26 Organic Acids in the Examination of Minerals. 



silicates are present, many of thern dissolve with great facility. 

 Those minerals which were hardly attacked by citric acid 

 alone, viz. ; olivine, wernerite, chondrodite, and prelmite, 

 together with the following not previously examined, ortho- 

 clase, albite, labradorite, augite, diopside, hornblende, alman- 

 dite, spodumene, kyanite, talc, and epidote, are more or less 

 readily decomposed. Of the latter, albite, labradorite, and 

 augite, dissolve quite freely, while epidote appears to be 

 slightly attacked by citric acid alone. 



That this method of attack must be conducted in platinum 

 vessels, goes without saying ; the silicon evolved as a fluoride 

 may be detected by suspending a moistened glass rod in the 

 vapors, causing a gelatinous precipitate. To obtain affirma- 

 tive results, it is essential that the silicates should be in very 

 fine powder; the common micas, muscovite and biotite, which 

 are obtained in pulverulent form with great difficulty, appear 

 to resist these reagents ; and ripidolite is but slightly attacked, 

 perhaps for the same reason. 



Tourmaline decidedly resists the action of these reagents, 

 as well as the fluorides, cryolite, and fluorite. Samarskite is 

 not attacked. 



It is hardly to be expected that this method of examining 

 minerals will be serviceable in field work, but it may prove 

 applicable to quantitative analysis. 



SUMMARY OF RESULTS. 



22. The results of this investigation establish the hitherto 

 unrecorded fact that organic acids not only decompose a con- 

 siderable number of minerals belonging to various groups, 

 but they also possess a remarkable selective power as regards 

 the degree of this decomposition; to make this selective 

 property of citric acid evident, and at the same time to present 

 a condensed recapitulation of its action on the ninety minerals 

 examined, we have drawn up the annexed table (p. 30). This 

 table shows that citric acid alone divides minerals into eight 

 groups ; A, those which dissolve in the cold without evolution 

 of gas; B, those which dissolve in the cold with liberation of 

 carbonic anhydride ; C, those which are decomposed in the 



