| 摘要 |
<p>1419189 Determining water hardness MILES LABORATORIES Inc 28 Sept 1973 [2 Oct 1972] 45608/73 Heading G1B A test device for colorimetrically determining the amount of hardness present in water comprises a carrier (particularly ash-free absorbent paper) incorporated with a test composition comprising an indicator undergoing a colour change in response to magnesium ions (e.g. Eriochrome Black T or Calmagite), an alkaline buffering agent and magnesium disodium ethylenediamine tetraacetic acid. The buffering agent preferably maintains a pH from 9À0 to 11À5 and may be tris (hydroxymethyl) amino methane. The device may further comprise a desensitizing agent, capable of binding magnesium and calcium ions so that they do not react with the indicator, such as tartaric acid, gluconic acid anhydride, sodium malonate, sodium oxalate, sodium citrate, 8-hydroxyquinoline or an aminopolycarboxylic acid salt not containing magnesium and calcium ions e.g. Na 4 EDTA. The device may further comprise a background dye e.g. tartrazine yellow. The amount of total hardness present in a water sample is tested for by contacting the water sample and the test device and comparing any apparent colour change developed in the test device with a colour chart standardized to indicate the amount of hardness present in a water sample.</p> |
