SILVER-MERCURY. 203 



7. Stannous chloride produces, in solutions of mercury, a white 

 precipitate, which turns dark-gray on heating with an excess of the 

 reagent. The reaction is due to the strong reducing or deoxidizing 

 property of the stannous chloride, which itself is.con verted into stannic 

 chloride, while the mercury salt is first converted into a mercurous 

 salt and afterward into metallic mercury : 



2HgCl 2 + SnCL, = Hg 2 Cl 2 + SnCl 4 ; 

 Hg 2 Cl 2 -f SnCl 2 = 2Hg -f SnCl 4 . 



8. Dry mercury compounds, when mixed with sodium carbonate 

 and potassium cyanide, and heated in a narrow test-tube, are decom- 

 posed with liberation of metallic mercury, which condenses in small 

 globules in the cooler part of the tube. 



9. A piece of bright metallic copper, when placed in a slightly acid 

 mercury solution becomes coated with a dark film of metallic mer- 

 cury, which by rubbing becomes bright and shining, and may be 

 volatilized by heat. 



10. All compounds of mercury are completely volatilized by heat, 

 either with or without decomposition. 



Antidotes. Albumen (white of egg), of which, however, not too much should 

 be given at one time, lest the precipitate formed by the mercuric salt and 

 albumin be redissolved. The antidote should be followed by an emetic to 

 remove the albuminous mercury compound. 



QUESTIONS. 281. How is silver obtained from the native ores, and how may 

 it be prepared from silver coin ? 282. State of silver nitrate : its composition, 

 mode of preparation, properties, and names by which it is known. 283. Give 

 analytical reactions for silver. 284. How is mercury found in nature ; how is 

 it obtained from the native ore ; what are its physical and chemical properties ? 

 285. Mention the three oxides of mercury ; how are they made, what is their 

 composition, what is their color and solubility? 286. State of the two chlorides 

 of mercury : their names, composition, mode of preparation, solubility, color, 

 and other properties. 287. Mention the same of the two iodides, as above, for 

 the chlorides. 288. State the difference between mercuric sulphate, basic mer- 

 curic sulphate, and mercurous sulphate. 289. What is formed when ammonium 

 hydroxide, calcium hydroxide, potassium or sodium hydroxide is added to either 

 mercurous or mercuric chloride ? 290. Give tests answering for any mercury 

 compound, and tests by which mercuric compounds may be distinguished from 

 mercurous compounds. 



