SILVER-CONTAINING RESIDUES

A silver-containing solution was basified with sodium hydroxide, and after filtration, ammonia solution was used to wash residual silver from the filter. Hydrazine sulfate was then added to precipitate metallic silver and when the mixture was heated it exploded. This may have been caused by formation of silver nitride and/or hydrazine-silver complexes, both of which are explosively unstable. 

Red phosphorus is less soluble than white in all solvents. In water and alcohol it is almost insoluble. It is somewhat soluble in ether and in hot acetic acid, from which it is reprecipitated by water. It is slightly soluble in phosphorus trichloride. These solubilities refer to the ordinary preparation, which, as shown on p. 32, usually contains residual quantities of the white form. Red phosphorus is able to reduce salts, especially those of the noble metals, in aqueous solution on boiling. Salts of mercury are reduced to the metal those of gold and silver give insoluble phosphides while ferric and stannic salts are reduced to ferrous and stannous respectively.5... 

As the formation of disulfide bridges between proximate cysteine residues plays a particularly important role in physical properties of wool, any reagents or conditions that interfere with these bonds will have a significant effect on the fibres. A particular and related problem associated with the deterioration of wool fibres is the release of volatile sulfur compounds, which may then attack adjacent materials many of the silver-containing metal threads found on the Tree of Jesse tapestry show signs of surface corrosion, in the form of silver sulfide. 

The silver salts of most carboxylic acids are only sparingly soluble in cold water, and hence are readily prepared. Moreover they very rarely contain water of crystallisation, and therefore when dried can be analysed without further treatment. The analysis itself is simple, rapid and accurate, because gentle ignition of a weighed quantity of the silver salt in a crucible drives off the organic matter, leaving a residue of pure metallic silver. 

Add, with stirring, a solution of 6 8 g. of the fiis-diazo ketone in 100 ml. of warm dioxan to a suspension of 7 0 g. of freshly precipitated silver oxide in 250 ml. of water containing 11 g. of sodium thiosulphate at 75°. A brisk evolution of nitrogen occurs after 1 5 hours at 75°, filter the liquid from the black silver residue. Acidify the almost colourless filtrate with nitric acid and extract the gelatinous precipitate with ether. Evaporate the dried ethereal extract the residue of crude decane-1 10-dicarboxylic acid weighs 4 -5 g. and melts at 116-117°. RecrystaUisation from 20 per cent, aqueous acetic acid raises the m.p. to 127-128°. 

No. 6 fuel oil contains from 10 to 500 ppm vanadium and nickel in complex organic molecules, principally porphyrins. These cannot be removed economically, except incidentally during severe hydrodesulfurization (Amero, Silver, and Yanik, Hydrode.suljurized Residual Oils as Gas Turbine Fuels, ASME Pap. 75-WA/GT-8). Salt, sand, rust, and dirt may also be present, giving No. 6 a typical ash content of 0.01 to 0.5 percent by weight. 

The removal of silver from lead is accomplished by die addition of zinc to the molten lead, and slowly cooling to a temperature just above the melting point of lead (600 K). A crust of zinc containing the silver can be separated from the liquid, and the zinc can be removed from tlris product by distillation. The residual zinc in the lead can be removed eitlrer by distillation of the zinc, or by pumping chlorine tluough the metal to form a zinc-lead chloride slag. 

The residue (12 g) which contains the 18-iodo-18,20-ether is dissolved in 200 ml of acetone, 5 g of silver chromate is added Note 3) and after cooling to 0°, 11.8 ml of a solution of 13.3 g of chromium trioxide and 11.5 ml of concentrated sulfuric acid, diluted to 50 ml with water is added during a period of 5 min. After an additional 60 min, a solution of 112 g of sodium acetate in 200 ml of water is added and the mixture diluted with benzene (400 ml), filtered and the benzene layer separated. The aqueous phase is reextracted with benzene, washed with half-saturated sodium chloride solution, dried and evaporated to yield 11.2 g of a crystalline residue. Recrystallization from ether gives 7.2 g (72%) of pure 3/5, 1 la, 20/5-trihydroxy-5a-pregnan-18-oic acid 18,20 lactone 3,11-diacetate mp 216-218°. 

The method may be applied to those anions (e.g. chloride, bromide, and iodide) which are completely precipitated by silver and are sparingly soluble in dilute nitric acid. Excess of standard silver nitrate solution is added to the solution containing free nitric acid, and the residual silver nitrate solution is titrated with standard thiocyanate solution. This is sometimes termed the residual process. Anions whose silver salts are slightly soluble in water, but which are soluble in nitric acid, such as phosphate, arsenate, chromate, sulphide, and oxalate, may be precipitated in neutral solution with an excess of standard silver nitrate solution. The precipitate is filtered off, thoroughly washed, dissolved in dilute nitric acid, and the silver titrated with thiocyanate solution. Alternatively, the residual silver nitrate in the filtrate from the precipitation may be determined with thiocyanate solution after acidification with dilute nitric acid. 

Procedure B. Pipette 25 mL of the diluted solution into a 250 mL conical flask containing 5mL 6 M nitric acid. Add a slight excess of standard 0.1M silver nitrate (about 30 mL in all) from a burette. Then add 2-3 mL pure nitrobenzene and 1 mL of the iron(III) indicator, and shake vigorously to coagulate the precipitate. Titrate the residual silver nitrate with standard 0.1M thiocyanate until a permanent faint reddish-brown coloration appears. 

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