SOLUTION OF IRON AND SILVER. 121 



Expt. 161. When a gas is to be brought in contact with a fluid so 

 as to be dissolved therein, as in these cases, the arrangement shown 

 in fig. 66 (p. 139) is usually more convenient than filling a jar and 

 then shaking up with the fluid ; the gas produced in an appropriate 

 generator being made to bubble through the liquid employed. 



Expt. 118. To dissolve Iron by Chemical Action. Put some 

 iron filings into a test-tube, and then pour upon them some 

 diluted hydrochloric acid. Effervescence will ensue, but in this case 

 due to the escape of hydrogen gas, produced exactly as it was 

 formed in Expt. 10, where zinc was used instead of iron. When 

 the action has gone on for some time, filter the liquid in the 

 generator through a paper filter (Expt. 56) ; a solution of the salt 

 called ferrous chloride (not the same thing as perchloride of iron 

 or ferric chloride) will then be obtained. Add to a little of the 

 solution some solution of ferricyanide of potassium (red prussiate of 

 potash, not the same substance as the yellow prussiate used in Expt. 

 57) ; a blue precipitate of a substance called TurnbuWs blue 

 (Expt. 83) will be at once formed, instead of a brown sherry- 

 coloured fluid, such as would be formed with perchloride of iron 

 and ferricyanide of potassium. If diluted sulphuric acid be sub- 

 stituted for hydrochloric acid in this experiment, solution of the 

 iron with evolution of hydrogen will equally take place, producing 

 sulphate of iron (ferrous sulphate) instead of chloride ; by filtering 

 the solution, evaporating and allowing to stand, this salt may be 

 obtained in pale green crystals, which become rusty on standing 

 moist in contact with the air for some time, owing to a further 

 chemical change somewhat akin to the oxidation of metals 

 (Chapter XIV.). 



Caution. Be careful how you add sulphuric acid to water in 

 this experiment (vide Expt. 98). 



Expt. 119. To dissolve Silver by Chemical Action. Nitric 

 acid has the power of dissolving most metals in the same way as 

 copper (Expt. 116). Place a small silver coin in a vessel contain- 

 ing concentrated nitric acid diluted with about twice its bulk of 

 water; the metal will be speedily attacked and dissolved. As 

 silver coins contain a little copper as well as silver (added to 

 harden the metal and enable it to resist wear and tear better), the 

 solution will have a blue colour, and will contain a mixture of the 

 nitrates of copper and silver. If, instead of a coin, a fragment of 

 pure silver be used, a colourless solution will be obtained, contain- 

 ing no copper. The liquid may be cautiously evaporated to dry- 

 ness, preferably on a steam bath (Expt. 89), when solid nitrate of 

 silver will be obtained, which may be dissolved in water, and the 

 solution bottled for future use. 



