26 Dr. Turner's Chemical Examination 



of 9 grains of the protoxide of manganese, and 10*01 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 man- 

 ganese. 



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 gradually, to keep the salt at a red heat for an hour or longer 

 without decomposing a particle of it. If the heat should ac- 

 cidentally 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 expel- 

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

 apt to be carried off mechanically by the acid vapour and lost. 

 This accident has occurred to myself, and always happens when 

 a large quantity of free acid is rapidly expelled. By employ- 

 ing a slight excess of acid, and raising the heat slowly, all loss 

 from this cause may easily be avoided. 



The dry salt obtained in my experiments was white, and 

 dissolved readily and completely in distilled water. 



Like many other neutral metallic solutions it reddened de- 

 licate litmus paper. It was nevertheless quite neutral ; for a 

 single drop of a dilute solution of potash occasioned a preci- 

 pitate which was not in the slightest degree redissolved by 

 agitation. 



Analysis of the Chloride of Manganese, — In an excellent pa- 

 per published in the Philosophical Transactions for the year 

 1812, Dr. John Davy states the chloride of manganese to be 

 composed of 54 parts of chlorine and 46 of metallic manga- 

 nese. The atomic weight of manganese calculated from these 

 data is 30*67, a number which is considerably beyond the 

 truth. Dr. Davy prepared the chloride by heating the mu- 

 riate in a glass tube communicating with the atmosphere by a 

 very small aperture. I have never failed by this method to de- 

 compose some of the chloride, a circumstance which complicates 

 the analysis, and probably gave rise to Dr. Davy's error. 



According to the analysis of M. Arfwedson (Annals of Phi- 

 losophy, N. S. vol. vii. p. 274), the elements of the chloride of 

 manganese are in the ratio of 8403 parts of chlorine to 6677 



of 



