Water [7732-18-5] M 18.0 , B 100.0°C Conductivity water (specific conductance ca. 10-7 mho) can be obtained by distilling
water in a steam-heated tin-lined still, then, after adding 0.25% NaOh and 0.05% KMnO4, distilling once more form a electricallly heated
Barnstead-type still, taking the middle fraction into a Jena glass bottle. During these operations, suitable traps must be used to protect against
entry of CO2 and NH3. Water only a little less satisfactory for conductivity measurements (but containing traces of organic material) can be obtained
by passing ordinary distilled water through a mixed bed ion-exchange column containing, for example Amberlite resin IR 120 (cation exchange) and IRA
400 (anion exchange) or Amberlite MB-1. This treatment is also a convienient one for removing traces of heavy metals. (The metals Cu, Zn, Pb, Cd and
Hg can be tested for by adding pure concentrated ammonia to 10mL sample and shaking vigorously with 1.2mL 0.001% dithizone in CCl4. Less than 0.1 ug
metal ion with impair a faint colour to the CCl4 layer.) For almost all laboratory purposes, simple water yields water of adequate purity, and most of
the volatil contaminants such as ammonia and CO2 are removed if the first fraction of distillate is discarded. |
