Water precipitation

Scale. Scale deposits are formed by precipitation and crystal growth at a surface in contact with water. Precipitation occurs when solubiUties are exceeded either in the bulk water or at the surface. The most common scale-forming salts that deposit on heat transfer surfaces are those that exhibit retrograde solubiUty with temperature. 

In appHcatioa, the automobile or other article to be coated is made the cathode ia an electro deposition system. A current differential on the order of 250 to 400 V is appHed, which attracts the positively charged coating aggregates to the cathode. At the cathode, hydroxide ions from the electrolysis of water precipitate the aggregates on the surface of the metal. As the conveyor removes the coated product from the bath, residual Hquid is tinsed off with water and the article is conveyed iato a bakiag ovea for a high temperature bake. 

Occasionally we have found iron contaminants in aromatic steroids that have not been adequately purified. The methylation of a phenolic steroid with methyl sulfate and alkali is often carried out just prior to a Birch reduction and iron in the tap water precipitates with the steroid during the... 

A solution of 1 g of the ethyleneketal of the trione in 40 ml of methanol is treated with 0.2 g of sodium borohydride and the mixture is stirred at 20° for 2 hr. Slow drop wise addition of water precipitates the reaction product as crystals. These are filtered, washed with water and dried, to give 1.02 g of hydroxy ketone, which after crystallization from methylene dichloride-hexane has mp 182-184° (reported 184-186°) -23° (CHCI3). 

A few drops of concentrated hydrochloric acid are added to a solution of 0.64 g of the above mixture in 40 ml of methanol and the solution is refluxed for 15 min. Addition of water precipitates 0.27 g of 19-norandrost-4-ene-3,17-dione mp 163-166°. 

Ammonia is often used to precipitate insoluble metal hydroxides such as Al(OH)3. The OH- ions formed when ammonia reacts with water precipitate the cation from solution as the hydroxide. The overall equation for the reaction is... 

In addition to superficially adherent water, precipitates may contain ... 

Wind Air-borne particulate erosion from dust or water precipitation... 

By extraction of poppy-heads or opium with water, precipitation with aqueous Na2C03-solution, washing of the precipitate with ethanol and dissolving in diluted acetic acid. 

Most Mg metal is manufactured by electrolysis of either anhydrous or partially hydrated MgCl2 from sea water. Addition of CaO to sea water precipitates Mg(OH)2,... 

Ninety water sources have been sampled. Deuterium content and global salt content were measured both in the underground sources (springs, drillings, wells) and in the surface sources (running water, precipitation), in order to include all the water types that might interact. 

The 5180 of rain water changes with the fraction x of water precipitated from atmospheric vapor according to the law... 

In a round-bottomed flask (capacity 0-5 1.) 8 g. of sodium are dissolved in 120 c.c. of absolute alcohol. Into the solution, which is kept cool in water (precipitation of ethoxide is not detrimental) a mixture of 36 g. of benzyl cyanide (p. 137) and 32 g. of ethyl nitrate (p. 148) is poured in small portions. The salt formulated above separates gradually in the shape of almost colourless crystals. In order to allow the reaction to proceed to completion, the flask is left for one hour without cooling, but with exclusion of moisture the precipitate is then collected at the pump and subsequently washed first with alcohol-ether (1 1) and then with ether alone. Yield 40-45 g. 

The breakdown of glucose by yeast to give ethanol, acetic acid, and carbon dioxide was examined quantitatively by Lavoisier (1789) and Gay-Lussac (1810). From his studies (Chapter 2) Pasteur described fermentation as life without air , attributing the process to the presence of yeast cells whose effects were dependent on the vital force. The first suggestion that an unorganized ferment was responsible for fermentation was due to Traube (1858). Support for his ideas came from Berthollet (1860) who extracted yeast with water, precipitated the extract with alcohol, and found that the redissolved precipitate could... 

Plate 15.VII Acid mine water precipitate, Ohio (courtesy J.M. Bigham). 

Addition of water precipitates out an oxysalt, Bi203N205 H20. The degree of hydrolysis and the product composition can vary with the amount of water and the reaction temperature... 

Toyopearl is used in this chapter since it is stable in most of synthetic conditions (reeNote 2 in details). Toyopearft is usually stocked in 20% EtOH. Therefore, resins were washed more than 6 times with 1 mL of NMP before usage, to remove water. Precipitation by flash centrifugation in a microcentri-fiige is useful for washes. Dryness of the resins is not recommended, since resins are sometimes irreversibly denatured. 

The isolation procedure that we have developed involves extracting the leaf tissue with boiling, deionized water, precipitation of phenolic components with lead acetate (Pb0Ac2 3H20) and... 

Preparation By extraction of poppy capsules or opium (opium contains 9-14 % morphine depending on the source) with water, precipitation with aqueous Na2C03 solution, washing of the precipitate with ethanol and dissolution in dilute acetic acid (Horner et al. (Knoll), 1977, Trauner et al.,1983, Hudlicky et al.,1996). 

The impure metal dissolves easily in mineral acids and in fluoroboric, sulfamic am trifluoromethylsulfonic acids to give Cr2+ solutions, but oxidation of Cr2+ by hydrogen ion (equation 6), °(Cr3+, Cr2+) = —0.41 V) even in an inert atmosphere is catalyzed by thi impurities and various ions.71 Indefinitely stable chromium(II) solutions can be obtained fron the pure (electrolytic) metal (99.5% or better), although the reaction with acid may need to b< initiated by heat and the inclusion of some metal previously attacked by acid. The use of ai excess of metal, which can be filtered off, ensures that little acid remains. In near neutra solution the hydrogen potential is lowered and the Cr2+ ion is stable. In alkaline condition brown Cr(OH)2, which slowly reduces water, precipitates.73,73... 

It is soluble, with a brown color, in strong sulphurio acid from which water precipitates the greater part of a yellow color, which retains a little of the acid by boiling with the same add tannin and charcoal are produced. Nitric acid changes it to a yellow resin, which gradually dissolves in the acid. Finely powdered, and boiled with solution of caustic or carbonated alkali, much succinic acid is removed and pure water ex tracts a resinate of the alkali from the residue, leaving amber bitumen. 

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