DETERMINATION OF ALKALIES IN MINERALS. 203 



for decomposing certain of the alkaline silicates, and more 

 successfully than carbonate of baryta; still in numerous in- 

 stances the decomposition was far from complete, and the 

 method unsatisfactory. Notwith standing these failures, I felt 

 convinced that lime was the most powerful decomposing agent 

 that could be conveniently employed for this purpose, as it could 

 be used in its caustic state in a platinum crucible without in- 

 juring the latter, although exposed to the highest temperature. 

 When its carbonate is used a red heat sufficed to drive off the 

 carbonic acid and bring the mineral under the action of caustic 

 lime — a circumstance that does not take place with carbonate 

 of baryta; and it is well that it does not, for otherwise the 

 platinum crucible would be seriously injured. 



15. It was evident that the only obstacle in the way of lime 

 decomposing the silicates as thoroughly as caustic potash was 

 the impossibility of fusing the mixture, and thereby bringing 

 the pulverized mineral and lime intimately in contact. This 

 difficulty overcome, I felt confident of success. Without de- 

 tailing the various methods resorted to, it will suffice to state 

 that the object in view was to use some flux along with the 

 mixture of the silicate and lime, which would render the mix- 

 ture fluid at a bright red heat. The two substances which 

 recommend themselves after many experiments are the fluoride 

 and chloride of calcium, neither of which have any marked 

 decomposing action on the silicates; in fact, their action is 

 simply that of fluxes, which enable the lime and silicate to 

 come in contact in a liquid state, effecting nothing beyond 

 that. It is with the fluoride of calcium that we have to do in 

 this part of the paper, leaving the details on the use of the 

 chloride of calcium until further experiments are made to test 

 fairly its value. 



16. The manner in which I proceed is as follows: Pulverize 

 the silicate to a sufficient degree of fineness; it is not required 

 that the levigation be carried to any great extent; mix inti- 

 mately in a glazed porcelain mortar a weighed portion of the 

 mineral with one part of pure fluor-spar and four or five parts 

 of precipitated carbonate of lime;* introduce it into a platinum 



* The fluor-spar used is the transparent variety, free from all impurities. 

 It is easily and abundantly procured in this as well as in all other countries. 

 The carbonate of lime is made by dissolving calc-spar or pure marble in 



