Fire Assay for Osmium W. J. ALLAN
AND
F. E. BEAMISH, University of Toronto, Toronto, Ontario, Canada
This research is part of a general investigation of fire assay losses of platinum metals. The conception of losses originated from the fact that if the acid and basic oxides of the noble metals reacted with flux constituents, resistance to reduction by lead might become significant. In the case of osmium losses of the easily formed octavalent oxide could occur. Osmium was lost during fusion, partly through volatilization of the tetroxide and partly through retention of osmium in the slag. The cupellation process also resulted in progressively increasing losses. The results of the research not only provide further data on the efficiency of the fire assay but indicate the probability that the fusion results in the formation of unusually stable osmium.
N
OBLE metals are isolated from ores, etc., by collection with molten lead. Lead is then removed by cupellation with or without additional d v e r , leaving a silver bead containing the precious metals. That the silver bead does not retain osmium may be clue, in part a t least, to the oxygen content of the molten silver. Certain authors ( 3 ,4)have recommended partial cupellation of the button in order to prevent these losses. Practically all the procedures for the determination of osmium involve the isolation through the formation of the octavalent oxide. Tcnnant ( 6 ) ,who discovered osmium in 1803, was the first to use oxidizing fusion and distillation processes. The general acceptance of the fire assay for the platinum metals seems to have been based on its success Tvith gold. Recently reported experimental data ( 2 , 4,6 ) indicate that losses of platinum metals occur and that these losses vary x i t h the identity of the metal. The authors record below their data dealing n ith the efficiency of the fire aclsay for osmium. APPAR i T U S
A Williams and Wilson pyrometrically controlled assay furnace was used for all fire treatments. A distillation apparatus ( 1 ) was used for parting the buttons and oxidizing the osmium contained in the buttons and acid solutions. The osmium was determined colorimetrically in a Lumetron 402 EF colorimeter ( 1 ) . EXPERIMENTAL
Preparation of Assay Crucibles and Composition of Assay Fluxes. A hole 0.78 inch in diameter was drilled in a 40-gram pot 0.25 to 0.5 inch below the upper rim of the pot to allow easy insertion of a Vycor tube 9/16 inch in outside diameter. Forty grams of the glazing flux were placed in the pot and melted a t 1200' C. The pot was removed from the furnace and manipulated so that the wall was completely washed with molten flux. The excess was poured out, and the pot, now with a vitreous glaze over the inside, was allowed to cool. Fluxes for various types of ores-e.g., acid, basic, neutral, reducing, and oxidizing-were made up and the efficiency of collection of osmium in each case was examined. The fluxes were thoroughly mixed by rolling them first on a cellophane sheet and then in a bottle. Methods of Salting Fluxes. Five by 5 inch envelopes were made from sheet cellophane and cellulose tape. Half the charge used (see Table I ) was placed in the envelope and a small paper tray which contained the weighed sample of ammonium bromoosmate was placed on top. The sample was covered carefully with the remainder of the charge and the envelope was sealed with tape. The package was agitated with a circular motion until the contents were thoroughly mixed, folded in half, placed in a prepared assay pot, and tamped down with a pestle. To release trapped air it was sometimes necessary to put a pinhole in the envelope before tamping. Assay Procedure. Thirty-five grams of flux, of the same composition as the charge in the envelope but without the flour or litharge for a button, were placed over the package as a cover. It was found necessary to seal the lid on the pot with Alundum cement to ensure the complete collection of the gases. The pot was placed in the assay furnace a t 820" C. and a Vycor tube
was used to conduct the gases to the absorbing towers. The temperature was raised as uniformly and as rapidly as possible ( 2 to 2.5 hours) to 1200" C. When this temperature was reached, the pot was removed, the lid knocked off, and the melt poured into a conical mold. The button, with its adhering dag, was held in an asbestos glove (to prevent scattering of the slag) and struck sharply with a hammer, Any dag still clinging to the button was removed by tapping it gently with a small steel rod. The slag was ground to pass a S o . 45 sieve, rolled with enough litharge and flour to produce another button on reassay, and placed in the original pot. A flux cover was not used in the reassays, but otherwise the procedure was that described above, Collection of Gases. Three absorption towers equipped with ground-glass joints were used to collect the gases during fusion. The first and second each contained 200 ml. and the third 50 ml. of 6 N hydrochloric acid saturated with sulfur dioxide. A bubbler, which contained a few milliliters of 10% aqueous thiourea solution acidified with hydrochloric acid, was attached to the third receiver to detect losses of osmium tetroxide. Cooling of the towers was found unnecessary. To decrease the possibility of losses of osmium tetroxide around the exhaust tube, the gases were removed very rapidly by a water pump connected to the end of the bubbler. The efficiency of gas collcrtion was investigated in the following manner. A small assay pot containing a "salted" charge was placed inside a larger one. Lids were placed on both, the lid on the outer pot being ground to fit tightly. The gases from the inner pot were collected by means of a Vycor tube inserted through the walls of both pots near the top. The gases from the outer one were drawn off a t the bottom. Both exhaust tubes were sealed in the wall of the outer pot with Alundum cement. The gases were conducted to separate absorption trains. Determination of osmium in the absorbing solutions revealed that 16 micrograms had been withdrawn from the outer pot and 68 micrograms from the inner one. Because of the loss to the outer pot, the lids were sealed as described in the previous section and a high rate of gas exhaustion was used. Two assays were poured under a hood placed over the mold. The gases collected during the pouring process were drawn off and absorbed as usual. No osmium was found in the absorbing solutions and it was concluded no osmium tetroxide was lost from the molten lead or flux during the pouring. The gases formed during cupellation were collected and analyped for osmium. Cupellations were made in a 250-ml. Vycor beaker. The bottom of the beaker was covered with a layer of bone ash, just above which a s/~s-inchVycor tube was sealed. The bone ash cupel, holding the button and any silver used, was placed on the bone ash and the beaker covered with a silica watch glass. The apparatus was placed in the furnace at a temperature of 980' to 1040' C. and the door was lowered, leaving enough clearance for the exhaust tube. The gases from the cupellation of the button from assay 50 (Table IV) were absorbed in two towers, each of which contained 400 ml. of icecold 6 X hydrochloric acid saturated with sulfur dioxide, followed by three towers each containing 200 ml. of the same solution. A bubbler containing thiourea solution was connected t o the last tower and a very high rate of gas removal was used. The gases from cupellations of buttons from assays 62 and 63 (Table IV) were absorbed in two towers, each of which contained 400 ml. of ice-cold 6 N hydrochloric acid and 7 grams of thiourea ( 1 ) . For the partial cupellations only one tower con-
1569
ANALYTICAL CHEMISTRY
1570 Table I. Flux
KO. 1 2
Flux Type
Silica G.
Glazing flux Very acid (medium yiscosity) Very acid (very fluid) Basic flux Keutral flux (without silica) Neutral flux (with silica) Oxidizing flux
8
The fluxes used for the various assays are described in Table I and the data obtained are included in Tables I1 and
Composition of Fluxes Calcium Oxide G. 2
Borax Glass G. 3
Sodium Carbonate G. 11
Litharge
Pqtaaslum Piitrate
G.
G.
111.
Ore G
DISCUSSIOX
16
Fluxes. -4crD FLUXES.Fluxes 2 and 3 10 21 .. 19 20 ,. 3 were of the same acidity but No. 3 4 3 23 72 .. .. 13 2 was very fluid when poured. Compari5 .. 22 J 35 2n .. .. son of results 1 t o 4, Table 11, with 43 6 12 6 J 35 20 .. .. to 49, Table 111, indicated that a flus 7 9 21 70 17 15 (reducing power, of l o a viscosity was desirable because R.P., 6.9) of high extraction per assay and small 8 .. 50 40 .. 15 Iron nail assay 2 25 gas losses. Several slow fusion assays (reducing power, R.P., 6.9) Y Cupel assay flu^ 16 ,. 40 40 .. of flux 2 showed even uoorer collection 3 6 g flour and hi@;hergas losses than those in I n fluxes 2 to 6, charges were made by adding flour and extralithaige to produce a 40-gram button. I n 1 7 and 8 necessary litharge Has already present and no reducing agent was required or desirable. Table 111, indicating that a quick fusion I n t$o.'9 neig'ht of flour and litharge used IS recorded. was desirable. BASIC FLUX. .4ssays 5 t o 10, Table 11, showed that retention of osmium taining 150 ml. of 6 S hydrochloric arid and 4 grams of thiourea by thc slag was greatest for the basic flux, even though when was used. When this solution became pink the cupellation molten it was very fluid. G~~ losses ere higher than device Mas removed from the furnace and allowed to cool, the for any flux other than the medium viscoxitp ncid flux 2. It gases being withdrawn continuously during the cooling period to prevent the escape of osmium tetroxide from the beaker. is possible that higher gas losses are associated with slags conAnalysis of Gases and Buttons. The gases, collected as tainlng higher proportions of osmium. described above, were analyzed for osmium colorimetricallv. NEUTRkL FLUX 5 , T~ deternine the ,f silica, charges of The buttons were parted with 72% perchloric acid ( 1 , 6) in t h r distillation apparatusand the osmium was determined coloriflux 5 which contained no silica were assayed (results 11 to 16, Table 11). The results were rather interesting in that of the 5 mg. metrically. The nails from the "iron nail" assay were also boiled of osmium presentonly 1.5% wm u n r e c o v e ~ , me collection with perchloric acid in the distillation flask until all the osmium tetroxide had been distilled. The distillate from a blank deterof osmium from this flux was the best of those investigated. The mination in which grams of nails mere dissolved had a tranpmolten flux was extremely fluid and this may account in part for nhittancy of 99.9%. Iron therefore did not interfere. 19
..
46
5
4
*
Table 11. Distribution of Osmium in Fire .4ssay Awal NO.
Ty1)e
Flux
SO.
Acid Acid dcid .4cid
3
4 4 4 4
10
Basic Basic Basic Basic Basic Basic
11 12 13 14 15 16
Neutral Keutral Neutral Neutral Neutral Neutral
5 5
17
Neutral Xeutral Seutral Neutral Iieutral Neutral Neutral Neutral Neutral Neutral Seutral Neutral Neutral Iieutral Iieutral Neutral Neutral Neutral Neutral
6 6 8 6 6 6 6 6
1 2
3 4
5 6 7 8 9
18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39
.... .. .
40 41 42
,...
.... .... ....
....
3 3 3
4 4
J
5
?
6
G 6 6 6 6
6 G 6 6 6
..
.. ..
.. , .
Osmium Taken Afg.
!Veig'it 1st
0.
of Button
2nd
G. 49 40 40 43
5.37 5.39 5.36 5.39 5 41 5.40 5.36 5.38 5.37 5 38
3G 41 40 37 44
31
43 40 42 43 42
31 43 36 36 39
5 37 5 38 5 37 5 37 5 40 5 39
43 46 4n
4i 33 41 43
0 194 0.222 0.172 0.508 0,482 0 535 2.00 2.10 2 25 2 25 2 55 3 20 4.34 5 41 5.39 5.35 5.37 :.36 a 38
41 44
43 45 40 40 45
.
38
47 44 45 35 43 40 40 38 40 45 43 42 43 44
5 40 5 36 5.35 5 38
45 38 36 40
5 39
40 40 40
5.36 5 36
41
39
4''
40 38 41 40 40 38 40 43 35 42 3Y 39 50 32 43 16 41 41
-in 1 s t button
Mg, 3 20 5 10 5.04 5.13 5.04 19
p
0.0i 4.98 4.95 5.04
5.28 5 28 5 25 5.30 5.30 5.25 0.193 0.212 0 169 0.493 0.470 0.523 1.98 2.09 2.17 1.92 2.40 3 .a2 4.14 5.28 5.16 5.16 5.16 5.20 5.18
Osmium Found I n 2nd I n 1st button gas
I n 2nd gas
Y
1
Y
8
n
0 0 0 0 2 1 8 0 8 15 20 0 0 0 0 0 1
31 28 8 1" 10 1 18 10 27
3 5 23 28 13 1 5 8
63 2 2 15 15 10 1
12 0 3
9
0 3 0 1
0
0 16 239 3 3 3 40 8 10 2 0 5
0
n
1
0 0 2 3 3
n
0 0 3 0 0 0 0
21 12 0 4 0
0
S i t e r Assay of Pyritic Ore (R.P. 6.9) 38 5.19 31 18 5.13 68 n 41 5.11 40 0 43 5 13 49 0 42
Iron r a i l Assay of Pyritic Ore (R.P. 6.9) 0 36 1,65 0.12 8 0.825 0.35 33 3 38 1.77 0.66
Osmium Found In,lst I n 2nd nails nails
.lf g.
.If
9,
.. .. ..
.. ..
.. ..
.. .. ..
n 0 6
5 0 0 0 0 3 0 0
..
..
0 8 8 0 0 0 0
..
.. , .
.. ..
0
n 0 0
0 25
1.87 1.10 0.510
0.10 0.49 0.52
~~~~l Osmium Recovered Mg. 5.21 5 13 5.07 5 14 3 08 5 22 5 09 5 00 4.97 5 09 5.36 5.29 5.26 5 32 5.32 5.26 0.195 0,214 0 171 0.507 0.478 0.524 1.98 2.09 2.19 2.16 2 40 3 . a2 4.14 5.35 5 19 5 17 5.17 5.20 5,19
osmium Unrecovered M g
0 16 0 26 0 29 0 25 0 0 0 0 0 0 0 0 0 0
33 18 27 38 40 29 01 09 11 05
n 08
0 13
-0 001 0 008 0 001 0 001 0 004 0 01 0 02 0 01 0 06 0 09 0 15 0 18 0 20
0 0 0 0 0 0
06 20 18 20 16 19
5.24 5 2! 5 lo 5 18
0.16 0.16 0.20 0.20
2.74 2.81 3.48
2.65 2.55 1.88
V O L U M E 2 4 , NO. 10, O C T O B E R 1 9 5 2
1571
Table 111. Distribution of O s m i u m in Fire Assay of Acid Flux 2 .4ssay
No.
Osmium
Taken IMQ.
I n 1st button
I n 2nd button
.MQ.
Mg.
Osmium Found I n 3rd I n 4th button button
3.98 0.67 43 5.38 44 5.36 4.46 0.20 0.31 45 5.40 4.18 0.24 46 5.36 4.70 0.48 47 5.34 4.22 0.67 48 5,38 3.98 49 27.71 25.12 0.51 Weight of buttons obtained in above assays
.MU.
Y
I n 5th button Y
0.13 22 38 0.16 40 20 0.22 20 14 0.08 16 .. 44 .. O,l6 0.13 22 38 0.05 94 20 ranged from 40 t o 45 gram!.
Table IV.
I n 1st gas Y 88 60 110
36 27
88
196
I n 2nd gas Y 122 40 66 48 110 122 21
So.
50 51 52 53 54 55
Osmium Taken
Weight of Button
J I g.
G.
5.38 5.35 5.40 5.36 5.40 5.35
48 45 45 45 44 46
I n 5th gas
Total Osmium Recovered
09miuin Unrerecovered
Y
Y
Y
.MU.
'MU.
116 40 40 16 24 116 36
48 20 26 8 0 48 24
40
5.25 5.06 5.02 5.14 LO7 5.26 26.08
0.18 0.30 0.38 0.22 0.27 0.12 1.63
70
37 40
10
Cupellation of Buttons Obtained from Neutral Flux 6 Osmium Found
Assay
Osmium Found I n 3rd I n 4th gas gas
I n gas from cupellation .Wg. 4.47 4.11 4.77 0.121 0.133 0.063
I n bead Y 8 0 0
.. ..
..
the improved collection. The pot, was badly corroded, owing t o the high borax content of the flux. SECTRAL FLUX6. Assays 17 to 23, Table 11, revealed t,hat, only 1% of the osmium was unrecovered if 2 mg. or less of osmium were present. These results were in agreement viith those of Russell, Beamish, and Seath ( 4 ) . When the osmium content became a8 high as 2.5 mg. as much as 6% of the osmium was unrecovered. From 2.5 t o 5 mg. the weight of osmium unrecovered remained const,ant and t,hus only 3.5y0 w t s unrecovered for charges containing -5 mg. of osmium. This flux was fluid and extraction of osmiuni per assay was the best of those investigated, with the exception of S o . 5 . Niter and Iron Nail Assays of Pyritic Ore. Siter and "iron nail" assays were made of 0.5-assay ton samples of a pyritic ore (reducing power, R.P., 6.9) "salted" with ammonium bromoosmate by rolling them, together wit,h a charge of flux 7 or 8, on a sheet of cellophane. The results are recorded in Table 11. The recovery of osmium from the niter assay x a s ahout, the same as from neutral flus 6. The slags from the iron nail assays were very hard and mostly iron sulfide. The collection was very poor and much of the osmium was "picked up" by the nails, partly because of lead which clung t o them. The nails were difficult t o recover, because much of the scale from them stuck to the walls of the pot and could not be removed. The iron nail assay for osmium cannot be recommended. During this investigation the authors found that, certain frequently used fluxes resulted in high osmium losses which were not due t o volatilization. It seemed probable that these errors were due to pot wall absorption and/or reactions with the slag material. .In investigat,ion was made t,o t,race the source of the loss. Table 111 illustrates the distrihut,ion of osmium associated with the use of an acid flux of medium viscosity. The pot walls from ays 45 and 49, Table 111, were corroded with a basic flux. The gases were collected and analvzed for osmium. The slag was ground, altered to bisilicate composition, and assayed. The results indicated insignificant losses (-10 micrograms) to the pot, wall. Fifty grams of the ground slag from assay 49, Table 111, were ignited with a Meker burner for 4 hours in a stream of oxygen. Forty grams of the same slag were ignited in a stream of chlorine for 12 hours at 1000" C. The dag in both instances was complet,ely fused, but no osmium tetroxide Tvas recovered from the vapor and spectrograms of the original ground slag were inconclusive. Further investigation of loss of osmium t o the slag was made and in experiments described below basic flux 4 was used.
I n cupel Y
188 70 72 42 , .
20
Weight of Osmium Found Partially in Partially Cupelled Button Cupelled Button G. .wg.
.. ..
, . , .
5 40 7
4: $2
Osmiu 1x1 Unrecoverei MU. 0.71 1.17 0.56 0.28
5 64
0: 22
..
1. .I sample of flux 4 was salted with a sample of ammonium bromo-osmate containing 5.36 mg. of osmium. No flour or extra litharge for a button was added. This mixture was fused as usual and t,he gas, containing large quantities of osmium tetroxide, was collected in the same manner as the gases from cupellation of the button from assay 50, Table IV (see Collection of Gases). The absorbing solution was analyzed for osmium and found to contain 0.58 mg. The fused flux was ground and mixed with enough flour and litharge to give a 40-gram button. One assay and two reassays were made. The first but'ton and gas cont.ained 1.96 mg. and 60 micrograms of osmium, respectively, while the second button and gas contained 20 and 10 micrograms, respectively. Only 5 micrograms of osmium were recovered from the third button and a like amount from the third gas. A total of 2.72 mg. of osmium was unrecovered from the slag, a spectrogram of which revealed the presence of osmium. 2. Fiftem grams of the final slag obtained as described above were ground, mixed with 15 grams of sodium chloride, and heated in a stream of chlorine for 16 hours a t 550" to 600" C. The gases from the chlorinat,ion were absorbed in 6 S hydrochloric acid solution saturated Lvith sulfur dioxide, into which sulfur dioxide was continuously bubbled during the chlorination. T h e absorbing solution was then boiled with i 2 5 perchloric acid but yielded no osmium. The sintered residue was boiled for 2 hours with 72Yo perchloric acid in the distillation apparatus and yielded only 2 micrograms of osmium. 4 spectrogram of this residue revealed that osmium was still present. 3. Forty grams of the same slag were ground and hoiled for 2 hours in 72% perchloric acid. Eight micrograms of osmium were found in the distillate. The residue was fused with sodium carbonate and the fusion cake was boiled with 72% perchloric acid in the distillation apparatus. X o osmium was found either in the gas from the fusion or in the distillate obtained from oxidation of the fusion cake. 4. An attempt to collect the osmium before it could combine with the slag was made by mixing about 15 grams of lead dust along with flour and litharge to give a 40-gram button with a portion of the basic flux. This attempt failed, the collection being less than usual and resulting in a 10% loss.
It is evident that chemical reactions occurred betiyeen osmium and some of the constituent's of the slag. The ext'ent of t.his react,ion may be indicated by the proportion of osmium in the reassay buttons. I n general, if these proportions were large the complete recovery of osmium would not be accomplished. Effect of Button Weight on Collection of Osmium. An investigation of the efficiency of collection of osmium by 20, 30, and 40 grams of lead was made. Xeutral flux 6 was used. The results shoived that collection by 20-gram buttons was only about 1% lrss than that t)y 40-gram buttons. Gas losses tended to be somewhat larger for smaller buttons. Cupellation of Buttons Obtained from Neutral Flux 6 . The cupellation of lead buttons containing approximately 5 mg. of osmium was investigated. The buttons were cupelled either
1572
ANALYTICAL CHEMISTRY
completely with 100 mg. of silver or to a weight of 5 to 7 grams without addition of silver. The gases produced during cupellation were collected (see Collection of Gases) and their osmium content was determined. Results 50 to 52, Table IV, show that practically all the osmium was lost when the buttons were completely cupelled. Cupellation was complete in about 1 hour and most of the osmium was lost during the last 15 minutes. The beads, which contained very little osmium, were parted in the distillation apparatus with 25 ml. each of sulfuric and perchloric acids. The osmium in the distillate was determined as usual. The partially cupelled buttons were parted and the osmium tetroxide was distilled in the same manner as first assay buttons. Partial cupellation of the buttons from assays 53 and 55 indicated that most of the osmium was lost after the button was cupelled below 7 grams, but 54 showed considerable loss when only 4 grams of lead had been removed. The cupels were ground, rolled with charges of flux 9, and assayed. Table IV shows that the loss of osmium to the cupel was small if the button were partially cupelled, but increased rapidly if it were completely cupelled. Obviously complete cupellation of buttons was not feasible and even partial cupellation caused losses.
higher gas losses and poor recovery per assay than the relatively quick fusion (2 to 2.5 hours). Two assays were sufficient for the maximum possible recovery, except in the case of the slightly viscous acid flux, 2, which required five assays. Maximum recovery (99%) of the osmium could be obtained by the quick fusion of a neutral (No. 6) or oxidizing (KO. 7) flux which contained less than 2 mg. of osmium and was very fluid when poured (1200" C.), Under the above conditions the increase in recovery afforded by reassay was negligible. The usual variation in the weight of button produced little change in efficiency of recovery of osmium, although gas losses tended to be somewhat higher when smaller buttons were produced Cupellation of buttons containing osmium was unsatisfactory, most of the osmium being oxidized and lost in the gases. Osmium was also lost to the cupel. Partial cupellation was found likely to cause large gas losses; consequently wet treatment of the complete button was the only satisfactory method for the determination of osmium collected by fire assay procedures. LITERATURE CITED
SUMMARY
Even under idealized conditions losses of 1 to 6% might be encountered in the fire assay for osmium, The magnitude of these losses, mainly due to retention by the slag, varied with the flux used, the rate of fusion, and the amount of osmium present. Gas losses for all assays except those involving acid flux 2 and basic flux 4 were negligible. Slow fusions (4 to 5 hours) of this latter flux resulted in even
Allan, W. J., and Beamish, F. E., 24, 1608 (1952). Allen, W. F., and Beamish, F. E., ANAL.CHEM.,22,451-4 (1950). Lathe, F. E., Can. J . Research, B18, 3 3 3 4 4 (1940). Russell, J. J., Beamish, F. E., and Seath, J., IND.€NO. CHEM., ANAL.ED.,9, 475-7 (1937). (5) Tennant, S.,Phil. Trans. London, 94, 411 (1804). (6) Thiers, R. E., Graydon, W. F., and Beamish, F. E., ANAL, CHEM.,20, 831-6 (1948). (1) (2) (3) (4)
RECEIVED for review March 11, 1952. -4ccepted June 2, 1952.
Analysis of Gas Mixtures Containing Oxides of Nitrogen In studying oxidation of organic compounds with nitric acid, a method was required for the analysis of gas mixtures containing nitrogen, hydrogen, carbon monoxide, carbon dioxide, nitrous oxide, nitrogen dioxide, and nitric oxide or oxygen. A chemical method was developed in which total nitric oxide plus nitrogen dioxide is determined in one sample by oxidation to nitric acid with hydrogen peroxide and titration of the nitric acid with standard caustic. In a second sample, nitric oxide and nitrogen dioxide are absorbed in 10 ml. of a mixture of sulfuric and nitric acids nearly saturated with sodium sulfate. The mixed acid is titrated with permanganate. The percentages of nitric oxide
I
T H E course of studies on the oxidation of organic compounds with nitric acid, a method was required for the analysis of gaseous reaction products containing nitrogen, hydrogen, carbon monoxide, carbon dioxide, nitrous oxide, nitrogen dioxide, and nitric oxide or oxygen. Methods for the analysis of mixtures of the carbon oxides and the elementary gases are well known, and the literature contains many reports on the determination of one or more of the oxides of nitrogen in relatively simple mixtures. However, a survey of available literature failed to disclose any method for the analysis of mixtures of the several oxides Present address, Burnside Laboratory, E. I. d u Pont de Nemours & Co., Inc., Penns Grove, N. J. 1
and nitrogen dioxide are calculated from total nitric oxide plus nitrogen dioxide and the permanganate titration. The residual gas from the mixed acid absorption is analyzed by absorption of carbon dioxide in potassium hydroxide solution and oxygen in alkaline pyrogallol, combustion of nitrous oxide with added excess hydrogen, and combustion of hydrogen and carbon monoxide with added excess oxygen. Nitrogen is determined by difference. Results are believed to be accurate to ~1.0% absolute for all components except nitrogen and possibly hydrogen. Organic vapors may interfere. The method should be useful wherever gas mixtures containing oxides of nitrogen are to be analyzed.
of carbon and nitrogen with the common elementary gases. The development of a chemical method of analysis was therefore undertaken. Because the volume occupied by nitric oxide and nitrogen dioxide is affected by the association of these gases into nitrogen trioxide and nitrogen tetroxide, and the determination of the degree of association was of no interest, it was decided to report these oxides as moles of nitric oxide and nitrogen dioxide. All results are therefore reported in mole percentages. ANALYTICAL APPARATUS AND REAGENTS
Because mercury was to be used as the confining liquid in the gas analyzer, nitrogen dioxide would have to be removed in a
