204 DETERMINATION OF ALKALIES IN MINERALS. 



crucible capable of holding three times the bulk of mixed pow- 

 der. The platinum crucible should then be placed in one of 

 earthenware, with a little magnesia on the bottom. (I always 

 prefer the crucible made in France, called Beaufay ; s crucible, to 

 inclose platinum crucibles when heated in a furnace, as their 

 form and cleanliness make them superior to the Hessian crucible 

 for this purpose.) The crucible may then be covered and intro- 

 duced in any form of furnace where a bright red heat can be 

 procured. 



17. I have been using a common open portable furnace, 

 heaping charcoal over the top of the crucible; and so easily 

 does the effect take place that in no instance has there been 

 a failure of complete decomposition with as simple a means 

 of heating as the above; and I have ascertained that an alco- 

 holic lamp with a large circular wick, such as Jackson's lamp, 

 urged with a bellows, will answer for making a complete de- 

 composition of zircon in twenty -five minutes. This circum- 

 stance is not stated to recommend the use of a lamp for every 

 mineral decomposition when a simple^ portable furnace and 

 charcoal are so accessible, and their effects so much more to 

 be depended upon than a lamp. From thirty minutes to one 

 hour's exposure to the heat is recommended. 



18. It was an important point to test first how far this 

 mixture could decompose the silicates without distinction as 

 to their containing alkalies; for it was a very simple conclu- 

 sion that if those silicates most difficult of decomposition, and 

 containing no alkalies, were completely decomposed by this 

 process, all others must naturally give way under its action. 

 The silicates experimented on were zircon, kyanite, beryl, topaz, 

 spodumene, margarite, margarodite, and feldspars of different de- 

 scriptions. All were readily decomposed by the method just 



hydrochloric acid (the common acid may he used), adding an*excess of the 

 carbonate; lime-water or milk of lime is then poured on the solution until it 

 is alkaline. By this means any oxide of iron, alumina, or magnesia will be 

 thrown down. To the hot filtered solution a solution of carbonate of ammonia 

 is added, and the precipitate washed several times with distilled water. It is 

 best to prepare one's own carbonate of lime, for as a general rule little reli- 

 ance can be placed on the carbonates of lime, baryta, strontia, etc., sold as 

 being precipitated by carbonate of ammonia, for in more than one instance I 

 have found the carbonate of baryta, sold as a carbonate of ammonia precipi- 

 tate, to contain soda. 



