hard water

hard water
water that contains magnesium, calcium, or iron salts and therefore forms a soap lather with difficulty.

* * *

Water that contains mineral salts of calcium and magnesium, principally as bicarbonates, chlorides, and sulfates, and sometimes iron.

Hardness caused by calcium bicarbonate is known as temporary, because boiling converts the bicarbonate to the insoluble carbonate; hardness from the other salts is called permanent. The calcium and magnesium in hard waters form a hard, adherent scale on boiler plates, increasing fuel consumption and leading to deterioration through overheating. Home water softeners consist of tanks containing zeolite minerals or ion-exchange resins, which contain sodium ions that change places with the calcium and magnesium.

* * *

      water that contains salts of calcium and magnesium principally as bicarbonates, chlorides, and sulfates. Ferrous iron may also be present; oxidized to the ferric form, it appears as a reddish brown stain on washed fabrics and enameled surfaces. Water hardness that is caused by calcium bicarbonate is known as temporary, because boiling converts the bicarbonate to the insoluble carbonate; hardness from the other salts is called permanent. Calcium and magnesium ions in hard water react with the higher fatty acids of soap to form an insoluble gelatinous curd, thereby causing a waste of the soap. This objectionable reaction does not take place with modern detergents.

      In boilers (boiler), the calcium and magnesium in hard waters form a hard, adherent scale on the plates. As a result of the poor heat conductivity of the scale, fuel consumption is increased, and the boiler deteriorates rapidly through the external overheating of the plates. Sodium carbonate, if present, hydrolyzes to produce free alkali that causes caustic embrittlement and failure of the boiler plates. Water is softened on a small scale by the addition of ammonia, borax, or trisodium phosphate, together with sodium carbonate (washing soda). The latter precipitates the calcium as carbonate and the magnesium as hydroxide. Water is softened on a large scale by the addition of just enough lime to precipitate the calcium as carbonate and the magnesium as hydroxide, whereupon sodium carbonate is added to remove the remaining calcium salts. In areas where the water is hard, home water softeners are used, making use of the properties of natural or artificial zeolite minerals. See also soft water; water softener.

* * *


Universalium. 2010.

Игры ⚽ Поможем сделать НИР

Look at other dictionaries:

  • Hard water — is the type of water that has high mineral content (in contrast with soft water ). Hard water minerals primarily consist of calcium (Ca2+), and magnesium (Mg2+) metal cations, and sometimes other dissolved compounds such as bicarbonates and… …   Wikipedia

  • Hard water — Hard Hard (h[aum]rd), a. [Compar. {Harder} ( [ e]r); superl. {Hardest}.] [OE. hard, heard, AS. heard; akin to OS. & D. hard, G. hart, OHG. herti, harti, Icel. har[eth]r, Dan. haard, Sw. h[*a]rd, Goth. hardus, Gr. kraty s strong, ka rtos, kra tos …   The Collaborative International Dictionary of English

  • Hard water — Water Wa ter (w[add] t[ e]r), n. [AS. w[ae]ter; akin to OS. watar, OFries. wetir, weter, LG. & D. water, G. wasser, OHG. wazzar, Icel. vatn, Sw. vatten, Dan. vand, Goth. wat[=o], O. Slav. & Russ. voda, Gr. y dwr, Skr. udan water, ud to wet, and… …   The Collaborative International Dictionary of English

  • hard water — Is hard water ever used to make soft drinks? …   English expressions

  • hard water — kietas vanduo statusas T sritis chemija apibrėžtis Vanduo, kurio kietumas >8 mmol/l. atitikmenys: angl. hard water rus. жесткая вода …   Chemijos terminų aiškinamasis žodynas

  • hard water — kietas vanduo statusas T sritis fizika atitikmenys: angl. hard water vok. hartes Wasser, n rus. жёсткая вода, f pranc. eau calcaire, f; eau crue, f; eau dure, f …   Fizikos terminų žodynas

  • hard water — kietas vanduo statusas T sritis ekologija ir aplinkotyra apibrėžtis Gėlas požeminis vanduo, kurio kietis dėl jame ištirpusių kalcio ir magnio druskų yra didesnis kaip 6 mg ekv/l. atitikmenys: angl. hard water vok. hartes Wasser, n rus. жёсткая… …   Ekologijos terminų aiškinamasis žodynas

  • hard water — water with high concentrations of dissolved calcium and magnesium salts, usually found in limestone areas …   Dictionary of ichthyology

  • hard water — water containing a high concentration of minerals and calcium …   English contemporary dictionary

  • hard water — noun water that contains mineral salts (as calcium and magnesium ions) that limit the formation of lather with soap • Ant: ↑soft water • Hypernyms: ↑water, ↑H2O * * * water that contains magnesium, calcium, or iron salts and therefore forms a… …   Useful english dictionary

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”