GB793792A - Improvements in or relating to the determination of impurities in water - Google Patents

Abstract

793,792. Purifying water. CENTRAL ELECTRICITY AUTHORITY, and SCRASE, H. F. J. Jan. 6, 1956 [Feb. 1, 1955], No. 3013/55. Class 46. [Also in Group XL(b)] A method for the quantitative determination periodically of a non-gaseous impurity in a water supply comprises adding to successive samples of the water at predetermined time intervals measured quantities of two or more reagents nephelometrically or colorimetrically responsive to said impurity, allowing an interval for the opacity or colour to develop and then passing the treated sample to an optical cell through which a beam of light passes to a photoelectric cell, the response of the cell providing a measure of the impurity content. The invention is described primarily as applied to the determination of the silica content in water taken from a treatment installation including ionexchange beds for removing silica, although reference is also made to the determination of the presence of phosphate ions. In a preferred form of the invention a reagent in the form of a hydrochloric acid solution of ammonium molybdate is used in conjunction with a solution of 1-amino-2-naphthol-4-sulphonic acid in sodium metabisulphite solution. The presence of silica results in a glue coloration, the density of the coloration being detected by the photo-electric cell by causing the beam of light to pass first through a red filter. In a first embodiment for carrying out the invention, liquid dispensers 37, 38, 39 containing the reagents are provided together with a sample dispenser 36 fed with the water to be tested from a constant head container 42. The reaction is effected in a vessel 40 provided with an electrically-driven stirrer 53, and the resulting coloration is measured by passing the solution to a chamber located between a light source 56 with red filter 57 and a photo-electric cell 58. Each of the reagent dispensers is associated with a pipette 46 arranged so that a predetermined volume may be drawn off, and the whole operation of the apparatus proceeds automatically by controlling the charge and discharge valves 43, 44, 47, 48, 49, 50, 51, 52, 55 throughout the apparatus electrically from a master time clock. A typical sequence of operations may be as follows : valve 43 opens and passes water under test to the dispenser 36 which is then discharged via valve 44 to the reaction vessel 40. Simultaneously the first two reagent dispensers 38 and 39 discharge to the reaction vessel measured volumes of hydrochloric acid and ammonium molybdate solutions. Valve 49 of the third dispenser opens during this period and allows 1 -amino-2-naphthol-4-sulphonic acid solution to pass from the reservoir to the pipette. This measured volume is discharged to the reaction vessel after 5 minutes. After a further 12 minutes valve 55 opens and passes the solution to measuring cell 41. During this time reagent dispensers 38 and 39 recharge their pipettes by operation of valves 47 and 48. The time required for the complete sequence is 20 minutes. The reagent circuits of the master time clock may be switched out and the water sequence alone continued so that the measuring cell is continuously flushed with fresh water to provide a " zero " reference output from the photoelectric cell. Where it is desired to detect the presence of phosphate, it is stated that the apparatus is modified by the inclusion of a further reagent vessel containing oxalic acid solution. Where the characteristics of the water and/or photo-electric cell are liable to vary, the water sample to be tested is divided into two parts, one being treated with reagents as described above and the other not being treated. The measuring light is then passed through the two portions to corresponding photo-electric cells connected to apparatus arranged to respond only to the difference of the cell outputs. A second generally-similar embodiment is illustrated in the drawing accompanying the Provisional Specification. The output from the photo-electric cell may be employed automatically to initiate the regeneration of ion exchange beds employed for the treatment of the water when more than a predetermined amount of silica is detected.