oj the Argillaceous Iron-Ore. 277 



. It is necessary to provide for that case, of very frequent oc- 

 currence, in which the liquid fihered from the oxalate of lime 

 may contain magnesia and oxide of manganese. When this 

 happens, let it be evaporated to dryness, then put the saline 

 residue into a platinum crucible and calcine it in a tempera- 

 ture below a visible red heat, until the whole of the ammonia- 

 cal salts are expelled. It is necessary to do this, for unless 

 these salts were previously got rid of, it" would be impossible 

 to effect a complete precipitation of the magnesia. Let the 

 residue from the calcination be next dissolved in muriatic acid, 

 and having neutralized the solution, either by evaporation or 

 by the addition of an alkali, pour into it a few drops of hydro- 

 sulphuret of ammonia, in order to throw down the manganese. 

 Calcination, under free access of the external air, converts this 

 precipitate into an oxide of manganese, 100 parts of which are 

 equivalent to 90 parts of protoxide, or to 145 parts of carbo- 

 nate of protoxide of manganese. If it be inconvenient, from 

 any cause, to calcine the precipitate, it may be dissolved in 

 muriatic acid, and thrown down, at a boiling temperature, by 

 carbonate of potash. This last precipitate will consist of car- 

 bonate of protoxide of manganese ; 100 parts of which contain 

 62.07 parts of protoxide. 



It now only remains to separate the magnesia. This will be 

 effected most accurately by concentrating the solution from 

 which the manganese had been precipitated by hydrosulphuret 

 of ammonia, and then adding to it, while still nearly boiling, a 

 slight excess of carbonate of potash, after which the mixture 

 should be rapidly evaporated to dryness. On digesting the re- 

 sidue with water, the carbonate of magnesia will be obtained in 

 a light pulverulent form. It may be collected upon a filter, 

 washed, and dried ; then let it be ignited strongly in a platinum 

 crucible. The residue will consist of pure magnesia, 100 parts 

 of which represent 210 parts of carbonate of magnesia. 



It frequently happens that some of the magnesia either re- 

 mains in the solution unprecipitated, or is redissolved from the 

 filter by the edulcorating water. It will be necessary, there- 

 fore, to search for this portion also, when it is desired to deter- 

 mine the entire quantity of the earth with exactness. In this 

 view, the liquid filtered from the carbonate of magnesia should 



