1839.] 



On Chemical Tests. 



317 



/. Iron ores, as magnetic iron ores, sometimes contain both protox- 

 ide and peroxide of iron. To detect them dissolve the ore in a closed 

 flask with concentrated muriatic acid : add to one portion of the solu- 

 tion a saturated solution of sulphuretted hydrogen, and a milky white 

 precipitate will indicate the peroxide. Dilute with water the other por- 

 tion of the solution and test it by red prussiate of potash and the dark 

 blue precipitate will indicate the protoxide. See 36; also letter d of 

 i this article. 



g. The protoxide salts of iron which are insoluble in water are 

 nearly all soluble in muriatic, or diluted sulphuric acid. This resulting 

 acid solution when supersaturated with ammonia, generally precipitates 

 the salt, Hydrosulphuret of ammonia added thereto blackens this 

 precipitate. The same remark is generally applicable to the persalts 

 of iron. 



h. Before the blow-pipe the salts of iron yield with borax a glass, 

 which, in the outer flame, is of a deep red, becoming lighter as it cools. 

 In the inner flame it is green when hot, but colourless when cold, 

 unless a large quantity of protoxide of iron is present. To microcosmic 

 salt, very small quantities of iron impart a green colour while hot, 

 which fades in cooling find disappears entirely when cold. With soda 

 on charcoal the salts of iron are reduced and yield after washing away 

 the particles of charcoal, a magnetic powder. 



6S. metallic is a good test for copper in solution, precipita- 



ting it in the state of pure copper. The solution should be slightly 

 acid, and the iron should be clean and free from rust. The weight of 

 the copper cannot however in delicate experiments be correctly ascer- 

 tained by this method of precipitation. 



67. IRON, protosulpJiaie of, detects 1, oxygen gas in water, which 

 shortly after the test is applied turns turbid : 2 gold: 3 palladium, both 

 of which are precipitated in the metallic state: 4, gallic acid, which 

 turns purple. It also detects hydrocyanic acid ; see 10. 



a. Sulphate of iron may be likely to contain copper; if used as a 

 test, the copper may be detected by ammonia : any copper that may be 

 present may be precipitated by clean iron, and the solution be thus pu- 

 rified. 



b. I am indebted to a friend for the following. Protosulphate of iron 

 is a convenient test for ascertaining whether a piece of chunam (or mor- 

 tar) is combined with . carbonic acid, or not. If a piece of plaister be 

 taken which is partly combined with carbonic acid and partly not, and 



