32 Organic Acids in the Examination of Minerals. 



may pass into it in considerable quantity. Falling fruits may 

 give it citric, malic, and tartaric acids." u Formic, propionic, 

 acetic, and butyric acids, or rather their salts, have been 

 detected by Jougbloedand others in garden-earth. The latter 

 are common products of fermentation, a process that goes on 

 in the juices of plants that have become a part of the soil or 

 of a compost." * 



How far these organic bodies assist in disintegrating rock 

 material is largely a matter of conjecture; that they do exert 

 considerable influence may be concluded from the existence in 

 the soil of the ulmates, humates, apocrenates, and cienates of 

 potash, soda, ammonia, lime, magnesia, iron, manganese, and 

 alumina. We have, moreover, numerous instances of min- 

 erals containing organic acids in combination : 



Berzelius and other chemists have remarked the occurrence 

 in marshes of compounds of iron and organic acids, of unde- 

 termined composition. Prof. T. Sterry Hunt t describes limo- 

 nites containing from 12.5 to 15 per cent, of humic acids ; Dr. 

 George A. Koenig,| in an investigation of the cause of the deep 

 green coloration of amazon-stone from Pike's Peak, concludes 

 that the coloring matter consists of some compound of iron 

 with an organic acid, the nature of which he has not yet de- 

 termined. Dr. Gideon E. Moore, in a paper on Cryptocallite, 

 recently presented to the New York Academy of Sciences, 

 refers to moresnetite containing iron combined with some or- 

 ganic acid. Forster§ conjectures that the color of smoky 

 quartz is due to the presence of an organic substance contain- 

 ing carbon and nitrogen. 



To these scattered notices may be added the small number 

 of minerals, mentioned in Dana's System of Mineralogy, of 

 which organic acids form constituents : 



Whewellite, calcium oxalate, occurring in small crystals on calcite. 



Thier8chite, another calcium oxalate, forming an opaline incrustation on 

 the marble of the Parthenon at Athens. Its origin is attributed to the 

 action of vegetation on marble. 



* Prof. S. W. Johnson in "How Crops Feed." New York. 1870. 



t Geol. Canada, 1863, 510. 



t Proc. Acad. Nat. Sci., Philadelphia, 1876, p. 155. 



§ Pogg., Ann., cxliii, 173. 



