possible in a single unit and to meet the requirements of widely varying conditions for application of the reagents selected. Reaction temperatures must be held constant or controlled within a predetermined range. Provisions to heat with steam or cool with brine permit control of temperature in the range -20" to 175' C. A versatile unit should provide for operations a t increased pressures and should be constructed of materials that are not corroded by the reagents used and will not contaminate the reagents The capacity of the unit should be adequate to provide sufficient uniformly treated product for evaluation and tests of the processes being investigated. Reactor i s suitable for treating fiber, yarn, and fabric under controlled pressure, temperature, and reagent flow
,
The pilot plant, initially developed for decrystallixing cotton with ethylamine, a volatile (boiling point 16.5" C.), flammable reagent, was assembled of elements made of carbon steel. These elements are indicated in the flow sheet (Figure 1). The plant consists essentially of systems for the storage and recovery of the reagents and of a reactor unit in which cotton fiber, yarn, and fabric can be treated under controlled conditions, including temperature, pressure, and time The reactor is of special design.
February 1955
Reactor Unit. The reactor unit (Figures 2, 3, and 4 ) provides for symmetrical loading of cotton material around a perforated central tube. Since the reagent fills the chamber there is a uniform static pressure through the cotton. The central tube is: pierced by 204 holes of a/,z-inch diameter in six vertical roiis staggered to give uniform distribution. It has an inside diameter of 1.875 inches, a cross-section area of 2.76 square inches, compared to a total cross-section area of 1.44 square inches of the holes pierced in it. This relation, together with high friction head loss through the small holes, reduces any variation in t h e pressure differential acroas the cotton layer due to friction head in the ccntral tube. The ends of this tube are designed to ensure tight sealing as well as convenient handling The lower end is locked in place by two small projecting pins which fit into grooves in the lower flange of the unit and pull the tube tightly against a lead washer under its lower end. At the upper end of the tube two similar prongs fit into notched slots in an upper cap which is welded t o the thermometer well extending to the outside of the unit through a packing gland. By means of this device it is possible to turn the inner tube in one direction to lock the bottom joint, or in the opposite direction to open it. By engaging the pins a t the top of the central tube in the notches in the cap, the bundle may be lifted slightly by a handle on the thermometer well. This permits draining the unit without opening the head and avoids either exposure of the cotton to air or escape of vapor to become a hazard. The reagent remaining on the cotton after draining can be removed either by evaporation under vacuum or by leaching with an inert solvent. The central tube is sealed a t its top by another lead washer within the upper cap, which is pushed down through the upper head and held in place by tightening the stuffing box. Any cotton material being treated is placed so that it covers all of the holes. Raw stock is held in place with glass fiber cloth, as shown in Figure 2. The exposed top and bottom form their own seals. When fabric is treated, both ends beyond the hole are tied with string. No tests with solid loading of yarn have been conducted, but yarn also can be arranged to form its own seals a t top and bottom. A liquid distributor is mounted a t the top of the unit (Figure 2) It has a vertical rim around its edge serrated with a uniform line of V-shaped notches. There are two rows of small holes just within this rim, located to open outside the cotton under treatment. This distributor facilitates soaking the cotton evenly, either a t the start of the treatment or with an inert solvent to remove the residual reagent by washing under suction. The distributor is loose enough on the central tube so that i t can be pushed down by the upper cap and sealed against the cotton. To provide further assurance of uniformity of applicatjon, provision was made for changing the direction of reagent flow-& feature usually found in package dyeing machines. In the original design the flow change was effected by means of the two
INDUSTRIAL AND ENGINEERING CHEMISTRY
187
ENGINEERING, DESIGN, A N D PROCESS DEVELOPMENT
BRINE
SURGE
1;
~
~
~
A
X
7 HEXANE ETHYLAMiNE
kiid I
L
'I/ ?
1
COLUMN STILL DJAIN +__ ..
VENT BRINE - VACUUM STEAM NITROGEN
__
5
4
PRESSURE GAGE THERMOMETER VALVE
a
-
._.... -..
_i
-
_.
The reactor has an inside diameter of 10 inches and a depth of about 45 inches, Thus, it can receive a quantity of material, as shown wrapped around the central tube (Figure 21, 8 inches iri diameter and 40 inches long. This leaves an annular space 1 inch wide around the bundle for free passage of the reactant. As the central tube is 2 inches in diameter, the material in the charge would have a volume of marc than 1 cubic foot, sufficient to hold up to 10 pounds of lint, more than 50 square yards of any medium weight fabric, or 25 pounds of yarn, each rnoderatelv closely packed. Half of these ttmountu of fahric,s and yarns will suffice for laboratory twt:;, iirc.liitlirig n.cvkthcririg, fo:, product, and procesa evaluation.
Controls. The unit provides for controlled variation of temperature, pressure. and flow of the reagent over wide ranges. The temperat,ures specified for treatments have ranged from 4' to about 60" C., t,hough removal of residual agent has required heating t o 100" C. Facilities connected to the unit include a %ton refrigerating machine capable of cooling brine to -20" C. and steam a t 150 pounds per squnrc inch &ge, corrcsponding to a temperature of 175' C Pi-essures can range hom about 28 inches of vacuum produced by a steam ejector to hundreda of pounds from c>lindernitrogen. The reactor and piping could withstand 200 pounds per bquaie inch gagc Vacuum ha6 bren enip1o)ed before treatment t o remove air and after the tieatmcnt to remove the agent The practical limits a t present of the use of these facilitieb are leakage into the system under vacuum or ePcal)r of nouious vapors of the agents under pressure Accurate control of i u t c of f l l o a 0 1 the speed \\itti which the reagent 19 applied to ttir cotton m?tcttii-il h a s h r r n wincwhat dif-
I;
NITROGEN
&--
VACUUM
r
THERMOMETER
LIQUID DISTRIBUTOR F E L T GASKET
DR%I N
Figure 1.
Flow sheet of pilot plant
reversing values shown in the diagram. Because the cmtiifugal pump became vapor bound with ethylamine, a positive displace ment pump was added to by-pass the centrifugal This geai pump is driven by a three-phase exploPionproof motor controlled with a reversing switch. The two pumps have been operated satisfactorily together to give high flow rates with the less volatile acrylonitrile. In applications of either ethylamine or ac1 ylonitrile the reactor has been filled a t the start of a treatment by evacuating it and then allowing the reagent to be drawn in This was specified for the ethylamine treatment to exclude air, but was used as a convenient filling procedure for either reagent. No accurate estimate has been obtained of the effect of this technique, but it is presumed to have been a factor in the iniproveinent of uniformity of product. Stainless steel was used in making the central tube, distributor plate, thermometer well, and packing gland in the reactor head to avoid sticking by rust in the joints which were to he opened and closed. A secondary consideration was the possibility that rusted parts in contact with the cotton might discolor it. Capacity. The unit was designed to treat lint cotton, yarn, or fabric. The controlling factor in determining size was the capacity for lint. A small scale test of carding, spinning, and weaving into a light fabrii requires a t least 5 pounds of lint.
188
THERMOCOUPLES
C O T T O N CLOTH GLASS C L O T H F E L T GASKET
FLOW DIRECTION
-----*
INTO T O P OF T A N K I N TO B O T T O M OF TANK-
Figure 2.
-*
LATING PUMP
Diagram of reactor unit
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 47, No. 2
PILOT PLANT sive tests were conducted to select materials that would resist such attack by ethylamine, acrylonitrile, and acetylation solution. The acetylation solution coiitained 25% acetic anhydride, 75% glacial acetic acid, and 0.1% of 60% perchloric acid by volume. The results of these corrosion tests are given in Tablc I. The hexane used to remove ethylamine in the decrystallization process exhibited only its known capacity t o swell and soften rubber materials and t o shrink and harden one type of plastic tube. As these tests were made primarily to guide the selection of materials for pilot plant units, certain special needs were considered, such as joint seals which could be readily opened and replaced for changes in the equipment and flexible tubing for the transfer of reagents from drums or other containers. Cost was considered in selection of materials for test because of its importance to any future commercial installation. qvery type of iron pipe thread cement available was tried to find one that would stand up against ethylamine. A few were abandoned without extensive tests. Lead and silver solders were rejected because of fire hazard during their application. Mineral cements, although resistant, were rejected because they formed hard permanent joints, which would hinder ready change in equipment. Plated coatings on ~ t e c began l to deteriorate within 24 hours in acetylating solutions, as reported in Table TI. Sprayed or clad metal coatings were not tested. No coating was found for carbon steel which would resist all three reagents.
.
Figure
3. Reactor with head opened
ficult becausie of varations in the resistance of the cotton layer wrapped around the central core. Pressure gages immediately before and after the reactor indicate ressure differential. A flowmeter indicates the rate of circuf)ation. The centrifugal pump operates a t a b e d speed while the gear pump is driven through a belt shifting device that permits speed variation in a ratio of 3.75 to 1. The delivery of the centrifugal pum can be regulated by the gate valve located in the discharge line $om 0 to about 10 gallons per minute against 5 pounds per s uare inch differential. The delivery of the gear pump, whicl is little affected by the resistance of the cotton layer, is rated a t 10.3 gallons per minute a t 1725 r.p.m. and can be shifted from about 4 gallons per minute at 700 r.p.m. to 15 gallons per minute a t 2600 r.p.m. This arrangement permits a theoretical flow variation from 4 to 25 gallons per minute. If the cotton material is wrap ed on the core with an outside diameter of 6 inches, the lengtg along the core being 36 inches, total external area is 680 square inches. These data indicate a range of linear flow throu h this layer from 1.4 to 8.3 inches per minute measured at tBe outer surface. The flow a t the inner surface immediately outsi,de the Pinch core would be three times this or about 2 feet per m n ute at maximum. Flow rates are important when the temperature of reaction is critical in obtaining a uniform product, such as in cyanoethylation. The flow sheet (Figure 1) indicates that the pilot plant. is limited to batch experimental runs of a few hours duration m t h manual control accomplished by reading indicating instruments. Thermocouples may be installed, as shown in Figure 2, for automatic controlling and recording the temperature of the cotton being treated. Maintenance. The rust which forms on the carbon steel between experimental runs may be removed by filling the system with 3% citric acid solution and allowing it to stand for 24 hours. This solution was found to be as effective as either ammonium citrate or sodium hydrosulfite, and more easily washed out with water. The citric acid solution should not be heated since it attacks the Weldwood cement used to seal the threaded joints. Extensive corrosion-resistance tests guide selection of gasket materials and sealing compounds
Although the system had been rigorously tested and made tight against pressures t o 40 pounds per square inch gage and vacuum to 28 inches, during the first experiment with ethylamine leaks developed from failure of conventional gasket materials and pipe thread cements. To overcome this and t o avoid corrosion of the exposed inner surfaces of the unit by any reagents, extenFebruary 1955
Figure
4.
Installed reactor
Test Methods. The tests allowed 6 days of exposure, which was sufficient for pilot plant experiments in general. These tests would afford only preliminary data for design of commercial installations. The tests on metals, bare or with coatings. were made on strips with 20 square cm. of exposure area. Tests of other materials were made on pieces of this same area, except that the test area of flexible tubes and other soft materials was only approximate. Separate tests at 10' C. were conducted with ethylamine to
-
INDUSTRIAL AND ENGINEERING CHEMISTRY
189
ENGINEERING. DESIGN. AND PROCESS DEVELOPMENT Table I.
Evaluation of Materials Ethylamine
144 hr. a t
5 O
C.
__.
144 br. a t -loo C. Wt. loss
W t . loss,
%
24 hr. a t 6’ C.
%
Color change of liquid
STRUCTURAL MATERIAL8
Lead Carbon steel Stainless 304 Tin metal Rubber, buna N Cellulose acetate sheet Phenolic fiber sheet
No change Corrodes slowly No change
No change Continues corroding No change
No change SwelLs Dissolves No visible change
No change
Hard rubber Gum rubber Red rubber Black rubber Plastic tube A Plastic tube B
Softens a n d weakens Swells slightlyc Swells Swells Swollen and yellow Black and brittle
Swells Swells Swells Swells
No visible change No visible change No visible change Swells and weakens Softens No change No visible change
No visible change No visible change Hardens slightly Swells twice size
Aluminum
Brass
......... .........
0.0 0.7 0.0
...
.......... ..........
0.0
No change
0.0
None Green None
... .. .. ..
None Brown None Light brown
0.05
Light brown Light yellow Yellow Light yellow None Brown
........
...
........ ........
, . .
........
........
0 0
..........
..........
Swells-attacks
No change
........
...
resin
........
0.72
PIPIXQ A X D TURIXG and softens f 2 3 . boa slightlyc 3.88 2.95 twice size twice size0 +0,07a
Softens slightly
........ ........ ........
...
... ... ...
.. .. ..
... ...
Brown and hard Black and brittle
33:20 10.90
17.82 4,90
No visible change No visible change
18.20 2.80
........ ........ ........
...
.........
..........
.....
.....
GASKETMATERIALS
Smooth-on No. 5 d Shellac Animal glue Weldwood glued Sauereisend Silicone grease Carnauba wax Litharge and gl cero1 Neoprene latex2 Ucilon paintd Weldit cement! Industrial baking ename Gain in weight. b 168 hours. o Returns to original dimension
No change Dissolves Softens No visible change No visible change Dissolves Softens Softens SoftensC Lifted from meta Dissolves Dissolvese
..........
8.20
...
.......... ..........
... ...
..........
, . .
No visible change No visible change
Crumbles
.......... .......... ..........
Swells and softens0
..........
4.8 0.78
... . . I
5.50
... ... , . .
........
.......
........ ........
...
...
...
...
...
... ...
No visible change
7.2
.. , .. , , , ........ ........
...
Softens0 No visible change Dissolves
5.5 0.2
........
. ., , , . . ,
... ... ... ... ...
Brown Light brown Yellois Dark brown Dark brown None Dark brown None Rrown Light-brown None None None Light brown Dark gra h’one Light yeiron None White
when removed from solvent and dried.
Results. Metallic tin was unaffected by ethylamine or acrylonitrile, but was corroded rapidly in acetylating solution with separation of long needlelike crystals, which deliquesced rapidly in moist air. The reaction did not occur in the absence of perchloric acid. Red rubber tubing compounded with about 33% of mineral
Resistance of Protective Coatings to Acetylating Solutions Exposure: 24 hours Acetylating solution Glacial acetic acid Acetic anhydride 60% Perchloric acid
VOl. 7%
75 24.9 0.1
Protective Coatings Lorn carbon steel (control) Stainless steel 304 (control) Steel, chromium plated Steel, silver plated Tygon, Series K P-5 Plicoat Lacquer primer Acid resisting marine paint Bitumastic Rust-o-leum Asphalt primer. Neolac protective coating Pliobond 20 Paraffin Rosin and beeswax Carnahua wax Ucllon 1501 a Differenoe in total weight (coating plus metal). b Gain in weight. c Slight discoloration.
190
........
No visible change 0.14 No visible change 5.40 SEALINQ Couporxos AND PROTECTIYE COATINQS No visible change 0.10
determine whether any advantage would be gained by maintaining storage units a t low temperature.
Table II.
35 30
Weight Loss, %, at 25’ C. 4.69 0.00
0.30Q 0.13a 1.46 1.96 5.01 3.97 2.67 1.86 0.10b,C
1.66 2.83 0.44 0.056, C
0.21 O.lZQ.b
filler and “purer” black rubber tubing suffered badly in acetylating solution. Where it has proved to be sufficiently flexible, aluminum has been used for temporary connections with ethylamine and acrylonitrile. Among gasket materials, Teflon was unaffected by either reagent. However, it is too hard and adheres too poorly to metals to give a good seal. A more resilient gasket with neoprene filler in a Teflon envelope is available. However, lead mill serve in most instances. Asbestos gaskets colored the liquors, although this effect mi ht correct itself in time. Of the pipe threacf cements, Weldwood glue served satisfactorily for both ethylamine and acrylonitrile in the new unit. In tests with acetylating solutione, the effect was even lese. Though it lost 5 to 7% in weight in each reagent, there was no other evidence of change, and no discoloration of the cotton. A mixture of soap and powdered graphite was used to lubricate three-way iron cocks. The results of a series of tests on corrosionresistant nickel alloys in block form with acetylating Eolutions are given in Table 111. Safety precautions include checks of system and stand-by vent lines
Besides the hazards that are normally encountered in the use of volatile, toxic, and flammable agents, there are a few specific to the particular chemical being used. The sealed system was checked continually to guard against dangerous accumulation of vapors in the air. Although ethylamine is detectable by smell below toxic or flammable limits, the exact point of leaks was found by the fog formed with sulfur dioxide. The system, including connecting piping, was tightened until there was less than 0.5 inch loss in 5 minutes from 28 inrhes of vacuum or 1 pound drop in pressure in the same period a t 40 pounds per square inch gage. With good room ventilation this limit ensured safe operation. Gas masks with commercially available canisters to protect against the vapor from the reagent mere kept a t hand. For
INDUSTRIAL A N D ENGINEERING CHEMISTRY
Vol. 47, No. 2
PILOT PLANT
Table 1. Acetylating Solution 144 hr. at 26’ C. Wt. loss,
%
24 hr. a t 25O C. No visible change Corrodes rapidly Corrodes slowly Corrodes rapidly No visible change No visible change No visible change Diasolves No visible change
0.13 5.69 7.99 5.93 0.07 16.64
No visible change Rough and pitted Continues to corrode Rough and pitted No visible change Turns black
.......... ..........
... ... 0.26
No visible change
Evaluation of Materials (Concluded) Color change of liquid
Acrylonitrile 144 hr. at 25‘ C. Wt. loss,
%
24 hr. a t 25’ C.
STRUCTURAL MATERIALS None No change Blue No change None ........ Dark red ........ Light red Clear (See text) No change Dark brown Discolors liquid Softens Light y d l o w NO visible change
........
No change No change
........ ........ ........
0.0 0.0
... ... ...
No change
0.0
Dissolves No visible change
...
........
...
0.84
Color change of Unuid None None
..... .....
..*
None Dark brown None None
PIPINQ AND TUBINQ No visible change Blisters Swells slightly No visible change Hard and brown No visible change
No visible change Turns dark brown Swells No visible change Hard and brown No visible change
0.I9 ++ 14.37a 1.58“ f10.65“
No visible No visible No visible Swells No visible No visible No visible
No visible change No visible change No visible ohange Swells Hardens when dry No visible ahange No visible change
3 56 6.98 f 3.17“ +14. 50n 11.10 0.13 0 75
change change change change change change
........
26.1 0.07
..........
..........
Dissolves .......... Becomes soft N o visible change No visible change No visible change No change .......... Dissolves slowly No visible change Discolors liquid .......... Dissolves Turns green No visible change No visible change No visible change Turns brown No visible change Lifts from metal d Use of trade names in reporting these tests is not of other manufacturem. e 30 minutes.
Light yellow Dark brown Brown Dark brown Dark brown None
GASKET~‘IATERIALS Brown No visible change Dark orange No visible change Dark brown No visible change Dark brown No visible change Brown No visible change None No chan e Yellow No visibk change
.....
.*. ...
Ni 54
Bo 69 85
Light Y h o w No visible change Light orange No change None No visible change None No visible change to be interpreted as an endorsement by the Dept.
ii:37 0.14 0.70
..
Resistance of Nickel Alloys to Acetylating Solution Exposure: Block samples submerged for 24 hours Acetylating solution compn.: ae in Table I1 Alloy Composition, 7% Av. Depth of Corrosion, Mo lie Cr Si Cu W Mm. 23 23 .. .. .. 0.0012 33 7 .. .. .. .. 0.0007 . 7 18 6 0.0001 ‘. . 11 4 .. 0.0006
..
.
February 1955
..
..
..
..
........
Light b r o a n None Light yollow
Softens slightly b No visible change No visible change No visible change Hardens No visible change
1.0 2.8 1.0 0.0 35.4
No No No No No No No
visible change visible change visible change visible change visible change change visible change
8.8 1.9 9.57 4.84 13.52
None Light yellow None Light yellow Orange
0.0
1.93
None Light yellow
visible ehangeb
0.14
None
visible visible visible visible visible
5.0 1.3
None None None None None
AND PROTECTIVE COATINW SEALINQ COMPOUHDS No visible change No ..... Dissolves No visible change None No None 6.94 No visible change No None 4.31 No visible change No None No change No Brown No visible change 0.28 No
...
...
agents that boil a t or below room temperature an oxygen hclmet was available. The main protection against development of pressure with volatile agents was large vapor vent lines connecting through the high capacity brine cooled condensers of the recovery system. The steam ejector vacuum pump was available for quick action in reducing pressure. Each reagent has its specific antidote in case of serious exposure of personnel. Ethylamine vapor is so readily detected and so disagreeable in amounts below those seriously toxic that dangerous poisoning from its vapor is unlikely. Liquid ethylamine in contact with the skin causes a very deep and slow healing burn. Areas of such exposure should be washed promptly and lavishly with tepid water and then with a dilute solution of acetic acid (6). A person is usually not immediately aware of the severity of a burn because of the numbing effect of the freezing temperature produced by evaporation of the volatile ethylamine. No concentration of vapor from acrylonitrile is likely to require a n oxygen helmet. Poisoning by acrylonitrile vapors must be guarded against, although the immediate effects are not too
Table 111.
No visible change No visible change No visible change No visible change White and hard No visible change
.......
change b change ehange change b change
No visible’change No change
2.7
... ...
...
0.57
None None None
.....
.....
None None ... None Dissolvas None No visible change 0.04 of Agriculture of these products OVPI , similar products 4:i
0.0
severe. Thc important danger sccms t o lic in extended periods of absorption and convemion within tho body to hydrogen cyanide. Although acrylonitrile is not nearly as irritating as ethylamine, its effect on the eyes is a fairly prompt warning. Extensive brochures have been published on treatment for acrylonitrile exposure ( 1 ) . Immediate first aid requires the use of amyl nitrite ampoules. Acknowledgment
The authors express grateful appreciation to Leon Segal and Leopold Loeb of the cotton fiber section of the Southern Regional Research Laboratory in which the decrystallization project originated for cooperation in the translation of that process to larger scale and to the staff of the mechanical shops under the supervision of Frank Weiser for effrctive handling of the plumbing and machine work constructions. Literature cited (1)
American Cyanamid Co., “The Chemistry of Acrylonitrile,” Nitrogen Chemicals Digest, Vol. 5, The Beacon Press, New
York, 1951. (2) Buras, E. M., Jr., Cooper, A. S., Kertting, E. J., and Goldthwait, C. F., Am. Dyestuf Reptr., 43, No. 7, 203-8 (1954). (3) Compton, Jack, Martin, W. H., Word, B. H., and Thompson, D. D., TextileInds., 117, No. 10, 138 (1953). (4) Segal, L., Nelson, M.L., and Conrad, C. M., J.P h y s . Chem., 55, 325 (1951). (5) Sharples Chemical Co., Detroit, Mich., “Storage and Handling of Amines,” October 1948. RECEIVEDfor review September 27, 1954. ACCEPTEDNbvember 29, 1954. Presented a t the Regional Conclave of the AVERIDANCHEMICALSOCIETY, Dec. lC-12, 1953, New Orleans, La. The use of trade names in reporting these tests is not to be interpreted a s a n endorsement b y the Department of Agriculture of these products over similar products of other manufacturers.
INDUSTRIAL A N D ENGINEERING CHEMISTRY
191
