OPERATING INSTRUCTIONS Parr Acid Digestion - Cole
Contents
1. Scope These instructions are to acquaint the user with the pro cedures to be followed and the precautions to be taken when using any Parr Acid Digestion Bomb except those designed specifically for microwave heating Microwave bombs are covered by separate instructions No 243M Parr PTFE lined digestion bombs provide a convenient means for dissolving analytical samples rapidly in strong acids or alkalis it is important that the user understand the capabilities and limitations of the equipment and will be well aware of the safety precautions to be ob served in its operation Pages 1 through 6 of these in structions apply equally to all Parr Acid Digestion Bombs with metal bodies and removable PTFE liners The user should read these basic instructions carefully before starting to use any of these bombs Then turn to pages 8 through 11 for the special instructions which apply to each individual model It must be understood that the excellent mechanism for sample digestion and dissolution provided by these bombs can be hazardous if a bomb is misused Therefore careful reading and full compliance with these instructions must be observed in all applications OPERATING INSTRUCTIONS Parr Acid Digestion Bombs No 249M Contents SCODG TT 1 COMETS UES A E A E EE E N 1 Assumption Of RISK siisi ene nananana cairia nnninaia 2 THE Nature OF PTF Eingo ii 2 Potential Hazar dS urisini kanra 2 Sample Selection isss n aa 3 Loading LIMIS ri2. Excessive pressure E xcessive pressure can be pro duced not only by overheating as mentioned above but also from uncontrolled gaseous reactions and from high vapor pressure or explosive materials or from overload ing the bomb as mentioned below Excessive loading When organic materials are treated in these bombs they may liberate gases as well as heat Since the PTFE liner is an excellent thermal insulator this internal heat will be translated into higher internal temperatures and pressures The loading limits pre scribed for these bombs are purposely conservative to ensure that the energy released from the sample will not over stress the bomb The user must also remember that when a water based solution is heated to 250 C it ex pands to fill a space approximately 25 percent larger than its volume at room temperature If there is insuffi cient vapor space in the bomb to accommodate this ex pansion the tremendous hydrostatic pressure which will be generated will destroy the bomb Explosive materials The nitro compounds produced when nitric acid reacts with certain organic materials may have explosive properties capable of destroying the bomb even when present in quantities well within the normal recommended charging limits Consider for ex ample what might happen if nitroglycerin were pro duced by reactions in the bomb For this reason fats fatty acids glycerin and similar materials must not be treated with nitric aci
3. pressures for each acid digestion bomb are shown in the individual listings on pages 8 through 11 Extreme care must be exercised to ensure that pressures do not exceed these prescribed limits The user must understand that in acid systems the solubility of gases such as NO2 HCI and SO3 will be reduced as the temperature rises having the effect of adding non condensable gas to the vapor phase in a closed vessel As a result the amount of acid present the acid concentra tion and the free head space above the liquid will all have a bearing on the pressure developed in a closed bomb F ree head space must therefore be provided in all procedures and the volume and concentration of the acid must be held toa minimum Maximum operating temperatures for each acid diges tion bomb are shown in the individual listings But these limits must be used cautiously because with certain acids pressures higher than the allowable limit will be generated if the bomb is heated to the listed maximum temperature For example Table on page 6 shows the heating only 3 mL of fuming nitric acid to 256 C in a 23 mL bomb will generate a pressure of 1565 psi which is well above the 1200 psi limit for the 4745 general pur pose bomb Table II shows that heating 10 mL of concen trated hydrochloric acid to 255 C in a 23 mL bomb will generate 2150 psi which is well above the allowable limit for the 4744 4745 and 4749 bombs But if the acid is diluted Table 111 s
4. the pressures and temperatures to which they are exposed Lifetimes as short as 10 to 30 runs or as many as 100 runs have been reported In general ex posure to high temperatures and or pressures can be ex pected to shorten the lifetime of a cup A PTFE cup should be considered no longer usable and it should be replaced if it loses one percent 1 or more of its contents when filled half full with water and heated for thirty minutes at the intended operating tempera ture Continued use of a leaky cup will expose the outer body to corrosive agents resulting in loss of strength and possible bomb failure When replacing a cup the cover must be replaced also Replacement cups and covers are readily available E i The A263AC Spanner Jack holds the 4746 Bomb firmly during opening and closing operations and provides a convenient tool for pressing the PTFE cup out of the body gt Bomb Maintenance These bombs have been designed to operate with little or no maintenance other than careful inspection to ensure that they have not been deformed by undetected high in ternal pressures Individual replacement parts are avail able The screw caps are made of either brass or a high strength bronze to minimize the need for a lubricant on the screw threads but a thin film of an antisieze com pound will be helpful if a bomb is to be used at tempera tures above 200 C The several procedures and precautions listed below shoul
5. 4 J on C Van Loon Selected Methods of Trace Metal Analysis Biological and Environmental Samples Vol 80 J ohn Wiley amp Sons 1981 ISSN 0069 2883 v 80 QD139 T7V 35 1985 548 85 3279 Vapor Pressure Tables Table Pressure developed at constant volume by 3 mL of fum ing 91 HNO3 Sp gr 1 48 in a 23 mL space Temperature Pressure Deg C psi 133 180 165 380 192 630 219 995 256 1565 285 2245 313 2945 326 3135 Data from J ournal of Research of the National Bureau of Standards Vol 30 February 1943 p 110 Table Il Pressure developed at constant volume by 10 mL of 36 HCl ina 23 mL space Temperature Pressure Deg C psi 178 705 223 1430 255 2150 285 3095 298 3615 Data from J ournal of Research of the National Bureau of Standards Vol 33 December 1944 p 468 Table Ill Pressure developed at constant volume by 10 mL of 22 9 HCI in a 23 mL space Temperature Pressure Deg C psi 132 70 159 125 191 265 220 510 250 920 285 1640 315 2250 338 3400 Data from J ournal of Research of the National Bureau of Standards Vol 33 December 1944 p 468 Py 4 Dw Table IV Pressure developed at constand volume by 10 mL of aqua regia in a 23 mL space Temperature Pressure Deg C psi 106 305 155 705 162 765 202 1375 221 1670 236 1960 258 2505 Aqua regia made with 20 volumes 36 HCI 1 volume fuming 91 HNO3 Data from J ournal of Research of th
6. ally shrink it back to its original size Then by alter nately heating and cooling the liner in the bomb its di mensions should stabilize Similarly if a liner is stuck in the metal body it usually can be removed by cooling the bomb gt With use these liners will absorb nitric and other acids and become discolored Generally this will not affect the usefulness of the liner unless it represents unwanted con tamination Absorbed material can sometimes be driven out by heating the liner but care must be taken to pre vent deformation as noted above A 2 or 3 percent solu tion of the sodium salt of EDTA ethylenediamine tetracetic acid has been found to be effective in remov ing heavy metal ions from these liners If the bomb has been used with nitric acid the PTFE liner should be removed washed thoroughly and stored outside of the bomb body to prevent possible corrosion of the metal parts from any residual acid absorbed on the liner If there is a long storage period between uses the cup may not fit in the cylinder To bring the cup back to size chill both the cup and cover in a refrigerator or freezer at 0 C for about an hour Then slide the cup and cover into the body and allow the assembly to come to ambient temperature Liner Lifetimes The lifetime of the PTFE liners used in Parr acid diges tion bombs is governed by the unique characteristics of PTFE as detailed on page 2 Cup lifetimes depend pri marily upon
7. asking such questions as Is the reaction exother mic What intermediate and final products might be pro duced and what will be their behavior When working with new or unfamiliar materials it is al ways advisable to run preliminary experiments using small samples and observing the behavior of the reac tants carefully This initial screening is best conducted in the heavier 4746 bomb which has a safety rupture disc Organic samples are typically treated with concentrated nitric acid Nitric sulfuric mixtures are not recom mended for digesting organic samples due to the possibil ity of forming potentially unstable reaction products Digestion with perchloric acid can be dangerous for the same reason and must not be used Typical heating Loading Limits Minimum and Maximum Maximum Maximum Nitric Bomb Size Inorganic Organic Acid to be used No mL Sample Sample with an Organic Sample 4744 45 2 0 gram 0 2 gram 5 0 6 0 mL 4745 23 1 0 0 1 2 5 3 0 4746 23 1 0 0 1 2 5 3 0 4747 23 1 0 0 1 4748 125 5 0 0 5 12 15 4749 23 1 0 0 1 2 5 3 0 A times range from 1 to 8 hours Temperatures in the 150 to 200 range are generally quite effective The following general digestion procedure for or ganic samples using the Parr 23 mL Acid Digestion Bomb Weigh no more than 0 1 g of sample dry weight basis into the PTFE digestion vessel Add 2 5 mL hot concentrated nitri
8. c acid and let stand open for 15 min utes Add 0 2 mL of hydrofluoric acid to dissolve siliceous materials contained in the sample In case that the sam ple does not contain siliceous material this step can be omitted Close the vessel and place into a preheated oven 100 150 C for 1 to 4 hours as required until the solution is clear If the solution is colloidal heat until clear Remove the vessel from the oven and let cool to room temperature 2 hours before opening Sample sizes and amount of reagents used are proportional to the free volume of the PTFE liner Acid Selection With the vigorous action that can be achieved in these bombs at elevated temperatures and pressures most organic samples can be decomposed in nitric acid alone without using mixed nitric and sulfuric acids as in oxida tions at atmospheric pressure Users should always try nitric acid alone and resist the temptation to add sulfu ric acid to the charge Sulfuric acid may not be needed at the higher temperature and it may tend to dehydrate the system and promote the formation of unstable nitro compounds Do not use perchloric acid We repeat again the warning that perchloric acid should not be used in these bombs because of its unpredictable behavior when heated in a closed vessel Also other reactions which are highly exothermic or which might be expected to release large volumes of gas should be avoided Pressure and Temperature Limits Maximum working
9. d be observed in all operations If the bottom plate is deformed by over pressure replace the plate Then before proceeding review the chemistry of the digestion which caused the over pressure If the inside of the metal body becomes discolored it should be repolished to remove any metallic corrosion products which might contaminate the liner Corrosion discs and rupture discs should be replaced whenever they show signs of corrosion or wear If several acid digestion bombs of the same style are used in the same laboratory do not interchange the cups or other parts of the assembly If the bomb or any of its parts should suffer any unusual damage contact the Technical Service Department of Parr Instrument Company to determine the proper corrective action or repairs which may be required References 1 J Dolezal P Povondra Z Sulcek Decomposition Techniques in Inorganic Analysis London Iliffe Books Ltd New York American Elsevier Publishing Co Czech Edition 1966 English Edition 1968 Li brary of Congress Catalog Card No 68 27170 2 Zdenek Sulcek Pavel Povondra Methods of Composi tion in Inorganic Analysis CRC Press Boca Raton FL 33431 ISBN 0 8493 4963 X QD75 3 S84 1989 543 88 10572 3 Wesley M J ohnson J ohn A Maxwell Rock and Min eral Analysis Second Edition 1981 Vol 27 J ohn Wiley amp Sons ISSN 0069 2883 v 27 QE 438 64 1981 552 06 81 1659 ISBN 0 471 02743 X AACR2
10. d in these bombs and cellulosic materials must not be treated with mixed nitric and sulfuric acids Similarly because of its unpredictable nature perchloric acid must not be used in these bombs Sample Selection Inorganic materials Most inorganic digestions pro ceed smoothly without unusual hazards using not more than 1 0 gram of samplein a 23 mL bomb 2 0 grams ina 45 mL bomb and 5 0 grams in the larger 125 mL size As in all reactions the bomb must never be completely filled as there must always be vapor space above the surface of the charge To be sure that there is adequate free space the total volume of the charge must never exceed two thirds 66 of the capacity of the cup when working with inorganic materials By observing these limits and taking precautions to prevent overheating there should be no unusual hazards in treating inorganic samples with mineral acids Ores rock samples glass and other inorganic materials can be dissolved in Parr acid digestion bombs using strong mineral acids HF HCI H2S04 HNO3 Aqua Re gia and others Digestion times for these materials can vary anywhere from 2 hours to several days Ordinary glass materials SiO2 will mandate the use of HF some times in combination with HCI or aqua regia Tempera tures in the range of 100 to 150 are routinely used Alumina is routinely digested using 10 sulfuric acid Temperatures used for these samples are typically in ex cess of 200 It is a
11. d to meet the liner and thereby prevent air binding between the liner and disc Place the 286AC Corrosion Disc and the 287AC Rupture Disc on top of the liner Notice that two discs are re quired with the thinner corrosion disc next to the PTFE cover and the thicker rupture disc on the outside of the sandwich next to the blowout opening Add the 241AC Spring with upper and lower pressure plates then attach the screw cap and turn it down firmly by hand Additional closing force applied with a hook span ner will be required to seal these bombs but avoid over tightening Set the bomb in the A285AC Holding Fixture and tighten the cap not more than one eight turn with the 264AC2 Hook Spanner Any further tightening in excess of one eighth turn will destroy the seal on the liner and it may put an excessive load on the screw cap causing it to deform and possibly crack and fail Place the bomb in a temperature controlled oven or other heating medium and follow the heating and cooling pro cedure described in the general instructions If mixing is required an optional tumbling ring A284AC can be at tached to the bomb body With this ring in place the bomb will roll smoothly when placed in a powered roller providing good agitation during long digestion proce dures After extended use the tapered rim on the PTFE cup will become thin and the cover may be deformed toa point where it is impossible to maintain a tight seal When this happ
12. dvantageous from the standpoint of minimizing the digestion time to reduce the sample to granular or powder form prior to digestion The increase in surface area of the sample has a significant impact on the reaction with the digestion aid The following general digestion procedure can be used for glass and other silicate samples using the Parr 23 mL Acid Digestion Bomb For the dissolution of glass sand and mineral silicate samples weigh 0 4 g of the powdered sample into the PTFE liner Moisten the sam ple with water and cautiously and 4 mL of 40 to 50 HF to the liner Cover the liner and allow it to stand until the initial reaction has taken place then seal the bomb Place the bomb assembly into a preheated lab oven for 2 hours at 130 1509C Remove the bomb from the oven and after cooling the room temperature the bomb may be opened Elements that form insoluble fluorides such as Al Ba Ca and Mg can be dealt with effectively by adding 1 gram of boric acid after cooling and re heating again for 1 hour A blank used throughout the dissolution and analysis procedure should contain the same amount of HF and boric acid For example it is important to have the boric acid blank subtracted from the sample spec trum in ICPES analysis to account for the boron interfer ences with other elemental lines Organic materials Many organic materials can be treated satisfactorily in these digestion bombs but care ful attention must be gi
13. e thinner corrosion disc should be on top of the thicker rupture disc in the bottom sandwich next to the blow out orifice No discs are used in the 4747 Nickel Bomb Place the sample and the digestion media in the PTFE cup attach the cover and push it down firmly with a twisting motion Slide the closed liner into the bomb body and push it down as far as it will go It may be help ful to push the bottom plug upward to meet the liner and thereby prevent air binding between the liner and disc Set the 254AC Pressure Plate on top of the PTFE cover add the 241AC Spring and the 261AC Top Cap then at tach the screw cap and turn it down firmly by hand A firm twist by hand should be sufficient to develop a tight seal but a slight additional force applied with a 264AC Face Spanner will be helpful However do not tighten the cap more than one eight turn with the spanner Place the bomb in a temperature controlled oven or other heating medium and follow the heating and cool ing procedures described in the general instructions Af ter use at the maximum operating temperature the PTFE liner may be deformed sufficiently to make it diffi cult to remove the liner from the bomb after cooling To overcome this problem an A263AC Spanner J ack Assem bly can be used to push the liner out of the bomb with a smooth uniform pressure without damaging the cup This spanner jack will also be helpful for holding the bomb when removing the screw cap wi
14. e National Bureau of Standards Vol 33 December 1944 p 469 Table V Saturation pressure of water Temperature Pressure Deg C psi 125 34 150 69 175 129 200 225 225 370 250 576 275 862 300 1245 325 1747 Data from Harr Gallagher and Kdl NBS NRC Steam Tables McGraw Hill New York Pay lt 4745 General Purpose Acid Digestion Bomb Bomb Number 4745 Size mL 23 Maximum charge grams Inorganic sample 1 0 Organic sample 0 1 Recommended max temperature C 150 Absolute max temperature C 250 Absolute max pressure psig 1200 Operating Procedure Always keep the bomb upright during assembly and clos ing operations Check the 239AC Bottom Disc to be sure that it is installed with the proper side facing upward to provide full diameter support for the liner Place the sample and the digestion media in the PTFE cup attach the cover and push it down firmly with a twisting motion Slide the closed liner into the bomb body and push it down as far as it will go It may be help ful to push the bottom disc upward to meet the liner and thereby prevent air binding between the liner and the disc Set the 254AC Pressure Plate on top of the cup cover add the 241AC Spring and the 283AC Upper Plate then attach the screw cap and turn it down firmly by hand A firm twist by hand should be sufficient to develop and maintain a tight seal No wrench or spanner is required Place the bomb in a temperat
15. ed by placing the bomb in the air flow from a small fan If it is difficult to remove the PTFE cup after a bomb has been cooled to the touch additional cooling in a refrigerator or freezer may be necessary to shrink the cup sufficiently to re move it from the bomb body Pre Treating PTFE Parts Before using a new PTFE cup and cover these parts should be heated in a bomb with a charge of pure water This pretreatment will help to develop the required seals and it may prevent annoying leakage in sub sequent procedures The amount of water used in this pre treatment should not exceed 40 percent of the capac ity of the cup Thus For 23 mL cups use 9 mL of pure water For 45 mL cups use 18 mL of pure water For 125 mL cups use 50 mL of pure water Assemble the bomb as directed in the individual instruc tions and heat the bomb in an oven at 150 C for one hour Although some digestion procedures may require longer heating periods a one hour preliminary treatment should be sufficient to prepare the PTFE parts for effective use Liner Maintenance Always handle PTFE liners with care to protect the seal ing faces from mechanical damage which would make it impossible to develop a reliable seal Never heat a PTFE liner without slipping it into a bomb body If heated outside of the bomb its dimensions will change and it will no longer fit in the body If this hap pens cooling the liner in a refrigerator or freezer will usu
16. ens the cup and cover must be replaced Any attempt to force a seal by over tightening the screw cap might crack the cap gt 4749 4744 Parts List Part No Description 241AC Spring 264AC2 Hook spanner 276AC Bomb body 23 mL 276AC2 Bomb body 45 mL 277AC Bottom disc 278AC Screw cap A280AC PTFE cup with cover 23 mL A280AC2 PTFE cup with cover 45 mL 282AC Pressure plate lower 283AC Pressure plate upper A284AC Tumbling ring A285AC Holding fixture 286AC Corrosion disc 002 287AC Rupture disc 003 241 AC a 283AC 282AC F 2874C 285AC 218C ps A2B0AC2 f 281AC 279AC2 ome A2B4AC OPTIONAL 276AC2 K L 2774C gt lt 4746 and 4747 High Strength Acid Digestion Bomb Bomb Number 4746 4747 Size mL 23 23 Maximum charge grams Inorganic sample 1 0 1 0 Organic sample 0 1 0 1 Recommended maximum temperature C 275 275 Absolute maximum temperature C 275 275 Absolute maximum pressure psig 5000 3300 Operating Procedure Always keep the bomb upright during assembly and clos ing operations Check the 262AC Bottom Orifice in the 4746 Bomb or the 262AC2 Solid Plug in the bottom of the 4747 Nickel Bomb to be sure that it is in place Then drop the 253AC Rupture Disc and the 252AC Corrosion Disc into the body of the 4746 Bomb When in place th
17. hows that much lower pressures are developed at temperatures to 250 C Diluting or reducing the amount of acid in the charge will generally allow the use of higher temperatures to develop a given pressure But in all operations the user must use good judgment in selecting the operating temperature and he must control the heating medium carefully to be sure that both tem perature and pressure are held within prescribed limits i a amp T E ie i T 1 Ss i i 3 The 4744 and 4749 z 4749 Bomb gE ij with A284AC Tumbling Ring Bombs can be held firmly in an A285AC Holding Fixture while tightening the cap with a 264AC2 Hook Spanner Heating and Cooling the Bomb Parr metal jacketed acid digestion bombs can be heated in a variety of ways including ovens water baths sand baths oil baths mantles or block heaters In all cases it is critical to ensure that proper temperature control is maintained to prevent the build up of dangerous high pressures When working with organic materials the bomb should be heated in a remote location or behind a protective barricade to shield all personnel in the labora tory in case the bomb should unexpectedly explode At the end of a run the bomb must be cooled to the touch before attempting to remove the PTFE cup Cooling must proceed slowly Do not submerge the bomb in a sink on an aluminum plate and run cold water over the plate but not over the bomb Cooling can be accelerat
18. ll laboratory operations the user must assume responsibility for and institute safety procedures to protect all personnel from any hazards as sociated with this equipment Rigid controls must be es tablished to guarantee that the operator does not overcharge or overheat the bomb The Nature of PTFE PTFE offers such unique inertness and high tempera ture usefulness that it is an obvious choice as the mate rial of construction for lining these acid digestion bombs PTFE does however have two characteristics which make it somewhat less than perfect for this application and the user who understands these deficiencies will be able to minimize the effect upon his work First PTFE has a tendency to creep or flow under pres sure or load This tendency is present even at room tem perature and it is accentuated at higher temperatures At operating temperatures below 150 C the creep effect will become more pronounced making it more difficult to maintain tight seals and resulting in deformation and shorter life for the PTFE components The extent of the creep effect will be roughly proportional to the maximum operating temperature Secondly PTFE is a porous material Although the mate rials and designs used in Parr Acid Digestion Bombs minimize the effects of this porosity users of these bombs can expect to see evidence of vapor migration across the cover seal and through the wall of the liner it self Parr is able to minimize these pr
19. mieaaaaiioarannaa a naain 3 Acid Selections stitial 4 Pressure and Temperature LiMits ccsccceereees 4 Heating and Cooling the BOMD eee 5 Pre Treating PTFE Parts ccceeeeeeeeeeeeeteeeeees 5 Liner Maintenance cecceeceeceeeeeeeeeeeeeeeeeteeeaees 5 Liner LifetiMes iescsisssecsasscsnnccntinassasecsesocsnassncevastnesss saz 5 Bomb Maintenance csiis aa daa 6 Referentes carea auca nee teneam aa aiia aaaea 6 Vapor Pressure Tables seessseesseseesesrnssrsereresreses 7 Operating Procedure 4745 General Purpose BOMD ssssssssssreeseresneee 8 4744 and 4749 General Purpose Bombs 9 4746 and 4747 High Strength Bombs 10 4748 Large Capacity BOMD cceeeeeeees 11 gt Assumption of Risk The Parr Instrument Company offers its PTF E lined Acid Digestion Bombs to skilled analytical chemists as an attractive means for digesting and dissolving analyti cal samples for analysis Parr designed and manufac tures these bombs to be as effective as possible when used within the limitations prescribed for each individ ual model But since the pressures generated within these bombs are solely dependent upon the nature of the materials being treated the filling level and the amount of heat applied to promote the reaction Parr will not be responsible for personal injuries or damage to the bomb to the oven or to other equipment resulting from the use of these bombs As with a
20. oblems by machin ing these parts from virgin PTFE which has been molded at an optimum pressure selected to reduce any porosity to an absolute minimum The thick walls and long path seals used in Parr bomb liners also help to overcome these undesirable properties Experiments have shown that the amount of solute lost in this man ner during a normal digestion is negligible but vapor migration will occur and frequently it will be sufficient to produce noticeable discoloration on the inner metal wall of the bomb body and the screw cap Potential Hazards While many thousands of these bombs have been used safely and routinely for treating a great variety of sam ples with different digestion media under a broad range of operating conditions it is possible to create conditions under which these bombs will explode The bulk of the reported incidents of this type have been caused by fail ure of the operator to recognize one or more of the following potential hazards Excessive temperature When a bomb is overheated two factors come into play 1 the vapor pressure of the materials in the bomb increases exponentially with tem perature and 2 the strength of the materials from which the bomb is made falls off again exponentially if the bomb is heated above its maximum temperature limit Dangerous overheating can be produced by ovens with defective temperature controls by water baths boil ing dry or by operator inattention or carelessness
21. orces will some Ry 4 lt times distort the liner making it difficult to remove the liner from the bomb body Usually the liner can be dis lodged by pressing the uncovered bomb against a brass or plastic projection about 3 cm in diameter and 5 cm high A firm tap against the projection may be required In extreme cases it may be necessary to cool the bomb in a refrigerator or freezer to shrink the liner After extended use the tapered rim on the PTFE cup will become thin and the cover may be deformed to a point Parts List Part No Description 301AC Bottom plate 302AC Bomb body A305AC PTFE cup with cover 306AC Pressure plate 307AC Compression ring A308AC Screw cap with cap screws 308ACF Cap screw 3 8 24 x 3 4 soc hd 309AC Bellville spring washer 310AC Corrosion disc 002 stainless 311AC Rupture disc 003 Inconel 311AC A308ACF 307AC A308AC 309AC 2 310AC 303AC 304AC A305AC 301 AC 11 PARR INSTRUMENT COMPANY 211 Fifty Third Street Moline Illinois 61265 USA 309 762 7716 800 872 7720 Fax 309 762 9453 http www parrinst com parr parrinst com Printed in USA 11 97
22. ram sample For smaller samples use 2 5 to 3 0 mL of nitric acid for each 0 1 gram of dry organic matter Slide the filled cup into the bomb and raise the bottom plate slightly to release any trapped air Place the 310AC thinner corrosion disc on top of the PTFE cover and the 311AC thicker rupture disc on top of the corrosion disc NOTE the PTFE cover will rupture and digestion media will be sprayed from the opening in the top plate if the corrosion and rupture discs are not included in the as sembly Add the 306AC pressure plate and two 309AC Bellville spring washers topped by the 307AC compres sion ring Back all of the compression screws out of the screw cap until they are slightly recessed then advance one screw until one full thread is observable on the underside At tach the screw cap to the cylinder and turn it down by hand as far as it will go Then using the TX31SK Allen wrench furnished with the bomb tighten the socket head screws firmly in a criss cross pattern moving in se quence around the circle Repeat the tightening sequence four times for a final torque of approximately 5 ft lbs on each screw Place the bomb in a temperature controlled oven and fol low the heating and cooling procedure described in the general instructions After digestion allow the bomb to cool to ambient temperature on an aluminum plate or a metal table top It is not good practice to cool the bomb in cold water or in a freezer The internal f
23. th a 264AC Face Spanner 10 Parts List Part No Description 241AC Spring 252AC Corrosion disc 002 253AC Rupture disc 010 254AC Pressure plate stainless 254ACCN Pressure plate nickel A255AC PTFE cup with cover 258ACAB _ Bomb body stainless 258ACCN Bomb body nickel 259ACBC Screw cap bronze plated 261ACAB_ Top cap stainless 262AC Bottom orifice stainless 262AC2 Bottom plug nickel A263AC Spanner jack assembly with 265AC spanner 264AC Face spanner only 241AC 261 AC 2574C 255AC C 252AC A2554C 253AC 262AC 4748 Large Capacity Acid Digestion Bomb Bomb Number 4748 Size mL 125 Maximum charge grams Inorganic sample 5 0 Organic sample 0 5 Recommended max temperature C 250 Absolute max temperature C 250 Absolute max pressure psig 1900 Operating Procedure There must always be adequate free space above the charge in the 4748 Bomb For inorganic samples which do not generate gases leave at least 33 of the capacity of the cup as free space and increase the space to 50 or more if the charge tends to liberate gases For organic samples leave at lease 50 free space for non oxidizing reactions and 66 to 75 if an oxidizing medium is used For Carius and similar decompositions use not more than 15 mL or less than 12 mL of 70 nitric acid with a 0 5 g
24. ure controlled oven or other heating medium and follow the heating and cool ing procedures described in the general instructions If mixing is required an optional tumbling ring A284AC can be attached to the bomb body the same as offered for the 4744 and 4749 Bombs Parts List Part No Description 239AC Bottom disc 241AC Sprint 243AC Bomb body 244AC Screw cap 254AC Pressure plate lower A255AC PTFE cup with cover 283AC Pressure plate upper 241 AC 244 AC V4 IZEN PYY L S N 234AC CLI ALLS SS Ug CILLI IY GLL KILL LES 243AC A 7 SDAS TENS SAAC ASS p ALLE Y 257AC ety a KILL LLL LLL 256AC 239AC 4744 and 4749 General Purpose Acid Digestion Bomb Bomb Number 4744 4749 Size mL 45 23 Maximum charge grams Inorganic sample 1 0 2 0 Organic sample 0 1 0 2 Recommended maximum temperature C 250 250 Absolute maximum temperature C 250 250 Absolute maximum pressure psig 1800 1800 Operating Procedure Always keep the bomb upright during assembly and clos ing operations Check the 277AC Bottom Disc to be sure that it is installed with the proper side facing upward to provide full diameter support for the liner Place sample and digestion media in the PTFE cup add the cover and slide the liner into the bomb body Push it down as far as it will go It may be helpful to push the bottom disc up war
25. ven to the nature of the sample and to possible explosive reactions with the digestion me gt dia In all cases the size of the sample and the amount of oxidant used must be carefully controlled For nitric acid digestions Carius decompositions of organic com pounds the dry weight of organic matter must not ex ceed 0 1 gram ina 23 mL bomb 0 2 gramin a 45 mL bomb and 0 5 gram in the 125 mL size The sample does not have to be dried before it is placed in the bomb but the amount used must not exceed the above limits when converted to a dry weight basis The amount of concen trated nitric acid sp g 1 42 added to the above charges must fall within the amounts shown in the table of load ing limits Notice that both minimum and maximum amounts of acid are specified If the sample contains less than the specified maximum amount of dry organic mat ter the amount of nitric acid must be reduced proportion ately As stated above fats fatty acids glycerin and similar ma terials which form explosive compounds in an intermedi ate stage must not be treated with nitric acid in these bombs Digestions involving other organic materials must also be handled cautiously since it is impossible to list all of the potentially dangerous combinations which might arise For best protection the user and his supervi sor should study each reaction carefully before proceed ing to use the Parr digestion bomb or any other pressure vessel
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