.12 Organic Acids in the Examination of Minerals,. 



quence of tliis pre-conceived notion, we overlooked in our first 

 paper the fact, that the decomposition of many silicates takes 

 place at ordinary temperatures, having in fact applied heat at 

 once when conducting the examination. 



A closer investigation, however, shows that a saturated solu- 

 tion of citric acid is able to decompose many silicates in the cold, 

 even to the formation of gelatinous silica. This necessitated a 

 revision of the silicates named in our first paper (16), with the 

 following results : — 



{a) Willemite, pectolite, calamine, natrolite, wollastonite, 

 chrysolite, chondrodite, chrysocolla, apophyllite, rho- 

 donite, analcite, chabazite, stilbitc, and deweylite, are 

 more or less strongly attacked by cold citric acid, — the 

 first four yielding a jelly. 

 Datolite, 2:)rehnite, serpentine, chrysotile, and retinalite, 

 are attacked on boiling the solution. 

 {])) The use of the iodo-citric solution as a solvent having 

 been discovered subsequent to the examination of the 

 silicates named in our first paper, a further revision of 

 this group became necessary. The results are briefly 

 as follows : — 

 Olivine, augite, almandite, and epidote, heated with the 

 iodo-citric mixtui'e, are strongly attacked. Orthoclase, 

 labradorite, liornblende, and spodumene, are very feebly 

 attacked, or yield only iron to the solution. 

 Wernerite, albite, diopside, kyanite, talc, mnscovite, bio- 

 tite, ripidolite, and tourmaline, are not attacked. 

 These changes do not invalidate the accuracy of our published 

 results, and are introduced simply to exj)lain the change in 

 position of these minerals in the Tables at the close of this 

 paper. 



Sundry Minerals. 



33. Under this head are grouped phosphates, arseniates, tung- 

 states, sulphates, etc., as stated in the list given in (27). 



A large number, chiefly phosphates, dissolve easily in a cold 

 solution of citric acid ; these embrace the following : — 



Mimetite, triphylite, triplite, libethenite, olivenite, ataca- 



