160 Vrofessor Apjony on a new Variety of Alum. 



(1) (2) (3) 



32.79 

 For Sulphuric acid . . jW-y = .817 4 



Alumina .... ^^ = .414 2.026 



7.33 

 Oxide of manganese . ojy = .205 1.003 



Water " ^-^ =5.350 26.315 



•7 



From a comparison of columns (2) and (3) the quotients will be seen to be 

 almost exactly as the numbers 4, 2, 1, and 26, so that the mineral is composed of 

 two atoms of the sesqui-sulphate of alumina, one atom of the sulphate of manga- 

 nese, and twenty-six atoms of water. Its formula is therefore 3so3, ^k^3-\- SO3, 

 MnO -f- 26 HO, or exactly conformable to that which belongs to soda alum. 



It is well known that the neutral sulphate which enters as a proximate consti- 

 tuent into the composition of alum is not necessarily always the same. Chemists 

 are long acquainted with the fact, that this sulphate may be one of potash, 

 ammonia, or soda. More recently also It has been shown, that the alumina 

 might be replaced indifferently by the sesqui-oxides of iron, chrome, and manga- 

 nese, without disturbing the formula, or even the crystalline form of the salt, 

 which in every Instance is an octohedron. The species, however, whose exami- 

 nation has been just concluded, differs from all these in not containing any 

 alkali, the place of this being occupied by the protoxide of manganese, and in not 

 crystallizing in the octohedral form. I have attempted to crystallize it by eva- 

 poration in the presence of oil of vitriol in vacuo, but could only obtain a mass of 

 a fibrous structure, closely resembling the mineral in its original state. I have 

 also attempted unsuccessfully the synthetic production of this alum, by mixing 

 sesqui-sulphate of alumina and sulphate of manganese in the proper proportions ; 

 the solution concentrated by evaporation, and then placed beneath the receiver 

 of the air-pump with the oil of vitriol, could not be brought at all to the solid 

 state. As this failure may be owing to the employment of too great an excess 

 of sulphuric acid, I purpose repeating the experiment with all the necessary pre- 

 cautions, and with the addition of the one per cent, of sulphate of magnesia 

 detected in the native product. This latter, indeed, can scarcely be considered 

 as an essential component, as it in all probability merely replaces some sulphate 



