IAD QUALITY OF E ARTHEKWAR K, ^^1 



fey as we opened them, were very diftinguifliable, as were 

 ibe feeds of the ruflies and the tops of the boughs. The whole 

 matter fmelt very four as it was dug, and tracing it I found it 

 34 feet long and about 20 or 22 feet broad." — *' I forgot td 

 mention that there was a great many nut-fliells found abou t 

 the bed, perhaps thofe might have been on the bulhes which 

 compofed part of the bed *.'* 



XVII. 



Obfervations on the Danger of tifing Earthen-ware or Pottery of 

 a bad Quality. By M. Poidevxn of Rouen \. 



AURE white argil forms the body of the fineft pottery Dlfferetit kinds 

 which bears the name of porcelain ; clays lefs pure, and °*^ ^^^' 

 coloured more or lefs with iron, ferve to form the (lone ware, 

 or hard earthen-ware, ai>d the common or foft fort, which 

 differs from the other, in not experiencing a commencement of 

 fufion at their furface in baking, like porcelain or ftone ware. 

 This badly prepared common earthen-ware is the kind 

 which Is occafionally attended with danger in its ufe, and is 

 the fubjeS of this paper, 



Eurthen-uare. 

 . , /. r Common brown 



Thebifcuit of brown earlhen-ware is prepared from a ferru- ware. 



ginous clay; that of white earthen-ware is compofed of a mix- 

 ture of ferruginous clay, of another clay containing much 

 fjlicious fand, a little lime, and finally of a porous clay, which 

 renders it lefs compa6t, and gives it whitenefs after baking. 



Nature not always affording Ihefe earths in the fame ftate differences la 

 I ■ ' • - 1 • rr- • 1 1 • r • .the ware inm 



of combmatjon, occadons differences m the bilcuif, when it the quality 



becomes fubjefted to the heat : other differences alfo arife in ^^ materia 

 the aflion of the enamel on the bifcuit. If the earth be too 

 ferruginous, or too much mixed with filicious particles, the 

 enamel, during the baking, a6ls as a flux on the bifcuit, foflens 

 it, and occafions the pieces to lofe their fbape. 



If the earti) is too porous it abforbs the enamel and remains 



* A Natural Hiftory of Ireland, in three parts, by Dr. Gcrrard 

 Boate, Thomas Molineux, M. D. F. ?.. S. and others. Pages 128 

 ^130. Dublin: 1755. 



f Annales de Chemie, T. 55, 



rough. 



