148 Dr TURNER'S Chemical Examination 



ror in the atomic weight of barium will at once vitiate an ex- 

 tensive series of his most elaborate analyses. My own observa- 

 tion, however, combined with the remark of BERZELIUS, has in- 

 duced me in the mean time to secure my own researches as 

 much as possible from any uncertainty respecting the atomic 

 weight of barium, and I have been therefore induced to ascer- 

 tain the composition of the sulphate of manganese synthetically 

 rather than by analysis. 



Nine grains of pure protoxide of manganese, prepared from 

 the red oxide by means of hydrogen gas, were dissolved in dilute 

 sulphuric acid, the solution was slowly evaporated to perfect dry- 

 ness in a platinum crucible, and the dry salt exposed for half an 

 hour to a red heat. It then weighed 19*01 grains ; and regard- 

 ing the increase in weight as owing to the acid combined with 

 the protoxide, the resulting sulphate must consist of 9 grains of 

 the protoxide of manganese and lO'Ol grains of sulphuric acid. 

 The atomic weight of the protoxide indicated by this process, is 

 35'96. The experiment was repeated with 4'855 grains, and the 

 resulting sulphate weighed 10'26 'grains, indicating 35.93 as the 

 equivalent of the protoxide of manganese. 



As some chemists may doubt the accuracy of this process, I 

 shall attempt to show the grounds on which its merits are to be 

 estimated. Dr THOMSON says it is scarcely possible to expel all 

 the water from the sulphate by means of heat, without at the 

 same time driving off some of its acid. It is indeed very easy 

 to effect the decomposition alluded to by Dr THOMSON ; but I 

 found no difficulty, by slow evaporation and raising the fire gra- 

 dually, to keep the salt at a red heat for an hour or longer with- 

 out decomposing a particle of it. If the heat should accidentally 

 become so intense as to decompose a little of the salt, the defect 

 is easily remedied by adding a drop or two of acid, and replacing 

 the crucible in the fire. 



Dr FORCHHAMMER has judiciously remarked, that in expell- 

 ing an excess of sulphuric acid, a portion of the salt is very apt 



