and part iadarly the Oxidation of Iron. 229 



lated sulphate of white iron, the sohitton of which is of a 

 fine green, reddens on its exposure to the air. 



Oxvsrcnated muriatic acid converts it all at once into acid 

 sulphate highly oxidated ; iron, on the contrary, converts it 

 into acidulated green or little oxidated sulphate ; the sul- 

 phuric acid makes it lose its red colour immediately, hy 

 transforming it into an acid sulphate almost colouilcGS, or at 

 least only slightly green. This acid sulphate may be cry- 

 stallized by a well managed evaporation ; the crystals formed 

 are something of an emerald green colour, and in this re- 

 spect it approaches an acid sulphate little oxidated ; they do 

 not sparkle nor deliquesce ; their solution in water, which 

 is but little coloured, does not, like the acid sdlphate of 

 white iron, absorb oxygen till after a long time : the excess 

 of acid which they contain fixes to a certain degree the oxide 

 of iron ; nevertheless by means of oxygenated muriatic acid 

 the oxide becomes red ; and by means of iron it passes to 

 the state of white oxide, particularly at the temperature of 

 boiling water. Both the acidulated and acid sulphates of 

 green iron precipitate themselves green by means of the al- 

 kalis. The precipitate edntains no acid when a great excess 

 of base is added, and particularly when heated : in every 

 instance it is green. It is by treating the red oxide of iron 

 with diluted sulphuric acid that we obtain the acid sulphate 

 of red iron ; the solution would not take place if the acid 

 were concentrated. The acid sulphate of red iron contains 

 more acid in excess than the acid sulphate of green iron, 

 and the latter much more than the acid sulphate little oxi- 

 dated. These properties are common to them with all oxides 

 of the same kind; they require the less of any acid for their 

 saturation the less oxygen they contain; and, on tlie con- 

 trary, they require the more acid the more they are oxygen- 

 ated ; this is proved by antimony, mercury, tin, copper, and 

 iron. They alone among all the metals combine with acids 

 at different degrees of oxygenation; and all, without excep- 

 tion, are subject to this law. This is the reason why the 

 solution of muiiatc of tin little oxidated becomes troubled 

 by the contact of the air, or when being crystallized we at- 

 tempt to dissolve it. It is also for this reason that this 

 P 3 same 



