METALLIC OXIDATION, 



225 



2. Acid sulphate of white iron. This is of an emerald green, Acid sulphate. 

 It contains a much greater excess of acid, and is rejected in 



almost all the arts in which sulphate of iron is employed. The 

 acidulous may be converted into the acid sulphate by the addi- 

 tion of a little sulphuric acid ; and the acid sulphate may be 

 converted into the acidulous by heating it with iron fihngs. 



Alkalis precipitate both these sulphates white : substances common cha- 

 that easily part with their oxigen, as oxigenatcd muriatic acid, lacters. 

 air, water, &c. decompose them, and precipitate a green or 

 red oxide. 



3. Acidulous sulphate of green iron. This is made by com- Acidulous sul- 



bining sulphuric acid with green oxide of iron. This salt does P'^^^® °^§^"^^" 

 ° ^ => iron, 



not crystaljize ; and is red, notwithstanding the green colour of 

 its oxide. 



4. Acid sulphate of green iron. This is nearly colourless. Acid sulphate 

 It is obtained by the addition of a little sulphuric acid to the ° S^een iron. 

 preceding sulphate ; and crystallizes, though with difficulty. 



The crystals approach the emerald green of the acid sulphate of ^ 

 white iron; are-^.ieither efflorescent nor deliquescent; and ab- 

 sorb the oxigen of the atmosphere but slowly. 



Both these sulphates are precipitated green by alkalis : the Common cha- 

 iron they contain is converted into the state of white oxide '■^'^*^"- 

 by the addition of iron filings, and to that of red oxide by oxi- 

 genated muriatic acid. 



5. Acidulous sulphate of red iron. M. Thenard calls this Acidulous sul- 



also neutral sulphate of highly oxided iron. It is yellow, com- ? ^^^ ^^^ 

 ' o J J ^ iron, or neu- 



pletely insoluble, and consequently incapable of being crystal- tral sulphate of 

 lized. It precipitates in the form of a yellow powder from so- ^^°^ ^ oxided 

 lutionsofthe acidulous sulphates of white or green iron. This Mistaken for a 

 salt has been taken for a yellow oxide of iron, different from the ^^ *^*^ °^' ^' 

 red and the green. 



6. Acid sulphate of red iron. This is obtained by dissolving Acid sulphate 

 red oxide of iron in sulphuric acid diluted with water. It con- ^ ''^ '^°"" 

 tains a greater excess of acid than the. other two acid sulphates ; 



is almost colourless, but assumes a pretty deep red if its excess 

 of acid be saturated by potash ; and does not crystallize. 



Such are the principal properties of the six sulphates of iron ^^^^ of tbe 

 distinguished by M. Thenard. Most of the other acids act other acids act 



, " . , . 1111 c nearly in the 



nearly m the same manner on iron, and the three degrees ot ^^^^^ manner 



Vol. XIV.— July, 1S06, G g oxida- on iron. 



