Aluminium sulfate and alums

The most important soluble oxosalts of A1 are undoubtedly Al2(S04)3-16H20 and the double sulfates MA1(S04)2-I2H2O (alums). In alums, M+ is usually K+, Rb+, Cs+ or [NH4], but Li, Na and T1+ compounds also exist Al may be replaced by another ion, but its size must be com- 

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The first significant step forward was the discovery that water is cooled when salts are dissolved in it, such as common salt (sodium chloride), saltpetre (potassium nitrate), sal-ammoniac (ammonium chloride) or alum (a mixture of aluminium sulfate and potassium sulfate). When the crystals dissolve, the strong bonds between the ions are broken, extracting heat from the surrounding water, so the temperature drops. Adding a mixture of 5 parts ammonium chloride and 5 parts potassium nitrate to 16 parts water at 10 °C causes the temperature of the mixture to drop to about — 12°C, sufficient to freeze a vessel of pure water immersed in it. This phenomenon was first recorded in an Indian poem from the fourth century AD, and described in detail in an Arabic medical textbook from 1242. Another book in Arabic, containing sorbet recipes, appeared at about the same time. 

Potassium aluminium sulfate (Alum) A1K(S04)2.12H20 The aqueous immunogen solution/suspension is mixed with 0.3 vol 10% alum. The pH is then ac usted to about 8.0 with sodium hydroxide solution and the resultant precipitate washed in 0.9% NaCl solution and administered. Acetone precipitates The aqueous immunogen is precipitated with 4.5 vol of acetone at -20°C for 1 h. The precipitate is collected by centrifugation at lO.OOOg at room temperature, washed in 80% acetone, and air-dried. The pellet is resuspended in saline using a Dounce homogenizer and then administered directly or in association with... 

Acute aluminium toxicity in one reported case followed the introduction of aluminium sulfate (alum) into the urinary tract to treat hemorrhagic cystitis there was apparently both increased absorption, due to the mucosal lesion of the bladder wall, and an increased susceptibility due to pre-existing renal insufficiency (SED-13, 585). 

The most commonly used coagulating agents are ferric and aluminium salts (e.g. ferric chloride, FeCla, ferric sulfate, Fe2(S04)3 and alum, Al2(S04)3 I4H2O), which are precipitated as the hydroxides, (e.g., equations 28.1, 28.2). Both reactions generate mineral acids which may need to be neutralised by the addition of an alkali to produce the required pH. 

Figure 9.3 Illustration of zeta potentials and turbidity (coagulation/removal of solids) in a raw water sample by adding aluminium sulfate (alum). (Adapted from Zeta-Meter [49]. Courtesy L.A. Ravina, Zeta-Meter, Inc., Staunton, Va.)...

Figure 9.4 Illustration of zeta potentials and coagulation of solids in New York City water treatment through sequential additions of aluminium sulfate (alum).

Merrifield (1849) describes how alumine zuccarino was alum (potassium/aluminium sulfates) groimd and heated with rose water, sugar and white of egg and allowed to harden by cooling. It was used as a base for lake pigments and in the preparation of verdigris qq.v.). 

Various aluminium sulfates are described in the chemical and pigment literature aluminium sulfate (Al2[S04]3) alunite (KAl3[804]2[0H]g) alunogen (Al2[S04]2.18H20) alum (AI2. [804)3) ettringite (Ca6Al2[S04]3[0H],2.26H20). 

Naturally occurring alum or rock alum is an important ore of aluminium and is used in numerous manufacturing processes. It is also used as a mordant in the dye industry. Commercial aluminium sulfate is also known as cake alum or patent alum. There is also an aluminium sulfate mineral, alunogen. Ettringite forms primarily as a component of hydrauhc lime plasters. It is also hsted as calcium sulphoaluminate in the Colour Index as Cl 77235/Pigment White 33. 

According to Kiilm and Curran (1986), during the nineteenth century Baltimore chrome yellow was likely to have contained calcium sulfate and lead sulfate (qq.v.), or, according to Mierzinski (1881), alum (hydrous potassium aluminium sulfate, KA1[S04]2.12H20). They state that the term is now applied to a pale chrome yellow precipitated on gypsum or asbestine (q.v.). 

This pigment is described by Riffault et al. (1874) as a combination of aluminium oxide and cobalt oxide. It is prepared by faking an alum solution and dissolving in it cobalt nitrate, sulfate or chloride. A pink-white precipitate is formed with sodium or potassium carbonate the product is then washed, dried and calcined in a crucible at high temperature. It would consequently appear to be a manufacturing variant of cobalt aluminium oxide (that is, cobalt blue ) and is also stated to be synonymous with Gahn s ultramarine qq.v.). 

Kiihn and Curran (1986), citing Mierzinski (1881), indicate that old forms of this pigment consisted of chrome yellow (. v.) and alum, a hydrous potassium aluminium sulfate. The same pigment mixture is also given for Spooner s chrome yellow and Baltimore chrome yellow q.v.) by the same source. 

Heaton and Hurst do not appear to say the same thing, though Heaton is a revision of the text by Hurst. Bristow (1996b) states that Hurst says it is made from calcium sulfate and aluminium sulfate, adding that he thinks that it was made with alum (potassium aluminium sulfate) as opposed to aluminium sulfate. 

Abundant yellow or white salt crusts are present on waste rock and at the surface of the soil. The crusts comprise alum-like sulfate minerals containing variable amounts of sodium, potassium, iron and aluminium, such as the mineral jarosite. They are often very soluble in water, releasing acid and precipitating ferric hydroxides. 

Mayer s hemalum 1 g of hematoxylin, 50 g of aluminium potassium sulfate, 0.2 g of sodium iodate, 1 g of citric acid, 50 g of chloral hydrate, and 1 L distilled water. Dissolve the hematoxylin in distilled water, using gentle heat if necessary. Add the alum, heat if necessary. Add the sodium iodate, mix well and leave overnight. Then add citric acid, mix well and add the chloral hydrate. 

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