ON-THE IMi»ROVEMENT OF POTTERY, 2^3 



the processes he has tiiscovered, tliough what he says ap- 

 pears sufficient, to give him a claim to our contidence. 



Without attempting to divine his secret, 1 shall add in stone-ware 

 support of its possibility, that it might reasonably have been "^^y ^^^ made 

 questioned, when the art wiis but a traditional practice, and fire. 

 when ail our stone-ware was of a close texture, incapable of 

 supporting the fire witliout cracking: it might have beeti' 

 questioned before the expevimeuts of Lauraguais in 1762, Lauraguais. 

 whence Mr. Jousselin dates the first conception of a com- 

 mon porcelain, and whose successes did not meet the en- 

 couragement thev deserved: before the property of magne-Useof magne- 

 • i . . 1 ^1 f • • ? . • X- 1 siaawdbarytes. 



sia to put a stop to the fusion without impartmg any colour- 

 ing principle, and that of barytes to supply the place of 

 saline fluxes, were known: before the analyses of feldtspar Artificial feldt- 

 had taught us to compose it artificially with very common ^^^^' 

 materials: before the property of pumice stone to afford a Pumice stone 

 covering not attacked by any menstruum was discovered ; ^^^S^^^®* 

 and before the inventor of this process, Fourmi, crowned 

 by the Institute in the year 12, had fabricated his ht/gio- Ilygiociramcs, 

 ccrames, a species of common porcelain capable of standing 

 the fire: before the effects of heat prolonged to devitrifica- Devitrification 

 tion had been observed : and before the productions of the ^^ ^^^^' 

 manufactories of Utschneider, Lambert, and Mittenhof, 

 had been seen, which the jury of the exhibition of I8O6 

 recognized as a true stone-ware capable of standing the fire, 

 that is to say common porcelain*. 



Thus 



* I have here pointed out only the principal facts. 1 might quote 

 many others, that tend nit less powerfully to confirm the opinion For 

 instance, the spuma maris, the keffekil of Kiiwan, to which the name KefFekil, 

 of magnasite has been given, and of which the Turks make their pipes, 

 contains according to Klaproth but 50 silex, and 17 magnesia I 

 have found, that it loses 023 of its weight in the fire. It has the pro- its use. 

 perty of stopping both the vitrification and the contraction of the com- 

 positions ill 10 which it enters. 



Mr. Giobert has shown, in the Memoirs of the Academy of Turin Magnesian 

 for 1802, that the earth of Baudissero, long considered as almost pure earth, 

 alumine, and used with success m the porcelain manufactory of Viuovo, 

 is a magnesian earth, containing about 0-14 of silex 



Among the results of the syuihetical essays made in my laboratory at 

 ^Jmj Imperial Polytechnic School, 1 obtained a ghis>s perfectly similar to Glass from ar- 



that 



