262 Gooch and Austin — Oxidation of Manganese. 



upon asbestos on a perforated cone with a filtering surface of 

 about 40 8<1 cm . The dilution of the nitric acid before filtration 

 tends to produce some solubility of the manganese, and the loss 

 then introduced, though trilling if the filtration is rapid, may be 

 considerable if the process of filtration is prolonged, as is the 

 case in the method approved by the " Verein der deutschen 

 Eisenhiitteleute." * 



Our experiments upon the chlorate process have been made 

 with manganous chloride prepared as detailed in a former 

 paper, viz : by boiling manganous chloride with manganous 

 carbonate, precipitating the filtered solution with ammonium 

 sulphide, dissolving the washed manganous sulphide in dilute 

 hydrochloric acid, precipitating the solution thus obtained with 

 sodium carbonate (after boiling out hydrogen sulphide), dis- 

 solving the greater part of the manganous carbonate (thor- 

 oughly washed by repeatedly boiling it in successive portions 

 of water) in the least amount of hydrochloric acid, and boiling 

 the solution thus obtained with the remainder of the pure car- 

 bonate and filtering. The standard of the solution thus pre- 

 pared, neutral and probably very pure, was fixed by evaporat- 

 ing definite portions with sulphuric acid and weighing the 

 residue as the normal sulphate in accordance with the proce- 

 dure outlined in a former paper, f 



Any method, by means of which the oxidizing power of the 

 higher oxygen compounds of manganese is discoverable, may, 

 obviously, be employed to determine the condition of the man- 

 ganese precipitated in this chlorate process. Convenient 

 processes for the determination of the available oxygen in the 

 higher oxides of manganese are the iodometric methods of 

 Bunsen and Pickering. Bunsen's method is applicable to any 

 of Ijhe higher oxygen compounds of manganese — though some- 

 what inconvenient because it involves the distillation of the 

 chlorine liberated by the action of strong hydrochloric acid 

 upon the substance and its collection in potassium iodide, the 

 iodine thus set free being estimated by standard thiosulphate. 

 According to Pickering's^: method the higher oxide is treated 

 immediately with potassium iodide and hydrochloric acid and 

 the iodine liberated is estimated by sodium thiosulphate. 

 Plainly, the latter method is limited to the treatment of the 

 less refractory or more finely comminuted oxides, and it fails 

 in the presence of ferric salts and all other substances capable 

 of liberating iodine from the acidified iodide. 



Still another general iodometric method for determining the 

 oxygen value of the higher oxides of manganese is suggested 



* Von Reis, Zs f. angewandte Ohem., 1891, 376. 

 f This Journal. IV, v. 2()9. 

 jjour. Chem Soc, xxxvii, 128. 



