1345
V O L U M E 28, N O . 8, A U G U S T 1 9 5 6 Upon evaporation liquefied petroleum gas deposits the elemental sulfur which i t contains. -4s sampling cocks in the field often have a deposit of sulfur around them, sampling cocks and tube. must be flushed out thoroughly before the bomb is attached. It is likewise important that the sample be taken from the liquid and not the gas phase. I n venting the bomb before completely filling it, it is important that only a part of the liquefied petroleum gas in the bomb be vented as a gas and most of the material be vented as a liquid. Corrosive Nature of Sulfur on Metals. Because elemental sulfur reacts with many metals, the material resistant to sulfur corrosion. found suitable for taking liquefied pet deterniination of elemental sulfur. Results of analysis by the recomniended procedurt. and the low temperature batch evaporation from an open beaker agree rea*onably ~ ~ 1 1Slightly . loxer results by the latter technique may indicate loss of sulfur in the valve of the sample bomb or in the sampling tul)cl during transfer of the material. Volatilization of the entirr, sample from the bomb is to be preferred. Hy varying the proportions of methanol, pyridine, and hydroc~hlorir ncid, it was found that the most readily interpretable polarographic curves are obtained when the recommendtd solvent is employed. Tormal sensitivity of the method is 0.01 p.p.ru. of elemental sulfur on the basis of a 400-gram sample of liquefied petroleum ga lov ii concentration of 1 p.p.m. of n :tiid accurary of the method are (.lementa1 sulfur the p within 0.02 p.p.m. From 3 to 4 hours are rrquired for a single determination, of which some 30 minutes is actnal operator time. The procedure was extended to higher boiling light hydrorarI)on fractions. T o volatilize these materials i t was necessary to place the Pample container in warm water. Results of analyses of pentane stocks are shown in Table 111. When the procedure was applied to straight-run garolines i t was necessary to heat to a higher temperature to effect volatilization in a reasonable time, and it a-as observed that sulfur is lost thereby. ( ) n the basis of the vapor pressure equations of Fouretier ( 5 ) and Taillade (14) this loss is to be expected. I n evaporating higher 1)oilirlg hydrocarbons a t atmospheric pressure, losses of clement:il sulfur shown in Table IIr should be anticipated.
Table I\'.
Yapor Pressure of Sulfur Vauor Pressure of Sulfur, Atm. X 106 ( = P.P.R.I. s o Lost)
Temp.,
" c. 0
0.00007 0.003 0.0013 0.0054 0.019 0.063 0.19
10
20 30
2 60
70
0.55 1.5
SO !IO 100 110
4.0 9.2 21 . o
this stud),, and to F. 0. Bartella, who prrformed the ariaI\scs. Permission of the Union Oil Co. of California to present and puhli-h thib paper is gratefull>r acknowledged. LITERATURE CITED
Am.8oc. Testing Materials. Designation D 130-5OT, "Tentative 1Iethod of Test for Free and Corrosive Sulfur in Petroleum Products." Ibid., D 1265-63T, "Tentative 1\Iethod of Sampling Liquefied Petroleum Gases." Bartlett, J. K., Skoog, D. -1.. ASAI.. ('HEY. 26, 1008 (1954). Eccleston, B. H., 11orrisou. AI., Smith, H. AI., I b i d . . 24, 1745 (1952).
Fouretier, G.. Compt. r e n d . 218, 194 (1944). Garner, F. H., Evans, E. B., J . Inst. P&de7ml. Technol. 17, 451 (1931).
Hall, 11.E., ANAL.C m Y . 22, 1137 (1950). Levin, H., Stehr, E., I s n . ENG.(,'HEM.. ANAL. ED. 14, 107 (1942). Mapstone, G. E., Ibid., 18, 498 (1946). .\Iit(.hell, 0 . li., P e t d e r m Refiner 31, S o . 6, 148 (1952). Proske, G., .4ngeus. Chem. A59, 121 (1947). Schulek, E., Z. anaZ. Chew. 65, 352 (1925). Shively. J. E€., Levin, H., Petroleum Processir~g8, 913 (1953). Taillade, AI., Compt. rend. 218, 836 (1944). Uhrig, K., Levin, H., dsar..CHEM. 23, 1334 (1951).
ACKNOWLEDGMENT
The authors wish to express their :rppreciation to TT'. \T. Howland and G. IT. Uroivn, who wpplied the necessary samples for
R E C E I V E for D review March 1, 1936. Acct7pted April 30, 1956. Symposium on Methods for Testing Liquefied Petroleiini Gases, St. Louis, Mo., September 27 and 28, 1954.
Dry Com bustion and Volumetric Determination of Isotopic Carbon and Hydrogen in Organic Compounds Removal of Nitrogen Dioxide, and Gas Temperature Correction Factors DAVID R. CHRISTMAN, JOAN E. STUBER,
and
AKSEL A. BOTHNER-BY
Chemistry Department, Brookhaven N a t i o n a l Laboratory, Upton,
Small aniounts of nitrogen dioxide in the presence of excess oxygen will pass through a dry ice-cooled radiator trap at low pressures, making possible the freezing out of water before the removal of nitrogen dioxide by external means during the dry combustion of organic compounds. In applying a temperature correction to the gas pressure measurements of carbon dioxide and water by means of a two-liquid manometer, an empirical correction of greater magnitude (about 0.5% per degree) than that calculated by means of the gas law gives the most consistent results.
N. Y.
W
HILE the nitrogen oxide is successfully removed by nian-
ganese dioxide from the gas stream during the dry comhnstiustion of nitrogen-containing organic compounds ( 2 ) , nitrogcri d'ioaide .' (the oxide normally present below 150' C . ) (6) would not be expected to pass cleaiily through a radiator trap at dry icc. tcniperature. Such :L trap is used in the present system to hold the water formed during the combustion, placed before the manganese dioxidr ti,ap for the removal of nitrogen dioxide. A question [vas raised as to whether the nitrogen oxidc present is actually nitrogen dioxide, which has a vapor pressure of 0.03 mm. a t -80" C. ( 4 ) , or is nitric oxide, which docs not freeze at -80" hiit h u l d
1346
ANALYTICAL CHEMISTRY
not be removed by manganese dioxide (1, 5 ) . Sitric oxide is tile oxide present a t the temperature of the combiistion furnace (6). Further investigation has shown the following facts to be true under these conditions. Manganese dioxide does not remove iiiti,ic oxide appreciably, if a t all, in agreement with previous obaervations ( 1 , 6j; manganese dioxide does remove nitrogen dioxide from the gas stream whether or not oxygen is present, if it is not passed through the trap too rapidly; nitrogen dioxide alone or \I ith relatively low proportions of oxygen will freeze to a large extcnt in a radiator trap a t -80" C.; and nitrogen dioxide in the presence of a large excess of oxygen (the actual conditions during :t combustion) will largely pass through the drv ire trap and bc siibseqiiently removed 1)y manganese dioxide.
Table I.
Removal of Nitrogen Dioxide from Combustion Gases
For the i'uns liuted in Table I, xtmples of the t v o oxides (Matheson Co., Inc., East Rutherford, S . J.), either done or mixed with oxygen, were introduced into 50-cc. bulbs and passed through the trap system a t flow rates approximating as nearly aa possible those existing during the normal conibustions (about 25 cc. per minute). Blanks were taken periodically by passing 50 cc. of dry oxygeii through thP system, and these amounts should be taken into account in noting the aniounts of gas trapped. The blanks, which were higher t,hari those normally encountered in the combustions, were mainly due to the fact that the oxygen used was not run through so rigorous a purification system as that used with the combustion train itself. I n summary, it i b apparent that nitrogen dioxide is the oxide produced during thest: combustions (as would be expected), that it does pass through a dry ice-cooled radiator trap in the presence of a large excess of oxygen, and that it is subsequently removed by the manganese dioxide employed for the purpose, as previoiisly descril)ed ( 3 ) . GAS TEWPERATURE CORRECTION FACTORS
Rise, Cm. Expected from condensable gas intro-
In In Sample dry ice liquid Riin Gas cc. trap0 N2 trapa duceda 1 Oxygen (blank) 50 0.03 0.12 . .. 2 Nitric oxide G O 0.09 12.17 15 8 3 Nitrogen dioxide 2,3 3.06 0.28 6.0 4 Oxygen (blank) 50 0.10 0.17b ... 0.7 Nitrogen dioxide 0.25 O.4lb 1.9 Oxygen 40 h Nitrogen dioxide 0.7 0.li 0.38 1.9 40 Oxygen i Oxygen (blank) 50 0.09 0.441 . .. X Nitrogen dioxide 10.8 11.91 15.22C 2 8 , 5 Oxygen 10 9 Nitrogen dioxide 1 ,6 0.41 3.29c 4.2 Oxygen 40 10 Nitrogen dioxide 1 .O 0.36 4.00C 4.2 Oxygen 40 11 Nitrogen dioxide 0.4 0.10 0.53 0.9.5 Oxygen 40 12 Water 25 mg. >30 0.48 72 Oxygen 40 13 Oxygen (blank) 50 0.04 0.45 ... a 1-om. rise equals 0.38 cc. of gae for carbon dioxide or nitrogen dioxidr; for water 0.42 C C . of gas. b Rise in blank between runs 4 and 5 is due to fact that several runs intervened in which large amounts of nitrogen dioxide were inadvertently passed through too rapidly. Thu seemed to raise the blank in the liquid nitrogen trap permanently (but reproducibly). C Not passed through manganese dioxide.
;.
.
I t was previously pointed out ( 2 , 3 ) that a temperature correction should be made in the gas pressures measured by the system in question. However, it has been found that a correction greater than that calculated by the gas lan should be applied, mainly berailbe of expansion of the mercury and oil in the manometer as the temperature rises I*kpanPionof the glass is a negligible factor in this case.
E
w
e W 0 I 4
I
0 z
E n
t u z
Tlie result,s of these experiinerits are summarized in Table J. It would appear t,hat the dry ice-cooled radiator trap does not efficiently remove nitrogen dioxide from the gas stream under the conditions that prevail during a normal combustion. A small amount of the gas (about 1- to 3-mm. rise on the manomrter) may be trapped in the dry ice trap diiring a normal conibustion, but this represents a maximum of ahout 2% of the water i n a t'ypical analysis and would not unduly affect the hydrogen value obtained. Compound9 containing 30 % nit,rogen have been analyzed by this syptem, with acceptahlc hydrogen values. Iiitroducing a large proportion of nitrogen dioxidr to the mixture (run 8 ) , or using nitrogen dioxide alorie, increasecl consic1c.rably the amount of gas trapped by the dry ice trap. That the trap was efficient in removing water was clearly demonstrated b y run 12, where no water appeared in the following liquid nitrogeii trap (the amount of water present in the dry ice tr:tp n.as too great t o be measured directly on the available volume system). I n the cases involving nitric oxide, some of the oxide introduced was not trapped by the liquid nitrogen trap. This might be expected, as vapor pressure of nitric oxide is 0.08 mm. a t - 196" C. (4), and 6he system was eventually pumped down to a pressure of 0.05 to 0.1 mm. The amounts trapped in other cases mere within the experimental error of measurement' of the amount of condensable gas introduced.
1.10
20
21
Figure 1.
22
23
24 25 26 27 28 29 GAS TEMPERATURE I'C,)
30 31
32
Variation of manometer readings with temperature
The correction calculated by the ideal gas law ( P J T , = IJY T2) amounts to approximately 0.33% per degree Centrigrade, assuming constant volume (approximately true). Empirically it is found that an additional correction of about 0.2% per degree Centigrade should be employed for the other causes mentioned above. This is strictly true only with a manometer of the construction previously described ($), and using dibutoxytetraethylene glycol as the oil phase. The correction factors listed in Table I1 are used to correct the pressure readings to 20' C., and the standard rise on the manometer for both carbon dioxide and water is also related to that temperature for each measurement system. Temperatures are read on thermometers in the wells in
1347
V O L U M E 28, NO. 8, A U G U S T 1 9 5 6 the 1:trge volumes or. the nieazuring system. The manometer rratling may take as miicli as 15 minutes to come to its equilihriuni v:due after an amhicnt temperature change of 1" C.
Table 11.
Gas Pressure Correction Factors at Various Temperatures"
Temp..
c.
Correction Factor
Temp.,
1.000 0,993 0,990 0.988
27 28
20 21 22 23
24
c.
29 30 31 32
0.980 0,97J
25 26 a
0
Correction Factor 0.965 0.961 0.956 0.951 0.946 0,941
0.970
Total correction fact,or is O.j';o/degree. -
.
. ~ _ _ _ _ _~ __ -_-~_
_
'l'lir empirical additloid correction is an average of several obQervations of this factoi \\ ith amounts of tank carbon diolide in t tie $\ stem giving almit I O - and 25-cm difference in readings on thP tno-liquid manomrtcr Figure 1 shows the change in these pi essiire readings, and 111 thr, zero reading, a t various temperatiires The differential redings a t each temperature are corrected by the gas lav to 20" C.; then the additional correction necessary is noted to t i e 0.2 =k 0.05%. The total correction used to calculate the valuee 111 Tahle I is 0.50% per degree. There is some variation in this wilue with the amount of carbon dioxide present, but an average v d u e gives sufficiently good rcsults and i q niiich more convenient to use For extreme accuracy, a sliding
scale of factors might be used, to vary with the actual amount of carbon present. The use of these correction factors rather than those calculated by the gas law alone has led to greater precision, both in carbon and hydrogen percentages and in carbon-14 activity results (because of the greater accuracy in measuring the amount of carbon dioxide placed in a counting tube). Carbon values determined by this method are regularly within 0.5% of the correct value. The average deviation of carbon results previously reported (2) was 0.33% (only the gas law correction being used), while a comparable set of analyses using the present correction factors showed an average deviation of 0.24%from the theoretical value. I n the case of the carbon-14 results, the error introduced from uncertainty in the amount of gas in the counting tribe is calculated to be less t h m 0.1% r h e n these correction factors are used, a percentage rvhirh ir negligible compared to the statistical and other systemitic errors affecting the activity determinations (3). LITERATURE CITED
(1) Belcher, R., Ingram, G., -4naZ. Chirn. Acta 4 , 124. 401 (1950). (2) Christman, D. R., Day, N. E., Hansell. P. H . . Anderson, R. C., ANAL.CHEM.2 7 , 1935 (1955). (3) Christman, D. R.. Wolf, d.P., Ibid., 27, 1939 (1955). (4) Hodgman, C. D., "Handbook of Chemistry and Physics," 35th ed., p. 2241, Chemical Rubber Publ., Cleveland, Ohio. 1953. ( 5 ) Ingram, G., Milcrochim. Acta 1953, 71. (6) Latimer, W. AI., Hildehrand, J. H., "Reference Book of Inorganic Chemistry," p. 199, Alacmillan, New York, 1940. RECEIVEDfor review February 6. 1956. Accepted M a s 8. 1956. Rewarch performed under auspices of t h e U. S. Atomic Energy Cornniiision.
Improved Rapid Colorimetric% of Dissolved Oxygen W.
F.
LOOMIS
The Loomis Laboratory, Greenwich, Conn.
(:otnparison of a colorimetric method for determining dissolved oxygen i n O..i-inl. samples with the standard Finkler method rmealed that the calibration curve did riot p u arctiratel) through the origin and was slightly concave do^ I I W ard. This paper describes three modifications of the method, whereby a strictly linear ciirve passing accurately through the origin can be obtained; other improvements make possible its use as :I rapid micmi alternatke to the standard Winkler method.
( '( )I,(
)RIkII~CTTtlC'tleterniiriation of dissolved oxygen in (l..j-inl. m p I e s ( Z j , which could he completed in about 1 n i i r i i i t t , . mnsisted of measwring the red color produced by partially osLlizing reduced indigo r:trmine wit,h the oxygen dissolved in the t w t sample of water. At'mospheric oxygen was excluded by out the reaction in an airtight syringe that could he c~:ti~i~ying pI:ic,ed directly in il. Becknian spectrophotometer. Iii R subsequent cwniparison of this method and the standard \\.itikler method ( I , 6'); it ivas found that the resulting calibratioii curve did not pass wciirately through the origin and was not .iti,icatly linear but slightly concave downward. Conseqiiently,
three modifications of the original method were devised, whereby a strictly linear curve passing through the origin was obtained. This paper describes these modifications, together with various other improvements developed while using this method as a rapid micro alternative to the standard Winkler method. The coefficient of variation between the two methods was 2.57, (Table I). APPARATUS
A 1-ml. Tuberculin syringe, graduated in 0.01 nil., with S o . 22 hypodermic needle (A. H. Thomas Co., 9404) is used. -4small steel ball (or nail head) is inserted into the barrel of the syringe, so that shaking the syringe effectively mixes its contents. A I-cm. piece of tape is wound around the barrel of the syringe between the 0.75 and 0.90 markings, as illustrated in Figure 1. This bushing of tape serves to hold the syringe snugly inside the borosilicate glass absorption rrll (10-mm. light path) of a Beckman spectrophotometer. If the tape is wound around four small pieces of wire set equidistantly around the barrel of the syringe, the resulting cross section is approximately square and the syringe may he locked into position with a slight twist. The syringe should always be placed in one predetermined position, with the graduations a t one side, so as to give as clear a ight path as possible. If the plunger descends during a determination, the spring clip a t the end of the barrel should he tightened.
