340 On definite Proporlions. 



stance also explains why none of the sails of the oxide of 

 iron observes the same proportions with any of the known 

 combinations of nieiallic iron and sulphur. 



What may be the difference between the white, the black, 

 the dark blue, and the green precipitates from the salts of 

 the protoxide, I must confess myself unable to explain. Is 

 it not possible that they may be subsalts, the white of the 

 protoxide, the dark blue and green, triple combinations, 

 « like the triple neutral salt, and containing the oxide and 

 protoxide in different proportions ? This at least appears 

 to me to be the most probable conjecture. 



[In a future number, the reader will find a more satis- 

 factory account of the nature of these substances by Mr. 

 Hausmann : Gilbert. We have not yet seen Mr. Haus- 

 niann's Essay; hut in the 6th number of Gilbert for 1811, 

 we find the following remarks of our author: " I am im- 

 patient to read Mr. Hausmann's Essay on the Hydrates ot 

 Iron : he has communicated to me some results, which 

 however do not agree well with my principles. I have 

 often tried in vain to obtain a pure hydrate of iron. It is 

 therefore impossible to determine the questiop satisfactorily, 

 since the presence of a third body often influences the quan- 

 tity of water taken up, as my experiments demonstrate. 

 My opinion of the nature of these precipitates is continijed 

 bv the frequent occurrence of such compounds in nature. 

 The black magnetic iron ores, for instance, contain an 

 oxide of which the oxygen is two, three or four tiines as 

 much as the oxygen of the protoxide, notwithstanding the 

 powdered mineral exhibits no traces of a red or unmagnetic 

 oxide. The grass-green viiriol of iron, and Piussian blue, 

 are both triple compounds of the protoxide and the oxide 

 with the same acid,"] 



* * * 



Froni the experiments which T have here circumstantially 

 related, the simple law of chemical affinity, which I stated 

 in the begmning of this essay, is demonstrated in a pretty 

 satisfactory manner. They show also the truth of the re- 

 lation which follows from this law ; that every acid re- 

 quires an equal quantitv of oxygen in every base with 

 which it forms a neutral salt; so that the quantity of the 

 base, by which an acid is neutralised, depends on the ca- 

 pacity of its inflammable radical for oxygen. I consider 

 myself therefore as now authorised to employ these laws in 

 the analysis of the alkalis. 



XIII. Ad- 



