CHEMICAL REPORT-APPENDIX.



cipitated alumina, which may be estimated correspondingly
too high.
  The large proportion of silica in the German clay (a part
of which is in the state of fine sand) is notable in comparison
with the Carter county clay; and this large proportion of
silica or sand increases the refractory quality of the clay.
But pure fine sand or pulverized quartz could quite cheaply
be added to our clay, which, in other respects, seems to be
at least equal in quality as a fire-clay to the German article,
containing even less of those ingredients which increase the
fusibility of clay, viz: iron oxide, lime, potash, soda, and mag-
nesia. How the phosphoric acid acts in this relation is said
not to have been fully determined by experiment; but it tun-
doubtedly increases the fusibility. As will be seen, the pro-
portion of this ingredient was not ascertained in the German
clay, although it is no doubt present in notable quantity.
  There can be little doubt that some of our native fire-clays
can be made quite refractory by a judicious process of prepa-
ration or purification, including, perhaps, washing with water,
or water containing chlorohydric acid, which is very cheap,
the addition of pulverized quartz, &c.
  In this relation we may notice a beautiful hydrated silicate
of alumina-the Indiana kaolin, or what is denominated midi-
anaite by Prof. E. T. Cox, of the Indiana Geological Survey-
a large and handsome sample of which was exhibited at the
Centennial.  This remarkable clay-like mineral, which was
discovered first in Illlliois, and called Golconda clay, was found
in Lawrence county, Indiana. in 1875, forming a six feet bed,
just under the coal measures conglomerate, and over a bed of
brown hematite iron ore. Where it has not been impregnated
with iron oxide it is a pure hydrated silicate of alumina, of
the composition of halloysite, passing in its greenish portions
into alophane.
  This so-called porcelain clay soon attracted the attention of
potters, and is now in great demand for the manufacture of
the finer qualities of pottery ware. The writer believes, how-
ever, from the brief examination he has given it, that it de-
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