Chemical Examination of American Minerals. 19 



111 some cases it is convenient to throw down the iron by 

 benzoate of ammonia. For this purpose the iron must be in 

 the state of peroxide. To this state it is easily brought by 

 adding nitric acid to the liquid containing it, and digesting 

 it for some time on the sand bath. The liquid must be free 

 from all excess of acid, otherwise the benzoate of iron will be 

 again partly re-dissolved during the washing. To tliis state 

 it may be brought, by adding caustic ammonia to it till the 

 iron has begun to precipitate. Expose it to a moderate heat 

 for an hour ; if the iron be all taken up again, add a little 

 more ammonia and heat it again. Continue these alternate 

 additions of ammonia and heatings, till (the liquid still retain- 

 ing a red color) a minute quantity of the iron refuses to re- 

 dissolve. Benzoate of ammonia will now throw down the 

 whole of the iron, and the benzoate may be collected upon a 

 filter without loss. When dry let it be weiglied by means of 

 a double filter. Then put a determinate portion of it into a 

 platinum crucible, and heat it till the benzoic acid is destroy- 

 ed. Let the remaining matter be drenched in nitric acid 

 and heated slowly to redness. It will now be pure peroxide 

 of iron, and from the portion thus got, the weight of the whole 

 iron in the mineral may be easily deduced. 



3. As no mineral requiring caustic potash to render it so- 

 luble in muriatic acid is treated of in this paper, it is needless 

 in this place to make any remarks on the methods of ana- 

 lyzing such bodies. 



1. NATIVE SODA- ALUM. 



The possibility of forming an alum by means of sulphate 

 of soda, has not been known for more than twenty years ; nor 

 is an account of it as a peculiar salt to be found in all, even 

 of the most recent works on chemistry. It is so soluble in 

 water, and the crystalization of it so troublesome, that du- 



