Acids silicic

Silica.—This acid is found pure in rock crystal, or in white quartz. Along vrith small and variable quantities of certain metallic oxides it forms many well-known minerals—as yellow or smoke rock crystal with oxide of iron agate, jasper, heliotrope, camelian, with the same metal amethyst with oxide of manganese prase with oxide of nickel rose-quartz with some fugitive colouring matter opal and calcedony with water, c. c. Many sands and sandstones are nearly pure silica, and quartz rock and flint are quite pure. 

Silicic acid may be obtained in a state of purity from any siliceous sand by fusing it with three or four parts of carbonate of potash, dissolving the fused mass in water, adding hydrochloric acid, which separates the silica as a jelly, which is a hydrate of the acid, and evaporating the whole to dryness. Water removes from the dry mass all soluble chlorides, and leaves the silica, which, when dried, is a snow-white pow der, insoluble in water, and all acids except the hydrofluoric acid. It dissolves in caustic or even carbonated alkalies with the aid of heat. 

No compounds are known of silicon with hydrogen or nitrogen. 

When silicon is heated in chlorine it burns and forms a compound, which is better prepared by passing chlorine over a red- 

Si Cl3 + 3 CO. The compound, which is called terchloride of silicon, condenses in the cold part of the apparatus as a very volatile, pungent, and colourless liquid, which decomposes water, forming hydrochloric and silicic acids Si Cl, + 3 HO = 3 H Cl + 4 O,. 

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The action of concentrated sulphuric acid liberates hydrogen fluoride, which attacks glass, forming silicon tetrafluoride the latter is hydrolysed to silicic acid by water, which therefore becomes turbid,... 

The product is sometimes contaminated with silicic acid from the glass of the condenser this may be removed by filtration. All corlcs should be covered with tin foil to avoid attack by the hydrazine hydrate. 

A. R. Marsh, G. Klein, and T. Vermeulen, Polymerisation Kinetics and Equilibria of Silicic Acid in Aqueous Systems, No. LBL 4415, National Technical Information Service, Springfield, Va., 1975. 

NaAlSigOs + 2 H+ + 9 H2O Al2Si2 O5 (OH) + 4 H4Si04(aq) + 2Na albite hydrogen water kaolinite silicic acid sodium... 

For exposure of reasons of observable discrepancy of results of the analysis simulated experiment with application synthetic reference samples of aerosols [1]. The models have demonstrated absence of significant systematic errors in results XRF. While results AAA and FMA depend on sort of chemical combination of an elements, method of an ashing of a material and mass of silicic acid remaining after an ashing of samples. The investigations performed have shown that silicic acid adsorbs up to 40 % (rel.) ions of metals. The coefficient of a variation V, describing effect of the indicated factors on results of the analysis, varies %) for Mn and Fe from 5 up to 20, for Cu - from 10 up to 40, for Pb - from 10 up to 70, for Co the ambassador of a dry ashing of samples - exceeds 50. At definition Cr by a method AAA the value V reaches 70 %, if element presences an atmosphere in the form of Cr O. At photometric definition Cr (VI) the value V is equal 40%, when the element is present at aerosols in the form of chromates of heavy metals. 

Liquid Water Linde Type 4 A Linde Type 5 A Activated Alumina Silicic Acid Gel... 

Sodium silicate solution [1344-09-8] pKj 9.51, pKj 11.77 (for silicic acid, H4Si04) Purified by contact filtration with activated charcoal. 

A higher content of AI2O3 and SiOj is critical for the composition of the protective films in the tubing, assuming the water contains silicates or silicic acid. The protective films have a maximum thickness of 1.5 mm and cannot grow further. The corrosion process can be stopped even in copper pipe networks with type I pitting [21] by providing a reaction tank with impressed current aluminum anodes. 

Silica fouling is the accumulation of insoluble silica on anion resins. It is caused by improper regeneration which allows the silicate (ionic form) to hydrolyze to soluble silicic acid which in turn polymerizes to form colloidal silicic acid with the beads. Silica fouling occurs in weak-base anion resins when they are regenerated with silica-laden waste caustic from the strongbase anion resin unless intermediate partial dumping is done. 

To a mixture of ethyl 5a-cholestan-3-one 2a-xanthate (2 g, 3.95 mmol) and 100 ml methanol is added sufficient ether to completely dissolve the solids. Sodium borohydride (90 mg, 2.36 mmol) is added directly to the reaction flask and the solution is stirred at room temperature for 4 hr. (The use of an excess of sodium borohydride and an extended reaction time produces 5oc-cholestan-2a,3a-thiirane.) The reaction is diluted with 200 ml ether and washed several times with ca. 100 ml water, dried (MgS04) and the solvent is removed under vacuum. The crude sticky gum is chromatographed on a column of 85 g silicic acid. The hexane eluates contain 5a-cholest-2-ene. Ethyl 5a-cholestan-3a-ol 2a-xanthate is obtained in ca. 30% yield by subsequent elution with benzene hexane (1 7) and the desired ethyl 5a-cholestan-3 -ol 2a-xanthate is eluted with ether hexane (1 3) in ca. 30% yield. 

Twenty grams of the resulting oily substances were mixed with 20 grams of silicic acid (Mal-linckrodt Chemical Co.),applied to a column 40 cm in length and 4.5 cm in diameter filled with silicic acid,and eluted with a be nzene-ecetone-methanol mixture. The initial eluate which eluted with a 1 1 0 mixture was discarded and the active fractions eluted with 1 3 0 and 1 3 0.3 mixtures were collected and concentrated to dryness in vacuo. 11 g of this crude substance was then dissolved in a small amount of ethyl acetate and applied to the same silicic acid column as above. After discarding the initial eluates by the 1 1 and 2 1 benzene-acetone mixtures, aclacinomycin 8 fractions were first eluted with the above mixtures of 1 3 and 1 5 ratio, and aclacinomycin A fractions were then eluted with the 1 5 0.5 and 1 5 1 benzene-acetone-methanol mixtures. The eluates were dried over anhydrous sodium sulfate and concentrated to dryness in vacuo. 4,8 g of crude aclacinomycin A and 3.5 g of aclacinomycin 8 were obtained as yellow powder. 

The crude product is dissolved in benzene-hexane (1 1) and applied to a column containing 125 g. of silicic acid (Note 10). Elution with the same solvent gives traces (less than 5 mg. each) of the two fast-moving components in fractions 2 and 4 (125-ml. fractions) and chromatographically pure cholane-24-aI in fractions 5-8 (Note 11). Evaporation of the pooled fractions yields 870 mg. (84%) of the pure crystalline aldehyde, m.p. 102-104°. Recrystallization from 5 ml. of acetone raises the melting point to 103-104° (Note 12). 

NaOH sodium hydroxide Mg(OH)t magnesium hydroxide Al(OH)3 aluminum hydroxide Si(OH) silicic acid (usually written H[Pg.375]

Seventh row of periodic table. 411 occurrence. 413 Significant figures. 9. 12 see also Unccriainty Silica, 309 dissolves in HF, 361 Silicates. 310 Silicic acid, 375 Silicon... 

The dispersions are very viscous they set to jelly-like masses known as gels. Examples sols of silicic acid, tin(IV) oxide, gelatin. 

Discussion. The determination of this anion is of little practical importance. The methods available for its determination will, however, be outlined. Alkali fluorosilicates are decomposed by heating with sodium carbonate solution into a fluoride and silicic acid ... 

Insoluble fluorosilicates are brought into solution by fusion with four times the bulk of fusion mixture, and extracting the melt with water. In either case, the solution is treated with a considerable excess of ammonium carbonate, warmed to 40 °C, and, after standing for 12 hours, the precipitated silicic acid is filtered off, and washed with 2 per cent ammonium carbonate solution. The filtrate contains a little silicic acid, which may be removed by shaking with a little freshly precipitated cadmium oxide. The fluoride in the filtrate is determined as described in Section 11.59. 

If an acid solution of a fluorosilicate is rendered faintly alkaline with aqueous sodium hydroxide and then shaken with freshly precipitated cadmium oxide, all the silicic acid is adsorbed by the suspension. The alkali fluoride is then determined in the filtrate. 

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