290 Refleétions on the Quality of Earthen-Ware, | 
the patfte, by grinding, a minutenefs fuited to the purpofe 
for which it is intended, and to all the parts the fame dimen- 
fions as far as poflible; 3d, to carry the baking to the 
higheft degree that the matter can bear without being fufed ; 
4th, to apply the glazing in thin layers, the fufibility of 
which ought to approach as near as poffible to that of the 
matter, in order that it may be more intimately united, 
C. Vauquelin, being perfuaded that the quality of good 
pottery depends chiefly on ufing proper proportions of the 
earthy matters, thought it might be of importance, to thofe 
engaged i in this hianel of manufa&ture, to make known the 
analyfis of different natural clays employed for this purpofe, 
and of pottery produced by fome of them, in order that, 
when a new earth is difcovered, it may be known by a fimple 
analyfis whether it will be proper for the fame object, and to. 
what kind of pottery already known it bears the greateft re- 
femblance. ; 
Heffian Argil of — Porcelain Wedgewood’s 
Crucibles. Dreux. Capfules, Pyrometers. 
Silex -- + = 69: . =<. 43:5 - \ 6% >, 6472 
111 OP Sa SR a: IN 
Fime, = ).« »--. 2 so Be me =. 6 
Oxyd of iron - 8 eee Kon ee oP) 
AY ERR os ieee te i olen ow cam 
Raw kaolin roo parts.—Silex 74, argil 16°5, lime 2, wa- 
ter 7. A hundred parts of this carth gave eight of alum, 
after being treated with the fulphuric acid. 
Wafhed kaolin 100 parts.—Silex 55, argil 27, lime 2, 
iron o'5, water 14. This kaolin, treated with the fulphuric 
acid, gave about 45 or 50 per cent. of alum. 
Petuntzé.—Silex 74, argil 14° 53 lime 5°95 lofs 6. A 
hundred parts of this fubQance, treated with the fulphuric 
acid, gave feven or eight parts of alum. But this quantity 
does not equal the lofs fuftained. 
Porcelain of retorts.— Silex 64, argil 28°8, lime 4°55, 
iron 0150, lofs 2°77. Treated with the {ulphuric acid, this 
porcelain gave no alum, 
XVI. Eleventh 
