Mercury sulphide

Post-precipitation involves the deposition of a sparingly soluble impurity of similar properties to the precipitate on the surface of that precipitate after it has been formed. It is particularly a problem where similar materials are being separated on the basis of their different rates of precipitation, e.g. calcium and magnesium oxalates or zinc and mercury sulphides. Copreci-... 

Prepare 9-12 ml of aqua regia. In what volume ratio do hydrochloric and nitric acids have to be mixed to prepare it Put small amounts of cinnabar (mercury sulphide) into two porcelain bowls, pour the freshly prepared aqua regia solution over one portion carefully , and concentrated nitric acid over the other. Put both bowls on a sand bath and heat them. What happens Write the equations of the reactions. 

Why is aqua regia a stronger oxidizing agent than nitric acid Explain, using the concept of the solubility product, why mercury sulphide does not dissolve in nitric acid, but does in aqua regia. 

Arsenic. — Shake the mercury sulphide obtained in above test with a mixture of 5 cc. of ammonia water and 45 cc. of water, filter, and acidulate the filtrate with hydrochloric acid. Neither a yellow color nor a yellow precipitate should appear. 

The former is deposited in yellow crystals, mixed with sulphur when acetoxime is treated with phosphorus pentasulphide in carbon bisulphide soln. the insoluble product extracted with alcohol and the alcoholic soln. heated to boiling the compound separates from cold water in large, transparent, seemingly monoclinic prisms, melts at 146° 150° with decomposition, and is readily soluble in water, but only sparingly in alcohol, and insoluble in ether and carbon bisulphide. It decomposes carbonates, gives a colourless precipitate with lead acetate, and is decomposed by hot dilute nitric acid with separation of sulphur and formation of phosphoric acid it is also decomposed by mercuric oxide, the filtrate from the precipitated mercury sulphide giving all the reactions of phosphoric acid. 

This derivative is obtained in a similar manner to the preceding one, from 3 5-diacetylamino-4-hydroxyphenylarsinic acid, the product being purified by solution in alkali and precipitation with dilute hydrochloric acid. In this ease, however, the reaction requires thirty days for completion. The mercurated arsinic acid melts at 234° C., and gives clear solutions in aqueous sodium carbonate, caustic alkalis, and ammonia, the latter solution when boiled with ammonium sulphide yielding mercury sulphide. The position of the mercury is ascertained by converting the compound into 2-iodo-3 5-dia-cetylamim-4s-hydroxyphenyU arsinic add. 

Mercury has been used by humans since antiquity. More than 10,000 years ago, prehistoric humans used the bright red stone of mercury ore (cinnabar, mercury sulphide, HgS) to color cave drawings. Theofrastos, the disciple of Aristotle, described the production of metallic mercury from cinnabar. Egyptians and Ro-... 

The Stone was often described as a red powder, and it was no doubt sometimes confused with the red ore, cinnabar. This is a naturally occurring form of mercury sulphide, which when heated yields metallic mercury (liquid quicksilver) and evolves sulphureous fumes (sulphur dioxide), identical with those arising in the burning of native sulphur. It seems possible that experiments of this kind may have led the Muslim alchemists to put forward the so-called Sulphur-Mercury Theory of the origin of metals. The most famous of these alchemists was Jabir ibn Hayyan, known to the Western world as Gcber. He is said to have lived in the eighth century a.d., and the theory is often associated with his name. The same may be said of numerous alchemical treatises which were undoubtedly written aflcr his time. 

Mercuric sulphide 26B1 HgS Bisulphide of mercury cinnabar protosulphide of mercury red mercuric sulohide red sulphide of mercury sulphide of mercury vermlllion. 

Very small traces of lead in water can be effectively collected by co-predpitation with mercury sulphide. After treatment with peroxide, the collected HgS is ignited and the mercury vaporized away. The residual lead can be tested with sodium rhodizonate. Lead at concentrations of 10 8 are detected easily by this method o. The method is also applicable to the analysis of reagents for traces of lead contaminant. 

---