J. L. Smith on determining the Alkalies in Minerals. 235 
this condition of things will be alluded to in another part of this 
paper, as reference is now had to the quantitative determination 
of the alkalies, discarding whatever else the mineral may contain. 
_ 3. In the determination of the alkalies in silicates not soluble 
acids, three important points present themselves ; 
_ 4, Ihe means necessary to render the silicate soluble. 
Il. The separation of the other ingredients from the alkalies, 
More especially magnesia. | 
I. The removal of the sal-ammoniac unavoidably accumula- 
ted in the process of analysis. ; 
Itall three of these, the processes adopted will be found to 
differ essentially from those now in use; and they are made 
town only after much experience by the author, in which their 
advantages have been most fairly tested, comparatively with me- 
ds already employed. In order that these processes may serve 
a well in the hands of others, they will be given with some 
I. Method of rendering the Silicate soluble. 
_A. To render the silicate soluble, various plans have been pro- 
posed, all of which have their objections. Among the agents 
used for the purpose, are baryta and several of its compounds, 
Wz.: the nitrate, carbonate, and chlorid. 
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- 
“ty, and this is not always capable of standing the requisite heat. 
According to Rose, “the silver crucible must be very strong, for 
uf thin, the action of a red heat might crack it, and a portion o 
used mass would ooze out through the crevices.” It also 
may happen that a heat higher than the point of fusion of silver 
Necessary to a complete decomposition of the mineral, _ 
6. All that is here said of caustic baryta is. equally applicable 
0 nitrate of baryta. . : 
7. The chlorid of baryum has been lately proposed ; but its 
decomposing properties are very feeble, as the chlorine in combi- 
nation with the baryum is not liberated at a white heat, and few 
. “les are able to produce the decomposition. It may succeed 
With Some of the feldspars, but decomposes very imperfectly even 
the . So it is rather a risk to employ it with an unknown 
Substance 
8. The carbonate of baryta is the compound of baryta most 
emnerally employed for silica decompositions ; still this is attend. 
iy with much difficulty, owing to the infusibility of this salt, and 
™Mpossibility of driving off the carbonic acid by heat alone ; 
and even if this latter were possible, the objection pertaining to 
suc baryta would then arise. | 
