1341 Oxygen Bomb Calorimeter Manual.pdf

8/14/2019 1341 Oxygen Bomb Calorimeter Manual.pdf

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No 204M

OPER TING INSTRUCTIONSfor the 34 Oxygen Bomb Calorimeter

SCOPEThese instructionscover the steps to be taken in setting upand operating a Parr 1341 Plain Oxygen Bomb Calorimeter.The user should study these instructions carefully beforestarting to use the calorimeter so that he will fully under-stand the capabilities of the equipment and so that he willbe well aware of the safety precautions to be observed in itsoperation. Instructions covering the operation of the HOOxygen Bomb and the use of other related apparatusare pr0-vided in separate instruction sheets listed below. Theseparate sheets which apply to a particular calorimeter in-stellation should be added to and made a part of theseinstructions

34 calorimeterwith Ignition Unit


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OPERJ.lTIM THE 1108 OXYGEN BOMBDetailed instructions for preparing the sample and charging the ll08 oxy go;. ')fib are given in Instructioo Sheet No.205M. Follow the>, .lstroCtiOns Cllnlfully, givingparticularattention to the precautions to be observed in charging andhandling the bomb.

OPERATING THE CALORIMETERAll operations requir d to teet an unknown sample or to standardize the 1341 phun calorimeter should proceed. step-wisein the following manner:

1. Prepare the sample and charge the oxygen bombas descrihed in 1c" ' ' ; n ~ Sheet No. 205M.2. Fill the calorimeter bucket by first taring the drybucket on a solution ortrin balance; then add 2001l{+I-O.5)

grams of ; ~ ~ o r . u LLlOO water is preferred. but demineralized or tap w r r '1taining less then 250 ppm 01 dissolvedsolids is satisfacl.v.J Thewater temperature should he approximately 1.50 C below room temperature. but this can hevaried to soIt t i u preference. It s not necessaryto use exactly 2000 grams. but the amount selected must


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TIME - MINUTES

Typical Temperature Rise Curve tor 34 Plain alorimeter


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been COIl. >tant for five minutes. Usually the temperature willreach a maximum. thl!ll drop very slowly. But this is notalways true since a low starting temperature may result ina slow continuous rise without reaching a maximUDl. Asstated above, the difference between su


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Gross Heat 01 Combustion. Compute the gross heat ofcombustion,H. in calories per gram by substituting in thefollowing equation:=tW el e2 ea

mExample.

a = 1:44:00 = 1:44.0b = 1:45:24 = 1:45.2c 1;52;00 = 1:52.0t, 24.428 + .004 = 24.432 Cto = 27.654 + .008 = 27.662 CII = + .010 'C15 min. = + .002 bC/min... = - .004 bCI5 min. = - .001 'Cimin.Cl 23.9 ml.C2 = 1.02% Sulfurca 7.6 em. Parr 45ClO wireW = 2426 calories/'Cm = .9936 gramst = 27.662-24.432-1.0021 (1.41-(-.0011 (6.6)= 3.234 'COJ = 23.9 caloriese, = (13.7) 1.021 (.9936) = 13.9 calorieses = 2.3) (7.6) = 17.5 caloriesHg = ,3.234) (2426) - 23.9 - 13.9 - 17.5

.9936= 7841 calories/gram= 1.81 (7841/ = 14,114 Bttlllb

Conversion to Other Bases. The calculstions de-scribed above give the calorific value of the sample withmoisture as it e 'sted when the sample was weighed. Forexample, if an airdried coal sample was tested. the resultswill he in terms of heat units per weight of airdry sample.


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then computed for the burned portion by assuming a heatof combustion of 2.3 calories per em. for Parr 45C10 (No. 34B S gaga ChromelC '1 wire. or 2.7 calories per em for No.34 B S gage iron wireRadiation Correction. The method recommended forcalculating the correction for heat gain or loss from a plaincalorimeter is that specified by the American Society forTesting and Materials as published under ASTM Designations D240 and D3286. I t is bru;ed upon the work of Dr.H. C. Dickinson at the National Bureau of Standarde whoshowed that the amount of heat leak during i test could beapproximated by assuming that the calorimeter is heated byits surroundings during the first 63 per cent of thetemperature rise at a rate equal to measured during the5minute preperiod The method then assumes that the cooling (or heating) rate during the remaining 37 per cent of therise is the same .s the rate observed during the 5minutepostperiod. For most experimental work the dividing pointbetween these two periods is taken as that point in time, b, when the temperature has reached sixtenths /in steed of 63%)of tbe total rise. Note that these two time intervals must beexpressed in minutes and decimal fractions (Example: 1.4min. and 6.6 min.l.

OPERATING SUGGESTIONSThermometer Reliability. It is essential that temperaturesbe mellB rod with a reuaWe calorimetric thermometer andthat scal. carroctions be applied where applicable. Roughbandiing in shipment or by tbe user may cause mercuryseperations which must be eliminated before a thermometer

Magnitude of Errors. The following examples illustrate themagnitude of errors which may result from faulty calorimeteroperations. They are based upon an llBsumed test in whicha 1.0000 gram sample produced a 2.800 0 C temperature risein a calorimeter havingan energy equivalent of 2400 caloriesper deg. C.

n error of 1 millillter in making the acid titration willchange the thermal value 1.0 caLn error of 1 centimeter in measuring the amount of fusewire burned will cbenge the thermal value 2.3 caln error of 1 gram in measuring the 2lrilograms of waterwill change the tbermal value 2.8 cal.n error of 1milligram in weighing the sample will cbangethe thermal value 6.7 cal.n error of .002 C. in measuring the temperature risewillchenge tbe thermal value 4.8 cal.

f all of these errors were n tbe same direction, the total . ..ror would be 17.6 cal


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PARTS FOR THE 34 CALORIMETERKey No12

3456

789101112131415

6

Part No1603A39C52C30033CA5 MEBA5 MEE36M437M237C2A27AA468EA30A2A39IDDA461AlOB

7

DescriptionThermometer, 19-35 CThermometer bracketThermometer support washerThermometer reading lensThermometer support rodMotor assembly with pulley,115v50/60HzMotor assembly with pulley,23Ov5 16 HzMotor pulleyStirrer drive beltStirrer pulleyStirrer bearing assemblyIgnition wireStirrer shaft with impellerOval bucketCalorimeter jacket with coverOxygen combustion bomb8 9 o 11

f o f i lJ 5


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OPERATING THE 1100 OXYGEN BOMBPrecautions. Combustion with oxygen in a sealed bombis II very effective and reliahle method for releasing all heatenergy obtainable from a sample and for preparing hydrocarbon compounds and CMbonacwus materials for analysis, butthere are certain precautioru; which must always be observed when using chis equipment. In particular: Do not overcharge the bomb with too much sample or witha sample which might react with explosive violence. Do not overcharge the bomb with too much oxygen. Theinitial charging pressure should not exceed 40 atID (590psig). Do not fire the bomb alone on an open bench withoutproviding II protec tive .cooling mediwn. Usually thebomb should be completely submerged in water duringfiring. Do not fire tbe bomb i f gas bubbles are released from anypoint on the bomb when it i submerged in water. Stand away from the bomb during firing and do not handle the bomb for at least 20 seconds after firing. Keep the bomb in good condition at all times. Any partsthat show signs of weslrn"". or deterioration must be replaced promptly. Read the maintenance and safety instructions on p. 8before startingto use the bomb, and urge all operating per-sonnel to re-read these instructions often.

Allowable Sample Size. To stay within safe limits. thebomb should never be charged with a sample which willreleasemore than 8000 calories when burned in oxygen. and

or twisting is required The procedure for binding the fuseto the 4A and SA plain electrodes in older Parr bombs is illustrated in instructionmanuals furnished with the originalequipment. For convenience, it Is recommended that th e userpurchase and install new 4AIO and SAIO quickgrip electrodes as replacements for the 4A and SA style in older equipment.Place the fuel capsule with it. weighed sample in the electrode loop and bend the wire downward toward the surfaceof tbe charge. I t is not necessery to submerge the wire ina powdered sample. In fact, bstter combustions will usuallybe obtained if tbe loop of the fuse is set sligbtly above thesurface, When using pelleted samples, bend the wire so thatthe loop bears against thetop of the pellet firmly enough to .keep it from sliding against the side of the capsule. I t is l egood practice to tilt the capsule slightly to one side so thatthe flame emerging from it will not impinge directly on thetip of tbe straight electrode.l iquids In the Bomb. Most bomb combustioJrocedu.rescall for a ,all amount of liquid to be placed in the bottomof the homb as II sequestering agent and absorbent. If theamount and type of liquid are not otherwise specified, add1.0 ml of distilled water from a pipet.ClOSing the Bomb. Care must be taken not to disturb thesample when moving the bomb head from the support steridto the bomb cylinder, Check the sealing ring to be SUIe thatit is in good rondition and moisten it with a bit of water sothet it will slide freely into the cylinder; then slide the headinto the cylinder and pUllh it down lIS far lIS it will go. Foreasy insertion, push the head straight down without twistingand leave the gas release valve open during this operation.When worlring with older bombs which have a removablecompression ring, be sure that the 104A2 ring is in place


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45


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c

29 1 Ignition Uni1

Fire the charge by pressing the firing button on the ignitionunit or on the calorimeter control panel, keeping the circuitclosed for about 5 seconds. The indicator light will come onwhen the button is depressed and will reromn on while current flows through the fuse. When the fuse burns off andbreaks the circuit, the light will go out. Normally this ta kesabout '/, second, but it is goo practice to keep the pushswitch closed for about 5 seconds regardiess of the light. fthe light continues to glow while the button is depressed,there is either a short circuit in the firing system or the fuseW8B not properly arranged_ f a 26 gao platinum wire is usedto fire the charge, hold the fuing button down for only oneor two seconds which should be sufficient to ignite the auxiliary fuse, A longer period may melt the wire, f the wiremelts, use the 7 em terminals on the ignition unit to obtaina lower firing voltage; or add a heavy, one-ohm resistor tothe 1 em firing circuit to lower the voltage.f he indicator light does not come on when the firing button is pressed there is either an open circuit in the systemor the A276E magnetic switch h8B burned out. An open cir

cuit can usually be located with an ohrometer. Flex the leadwires during any continuity check aB the wires may be brokenand making only intermittent contact. f the red indicatorlight glows during ignition but the bomb fuse does not burn,check the system for a voltage l8Bk to ground, most likelyin the insula ted electrode on the bomb head. Check the electrode using the high impedance scale on an ohmmeter endreplace the electrode insulator and seal i leakage is indicated.

Recovering the Combustion Products. Let the bombstand in the calorimeter or water bath for at least 3 minutes,then i t it out of the water and wipe with a clean towel. Openthe valve knob slightly to lease all residual gas pressurebefore attempting to remove the screw cap, Gas releaseshould proceed slowly over a period of not less than oneminute to avoid entrainment losses. After all pressure hasbeen released, unscrew the cap; li t the head out of thecylinder and place it on the support stand, Do not twist thehead during removal Pull it straight out to avoid sticking.Examine the interior of the bomb for soot or other evidenceof incomplete combustion. f such is found the test will haveto be discarded. Wash all iQterior surfaces of the bomb andthe combustion capsule with a jet of distilled water and col-lect the washinge. f any precipitate or residue is present,remove it with a rubbeJ: policeman. Do not filter the washingsas this might remove valuable constituents. Titrate thewashings and meBBUre the unburned fuse wire as requiredfor calorific tests then analyze the washings for sulfur andother elements, i required.

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1341 Oxygen Bomb Calorimeter Manual.pdf