(iv.) Porcelain of Tournay—Clay, chalk, and soda enter into its composition. It is very fusible, but not very fragile. [p479]
| POTTERY. | |||||
|---|---|---|---|---|---|
| Nevers. (i.) | Paris. (ii.) | Gergovia. (iii.) | |||
| Silica | 0.572 | 0.541 | 0.544 | ||
| Alumina | 0.124 | 0.127 | 0.220 | ||
| Lime | 0.226 | 0.063 | 0.064 | ||
| Oxide of Iron | 0.066 | 0.070 | 0.098 | ||
| Magnesia | . . | 0.024 | 0.038 | ||
| Water | . . | 0.173 | 0.020 | ||
| 0.988 | 0.998 | 0.984 | |||
(i.) Earthenware of Nevers—Paste of a pale red. Made of a marle occurring close to the town; the glaze is a white enamel, containing both tin and lead.
(ii.) Paste of the brown earthenware made by M. Husson at Paris. The biscuit is red, but is covered by a brown glaze, coloured by oxide of manganese.
(iii.) Red earthenware resembling the Etruscan, and found in the ruins of Gergovia near Clermont.
| CRUCIBLES, &c. | |||||||
|---|---|---|---|---|---|---|---|
| Hessian. (i.) | Paris. (ii.) | English. (iii.) | St. Etienne. (iv.) | ||||
| Silica | 0.709 | 0.646 | 0.637 | 0.652 | |||
| Alumina | 0.248 | 0.344 | 0.207 | 0.250 | |||
| Oxide of Iron | 0.038 | 0.010 | 0.040 | 0.072 | |||
| Magnesia | trace | . . | . . | trace | |||
| Water | . . | . . | 0.103 | . . | |||
| 0.995 | 1.000 | 0.987 | 0.974 | ||||
| Nemours. (v.) | Bohemia. (vi.) | Le Creusot. (vii.) | |||||
| Silica | 0.674 | 0.680 | 0.680 | ||||
| Alumina | 0.320 | 0.290 | 0.280 | ||||
| Oxide of Iron | 0.008 | 0.022 | 0.020 | ||||
| Magnesia | trace | 0.005 | trace | ||||
| Water | . . | . . | 0.010 | ||||
| 1.002 | 0.997 | 0.990 | |||||
(i.) Hessian crucibles—formed of a clay very aluminous, with which siliceous sand is mixed. They sustain rapid changes of temperature without fracture, but cannot retain fused litharge very long together, and have too coarse a grain for many purposes.
(ii.) Paris crucibles, manufactured by Beaufaye—they are made from the clay of Andennes, near Namur; part of the material being baked and coarsely powdered, and the rest in its natural state: no sand is mixed with it, and the inner surface of the vessels is finished with a thin coat of the unbaked material. They are said to be more refractory than the Hessian vessels, not more liable to fly by change of temperature, and more retentive of litharge.
(iii.) Fragment of an unbaked crucible prepared for an English cast-steel work.
(iv.) Paste with which the crucibles are made for the steel works of Berardière, near St. Etienne.