(C) Peter Meiers - http://www.fluoride-history.de
|Early Patents on Fluoride for Water Softening|
On May 29, 1889, Charles Avery Doremus, of New York, filed a German Patent (DE 51,601) on a "Process for purification and softening of water" (publ. March 21, 1890). His method aimed at removing calcium and magnesium from water by precipitation as the rather insoluble fluorides. For that purpose, fluorides of either sodium, potassium, or ammonium, as well as hydrogen fluoride or cryolite (a double fluoride of sodium and aluminum) are added to water to be used for technical or household purposes. Doremus claimed a complete precipitation of the calcium and magnesium as the fluorides. "The precipitation of magnesium is especially thorough and noteworthy" he claimed in one of his related articles (1). The fluoride addition may be combined with sodium hydroxide or sodium carbonate to get easily filterable precipitates. Any remains of aluminum used for treatment of water for household purposes is likewise removed by the fluoride addition, the patent claims.
One of the chief difficulties met with in the pursuit of the work "was my inability to obtain in open market any fluoride in quantity, or at any but an exorbitant price. This has been so far overcome that sodium fluoride has been manufactured for me in large quantities at a figure which to the consumer will not prove prohibitive" (1).
While one might think that not every patented idea has found practical application, and that perhaps Doremus´ patent might belong to that ignored group of otherwise nice thoughts, the chemistry professor of the College of the City of New York (2) found it pleasant to be able to record in 1893 that "it is in successful operation in nearly every section of the country" (3). "The various types of water from New York to Albany and from there through the salt district to the lakes at Buffalo are now under this treatment with entirely satisfactory results. The employment of so small an amount of the chemical naturally reduces the cost of purification, while the ease of handling pleases the engineer. More than once it has happened that the boilers were heavily incrusted when the use of the fluoride was begun. The old scale was found to loosen rapidly, falling off in some cases by the bucket full. In others it was rotted and softened so that on the first cleaning it was easily scraped off."
Doremus´ method was found in a laboratory investigation to be only partially efffective (4), but it was nevertheless widely accepted as a standard method. Thus, in a review of a book on "Industrial uses of water" the reviewer criticized: "The chapter on feed-water for boilers is long and well-illustrated. The formation of boiler incrustations, and the sundry methods in use for their prevention are fully treated, although we find no mention of the employment of sodium fluoride for such purpose, a method first suggested by Doremus. ... To American readers the chapters on purification of water will be found disappointing. A number of foreign devices for water improvement are illustrated and described, but the results of their operations, which would give an idea of their relative merits, are not given, nor do we find mention of the excellent processes in use in this country" (5).
(1) J. am. chem. Soc. 12 (1890) 303; (2) Ind. Eng. Chem. 18 (1926) 214; (3) J. am. chem. Soc. 15 (1893) 610; (4) J. am. chem. Soc. 21 (1899) 665; (5) J. am. chem. Soc. 26 (1904) 717;
SOME EARLY PATENTS
Charles Avery DOREMUS, New York: "Verfahren zum Reinigen und Weichmachen von Wasser", German Patent (DE) 51,601; filed May 29, 1889; granted March 21, 1890 (method to remove calcium, magnesium and similar substances from water by addition of the fluorides of sodium, potassium or ammonium, hydrogen fluoride or cryolite to precipitate the insoluble compounds)
Adolph FRANK, Charlottenburg, Germany: "Verfahren zum Klären und Reinigen von Wasser mit Hilfe von Fluorsiliziumverbindungen", German Patent (DE) 224,192; filed Jan. 16, 1909; published July 8, 1910 (Method to clear and purify water by first treating it with alkali silicate and then adding Aluminum fluosilicate until a neutral or slightly acidic pH is reached)
Chemische Fabrik Flörsheim Dr. H. Noerdlinger, Flörsheim: "Verfahren zum Klären und Reinigen von Wasser", German Patent (DE) 236,754; filed June 10, 1910; published July 10, 1911 (treatment of waste water; addition of fluosilicates of magnesium, copper, aluminum, iron etc.)
Stanley A. SANFORD, Shaker Heights, Ohio: "Process of softening water", US Patent 1,705,589; filed Nov. 30, 1926; patented Mar. 19, 1929 (treating water to obtain water of zero hardness for either domestic or industrial purposes by adding barium sulfate, aluminum oxide and calcium fluoride)
Dr. Rickmann & Rappe: "Verfahren zum Enthärten von Wasser mit Hilfe von Fluoriden", German Patent (DE) 903,800; filed Oct. 2, 1948; granted June 3, 1953 (softening water by addition of fluorides of sodium or ammonium, or of cryolite)