298 ANALYSIS OF MATERIALS 



A little water is added and a trace of pure tartaric 

 acid, which being evaporated to dryness is disengaged 

 with the vapors of nitric acid. The interior of the 

 capsule will be filled with beautiful crystals of vola- 

 tilized oxalic acid; it is heated to dull redness by 

 covering the capsule in such a way that the carbonic 

 acid may not be burned in the interior. In this ope- 

 ration the oxalic acid has driven off the nitric acid 

 and changed the nitrates into oxalates ; these at a red 

 heat are converted into carbonates, and if by chance a 

 small quantity of nitrate has escaped during the reduc- 

 tion, the carbonic oxide and tartaric acid would have 

 eliminated it, so that there would remain only carbo- 

 nates. 



Water is now added to the magnesia and manga- 

 nese remaining in the capsules, and the alkaline car- 

 bonates are dissolved. It is decanted upon a very 

 small filter, because it is not necessary to wash the 

 carbonate of magnesia much ; it is remarkably soluble, 

 particularly in cold water, and therefore the washing 

 water should be boiling hot when used. 



The mixture of carbonate of magnesia and manga- 

 nese is heated to redness and thus converted into 

 magnesia and red oxide. The mixture is weighed in 

 the same capsule in which the evaporation has been 

 made. It is then treated with a boiling concentrated 

 solution of nitrate of ammonia, and heated until no 

 more ammoniacal fumes are given off. It is decanted, 

 and the insoluble material washed, if any exists, and 

 should be of a brown color. The capsule is then 

 heated to redness and weighed. The difference be- 

 tween these two weights gives the magnesia, and 

 what remains in the capsule gives the weight of the 

 manganese, the ammoniacal fluid containing the mag- 

 nesia is placed aside to be examined as directed hereafter. 



The soluble carbonates of soda and potassa are 

 treated with hydrochloric acid for experiment in a 



