Organic Acids in the Examination of Minerals. 9 



way of comparison the behavior of the same with hydrochloric 

 acid was also noted. The results may be summarized as fol- 

 lows : 1, signifying that the minerals effervesce quickly when 

 the acid is dropped on their smooth surfaces ; 2, that they are 

 feebly and slowly attacked ; 3, that they do not effervesce. 



Mineral. HC1. Sp. Gr. 1.055 Citric Acid. 



Calcite 1 1 



Dolomite 3 3 



Gurhofite , 1 1 



Ankerite 2 3 



Magnesite 3 ... 3 



Siderite 3 3 



Khodochrosite 3 — 3 



Smithsonite 2 3 



Witherite 1 2 



Strontianite 1 2 



Baryto-calcite 1 2 



Malachite 1 2 



Azurite 2 ? 



Porous minerals, and those having highly polished cleav- 

 age or crystalline surfaces, appear to resist the action of the 

 acids, but for very different reasons ; the former (smithsonite, 

 for example) absorb the liquid and conceal its action within 

 their pores; the latter (dolomite, siderite, etc.) seem to repel 

 the liquid, or rather to prevent its actual contact. In the latter 

 case the action of the acid may be rendered visible by scratch- 

 ing the surface with a knife and applying the acid liquid to 

 the roughened surface or to the small amount of powder pro- 

 duced by the scraping. The observations above recorded 

 were made on smooth surfaces. 



In earthy minerals, the acid should be applied repeatedly 

 at the same point until, the pores being filled, the action of the 

 acid on the surface becomes apparent. * 



6. The mineral carbonates behave with a solution of tartaric 

 acid much in the same manner as with citric acid, but the 

 tartrates being in general a little less soluble than the citrates, 

 crystalline precipitates form more readily on cooling the satu- 

 rated solutions. 



