GB902884A - Improvements relating to the testing of water by the use of reagents in tablet form - Google Patents

Abstract

Tablets for the testing of water to evaluate impurity therein comprise a standard reagent and an indicator compressed together in the same tablet. The standard reagent is a chemical able, under the conditions of test, to react quantitatively with the substance to be determined, and the indicator is one able, by change of colour, to denote completion of the quantitative reaction. Standard reagent indicator couples specified are (1) a polyaminocarboxylic acid, e.g. EDTA, or a salt thereof, and a metal indicator, e.g. Eriochrome Black T or Murexide (ammonium purpurate) which couple may be used for determining the sulphate content or the hardness of water, (2) sulphamic acid or a soluble bisulphate, e.g. KHSO4, and a pH indicator, e.g. methyl orange, methyl red, thymol blue, or phenolphthalein, which couple may be used for determining the alkalinity of water, (3) a reducing agent, e.g. ferrous ammonium sulphate, and an oxidation-reduction indicator, e.g. methylene blue, which couple may be used for determining the dissolved oxygen content of water, (4) an oxidizing agent, e.g. KMnO4, and an oxidationreduction indicator, (5) a soluble silver salt, e.g. AgNO3, and a soluble chromate, which couple may be used for determining the chloride content of water, (6) Na2CO3 or K2CO3 and a pH indicator, e.g. thymol blue or phenolphthalein, which couple may be used for determining the free carbon dioxide content of water, (7) a soluble iodide-iodate mixture, e.g. Kl with KlO3, and an iodine indicator, e.g. starch, which couple may be used for determining the sulphite content of water, and (8) a soluble permanganate, e.g. KMnO4, used in the presence of a soluble iodide and an acidifying agent, for example, a soluble bisulphate, and an iodine indicator, e.g. starch, which combination may be used for determining the content of organic matter in water. The tablets may contain buffering and masking agents, examples of which are given where applicable, and also fillers, e.g. NaCl, KHCO3, or sucrose, disintegrants, e.g. starch, and lubricants, e.g. talcum or boric acid. The examples give a number of specific tablet compositions. In determining an impurity, the tablet is added to a determined volume of water. If more than one tablet is necessary, the tablets are added in succession until a colour change defining the end-point of reaction between the standard reagent and the substance being determined is produced. Specification 686,817 is referred to.