Organic Acids in tlte Examination, of Mincrah. 11 



Silicates. 



31. Silicates ai'C very Tuiequally attacked by citric acid as well 

 as by mineral acids. 



{a) Neplielite, lapis lazuli, lanmuntite, hersclielite, thom- 

 sonite, mcsolite, and proclilorite, are decomposed by 

 citric acid in the cold, a portion of them with forma- 

 tion of a jelly. 



Tephroire, ilvaite, gieseckite, jefferisite, henlandite, and 

 genthite, are strongly attacked on boiling with the citric 

 acid alone. Pargasite, ]'yrope, almandite, colophonite, 

 phlogo])ite, bastite, masonite, and allanite (?), are feebly 

 attacked. Some doubt obtains, however, as to the last 

 named, becanse the specimens examined were partially 

 decomjoosed on the surface. 

 (b) The addition of sodinm nitrate to the solution of citric 

 acid does not notably increase its solvent power as re- 

 spects silicates, bnt the addition of potassium iodide 

 aids decidedly in effecting their decomposition. The 

 iodo-citric mixture strongly attacks the garnets named, 

 as well as enstatite, liyj)ersthene, pargasite, epidote, 

 and those named in paragraph 32. 

 The feldspars resist these reagents, yet orthoclase and labra- 

 dorite give up iron to them. Petalite, actiuolite, asbestus, 

 beryl, ziicon, vesuvianite, zoisite, iolite, lejiidolite, leucite, an- 

 dalnsite, tibrolite, topaz, titanite, staurolite, and kaolin, either 

 wholly resist or give to the attacking solution only a trace of 

 iron. 



The variety of serpentine known as bowenite resists citric 

 acid, while serpentine itself, of a normal character, is decom- 

 posed. 



On the whole, citric acid attacks the silicates w^ith a power 

 nearly apiu'oaching that of hydrochloric acid. 



Revision of the Silicates. 



32. While carrying on these researches we were continually 

 compelled to combat the iirmly grounded impression that the 

 organic acids are weak as respects mineral species. In conse- 



