Mercuric solid sample

Procedure. A drop of the test solution or a small quantity of the solid sample is placed in a small test tube and treated with several drops of a mixture of equal volumes of a 2 % solution of mercuric cyanide and 0.1-0.2 JV sulfuric acid. The mouth of the tube is covered with a disk of filter paper which has been moistened with a solution containing 5 mg each of Cu ethylacetoacetate and tetrabase in 3 ml chloroform. A blue stain develops on the paper immediately or after brief warming depending on the amount of alkali halide present. 

Procedure. A small quantity of the solid sample or a drop of its solution is treated on a spot plate with a drop of a strong alkaline 5 % solution of mercuric cyanide, A black or gray precipitate indicates the presence of antimony. 

Procedure. A little of the solid sample is placed in a micro test tube or a drop of the test solution is evaporated there to dryness. Several eg of solid KjSgOg are added and the mixture is kept molten for 2-3 minutes over a burner. The mass is then cooled and dissolved in a few drops of water, with gentle heating if need be. A 10 % solution of sodium hydroxide is added until the solution becomes alkaline and then one drop of a 6 % solution of NaOH containing mercuric cyanide is introduced. A positive is indicated by a black or gray precipitate on centrifuging. 

The majority of inorganic systems reported to exhibit photochromism are solids, examples being alkali and alkaline earth halides and oxides, titanates, mercuric chloride and silver halides.184 185 The coloration is generally believed to result from the trapping of electrons or holes by crystal lattice defects. Alternatively, if the sample crystal is doped with an impurity capable of existing in variable oxidation states (i.e. iron or molybdenum), an electron transfer mechanism is possible. 

Samples with particulate matter may present quite serious problems, and it may be desirable to remove particles, for example, by centrifugation, and examine this fraction by procedures applicable to solid phases which are discussed in Section 2.2.5. Tangential-flow high-volume filtration systems have been used for analysis of particulate fractions (>0.45 jum) where the analytes occur in only low concentration (Broman et al. 1991). Attention has already been drawn to artifacts resulting from reactions with cyclohexene added as an inhibitor to dichloromethane. It has also been suggested that under basic conditions, Mn2+ in water samples may be oxidized to Mn(III or IV) which in turn oxidized phenolic constituents to quinones (Chen et al. 1991). Serious problems may arise if mercuric chloride is added as a preservative after collection of the samples (Foreman et al. 1992) since this has appreciable solubility in many organic solvents, and its use should therefore be avoided. 

Procedure. A small quantity of the sample is placed in a micro test tube along with 20-30 mg solid mercuric cyanide. The tube is then immersed in a glycerol bath which has been preheated to 130 C and the open end of the tube is covered with a disk of filter paper that has been moistened with a drop of the Cu ethyl acetoacetate and tetrabase reagent. The presence of sulfur, selenium or tellurium is indicated by the development of a blue color on the paper within 3 minutes. 

Procedure. A tiny bit of the solid or a drop of its solution is stirred on a spot plate with a drop of concentrated mercuric solution, which has been saturated with sodium chloride to repress the hydrolysis of the mercuric chloride. In addition to common ion effect, there is formation of Na2[HgClJ. A drop of phenolphthalein solution is added, or the solution is tested with pink litmus paper. If free alkali is present in the sample, a red color will appear or the paper will turn blue. 

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