IYDUSTRIAL -4ND ElVGI.VEERI-VG CHEMISTRY
June, 1928
which is supported 2.5 cm. above beaker by three legs which rest on the rim. IGNITION OF CHARGE-sodium peroxide combines with certain organic compounds with sufficient energy to inflame them, among which are the primary alcohols. This property is useful because the fusion cannot be started from without as with coal or coke. Onehalf milliliter of alcohol is run in from a pipet after the canopy is set in place, and spontaneous ignition occurs in 10 seconds when using absolute methanol. The ignition can be retarded by mixing benzene (sulfur-free) with the alcohol, or denatured alcohol may be used. The writer has found 10 seconds ample time for safety, and prefers methanol without any admixture because it burns without depositing carbon, whereas benzene and sometimes ethyl alcohol will deposit carbon, which may be due to insufficient time for complete mixing with the peroxide.
645
An energetic combustion is preferred and, in fact, is necessary to insure completeness; nevertheless it must be under control. Too little peroxide increases the violence of combustion while too much may retard combustion to the point of incompleteness. A little experience will simplify this adjustment. The manner of ignition is important. The method in use in this laboratory is to heat an iron rod to incandescence and plunge it into the crucible through a hole in the cover. The action of the peroxide on the iron rod introduces a large amount of iron into the fusion, which when dissolved requires considerable time to filter, and a possible source of error lies in the danger of some sodium sulfate being carried down with the precipitated iron. Ignition by alcohol obviates this danger.
Automatic Apparatus for the Determination of Small Concentrations of Sulfur Dioxide in Air' Moyer D. Thomas and Robert J. Cross DEPARTMENT OF . 4 G R I C r L T U R A L RESEARCH, AMERICAN SMELTING
K T H E study of smelter-
ASD
RSFININGC O M P A N Y , S A L T L A K E CITY, U T A H
An automatic apparatus has been constructed to to 20 liters per minute. This analyze continuously air containing sulfur dioxide in observation was also made ins m o k e p r o b l e m s it is concentration from 0.1 to 60 p. p. m. The apparatus de pen d e n t 1y by Houston essential to have an anameasures out the absorbing liquid, draws a definite volLetcher, of Stanford Univerlytical method which will ume of air sample through it, and discharges the assity. The method described estimate rapidly and continupirated solution into a bottle ready for titration. in this paper makes use of this ously small amounts of sulfur The method has been checked with satisfactory redioxide in air. Although the fact by drawing the air sample sults by comparison with the Selby method and also continuously, and the analyconcentration of this gas in by analyzing known mixtures of sulfur dioxide and air. t h e n e i g h b o r h o o d of a sis is made automatic to the Data are submitted to indicate the stability of the modern smelting plant probpoint a t which the solution iodine solution and its efficiency in absorbing sulfur ably never exceeds 10 p. p. m. is titrated. This method has dioxide. by volume, it is desirable for been extensively used with A modification of the automatic apparatus suitable investigational work that the entire satisfaction in fumigafor field determinations of sulfure dioxide in air is a n a l y t i c a l method should tion studies and in the field. cover-a range of concentration described. Apparatus from 0.1 to a t least 30 p. p. m. The method of Marston and Wells, as described by the A diagram of the automatic apparatus is given in Figure 1. Selby Smelter Smoke Commission12has been the best one Operation is accomplished by means of eight cams, 8 , which available for this purpose. The process consists in drawing open and close a series of valves in proper sequence. The a sample of air into a partially exhausted 20-liter bottle camshaft is geared through a speed-reducing system directly containing a solution of iodine colored with starch, and ab- to a motor, which also operates a Nelson vacuum blast sorption is accomplished by shaking the bottle vigorously. and pressure pump. Poppet valves, D , F J , are used in the The method has the drawback that it is laborious and inter- liquid system and consist simply of beveled glass rods ground mittent. Objections urged against it by Weierbach3 on the t o seat against the sloping walls above the constriction in ground that the iodine attacks the rubber stoppers and tubing glass tubes. Mercury-seal valves, N , mounted on pivoted are without foundation if the rubber is first soaked in a 0.002 boards are employed on the air line, and are operated by N solution of iodine and subsequently in a more dilute solu- long levers from the cams which permit a tipping movement tion of about the concentration used in the analysis. Error of about 2 cm. in analysis due to oxidation of sulfur dioxide by oxygen from The reagent reservoir is a 20-liter bottle containing starch- , the air a t the surface of the glass seems to be inappreciable iodine solution of sufficient strength to absorb all the sulfur if the walls of aspirator are kept moist with iodine solution dioxide in the sample of air a t the maximum concentration while the sample is being drawn in. However, unless pre- of a given experiment. This bottle is closed a t the top and cautions are taken it is possible to introduce an error as provided with a discharge tube a t the bottom, which extends great as 5 per cent due to adiabatic cooling of the bottle on into a 500-cc. constant-level bottle, B. The latter comexhausting and adiabatic heating on admitting the air sample. municates through a g1a.s-wool filter, C, and two valves, It was observed by one of the writers in 1926 that complete D, with two inverted 100-cc. pipets, E ; and as these are absorption of sulfur dioxide could be attained by bubbling successively filled, the level of the liquid in the small reservoir the gas through a suitable absorber a t a rate as high as 10 bottle is maintained, because air is permitted to enter the large bottle when the lower end of its discharge tube is un1 R e c e i v e d February 6, 1928. covered. The pipet delivers its liquid to the absorber, G, 1 U 5'. But.. Mines, Bull. 98 (1915). * A m . J Botany, 13, 81 ( 1 9 2 6 ) . below, and when the gas sample has been drawn through
I
646
INDUSTRIAL AND ENGINEERIXG CHEMISTRY
J-01. 20, s o . 6
of potassium iodide per liter together with the necessary iodine. Its strength is determined by titration with 0.002 N sodium thiosulfate, 1 cc. of which corresponds to 1p.p.m. of sulfur dioxide when the air sample is 1 gram-molecular vol1 n ume. The end point is a standard light blue color. The volume of each solution is measured after titration to make sure that the machine is operating properly. The large reservoir holds enough reagent for about 5 hours’ continuous operation and the solution can be used several times. The modification of the apparatus as used for field determinations is indicated in Figure 2. The apparatus is mounted in a box and is carried about in an automobile. Suction is obtained by direct connection through a stabilizing bottle with the intake manifold of the automobile engine. The speed of the engine can then be regulated to draw air uniformly as indicated by the flowmeter reading. The large reservoir and automatic valves are eliminated from this a p p a r a t u s , but one man can easily operate the valves by hand and titrate the aspirated solution. After the solution has been titrated, a measured volume of iodine is added and it is returned to the absorber. Pinchcocks on rubber tubing are probably better valves than glass stopcocks. I n order to facilitate J a has been Figure 1-Diagram of Automatic Apparatus for Determining Small Concentrations of Sulfur ca‘culation Of the Dioxide i n Air worked out indicating the time required to aspirate one or more gram-molecular the iodine solution, the latter is discharged into titration volumes of air under different atmospheric conditions with bottles, K , carried on a turntable in an enclosed space under- a gken flowmeter reading, and it is then a very simple matter neath the absorbers. The capacity of the turntable is twenty to convert the titration values into parts per million of sulto thirty bottles. fur dioxide. On the air line a flowmeter, L , and a mercury valve, N , Precision of Method are provided for each absorber. One mercury valve closes a t the same time that the other opens, causing the air to The laboratory method was first tested by a comparison switch from one absorber to the other. While an air sample with the Selby method. The results given in Table I is being drawn through one absorber, the aspirated liquid indicate a fairly close correspondence between the two is discharged from the other and a fresh portion of reagent methods over a range of concentration from 0.5 to 20 p. p. m. is run in. A mercury air-relief valve, H , which is opened Each group of figures mas obtained in the course of a by the same cam as the pipet discharge valve, permits the fumigation experiment. Comparison is made of samples escape of air when the reagent flows into the absorber. The drawn in a few seconds by the Selby method and samples apparatus operates on a 2-minute schedule, and is timed very drawn continuously over a period of 6 minutes by the new uniformly by the motor. The Kelson pump delivers about method. 30 liters of air in 2 minutes, corresponding approximately The precision of the apparatus was further tested over a to 1 gram-molecular volume under the conditions of opera- greater range by determining the concentration analytically tion (30” and 640 mm. Hg). The rate of discharge of the of known mixtures of sulfur dioxide and air. The following pump is steady provided it is water-cooled during the hot procedure was used: weather, and it is only necessary to read the flowmeters sulfur dioxide flowmeter was carefully calibrated by absorboccasionally in order to determine with sufficient precision ingA all the gas discharged in standard alkali and titrating the the volume of the air sample. excess of sodium hydroxide after adding enough hydrogen peroxThe absorber consists of a standard “salvarsan tube.” ide to oxidize the sulfite to sulfate. The calibration curve obIt is not difficult to grind a glass rod with conical end so that tained was a straight line which extrapolated to the origin. fan having a capacity of about 10,000 liters per minute was it seats on the sloping bottom of the absorber to form a valve. A provided with a shutter over the intake so that the volume The rod passes through a glass sleeve in the center of the delivered could be varied a t will. The delivery of the fan was stopper. Gas-tight flexible joints between the rod and the then determined with various sized openings in the intake by sleeve are made with thin rubber tubing on valves D, F, and means of accurately calibrated anemometers which were placed the position of average velocity in a 6-inch (15-crn.) discharge J . The bubbler, M , consists of a 4-mm. glass tube bent at pipe. in a loop to fit near the periphery of the absorber, and pierced with ten holes, each about 1 mm. diameter, on the underside. In this way synthetic mixtures of sulfur dioxide and air of The solution contains about 1 gram of starch and 2 grams known concentration could be made a t will over a range
I
I
ISDUSTRIAL AiVD ENGIiVEERI-1‘G CHEMISTRY
June, 1928
of concentration up to 60 p. p. m. This apparatus is a part of fumigation equipment and is used in connection with a cabinet (6 by 6 by 5 feet), consiqting of an iron framework covered with celluloid. The data are presented in Table I1 and show agreement within the experimental error of measuring the air volume delivered by the fan. At the highest concentrations the analytical values are somewhat low, indicating incomplete absorption. This raises a question as to the stability and efficiency of the iodine solutions in absorbing sulfur dioxide, since it is possible that the agreement noted above is due to compensating errors of volatilization of the reagent and incomplete absorption. T a b l e I-SO2
in M i x t u r e s of SO2 a n d Air a s Given b y M e t h o d of
M a r s t o n a n d Wells a n d Kew M e t h o d ( E d c h group of figures represents several analyses made during a 1-hour fumigation)
P ~ . m .P . p m. P . p . m . P . p . m . P . 0 . m . P . 6 . m . P . 9 . m . P . 6 . m . 1.6 1 4 2 6 2.4 5.8 6.2 0 2 0.7 1.8 1.6 2 5 0 , 0.7 2 6 5.8 5.6 0 5 0.4 2.4 1.6 1.6 2 4 5.8 5.8 1.8 1.6 0 6 0.6 5.6 5.8 0 6 0.5 0 5 0.4 1 I
Av.
067
11 11 I 11 7 11 7 11 6
4
..
j . .
116
065 12.0 10.0 11.8 11.2 11.0
1
I
1 7
15.0 l5,4 15.7 15.6 15.4 15 9 1 1 2 1 1 5 6
T 8; C
I
2 5
15 2 15.2 15.2 15.4 15.0 15.2 1 5 2 1
17 5 17.5 17.7 17.4 17.2 17 I 1 7 6
1 6
= Thomas and Cross;
2 5
!
16 8 16.6 16.6 17 3 17.8 17 0 1 6 9 1
5 8
5 8
19.8 21.0 20.8
19.6 21 0 21 6
2 0 5
207
647
sulfur dioxide and volatilization of iodine-the errors partially compensating each other. At lower concentrations these errors are both negligible. Thus the method can be expected to give good results up to at least 60 p. p. m. The strergth of the iodine solution does not change appreciably over a 5hour period, provided it was several hours old when first used. It is necessary to protect the solution from direct sunlight. Table 11-Concentration
of Sulfur Dioxide i n S y n t h e t i c M i x t u r e with Air
RATEOF
FLOW Air
SO?
SO^ Calcd.
cONCN.
Found
I
1
RATEOF FLOW
Air
SOz
I
L./min. Cc./min. P. p , m. P . p . m. 1000 63.2 63 2 60.7 1000 61.0 61.0 58.9 52.5 1030 54.2 51.5 1030 34.2 33.0 32.2 1450 73.2 50.5 49.2 48.8 48.2 1450 70.9 1450 46.0 31.7 31.7 22 4 22.6 1450 32.4 1420 45.2 31.8 31.0 1420 22.7 16.0 16.4
1
SO, c o s c s .
Calcd.
Found
L . / m i n . Cc./min. P . p. m. P. p . m. 1550 16.2 10.6 11 2 13.8 9.1 9 4 1550 1550 10.6 7.0 7 3 1 Y 1550 2.8 1.9 5050 10 6 52.8 10.5 5050 8 0 40.0 7.9 0 0 5050 5.3 1.0 2 2 4920 10.5 2.1 13,300
1.4
0.10
0 105
,
?:z
hl & \V = Marston and \Tells
ating
The question was studied by connecting two absorbers in series. The second absorber contained a weak solution of iodine, while the concentration in the first was varied. (Table 111) When 28 liters of pure air are aspirated through 100 cc. of 0.0011 N solution, the losj of iodine is about 4 per cent. Only about half of this material is caught in the second absorier. The 0.0006 N s o l u t i o n is changed only about 1 per cent by this treatment a n d t h e more dilute s o l u t i o n s a r e q u i t e s t a b l e . At 0.0000751%’ the solution does not change when 400 l i t e r s of air are drawn through it. This is an important observation because it suggests the possibility of estimating if necessary minute traces of sulfur dioxide of the order of 1 part in 100 million parts of air. An experiment with 1 part sulfur dioxide in 10 million of air (Tables I1 and 111) gave satisfactory c o n c o r d . ance between the observed and calculated values. W i t h o t h e r mixtures of sulfur dioxide and air the highest c o n c e n t r a t i o n of F i g u r e 2-Portable A p p a r a t u s f o r t h e iodine indicates both inC o n t i n u o u s D e t e r m i n a t i o n of t h e C o n complete absorption of c e n t r a t i o n of S u l f u r Dioxide i n Air
Liters
After
Before ~ifi.
ating
ating
Affer
asplr. ating
Found
~ifi.
Calcd.
~
P U R E .IIR A S P I R A T E D
28 26 26 30 30 26 400
11.50 1 1 . 3 5 11.05 10.65 6.45 6.35 6.02 6.00 4.18 4.16 0.86 0.86 0.75 0.75
I 26 26 26 26 26 350
-0.45 -0.40 1:29 1 ’ 4 8 -0.10 0 . 7 5 0.80 -0.02 .. .. -0.02 0.00 0 : 8 6 0’86 0.00 .. ..
+6:i9 +0.05
...
0.00
...
II 0 7 5
0 96 4 so 0 30 3.26 0 44 0 49
-10.09 -6.25 - 5 95 -3.02 -0.42 -0 26
1.28 1.28 1.28 1.28 0.86
1.26 1.32 1.28 1.28 0.86
0 0 0 0
0 0 0
0 0
1
&CIIXTURES SO? AND A I R A S P I R A T B D
11 05 11 05 6 28
2.3 1.1 0.3 0.1
-0.02 +0.04 0.00 0.00 0.00
. .
I
51.5 32.2 31.0 16.4 2.2 0 104
52 5 33 0 31 8 16 0 2 3 0.10
The field apparatus was not checked, but it is evident that since it is identical in its principal features with the laboratory apparatus, results with it should be quite reliable. Acknowledgment
The authors desire to acknowledge assistance of J. K. Abersold and L. V. Olson in the experimental work reported in this paper. Mr. Olson used the field method a t El Paso, Texas, for the first time, and worked out a number of the details of operation. Geo. R. Hill, Jr., director of this department, has given constant advice and encouragement in this work.
Kew Series of Bulletins on Insecticides The Chemical Division of the Bureau of Foreign and Domestic Commerce of the U. S. Department of Commerce has recently inaugurated a new series of bulletins entitled “World Trade in Insecticides.” I t is hoped that these bulletins will fill a longfelt need of American manufacturers of insecticides who are seeking outlets for their products abroad. The plan is to survey the insecticide trade in all the important markets of the world in a fairly concise manner. The first bulletins will cover the Latin-American countries and will be followed by reports on other world markets. Copies of the bulletins may be obtained, without cost, by application t o the Chemical Division.
