T H E JOURNAL OF INDUSTRIAL A N D ENGINEERING C H E M I S T R Y MATERIAL TESTGD Blank of Reagents.. Blank of Reagents.. Sulfur.
.................... .................... ................................ 0,0200 0.0200 .... 0.0200 ......................
Potato Potato Potato Potato Potato
S t a r c h . . .................... Starch..
.................... Starch Starch S t a r c h , ., , . , . , , . . ,
0.1000 0.5000 0.5000 0,5000
....
0.5000
.... ....
,
.........
.... ....
.... .. .. .. ..
.. .. .. .. ....
.... ....
.... ....
.. .. .. ..
.... ....
Linseed Oil.. . . . . .
........................
Cane Sugar Cane S u g a r . , ...................... M. R , ............................. M. R. ............................. Ceresine.. Ceresine..
......................... .........................
4.18 4.00 3.90 4.16 3.50 3.80 4.00 4.00
1.0000 1,0000 1 .OOOO 1.0000 1,0000 1.0000
....
.. .. .. .. .... .... ....
Standard I Value G. per Cc. 0.005121 0 005121 0.004798 0.004798 0.005 12 1 0.005141 0.004727 0.004727 0.004727 0.004727 0.004727 0.004727 0.004727 0.004727 0.005121 0.005121 0.005121 0.00512 1 0.005121 0.004768 0.004768 0.004768 0.004768 0.005 121 0.005121 0.005121 0.005121 0.004727 0.004727 0.004727 0.004727 0.004727 0.004727 I
The above is a tabulation of results: The advantages of this method are its accuracy, ease of manipulation, rapidity, and cheapness. When the dried acetone extract from a rubber compound is obtained, eighteen samples may easily be determined in 21/2 hrs. The operator need not spend more than an hour's time in actual manipulation. This method may be used t o determine sulfur, and mixtures of soluble sulfides and thiosulfates. ATLANTIC INSULATED WlRE AND CABLE COMPANY STAMFORD, CONNECTICUT
RAPID DETERMINATION O F CARBON IN STEEL BY THE BARIUM CARBONATE TITRATION METHOD1 By J. R. CAIN AND L C . MAXWELL Received May 3, 1918 INTRODUCTIOK
Because of t h e increased demands now made on t h e testing and steel works laboratories which analyze steel delivered on government contracts, and because of the reduced number of chemists available for such work. it becomes desirable t o increase t h e efficiency of laboratories in all possible ways. Short-cuts or simplifications which will reduce t h e time required for determination by standard methods, or reliable new methods which require less time t h a n those now in use are of value in contributing towards increased output of work. With this idea t h e following modification of t h e barium carbonate titration method originally described by Cain2 has been developed. The work was carried on recently a t t h e Bureau of Standards in connection with a military problem where speed was considered important. The barium carbonate method is much used, especially by testing laboratories which usually have t o analyze steels of unknown composition from many sources. It has been recognized t h a t this method as heretofore used is not as rapid as t h e soda-lime method, b u t it is also felt by many t h a t it is less subject to disturbing influences and is in most respects 1 2
Published by permission of the Director of the Bureau of Standards Bureau of Standards, Techltologzc PaOer No. 33.
( a ) Titration (a) Blank
Standard I Used cc.
Standard I Used cc.
....
0 60 0 50 0.60 0.60 0.60 0.60 0.60 0.60 0.60 0.60 0.60 0.60 0.60 0.60 0.60 0.60 0.60 0.60 0.60 0.80. 0.80 1.00
....
8.10 8.00
8.35 32.60 14.55 13.65 13.20 12.55 13.50 14.25 14.20 13.40 8.00 8.00 8.70 8.00 8.50
.... .... .... .... .... ....
....
8.85 8.90 10.00 10.00 10.70 9.15
1 .oo
0.85
0.80
0.70 0.70 0.60 0.60 0.60 0.60 0.60 0.60
( bStandard ) Titration ( b ) Blank Standard I Used I Used cc. cc.
.... ....
5.40 5.15 3.80 24.90 0.75 0.75 I . 70 1.85 0.40 0.40 0.40 0.40 3.60 3.75 3.60 4.40 4.20
.... ....
.... .... .... .... ... . I . .
5.50 5.60 2.80 2.70
3.10
3.55
0.30 0.35 0.40 0.40 0.40 0.40 0.40 0.40 0 40 0.40 0.40 0.40 0.40 0.40 0.40 0.40 0.40 0.40 0.40 0.35 0.30 0.30 0.30 0.55 0.30 0.50 0.40 0.40 0.40 0.40 0.40 0.40 0.40
Vol.
Free S by New Method Gram None None 0.0200 0.0200 0.0211 0.1007 0.0326 0.0304 0.0300 0.025h 0.0300 0.0316 0.0316 0.0296 0.0201 0.0203 0.0219 0.0207 0.0219 &Tone None None None None
None None hTone
0.0221 0,0222 0,0230 0.0229 0,0249 0.0210
IO,
NO.7
Free S Present Gram h'one None
0.0200 0.0200 0.0200 0.1000 0.0200 0.0200 0,0200 0.0200 0.0200 0.0200 0.0200 0.0200 0.0200 0.0200 0.0200 0 ,0200 0.0200
None None None None None None None None
0.0200 0.0200 0.0200 0.0200 0.0200 0.0200
simpler than the latter method. It is believed t h a t t h e modifications herein recommended p u t t h e barium carbonate titration method more nearly on t h e same basis with t h e soda-lime method as t o time requirement, with b u t little loss in accuracy, and with added simplicity in manipulation. The time required per determination has been reduced j o per cent and it is now possible for a chemist during an 8-hr. day t o make jo determinations by the barium carbonate titration method. The procedure recommended in t h e cited paper was briefly as follows: The combustion of t h e steel was carried o u t by admitting oxygen a t a moderate rate to the combustion tube. K O details were given in t h a t paper as t o furnace temperatures at t h e time t h e boat was inserted in t h e furnace, nor as t o whether the boat was allowed t o preheat before admitting oxygen. Actually, t h e results given in t h e paper were obtained by placing t h e cold boat in a furnace kept a t 1000 t o 1050' and admitting t h e oxygen immediately; t h e passage of t h e oxygen a t t h e moderate rate specified was continued for 2 0 t o 2 5 min. The oxides t h u s obtainedwerefrequently not well fused, If a n incomplete combustion was suspected, t h e oxides were crushed and reburned. This method of burning corresponded t o practice here and elsewhere a t t h a t time. The barium carbonate was filtered under an atmosphere free from carbon dioxide, using a special apparatus illustrated and described in t h e cited publication. The filter consisted of a carbon tube fitted with a perforated porcelain plate; on this was placed a bed of coarse quartz particles, and on this a layer of asbestos. When filtration was finished t h e porcelain plate and superimposed layers of quartz and asbestos were transferred t o a wide-mouth flask, treated with excess of t h e standard hydrochloric acid, and t h e solution titrated against sodium hydroxide,, using methyl orange as indicator. Various precautions in manipulation and filtration were described. These precautions, t h e necessity for preparing a filter of this type each time, and t h e slow-
July, 1918
T H E J O C R - V A L O F I W D C S T R I A L ALVD E N G I N E E R I N G C H E M I S T R Y
521
ness of t h e combustion all contributed toward making t o t h e line voltage t h a t initially t h e furnace gives t h e t h e barium carbonate method as described longer t h a n proper temperature with nearly all t h e rheostat reothers in use. This was compensated b y t h e high sistance inserted. As t h e furnace is used its winding degrce of accuracy attainable and t h e insurance against deteriorates and increases in resistance, and this should numerous sources of error, as detailed in t h e paper. be compensated b y removing resistance on t h e rheostat T h e present method saves time in t h e following ways: so as t o maintain t h e furnace temperature as specified. I---Admission of oxygen a t a very rapid rate t o t h e If t h e temperature is too low when all t h e rheostat burning sample with automatic provision against too resistance is removed, t h e furnace must be supplied rapid passage a t t h e exit end of t h e combustion tube. with a new winding. Temperatures are checked b y (This would cause loss of carbon.) This rapid ad- t h e melting point of pure gold. A piece of this metal mission of oxygen, coupled with t h e use of a preheated is flattened o u t , placed on a clean porcelain or alundum boat and t h e practice of allowing t h e sample t o pre- boat and left in t h e furnace (previously brought t o heat in t h e furnace a minute before admitting oxygen, full heat) for I O min. If t h e gold is not t h e n melted gives complete combustion of a 2-g. sample in I'/* t h e temperature is too low.' The same piece of gold t o z min. If combustion is allowed t o take place may be used repeatedly provided care is taken always gradually, instead of rapidly, as specified, t h e rapid t o place i t on a clean surface of either alundum or porcemethod herein described cannot be used. T h e criteria lain. of a successful combustion b y this method are: 2-BOATS AND LINING MATERIALS ( a ) Well-fused oxides in which no trace of t h e origBoats may be of alundum, porcelain, platinum or inal grains of steel is apparent. nickel. Nickel boats may be made very cheaply b y ( b ) Much accelerated oxygen inflow during t h e cutting a sheet of nickel of proper size a t t h e corners actual combustion of t h e sample. and bending these up. Such boats should be ignited (c) Vivid incandescence while t h e sample is burning, in t h e furnace in a current of oxygen until free from visible if a quartz combustion t u b e is used. carbon. To protect t h e combustion t u b e from t h e Should these signs of a good combustion be lacking, effects of spattering oxides i t is provided with a sleeve determinations should be rejected. of nickel sheet (also ignited until free from carbon). 2-Use of glass plungers t o t a k e u p dead space in Boats are lined with alundum sand, free from materials t h e forward end of t h e combustion t u b e so as t o de- causing a blank, The special grade supplied b y the crease t h e amount of gas t h a t has t o be flushed out a t Norton Company is quite satisfactory. each determination. 3-COMBUSTION TUBES AKD CATALYZER 3-Rapid filtration as described in Section 6. Combustion tubes may be standard forms of porce4-The delivery of all t h e reagents from reservoirs lain or well-glazed quartz, or in fact, any material by air pressure. The main prerequisite for t h e use of t h e modified which has been carefully tested for freedom from porosity. To facilitate fitting of stoppers t h e crossmethod is a laboratory atmosphere not contaminated section a t t h e end should be circular. I n t h e forward with excessive amounts of carbon dioxide, SO t h a t t h e barium carbonate may be filtered in a simple apparatus end of t h e tube a roll of copper gauze 3 in. long and not requiring exclusion of t h e carbon dioxide contained of a diameter sufficient t o fill t h e t u b e is inserted so in t h e laboratory air. This requirement is met b y t h a t i t is heated b y thermal conduction from t h e heated a n y modern laboratory with even fairly good ventila- zone of t h e furnace t o a temperature of 2 0 0 t o 300' C. tion a n d without a n excessive number of gas burners The copper should not, however, be placed SO far in t h e furnace t h a t there 1s danger of its melting. The operating a t one time in a confined space. Practically this point may be tested b y comparing blanks r u n copper is then oxidized b y bringing t h e furnace t o a with t h e filtering apparatus described in t h e original proper temperature while passing oxygen. This copper paper' a n d t h a t herein recommended. If t h e differ- oxide serves t o oxidize any carbon monoxide t h a t ence in t h e blanks is such as would cause a n error might be formed, also any sulfur dioxide, which is exceeding o . o o j per cent carbon when a 2-8. sample oxidized and fixed as copper sulfate. Should too great a n accumulation of copper sulfate take place t h e catais used, i. e . , O . O O O I g. carbon, either t h e longer method lyzer should be renewed. must be used or steps t a k e n t o reduce t h e carbon dioxide content of t h e laboratory atmosphere. 4-RATE OF PLOW OF OXYGES METHOD I-FURNACES
AND TEMPERATURE
An electric furnace operating a t not less t h a n 1063' C. (the melting point of pure gold) is usedn2 Such a furnace may be obtained upon specification or as a standard article from manufacturers or may be constructed b y t h e operator. T h e furnace should be equipped with a rheostat so designed with respect cit. Lower temperatures may be used with very fine chips, the temperature recommended will burn successfully chips that will just pass a IO-mesh sieve, 1 LOC.
8
T h e rate a t which oxygen is admitted t o t h e forward end of t h e t u b e should be not less t h a n I O t o I j 1. per min. At t h e exit end of t h e t u b e t h e rate should not exceed 2 2 5 cc. per min. This latter rate of flow is attained most simply b y constricting a glass capillary tube inserted in t h e forward stopper of t h e combustion t u b e so t h a t t h e desired rate of outflow is obtained with t h e specified rate of inflow. A plug of glass wool precedes t h e capillary. The rate of outflow is especially important, for if this is much ex1 The melting point of pure silver (960.5' C . ) , determined in the same way, is a convenient check on the lower temperature limit.
52-7
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
Vol.
IO,
No. 7
ceeded, carbon dioxide will be carried past t h e absorption tube containing t h e barium hydroxide. The dead space in the combustion tube in front of t h e copper oxide catalyzer is taken up with a glass tube closed a t both ends. This decreases t h e amount of gas t o be flushed out of t h e tube a t each combustion, and malerially shortens t h e time required for a determination.
successful (see Introduction), the Meyer tube may be disconnected and t h e boat removed from t h e furnace t o cool shfficiently for introducing t h e second sample. The filtration and washing of t h e barium carbonate is then carried out as described. By this time t h e boat is ready for t h e second sample, which has already been weighed out. The combustion of this sample is then started, using another Meyer tube. The absorption tube used for t h e previous j-MEYER ABSORPTION T U B E S AND BARIUM HYDROXIDE determination is now washed out by adding t o i t SOLUTIONS The form of Meyer tube shown in t h e cited paper from t h e burette t h e necessary amount of standard has many advantages and may be obtained from dealers acid (this being usually about j cc. more t h a n is acon specification. It should be filled with sufficient tually needed t o dissolve t h e carbonate). The acid barium hydroxide solution ( - 7 j g. Ba(OH)2.zH20 is transferred from t h e Meyer t u b e t o a wide-mouth per liter) so t h a t when gas is passing for a determina- flask, as is also t h e filter paper carrying t h e precipitate. The Meyer tube, after washing twice with water, is tion t h e liquid fills all t h e small bulbs and one-half the large bulb a t the exit end. The barium hydroxide filled with barium hydroxide solution for t h e next solution is held in a 10-1. bottle and is delivered by determination. The flask containing t h e precipitate is placed on t h e hot plate until t h e carbonate is dispressure of air free from carbon dioxide. solved. Titrations are conveniently made when 6-FILTERING AND WASHING several flasks are ready. During filtration, washing, A Buchner funnel fitted t o a suction flask and supetc., of t h e first determination, t h e combustion of t h e plied with two superimposed, open-grain, 7-cm. filter second proceeds, b u t there is still time before its compapers is used for filtrations. Much time is saved by pletion for t h e operator t o adjust t h e acid burette not having t o fold and fit t h e papers. The large surfor t h e second determination, t o fit papers t o t h e face exposed insures rapid filtration. The Meyer Buchner funnel, and t o weigh out t h e third sample. tube is washed three times, using care t o reach all TABLEI-RESULTS OBTAINEDBY MODIFIEDBARIUMCARBONATE TITRApoints. The precipitate on the filter is then washed TION METHOD ON BUREAU O F S T A N D A R D S ANALYZED STANDARD SAMPLE s four times, washing t h e t o p of t h e funnel carefully. Certificate Mean Varia. Value Carbon Found by The wash water is free from carbon dioxide and is (by Direct Method Herein tion from Sample Combustion) Described Number of Certificate delivered from a large glass reservoir by air pressure. Per cent Per cent Determinations Value 1 . 0 1 6 t o 1.027 3 -0.01 1.03 0.805 ' 0.81 3 +o. 0 0 5 ( a ) 0.380 2 + O .007(a) 0.373 0.605 t o 0.620 12 -0,005 21a 0.617 ( a ) The corresponding differences in t h e determinations of carbon in Sample 23 given in the cited paper were: 0,000 per cent, 0,000 per cent, 0.000 per cent, and -0.005 per cent: in 10b they were: 0,001 per cent and -0,001 per cent. NO.
7-STANDARD
ACID A S D ALKALI
Tenth-normal hydrochloric acid is used. This may be conveniently standardized against weighed portions of chemically pure sodium carbonate which has been fused in a platinum crucible and cooled in a current of pure, dry carbon dioxide. The carbon dioxide is conveniently obtained by heating acid sodium carbonate in a hard glass test tube and passing t h e liberated gas through a calcium chloride tower. The alkali is standardized sodium hydroxide solution adjusted t o be equivalent t o t h e acid. Methyl orange is used as an indicator, Both acid and alkali are delivered from t h e respective stock bottles t o t h e burettes by air pressure. 8-PROCEDURE The furnace being a t t h e proper temperature and t h e filled Meyer t u b e connected, z g. of steel are weighed and transferred t o t h e boat filled with alundum sand. This should have been placed in the hot furnace previous t o weighing the sample and then removed so t h a t a t t h e time of placing t h e sample on it its temperature is just below a visible red. (This will not cause loss of carbon unless t h e particles of t h e sample are extremely small-less than 6 0 mesh.) The boat is then immediately placed in t h e furnace and allowed to heat for one minute with no oxygen passing. During this time a second sample is being weighed (the balance should be placed in t h e same room with t h e furnace for convenience). Oxygen is now admitted a t t h e rate prescribed in Section 4 . and a t t h e end of j min., if t h e combustion has been
35 23 lob
BUREAUO F STANDARDS WASHINGTON, D. C.
T H E PREPARATION AND TESTING OF P U R E ARSENIOUS OXIDE2 By ROBERTM . CHAPIN Received March 12, 1918 INTRODUCTION
A supply of assuredly pure arsenious oxide is a n important matter t o t h e modern analytical chemist. Analytical methods t h a t involve titration with standard iodine, b y virtue of their accuracy and convenience, are constantly finding new applications in addition t o t h e already considerable list, and for standardizing such iodine solutions pure arsenious oxide is generally useful and frequently used. Moreover, employment of t h e substance as a n alltalimetric standard has been advocated by Menzies and M ~ C a r t h y . ~ From textbooks and various papers dealing with the applications mentioned above, i t appears t h a t pure arsenious oxide is very easily obtained. Typical are t h e statements of Menzies and McCarthy4 1 Avoid long continued heating, which apparently causes some action on the filter paper involving a slight error in the determination. 2 Published by permission of t h e Secretary of Agriculture. 3 J . Am. Chem. Soc., 37 (1915), 2021. 4 LOG.
czt.
