406
ANALYTICAL EDITION
along the upper base, bc. Similarly to represent the causticity of boiler waters, the hydroxyl ion should be plotted as a segment along bc. 1 APPLICATIONS As an illustration of the utility of the rectangular diagram, a specific application of this method to represent the municipal water supply of New Orleans both before and after purification by the lime-iron process is given in Figure 2. Average
Vol. 4, No. 4
analyses sodium is obtained by calculation, the difference between the values reported for this ion in river and in filtered waters arises from cumulative errors in sampling, storage, and analysis. It should be noted that free carbon dioxide in river water and residual bicarbonate alkalinity in treated water are plainly indicated in the plot. TABLEI. AVERAGE ANALYSES OF MISSISSIPPI RIVERWATER AND OF NEWORLEANS TAPWATER FOR 1931 I
ITEM Si02
Tt2} CATIONS: Ca
EQUIV.WT.
.... ....
RIVERWATER Milli-
P. p . m. equin./?iler 5.9
...
0.0
...
38.6 18.5
1.926 0.822 0.806
16.8 7.1 22.8
0.839 0.584 0.992
0.0164 0.0208 0.0282 Solids by analysis (all HCOs as COS) Sohde by evaporation Incrustants (as CaCOs) Alkalinit (as CaCOs): Methyyoran Phenolphthafem Free COL
115.9 41.9 27.7
1 * 900 0.872 0.782
45.0 43.0 27.7
0.738 0.895 0.782
10.0
so4
c1
analyses for the past year are given in Table I. The solid lines, rectangle ABCD, represent the mineral analysis of raw Mississippi River water. This plot shows clearly that river water is relatively low in dissolved solids, fairly hard, most of the hardness is due to calcium, magnesium is small relative to calcium, and the molar sulfate carbonate ratio is about 0.5. The smaller rectangle, AEFG, represents the composition of partially softened tap water and indicates reduction principally in calcium and bicarbonate. Magnesium has been reduced slightly, but noncarbonate hardness just barely increased by addition of the coagulant. The molar sulfatecarbonate ratio has been doubled. Since in the
Milli-
P. p . m. squiv./liter 7.8
0.0499 0.0822 0.0435
ANIONS: HCOi
FIGURE2. RECTANGULAR DIAGRAMS FOR NEW ORLEANSWATER SUPPLY
... ...
0.0
TAPWATER
201.5 221 29.4
148.1 158 33.3
95.0 0.0 1
36.9 16.4 0.0
If all hardness were removec by zeolite treatment, L.2 rectangle AEFG would still show the anions in the completely softened effluent, but the sides EF and FG would now represent sodium. A single set of related rectangles has thus effectively described the characteristics of a given water and its modifioations. LITERATURE CITND (1) Collins, IND. ENG. CHEM.,15, 394 (1923). (2) Greenfield and Baker, Ibid., 12, 989 (1920). (3) Reistle, Bur. of Mines, Tech. Paper 404 (1927). (4) Tickell, Report of California State Oil and Gas Supervisor, Vol. 6, No. 9, pp. 5-11 (March, 1921). REOICIVED April 7, 1932. Presented before the Division of Water, Sewage, and Sanitation Chemistry at the 83rd Meeting of the American Chemical Society, New Orleans, La., Mamh 28 to April 1, 1932.
Determination of Benzene in Solvent Mixtures WARRENA. COOK,Connecticut State Department of Health, Hartford, Conn.,
AND
JOSEPH B. FICKLEN,
Travelers Insurance Company, Hartford, Conn.
A
SIMPLE and rapid method for the detection and estimation of benzene in solvent mixtures, of sufficient sensitivity to be further adapted to the determination of the concentration of benzene vapors in air when of interest from a health standpoint, has been deemed necessary. This method should make the results attainable immediately in the plant without reverting to the laboratory. There are data available (7) to show that concentrations of benzene in air as low as 100 parts per million are objectionable. Since the type of absorption apparatus usually employed for collecting samples of vapors in air handles a liter of air per minute, a 30minute run would make only about 0.012 ml. of benzene available when the above concentration occurs. Consequently, it was considered necessary to have a method of sufficient sensitivity to detect this small amount. This discussion will be confined to a survey of possible
methods, their relative advantages and disadvantages, and a description of sufficient experimental data covering two methods investigated in the laboratory, one of which fulfils the above requirements rather well and is adaptable where there is as little as 0.010 ml. of benzene available in the liquid phase. I n a subsequent work the authors hope to show that this method is also adaptable to the determination of benzene in air.
POSSIBLE METHODS Four reactions were found in the survey of the literature which gave promise of being applicable. 1. Bromination in presence of anhydrous aluminum bromide j n* 2. Nitration with a mixture of concentrated sulfuric and fuming nitric acids (6).
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INDUSTRIAL AND ENGINEERING CHEMISTRY
3. The “pernitric acid” method (6). 4.
The oxidation method with hydrogen peroxide in presence of iron salts (8).
BROMINATION. The method of Gustavson (3) for the detection of aromatic hydrocarbons in gasoline is based on complete bromination in the presence of anhydrous aluminum bromide. The hexabromobenzene and the pentabromotoluene are crystalline products, whereas the aliphatic bromine compounds are liquids. Because of this, the hexabromobenzene and pentabromotoluene may be filtered off and weighed. Schultz (4) has shown that even a few milligrams of benzene
407
of lower (aqueous) layer with a pipet. To these 3 ml. add a piece of sodium hydroxide about the size of a small pea. Formation of a distinct brick-red ring a t bottom of the test tube indicates presence of benzene. This method, as well as slight improvements on it, such as use of nitric acid and hydrogen peroxide in place of sodium nitrite, hydrogen peroxide and sulfuric acid mixture and also alcoholic potassium hydroxide in place of solid sodium hydroxide, were tried. The limit of sensitivity was 0.05 ml. of benzene, and in this range one ml. of toluene produced approximately the same color reaction. This method is regarded as unsatisfactory because the p r e p a r a t i o n of n i t r i c oxide or its transportation in sufficient amount in the field is relatively i n c o n v e n i e n t , a n d because toluene seriously i n t e r f e r e s a t the lower limits of sensitivity on the reaction.
OXIDATIONMETHOD BY MEANSOF IRON SALT6 AND HYDROGEN PEROXIDE Since t h e a u t h o r s were not int e r e s t e d in t h e r e a c t i o n of large quantities of benzene but rather in the development of the reaction to give a test for the smallest possible amount of benzene, experiments were first run to arrive a t the optimum amounts and concentrations of the reagents for this purpose. It was found that a reddish brown coloration developed and a fine black precipitate was formed on the addition of 5 ml. of 0.5 per cent ferrous sulfate solution and 2 ml. of one per cent hydrogen peroxide to as little as 0.01 ml. of benzene. Even amounts FIGURE1 down to 0.005 ml. of benzene caused the development of the characteristic or toluene can be determined in air in the presence of ethylene. reddish brown coloration. I n conducting these tests, the benFor the purpose desired, this method is regarded as unsatis- zene was measured in a capillary pipet of such bore that the factory by the authors for the following reasons: The neces- hundredth milliliter graduations were a centimeter apart. On sity of using bromine and aluminum powder was objection- account of its convenience, the volumetric measurements were able in field work; washing, drying, and weighing the pre- used and considered permissible since careful technic was obcipitate are manipulations which are not feasible in field work; served and gravimetric checks run from time to time. and the test for benzene is not specific. A group of experiments was then conducted to determine NITRATION WITH CONCENTRATED SULFURIC AND FUMINGwhether other solvents interfered with this reaction. It was NITRICACIDS. This method involves, after the absorption found that most other solvents inhibited the reaction, and and nitration of the benzene by a mixture of concentrated that generally the more water-soluble, the smaller the amount sulfuric and fuming nitric acids, the steam distillation of the necessary to cause interference. nitration product, mdinitrobenzene. The m-dinitrobenzene DESCRIPTION OF APPARATUS. I n order to avoid this interis quantitatively reduced in an excess of standard titanous ference, an apparatus was designed to remove the more waterchloride, the excess of this reagent being estimated by ferric soluble substances from the solvent mixture. This is illuschloride using potassium thiocyanate as indicator. I n the trated in Figure 1. It consists of a vaporizing tube, A , a words of the investigator ( 5 ) ,“The method is admitted to be bubbler type absorption bottle, B, and a trap, C, immersed somewhat cumbersome and slow, but it is specific for benzene in a freezing mixture of solid carbon dioxide in acetone. in the presence of many compounds known to be interferences These units are joined by ground-glass connections. A in previously used methods. It will satisfactorily estimate rubber tube attached to the flowmeter leads to suction. The benzene for hygienic purposes in the presence of as much capillary part of the vaporization tube is graduated to 0.02 as four times as much toluene as benzene, which is a strong ml. and has a capacity of slightly more than 0.3 ml. point in its favor.” I n view of the foregoing, this method EXPERIMENTAL PROCEDURE. One- to three-tenths millidoes not meet the authors’ requirements. liter of the solvent mixture is placed in the vaporizing tube, PERNITRIC ACID METHOD.This method as used by and air drawn through the apparatus a t the rate of one-third Trufonow (6) is as follows: To 2 ml. of the sample add 4 ml. liter per minute. To facilitate vaporization, a capillary is of an equivolume mixture of 4 per cent sodium nitrite solution inserted well into the vaporizing tube. The vapors are and a 3 per cent hydrogen peroxide solution. Shake thor- bubbled through the absorption bottle in which are placed 25 oughly. Add 2 ml. of 2 N sulfuric acid and again shake ml. of water. A small amount of pure benzene is run through thoroughly. Allow to stand for one minute and remove 3 ml. the apparatus previously in order to saturate the water under
408
ANALYTICAL EDITION
Vol. 4, No. 4
TABLEI. EXPERIMENTAL RESULTS these conditions. Most of the benzene and a small portion of the more water-immiscible solvents pass over into the AMT. OF AMT. OTHERSOLVENTS TAKBN R~ACTION trap which is placed in an acetone-solid carbon dioxide bath. BENZBNB MI./lo00 M1./1000 Here the benzene is frozen out of the air stream and de0 Toluene 200 None Toluene 10 90 Black ppt. posited. After passing air through the system for 2 minutes, 20 Toluene 200 Black ppt. the trap is removed. Five milliliters of 0.5 per cent ferrous 0 Xylene 200 None 10 Xylene 90 Blark ppt. sulfate are directed down the inlet tube, followed immediately 20 Xylene Black ppt. 200 with 2 ml. of one per cent hydrogen peroxide. Both these 0 Methanol 200 None 10 Methanol 90 Black ppt. reagents should be made up shortly before running the tests. Methanol 20 Black ppt. 200 The trap is shaken 2 minutes and the contents poured into a 0 Ethyl alcohol 200 None 10 Ethyl alcohol 90 Black ppt. test tube. If benzene is present in amounts of 0.010 to 0.050 Ethyl alcohol 20 200 Black ppt. tnl. in the solvent mixture added to the vaporizing tube, a 0 Isopropanol 200 None 10 Isopropanol 90 Black ppt. brown coloration suddenly develops and then a n amorphous 20 Isopropanol 200 Black ppt. black precipitate. This may occur in 2 to 5 minutes after the 0 n-Butanol None 200 10 n-Butanol 90 Black ppt crystals in the trap have melted. 20 n-Butanol 200 Black ppt. A procedure which assisted in the utilization of this method 0 Isobutanol 200 None Isobutanol 10 90 Black ppt. quantitatively was developed as follows: 0.200 ml. of the Isobutanol 20 200 Black ppt. solvent mixture is placed in the vaporizing tube, the pro0 n-Amyl alcohol 200 None 10 n-Amyl alcohol 90 Black ppt. cedure outlined above is followed, and the results noted after n-Amyl alcohol 20 200 Black ppt cleared t o brown the reaction mixture has been removed from the trap and 0 Ethyl acetate 200 None Ethyl acetate 10 90 Black ppt. allowed to stand for 3 minutes. If the black amorphous Ethyl acetate 20 200 Brown precipitate is formed, 0.010 ml. or more benzene was present. 0 Ethyl propionate 200 None Ethyl propionate 10 90 Black ppt. (Between 0.010 and 0.012 ml., the black precipitate is pron-Butyl acetate 0 100 None duced in an exceedingly finely divided state and does not 10 n-Butyl aoetate 90 Black ppt. cleared to brown coalesce or readily settle out. Therefore, it is desirable for 0 Isoamyl acetate 200 None Isoamyl acetate 10 90 Black ppt. the one conducting the test to run through the procedure Isoamyl acetate 20 200 Black ppt and determine exactly the minimum amount of benzene Ethylene chloride 100 None 0 Ethylene chloride 20 20 Black ppt. which, in his opinion, gives the black precipitate.) The Trichloroethylene 100 None 0 total amount of solvent placed in the vaporizing tube should Brown ppt. Trichloroethylene 20 20 200 None Tetrachloroethane 0 then be decreased until the reaction mixture just shows the Black ppt. Tetrachloroethane 200 20 black amorphous precipitate. Since 0.010 ml. is the minimum 100 Carbon tetrachloride None 0 Black p p t ~ 90 Carbon tetrachloride 10 amount of benzene which will produce this precipitation, the None 200 Acetone 0 percentage of benzene in the solvent mixture can be calculated. 200 Black ppt. 20 Acetone If the characteristic brown coloration develops without 100 Soln. greenish, amorphous Carbon disulfide 0 sulfur ppt. the black precipitate, 0.005 ml. or more benzene was present. Black ppt. plua amorphoua 90 Carbon disulfide 10 sulfur Both in this case and also when there is no reaction, an 200 None Cellosolve 0 indication of the presence of benzene, qualitatively and 100 Black ppt. cleared to brown Cellosolve 10 quantitatively, may be obtained by running a series of tests 200 Black ppt. cleared to brown Cellosolve 20 200 None Gasoline 0 in which measured amounts of pure benzene are added to the Black ppt. 200 Gasoline 20 solvent mixture. MIXTVR~S Upon the addition of 1 ml. of 2 N nitric acid, the black Eouivolume mixture of all 0 amorphous precipitate will dissolve and the solution may None 20 then be diluted with water and compared with standards. This colorimetric method permits greater accuracy in the Brown ppt. Equivolume mixture of 0 quantitative estimation of benzene. toluene and xylene 200 None If carbon disulfide is present, amorphous sulfur is liberated. Equivolume mixture of 20 toluene and xylene 200 Black ppt. This is of course not dissolved on the addition of the nitric Equivolume mixture of 6 0 acid and should be filtered from the solution. The benzene alcohols aboye 200 None Eauivolume mixture of 6 20 may then be estimated from the coloration of the filtrate. alcohols above 100 Black ppt. Eouivolume mixture of 3 0 Inasmuch as this reaction is decidedly complicated, yielding ‘acetates above 200 None a mixture of phenol, catechol, hydroquinone, and the black Equivolume mixture of 3 20 acetates above 200 Black ppt. amorphous precipitate mentioned above, it could hardly be expected that the colors of the resultant liquid described in ACKNOWLEDGMENT the preceding paragraph would lend themselves to anything more that a rough quantitative estimation, except over a very The authors wish to express their appreciation to Eimer narrow range such as around 0.010 ml., as described above. and Amend, New York, N. Y., for the helpful suggestions in For the same reason it is highly important to observe the same designing the apparatus shown in Figure 1, technic in all tests. However, the entire estimation takes less than 10 minutes to run, so the number of these estimations LITERATURE CITED can be run rather economically in order to get the desired (1) Allen, “Commerical Organic Analysis,” 5th ed., Vol. 111, Blakisquantitative accuracy. ton, 1925. Table I shows the results obtained with the reaction on (2) Cross, Bevan, a n d Heiberg, Ber., 33, 2015 (1900). mixtures of benzene and various other solvent’s. The solvents (3) Gustavson, G., J. SOC. phys.-chim. Tusse, 15, 401 (1883). listed include most of those ordinarily used for industrial (4) Sohultz, F., Collection Czechoslov. Chem. Comm, 1, 228-33 (1929). operations and having boiling points relatively near that of (5) S m i t h , H. F., Jr., J.Ind. Hug., 11, 338-48 (1929). Trufonow, Z. anorg. allgem. Chem., 124, 136 (1922). benzene. Solvents boiling a t temperatures appreciably (6) (7) Winslow, C. E. A,, Final Rept. Comm. Benzol, National Safety higher than the boiling point of benzene were not included, Council, May, 1926. since they would not be sufficiently vaporized under the exRECEIVIDJune 10, 1932. perimental conditions to impede the reaction.
