272 M. Arfwedson on [April, 



require very nearly 3*51 parts of oxygen to be converted into 

 black oxide. The constituents by calculation in 100 parts are, 



Oxidum manganoso-roanganicum .... 86' 85 



Oxygen 3*07 



Water 10-08 



100-00 



Now the 86-85 parts of the oxidum manganoso-manganicum 

 contain 23-6 parts, and 10*08 parts of water contain 8-895 parts 

 of oxygen. Thus it appears that the oxygen in the oxide which 

 has been heated to redness is not a multiple of the oxygen in 

 the water; but if we add the 3-07 parts of oxygen driven off by 

 the red heat to the 23-6 which are found in that oxide, then the 

 unheated mineral will be a chemical compound with water, 

 whose oxygen is just one-third of the oxygen in the oxide. The 

 hydrogen of the water driven off and its oxygen, added to the 

 oxide, make up the constituents of the superoxide. 



It is plain from the preceding experiments that the mineral 

 just examined is a hydrate of manganese-oxide, whose oxygen 

 contains three times as much oxygen as that in the water. The 



formula for this compound is Mn Aq. 



II. Common Grey Ore of Manganese. 



a. 5-03 grammes of this mineral in powder freed from water 

 mechanically lodged in it were put into a small glass retort, to 

 the beak of which was luted a glass tube filled with dry chloride 

 of calcium. The retort was heated over a spirit-lamp as long as 

 any moisture was disengaged. The apparatus being allowed to 

 cool was found to have lost 0-143 gramme of its weight; this 

 was gas disengaged. The chloride of calcium had increased in 

 weight 0-077 gramme, which was water. The residue weighed 

 4-810 grammes. 



b. Three grammes of the powder thus freed from water and a 

 portion of gas were exposed to a strong red heat in a platinum 

 crucible. After three repetitions of this process, the loss of 

 weight was 0-286 gramme ; and the blackish-grey colour of the 

 mineral was changed into brown. A fourth exposure to heat 

 was tried without any diminution of weight. Since 3 grammes 

 by this treatment lost 0-286, it is evident that if the whole quan- 

 tity had been thus treated, it would have lost 0-458 gramme. If 

 to this we add the 0-143 lost over the spirit-lamp, we see that 

 the 5*03 grammes of the mineral had lost 0-601 gramme of oxy- 

 gen and 0-077 of water. 



c. The 3 grammes employed in the preceding experiment were 

 dissolved in muriatic acid. The solution was evaporated to 

 dryness, and the dry mass again dissolved in water acidulated 

 with muriatic acid. There remained undissolved silica and 

 earthy matter, which, after being washed and heated to redness, 



