Si a a 
Messrs. Johnson and Blake on Kaolinite and Pholerite. 359 ~ 
it agrees with the formula deduced by HOTEL ATEAT from his 
analyses of porcelain clays, viz., 3&1 48i 6 
This substance is not the nacrite of enn or Thomson, 
which contained at the most but one per cent of water. It i is 
not the pholerite of Guillemin, as we shall preoay see. The 
old terms kaolin, steinmark and eanomntEe ave been so loosely 
applied that they do not define 
The massive yellow oe from Rochlitz has the compo- 
sition of eaolae but with a portion of the alumina replaced 
by sesquioxyd of iron. Klaproth’s analysis (Chemische Ab- 
handlungen, vi, 987) is as follows: 
od 
peri - - 45°25 
lumina, . - 36°50 
Sleaguiecced of iron, - - 2°75 
i - - 14:00 
Potash, - - . trace. 
98°50 
Digested in hot concentrated hydrochloric acid it is scarcely 
acted upon, but retains its yellow color without falling to pow- 
der, as we have observed with a specimen in Professor Brush’s 
cabine 
ee examined by Rammelsberg ( ndbu 
576), that from Saszka analyzed by v. Hauer (Jahresbericht der 
uae ; ere 860), and the severite of the lat an 
kaolins, and some of the results of their analyses have led to 
the adoption of t the etn A Sieh (or 2A13sSi4H). But of the 
31 ana | M. but four agree to the above pene 
Furthermore, the data from which this formula has been 
posed, were not derived from the original analyses of the clay, ne 
from these analyses “corrected” by deducting from the total 
Silica (exclusive of quartz), the loss suffered by boiling the kao- 
alloysite cannot be confounded with kaolinite although it is nto hydrate 
of the ilicate of alumina that exists in the latter. Its formula isHl 
12H, r 28 i ai. The speci of this mi m Guatequé snaiiial ial 
ussingault, and those from Houscha and Anglar examined by Berthier, lost one- 
half their water (8-9 per cent) on drying at 212°, and “xr a the formula of 
kaolinite. It can a st ts staan that this loss was due to hygro pane pre a 
many unbetaeade-s when dried at 212°, or below that temperature, lose a or all 
seg pain: water. Thus selenite loses about three-fourths of its water at 212°. 
uantity is not, however, definite. Halloysite is of Pager Peer" density 
cp p gr=-1) to kaolinite, fe more easly decomposable by acids, and is without doubt 
ly characterized species. 
