Sulphur identification test

Detection and Estimation.—The decomposition of thiosulphates by means of hydrochloric acid to yield sulphur dioxide with separation of sulphur serves as a primary identification test, the limit of sensitiveness being about 0-1 mg. S203 per c.c.3 The alkali thiosulphates produce with silver nitrate solution a white precipitate of thiosulphate which gradually turns yellow, then brown, and finally black, due to the formation of sulphide the change is accelerated by warming 4... 

A reversed-phase liquid chromatographic method was developed for simultaneous determination of carboxylic acids, phenolic compounds, and SA in white wines (84). The diluted samples are injected into a Spherisorb ODS-2 column with a gradient of sulphuric acid (pH 2.5)/methanol as mobile phase. A diode array detector is used, set at 210 nm for carboxylic acids and altered to 278 nm, during the run, for phenolics and SA. The identification of compounds is based on retention time and UV spectra. Some cleanup methods (Sep-Pak C18 and an ion-exchange column) were tested and did not improve the results. The analysis was considered simple, with no sample preparation. Application of this method was illustrated by analyses of Brazilian Welchriesling wines (84). 

Detection of the Paraffins.—The identification of the paraffins is difficult on account of the lack of definite analytical tests. The paraffins are characterized by their inertness. They can be shaken with fuming nitric acid without appreciable change. They are insoluble in concentrated sulphuric acid and are not attacked by it. The liquid hydrocarbons react slowly with bromine a solution of the halogen in the hydrocarbon retains its color for some time. As reaction takes place hydrobromic acid is evolved. The hydrocarbons are insoluble in water and float. They dissolve in alcohol and benzene. 

Two of the reactions of aldehyde which have been described are much used in the identification of members of this class of compounds, namely, the formation of a mirror when an ammoniacal solution of silver nitrate is gently warmed with an aldehyde, and the change of the latter to a resin when heated with a strong solution of a caustic alkali. If these reactions take place when a substance is treated as described, there is a strong probability that it is an aldehyde. Compounds other than aldehydes, however, reduce an ammoniacal solution of silver salts, and other tests should be applied in addition to the ones just given. When an aqueous solution of rosaniline, which is a red dye, is treated with a saturated solution of sulphur dioxide in water, the color is destroyed. The colorless solution, known... 

Identification of Carbohydrates.—All carbohydrates give a marked color when treated with a-naphthol (532) and concentrated sulphuric acid (Molisch carbohydrate reaction). The test is carried out by treating about 5 milligrams of the substance with 10 drops of water and 2 drops of a 10 per cent solution of a-naphthol in chloroform about 1 cc. of pure concentrated... 

Identification of Nitro Compounds.—The definite identification of a substance as a nitro compound is difficult, as substances exist which are closely related to nitro compounds and show many of the reactions of the latter. Nitro compounds are insoluble in water, but dissolve in many organic solvents. They are, in general, soluble without decomposition in concentrated sulphuric acid, and are precipitated when the solution is poured into water. The specific gravity of nitro compounds is greater than one. When treated with tin and hydrochloric acid, they are reduced to amines. This reaction serves as a valuable test. The nitro compound, which is insoluble in hydrochloric acid, is converted into a salt of an amine, which is soluble. A... 

Identification of Phenols.—The reactions of phenols which are of particular value in their identification, are those that take place with alkalies, ferric chloride, and bromine water. Most phenols react with an aqueous solution of sodium hydroxide to form soluble salts, but are insoluble in a solution of sodium carbonate. The behavior of phenols with these two reagents shows their weakly acidic properties, and serves to distinguish them from acids. Phenols which contain strongly negative substituents decompose carbonates, and show all the properties of acids. It is difficult, therefore, to identify as a phenol substances which contain such substituents. Ferric chloride produces marked colorations in aqueous solutions of most phenols. The reagent produces a similar effect with certain other compounds, and the formation of a color with ferric chloride can be taken, therefore, only as an indication of the presence of a phenol. With bromine water most phenols yield a precipitate of a brominated phenol. Other compounds, amines for example, are also converted into insoluble substitution-products by bromine water. Notwithstanding this fact the test is of value. Many phenols form colored products when heated with phthalic anhydride and concentrated sulphuric acid. The reaction will be described under phenolphthalein (558, 639). 

The electrical conductivity of molten sulphur at temperatures up to 200 C has been studied on samples which were specially purified, as well as doped with impurities (paraffin, phenanthrene, benzidine, bromine, and iodine). The current flow below 160 C results from electrophoretically migrating impurities and, by interaction with the impurities, ionized molecules, whereas at higher temperatures conduction is caused by electrons. At the minimum of viscosity of the molten sulphur (154.5 °C) the conductivity shows a maximum, which is shifted by impurities (especially halogens) as much as 10 °C towards lower temperatures, llie effect on the mechanical properties of sulphur by the presence of has been studied. The preparation (3 methods), identification, and testing of are reported. Specimens with an content of more than 16% may be prepared by pouring hot sulphur into cold CSg. An analysis of the results of the study indicates that acts as a typical low-modulus material,... 

Other colour tests which do not interfere in the subsequent quantitative determination, can be of only limited application. An example is with organic phosphorus compoimds, where the substance can be ignited and determined through its phosphorus content [166, 258]. Glycolipoid fractions have been localised with ammoniacal bromothymol blue indicator and then, after extraction, evaluated with anthrone/sul-phuric acid [324]. 17-Hydroxycorticosteroids have been sprayed with blue tetrazolium and then determined with phenylhydrazine/sulphuric acid [11] the steroids partly reacted with the identification reagent which led to difficulties. 

Simple methods of chemical analysis are useful in certain cases. Qualitative chemical tests such as the Beilstein and Lassaigne tests for the presence of particular elements (e.g. halogens, nitrogen, sulphur) are of use in the identification of an unknown polymer. Combustion analysis for quantitative determination of elemental composition can be used to confirm the purity of a homopolymer and to determine the average... 

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