16 Chemical Examination of American Minerals. 



require to be purified, and the bicarbonate, tbougb pure, is 

 much more expensive than carbonate of soda. 



The mineral previously reduced to an impalpable powder, 

 is weighed out in a platinum crucible, and then mixed with 

 about thrice its weight of dry carbonate of soda in powder. The 

 two materials are mixed as intimately as possible, by means 

 of a platinum spatula, and then exposed to a red heat for about 

 half an hour. It is not necessary to fuse the mixture, though 

 I often do so. A good spirit-lamp answers well enough to heat 

 the crucible, though I find it more convenient to apply the heat 

 of my common furnace, which is always at hand, and almost 

 always fit for the purpose. If the mixture has not been fused, 

 it may be easily taken out of the crucible by inverting it over 

 an evaporating dish, and tapping it on the bottom. After 

 fusion it adheres too strongly to tlie crucible to be so re- 

 moved. In either case it is to be dissolved in diluted muri- 

 atic acid. L is easy to judge by the eye whether the mineral 

 has been sufficiently acted upon by the alkali. The muriatic 

 acid solution in that case is complete, or only a few light white 

 flocks remain undissolved ; whereas, when the powder has 

 not been sufficiently acted on, it remains in the state of a dense 

 mass at the bottom of the dish. When this happens, we may 

 in general conclude that the mineral has not been sufficiently 

 pulverized. We must reduce the undissolved portion to a 

 finer powder, and heat it again with a new portion of carbo- 

 nate of soda. 



The muriatic solution must be treated precisely as describ- 

 ed in a former part of this paper. But in minerals which 

 require the assistance of an alkaline carbonate to make them 

 soluble in muriatic acid, magnesia is a frequent constituent. 

 Now minerals which contain magnesia require a peculiar 

 treatment. It is diflicult to separate magnesia completely 

 from alumina. When we precipitate the alumina in the way 

 formerly directed, it carries down with it a portion of mag- 

 nesia. Such alumina is distinguished by a peculiar property 



