220 DETERMINATION OF ALKALIES IN MINERALS. 



parts of chloride of calcium and one of caustic lime. Expe- 

 rience proves that, however readily such a mixture may reduce 

 the feldspars, it fails when tried on kyanite, zircon, micas, and 

 other silicates difficult of decomposition. This arises from 

 the fact that the chloride of calcium has but little decom- 

 posing effect on the silicates, its action being simply that of 

 a menstruum in which the lime can act conveniently on the 

 mineral. 



62. The use of lime or its carbonate mixed with chloride of 

 calcium or chloride of ammonium, for the purpose of effecting 

 the decompositions alluded to, would be considered by me of 

 questionable utility if the mixture were not so proportioned 

 and employed as to decompose the most difficult silicates, if 

 necessary; for unless this be done we can at no time be cer- 

 tain that the decomposition is complete. As a general rule 

 for decomposing silicates by lime or soda, it is far better to 

 use a charcoal fire than the flame of a lamp, as it is better to 

 heat too high than not to heat sufficiently the mineral to be 

 acted on. 



Complete Analysis of an insoluble Silicate on one Portion 

 of the Mineral. 



63. The effort to accomplish an analysis of this description 

 deserves no encouragement, from the almost invariable inaccu- 

 racy attending the results. If we have a given quantity of any 

 one of the silicates alluded to requiring analysis, we had better 

 subdivide it, however small the entire quantity may be, ascer- 

 tain one set of ingredients by the soda and the other by the 

 lime fusion; for the results thus obtained may be relied on as 

 more accurate than those furnished by an analysis of the whole 

 quantity through the agency of baryta or hydrofluoric acid. 



64. Should it be desired to undertake the analysis on a single 

 portion, I would recommend the silicate to be attacked with 

 carbonate of baryta mixed with the chloride — three to four parts 

 of carbonate and two of chloride. This mixture can be made 

 to decompose all silicates at a much lower temperature than 

 when the carbonate alone is used, but its action is not near so 

 powerful as the carbonate of lime and sal ammoniac. 



65. This terminates an account of my labors in the deter- 

 mination of the alkalies in insoluble silicates. The conclusions 



