January 1953
i .
INDUSTRIAL AND ENGINEERING CHEMISTRY
Hydrofluosilicic acid installations have not been very numerous, because of the lack of supply; however, with the present endorsement being given the program, this acid will soon be available a t a cost competitive with sodium silicofluoride. Usually, the acid is fed directly from the shipping container, which is placed on a scale and taken by suction directly from the container. This makes a simple installation with a means of rapidly determining the amount fed. The question of whether the acid should be diluted depends on the particular product. I n some cases, there is an excess of silica or hydrofluoric acid in the product. If the resulting dilution approaches neutrality or alkalinity, a fine silica precipitate may result, with some loss of fluoride. If diluted, a rubber- or plastic-lined container should be used, since this acid attacks glass or ceramic vessels. Equipment is available for transferring the last few quarts of the hydrofluosilicic acid t o a new container. As is the case with any concentrated chemical coming in contact with another liquid having a high mineral content, a supersaturated solution may result at that point with precipitation. I n solution feeding, this may result in the “plugging” of the injection nozzle. Adequate provision should be made for rapid removal of the nozzle and its cleaning, or, if possible, in open channel feeding, a n air gap should be provided between the tubing and the main flow. ANALYTICAL METHODS
The most accurate method of determining fluorides in potable water supplies is the Willard and Winter (18) method of distilling from a sulfuric or perchloric acid solution. This procedure (1) is the most accurate determination eliminating all interfering compounds. Although it is accurate, it is one of the most exacting and time-consuming tests. An alternative test (ScottSanchis) depends on the decolorization of zirconium-alizarin lake by the fluoride. This is less tedious, but is affected by a number of compounds. I n the range of 1.2 to 1.6 p.p.m., the determination is unreliable for operators not familiar with the color, because it depends on the matching of a straw color, for depth and shade. When the initial test shows a reading of 1.2 t o 1.6 p.p.m., it is common practice to dilute the sample with distilled water t o bring the color in the 0.6 to 1.0 p.p.m. range There are three commercial test kits available. While some states permit their use for all routine testing, others insist that the “Standard Methods” procedure (1) be followed, and test kits used only t o facilitate adjustment of dosage. One of these test kits makes use of glass color standards. The test itself is essentially the Scott-Sanchis method. At first, the reagent was found t o be unstable, even under refrigeration, and now the components are shipped in separate bottles for mixing as required. Many operators prefer this test set, because the comparator tubes are long, and are fully enclosed with a n artificial light source. This test requires 1 hour for the development of the correct color intensity, the range being from pink (0.0 p.p.m.) to yellow (1.6 p.p.m.). Another test set, employing liquid standards, uses the Lamar method. This is similar to the Scott-Sanchis method, but in preparing the reagent the Lamar method uses hydrochloric acid, whereas the Scott-Sanchis uses sulfuric and hydrochloric acids. Suppliers recommend the purchase of a small amount a t a time. This test has the same coloring agent and the same difficulty in determining the exact match. The third test provides for the preparation of the reagents and standards a t the time the test is run. All these tests are susceptible to interfering compounds requiring check tests by the distillation method, t o prove presence or absence of interfering compounds. When free chlorine is the interfering compound, it can be removed by thiosulfate or arsenite. An excess of thiosulfate may cause turbidity due to sulfate precipitation. A final concentration below 100 p.p.m. is a safe value for thiosulfate. Arsenite and sulfite have also been used for dechlorination and an excess of 200 p.p.m. has given no itrouble.
111
Within the past few months there have been a t least two new developments in fluoride test procedures. The Megregian-Maier method is an attempt to provide a more pronounced coloring. Procedures are given for both visual and photometric comparison (11). Another procedure, which provides a n abrupt color change t h a t develops in 5 minutes (Is),has been used in Massachusetts for the past 5 years with excellent checks with other procedures. Details of the strict preparation of the reagent are outlined by Rubin (IS). LITERATURE CITED
Am. Pub. Health Assoc. and Am. Water Works Assoc., New York, “Standard Methods for the Examination of Water and Sewage, pp. 76-9, 1947. Armstrong, W. D., and Brekhus, P J., J . Dental Reseaich, 17, 27-30 (1938).
Ast, D. B., J . Am. Water Works Assoc., 35, 1191 (1943). Biddle, E. S., Pub. Works, 82, 55-6 (1951). Dean, H. T., Arnold, F. A., Jr., and Elvove, E., U. S. Pub. Health Service, Pub. Health Repts., 57, 1155-79 (1942). Dean, H. T., and McKay, F. S., Am. J . Pub. Health, 29, 590-6 (1939).
Harper, L. E., J . Am. Water Works Assoc., 43, 744-62 (1951). Kleber, J. P., private communication. McKay, F. S., Dental Cosmos, 67, 847-60 (1925). Maier, F. J., J. Am. Water Works Assoc., 42, 1120-32 (1950). Megregian, Stephen, and Maier, F. J., l b i d . , 44, 239-48 (1952). Roholm, K., “Fluorine Intoxication,” London, H. K. Lewis and Co., 1937.
Rubin, L. J., J . New Enol. Water Works Assoc., 66, 97-8 (1952). Smith, L. A., Water and SewaQe Works, 96, 125-9 (1949). Todd, A. R . , Am. City, p. 87 (November 1951). Waldrep, B., J . Am. Water Works Assoc., 44, 10-14 (1952). White, E., Gillespie, C., and Smith, 0. M., Ibid., 44,70-1 (1952). Willard, H. H., and Winter, 0. B., IND. ENQ.CHEM.,ANAL.ED., 5, 7 (1933). RECEIVED for review April 23, 1952. ACCEPTED ilugust 23. 1952. Presented before the Division of Water, Sewage, and Sanitation Chemistry, at the 121st Meeting of the AMERICAN CHEMICAL SOCIETY,Milwaukee, Wis.
Liquid-Liquid Equilibrium Data for System Carbon Tetrachloride-Acetone-Water-Addendum I n the article entitled “Liquid-Liquid Equilibrium Data for the System Carbon Tetrachloride-Acetone-Water,” by Robert H. Buchanan [IND.ENG.CHEY., 44, 2449 (1952)], the author presented the system water-acetone-carbon tetrachloride as though it were entirely new. Reference shculd have been made to Herz and Rathman 12. Elektrochem., 19,553 (1913)l; “Seidell’s Solubilities,” Vol. 11, page 181 (1941) which gave distribution values; and to Leikola [Suornen.Kemislilehti, 13B,13-17 (1940)], who gave data for t h e binodal curve. The graph is shown with numerical data in Seidell’s supplementary volume, page 840 (19521, and is in good agreement with Buchanan. ALFREDW. FRANCIS
Four Ternary Systems Involving Monochlorobenzene-Addendum I n the article entitled “Four Ternary Liquid Systems Involving Monochlorobenzene,” by John S. Peake and Kenneth E. Thompson, Jr. [IND.ENG.CHEM.,44, 2439 (1952)], the authors state that only two references in the liturature present data on systems involving chlorobenzene. I n making this statement the authors overlooked the papers by Siggia and Hanna [Anal. Chem., 21,1086-9 (1949)], on water-methanol-chlorobenzene, and by Newman, Hayworth, and Treybal [IND.ENG.CHEiv., 41, 2039 (1949)], including water-methyl ethyl ketone-chlorobenzene. ALFREDW. FRANCIS
