DETERMINATION OF ALKALIES IN MINERALS. 201 



with methods already employed. In order that these processes 

 may serve equally well in the hands of others, they will be 

 given with some detail. 



I. Method of rendering the Silicate soluble. 



4. To render the silicate soluble various plans have been 

 proposed, all of which have their objections. Among the 

 agents used for the purpose are baryta and several of its 

 compounds; viz., the nitrate, carbonate, and chloride. 



5. The first of these is undoubtedly the best decomposing 

 agent of the four, could we use a platinum crucible to heat the 

 mixture of it and the mineral ; as it is, a silver crucible is neces- 

 sary, and this is not always capable of standing the requisite 

 heat. According to Hose, "the silver crucible must be very 

 strong, for if thin the action of a red heat might crack it, and 

 a portion of the fused mass would ooze out through the crev- 

 ices." It also may happen that a heat higher than the point 

 of fusion of silver is necessary to a complete decomposition 

 of the mineral. 



6. All that is here said of caustic baryta is equally appli- 

 cable to nitrate of baryta. 



7. The* chlorides of barium and calcium have been lately 

 proposed by Prof. Henry Wurtz, but its decomposing properties 

 are very feeble, as the chlorine in combination with the barium 

 is not liberated at a white heat, and few silicates are able to 

 produce the decomposition. It may succeed with some of the 

 feldspars, but decomposes very imperfectly even the micas. So 

 it is rather a risk to employ it with an unknown substance. 



8. The carbonate of baryta is the compound of baryta most 

 generally employed for silicate decompositions; still this is 

 attended with much difficulty, owing to the infusibility of this 

 salt and the impossibility of driving off the carbonic acid by 

 heat alone; and even if this latter were possible, the objection 

 pertaining to caustic baryta would then arise. 



y. The following extract from Eose's Analytical Chemistry 

 (translation by Normandy, in a note by the translator) pre- 

 sents fairly the difficulties attending this method of decomposing 

 the silicates: 



"The heat applied is so intense that some precautions must be taken. 

 The platinum crucible containing the mixture should be exposed first to the 



