98 Biography of Johann Nepomuk von Fuchs. 
ing in it but alumina and water. Since, however, I have become 
satisfied,” &. His analysis in fact proved the identity of these 
minerals, 
Already Fuchs had remarked that silica forms compounds in 
the wet way which perfectly correspond with some that occur in 
nature. The further study of these bodies continued to occupy 
im, and therewith are connected his later researches on the 
formation of porcelain clay, on soluble glass, and hydraulic lime. 
In his paper on Lazulite, besides proving in this mineral the pres- 
ence of phosphoric acid, which had been overlooked by Tromms- 
dorf and Klaproth, Fuchs makes the first mention of the fact 
that various insoluble silicates, viz., lazulite, prehnite, zoisite and 
vesuvian, are decomposable by acids after strong ignition. 
In 1821, Fuchs analyzed wagnerite which had been previously 
confounded with topaz, and showed it to be a compound of phos- 
phate of magnesia and fluorid of magnesium. 
In the train of these researches appeared that on the formation 
of porcelain clay. At that time it was thought that potash feld- 
a was the material from which this clay was produced. Fuchs 
showed that clay may originate from other minerals, and 
proved that the porcelain clay of Passau results from the decom- 
peer of the so-called porcelain spar, which, it is remarkable, 
ness still exists among mineralogists with regard to the process 
of weathering, that it may not be useless to recall the explana- 
tion of Fuchs. He says: the process of weathering is something 
similar to the spontaneous decomposition of organic bodies, and 
has been not unaptly compared with fermentation. Hence poree- 
lain clay has a constant composition, and for this reason we mus 
consider it as a distinct species, and not merely append it to 
poor spar, as Hauy, in the belief it originated from feldspar, 
attached it to that mineral, under the name Feldspath-Decom- 
posé. The porcelain clay has no more in common with porcelain 
spar, than alcohol has with the sugar from which it is derived, 
and it sounds just as strangely to call the clay decompose 
porcelain spar as it would to designate alcohol as Jexcanganel su- 
