10 Organic Acids in the Examination of Minerals. 



The results recorded below were obtained with a solution 

 saturated in the cold : 



(a) Calcite, gurhofite, witherite, strontianite, cerussite, and baryto- 

 calcite dissolve readily in the cold; on boiling, the action is increased, and 

 the solutions deposit crystalline precipitates on cooling ; the precipitates 

 of calcium tartrate and of barium tartrate form readily, and may be 

 recognized with a little experience. (Cf. $10.) 



(&) Dolomite, ankerite, rhodochrosite, smithsonite, malachite, and 

 azurite effervesce feebly in the cold, and dissolve rapidly on heating. 

 Dolomite and smithsonite deposit crystals on cooling the solutions; mala- 

 chite yields a bluish green precipitate; azurite dissolves readily without 

 residue. 



(c) Magnesite and siderite are not attacked in the cold, but dissolve 

 readily on heating. The specimen of siderite from Roxbury effervesced 

 very slightly in the cold and appeared to be more soluble than the speci- 

 men from Dauphiny. - 



7. Oxalic acid decomposes the carbonates in a similar 

 manner, forming, however, still more insoluble precipitates, 

 which are in some cases characteristic of the bases contained 

 in the minerals ; especially is this true of the white pulveru- 

 lent calcium oxalate, the light yellow granular ferrous oxalate, 

 the beautifully feathered crystals of barium oxalate, and the 

 heavy white precipitate of lead oxalate. Ankerite contains 

 enough ferrous carbonate to communicate a decided yellow 

 color to the insoluble calcium salt, by the formation of ferrous 

 oxalate. Baryto-calcite dissolves freely on boiling, with for- 

 mation of insoluble calcium oxalate j by decanting the super- 

 natant liquid it deposits as it cools the feathered needles 

 characteristic of acid barium oxalate, easily distinguishable 

 from the stouter, lengthened, monoclinic prisms of oxalic acid 

 which likewise form in concentrated solutions. 



Magnesite, which resists the action of cold citric and 

 tartaric acids, succumbs to oxalic acid. Siderite is also more 

 readily decomposed. Malachite and azurite are feebly attacked 

 in the cold, dissolve slowly on heating, and yield precipitates 

 which are respectively grayish-green and bluish-white in color. 

 Cerussite and smithsonite also furnish solutions which deposit 

 crystalline precipitates on cooling. 



