IIEINRICII ROSK OX yKTUERIFICATlON. 385 



is the peroxide of iron throAvn clown, so that with a certain dilu- 

 tion, as M. Scheerer has shown*, scarcely a trace of the per- 

 oxide of iron remains in solution, but the entire quantity is sepa- 

 rated as basic salt. As stronger bases are not precipitated by 

 water on boiling, this property of the peroxide of iron has been 

 employed to separate it from the oxides of cobalt, nickel, and 

 other metalsf. It may even be separated, by boiling the solu- 

 tion, from alumina, which, although it has with regard to its 

 properties much similarity to the peroxide of iron, is evidently 

 a stronger base ; this separation of alumina from the peroxide 

 of iron by means of water at a high temperature, is of some 

 importance to the arts, as in the fabrication of alum the per- 

 oxide of iron contained in the mother-liquor is precipitated by 

 mere boiling, and is thus more easy to separate from the alumina 

 than the protoxide of iron, although the former, with sulphuric 

 acid and an alkali, forms an alum which has quite an analogous 

 composition with alumina-alum ; and, from being isomorphous 

 with that alum, could crystallize with it in all proportions. 



Several other bases have the same property as the peroxide 

 of iron, which like it belong to the class of weaker bases, and 

 also several substances which act as bases towards strong acids, 

 and also as acids towards strong bases, and which on that account 

 are frequently classed among the acids. Among these are the 

 oxide of zirconium, thorina, the peroxide of cerium, peroxide of 

 tin, titanic acid, tellurous acid, columbic acid ; also in certain 

 respects molybdic acid, tungstic acid, and vanadic acid. Several 

 combinations of these oxides with acids are soluble in the cold 

 in water, and are precipitated from the solution, on boiling, as 

 oxides or basic salts. 



Several of the oxides precipitated in this manner possess, 

 after precipitation by boiling, properties which they do not 

 evince before their solution in acids and precipitation ; they are 

 more indifferent than before, are partly of difficult solution in 

 acids, partly insoluble, and do not combine after precipitation 

 with them, even when these are employed in a concentrated 

 state. Titanic acid, peroxide of tin, and many others may 

 be classed here. This peculiarity is in a certain degree ana- 



* Poggcndorff's Annalen, vol. xliv. p. 153. [or Lend, uiid Ediiib. Phil Ma-r 

 vol. xvi. p. i;jO — Edit.] °'' 



t Scheerer in PoggendorfF's Annalen, vol. xlii. p. 104. [or Lond. and Edinb 

 Pliil. .Mag., vol. xvi. p. 1:51.— Edit.] 



