360 Messrs. Johnson and Blake on Kaolinite and Pholerite. 
lin for one and a half minutes with a five per cent solution of 
caustic potash, this loss being assumed to be accidental hydrated 
silica. This mode of correction is obviously of no value. On 
the one hand, the caustic potash might dissolve the kaolinite 
itself from the more finely divided specimens. Berthier and 
Rammelsberg have both observed the solution of kaolin in 
strong potash ley. On the other hand, treatment for so short a 
time would scarcely suffice to remove all the free silica from a 
kaolin that contains a large proportion of that substance, if our 
analytical experience enable us to judge. Again, the analyses 
appear to have been intended in the first place for technical pur- 
poses, and were made, not on specimens selected with reference 
to their purity, but on the clays in bulk employed in the porce- 
lain manufacture. It is plain that they are not adapted to throw 
light on the chemical composition of the basis of kaolin. Least 
of all do they give evidence of the existence of the compound 
numerous they may be. But the fact that the composition of a 
substance whose purity cannot be ascertained by mechanical or 
_ Optical means, agrees with that of another of like origin an 
currence seen to be homogeneous by the help of the microscope, 
is demonstration that the first is unmixed with foreign matters. 
Pholerite—That other crystallized hydrous silicates of alumina, 
xi, 489.) ; 
In 1851 Prof. J. L. Smith published analyses of two minerals, 
one from Naxos, associated wi i 
Schemnitz, associated with diaspore, w , 
tical in composition with pholerite. (This Journal, [2], xi, 58.) 
