Graphical Representation of Mineral Components in Water Analyses A. ADLERHIRSCH, Sewerage a n d Water Board of New Orleans, New Orleans, La.
A
GRAPHICAL method for expressing water analyses how widely in total concentration, rectangular diagrams are should depict adequately composition and significant geometrically similar. Only the size will change. If a water undergoes change chemically, its diagram will relationships. Previously reported diagrams for representing results of water analyses include those of Tickell (4,vary in size, shape, or in special cases, merely by segmentation. Reistle (S), Collins ( I ) , and others. Although the width of the diagram for a typical natural The method presented herein consists in plotting milliequivalent concentrations of the various ions along the sides water may become relatively small by elimination of bicarof a rectangle in such a manner that its segmentation, form, bonate through treatment to its solubility limit, the figure and size completely describe the dissolved minerals. Refer- will in general retain its height except in cases where sulfate is ring to Figure 1, the construction of the rectangular diagram changed intentionally by addition of some soluble sulfate, or is reduced by barium softening. from an ionic analytical statement is as follows: Let OX and OY be horizontal and vertical coordinate axes, Y respectively. On OY scale off a length, Oa, proportional to the magnitude of chlorideion in the water. Starting at a, lay off a length, ab, proportional to the amount of sulfate. At point 6 , perpendicular to axis OY lay off bc proportional to the bi-Total Hardness carbonate content, or in cases where both bicarbonate and -Carbonate H s r d n e ss carbonate ions are present together, the equivalent of their sum may be used. Drop from point c a perpendicular, cd, - Ca+*-+-Mg++ to axis OX. To represent chions, commence a t point b and lay off be proportional to calcium and ec plus cf proportional to 2 e / magnesium. If in a sample calcium is greater than bicar/ f bonate, then point e will be located on vertical dc. The re/ sidual length, fd,represents the amount of sodium present and / / may be used in this way to solve graphically for the sodium / content of a water or to check the analytical value obtained i therefor. I n most cases the alkali ions sodium and potassium may be considered entirely as sodium. The lengths be, repreNa' senting calcium, and ec, a part of the magnesium, might just as well have been located along the base od, except that this part of the diagram as drawn gives the advantage of coincidence to aid in comparisons.
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LI
RELATIONMIIPS A rectangular diagram can readily be drawn on ordinary graph paper and shows a t a glance several important characteristics of the water. The perimeter represents the total concentration of minerals in the water; one-half of the perimeter measures the normality of the solution. Relative lengths of segments indicate relative concentrations of the various ions. The width of the figure shows the so-called temporary hardness, or more properly the carbonate hardness of the water. Segments be and (ec plus cf) indicate relative amounts of calcium and magnesium; their sum represents the total hardness. Incrustants, or noncarbonate hardness, is shown by the length cf. If a water sample shows negative hardness, point f will lie somewhere along the line bc, in which case segment fc will geometrically represent the amount of negative hardness. The sulfate-carbonate ratio, if the water is completely softened by zeolites for boiler feed, is indicated by the ratio of segments ab to bc, or the slope of the diagonal ac. As it stands, the diagram pairs off cations and anions by assigning them homologous positions. No imaginary compounds are hypotheticated. All graphical relationships arise solely from the choice of appropriate positions for the various ions. For waters constitutionally similar but varying no matter
RECTANGULAR DIAQRAM
I n special instances of waters having unusual composition, such as those from some mineral springs, any rarely occurring ions may be included in the diagram in positions occupied by chemically similar ions. For highly siliceous water, the silicate radical should be included in the figure. In segment bc the carbonates have been reduced to equivalent bicarbonate ion mainly because the bicarbonate condition is usually associated with natural waters. If preferred, this detail may be reversed and the carbonate ion plotted instead. If maximum differentiation is desired, the proportion of carbonate and bicarbonate may be indicated by a secondary division along line bc. Free carbon dioxide may be appended in the diagram by extending line bc across its intersection with the vertical dc. Since the ratio of free carbon dioxide to the bicarbonate alkalinity in many waters is an index of the the diagram affords pH, as shown by Greenfield and Baker (i?), a graphic approximation thereof. When representing acid mine or volcanic waters, the total amount of titratable hvdrogen ion should be dotted as a cation, Dreferablv
405
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 MilliP. p . m. equin./?iler 0.0
...
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
... ...
5.9
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).
