of the Oxides of Manganese. 163 



with whose observation my own experiments correspond ; none 

 of the native oxides yield a trace of chlorine on the addition of 

 sulphuric acid, provided the muriates have been previously re- 

 moved by washing. 



The ores, before being submitted to analysis, were dried at 

 212 F., by which means they were brought to the same degree 

 of dryness which they possessed before being washed. The water 

 naturally contained in them was ascertained in every instance 

 by heating a known quantity of the ore to redness, and collect- 

 ing the water in a tube filled with fragments of the chloride of 

 calcium. 



The quantity of oxygen was in most cases ascertained both by 

 bringing the ore to the state of red oxide by exposure to a white 

 heat, and by converting it into the protoxide by means of heat 

 and hydrogen gas. When performed with the precautions stated 

 in the first part of this communication, either of these methods 

 may be relied on with confidence ; but the first is more conve- 

 nient in general practice, because it requires less time and a 

 more simple apparatus. The latter is sometimes very trouble- 

 some, owing to the difficulty with which some of the ores of 

 manganese, the native peroxide for example, are reduced by 

 hydrogen to the state of pure protoxide. I have in no instance 

 estimated the quantity of oxygen by means of the deutoxide, the 

 formation of this compound being in my opinion too uncertain 

 to admit of any analytic process being founded upon it. 



In searching for the presence of foreign matters I have em- 

 ployed the following processes. The water which was expelled 

 from the ores by heat, was examined with test paper, but was 

 always found quite free from alkaline or acid reaction. The ab- 

 sence of carbonates was ascertained by the entire want of effer- 

 vescence on the addition of dilute nitric acid. Strong sulphuric 

 acid did not cause the evolution of chlorine or any acid fumes. 



x 2 



