a i 
fome Mineral Subfiances. 
oil of tartar, per deliquium. This ware is made with 
tobacco-pipe clay and fand, and when well burnt is not 
acted on by either acids or alkalies. «. 
This thews the union of clay with alkalies, and that 
may be the chief reafon why it fhould, when helped 
with heat, be fo ufeful in obtaining the acids of nitre 
and of fe.a fait. 1 have alfo obtained this gelatinous fub- 
Itance by mixture of tobacco-pipe clay and oil of tartar,. 
per deliquium', for after fome months, the alkaly being 
diflblved with water and evaporated, had in great part 
a gelatinous confidence. This mixture was ftirred now 
and then, and had a remarkable volatile alkaline fmelh 
Mr. eoyle fays, that clays diftilled with fea.falt produces 
a fal ammoniac , and I found it to be always true when 
the diftillation is at firft flowly conducted. 
I have often made allum with tobacco-pipe clay cal- 
cined with oil of vitriol, but kept no notes of the quan- 
tity I obtained ; and as for the refduum ufed in this ex- 
periment, it was loft. I can, however, tell the quantity of 
allum which the porcellane clay from Cornwall affords. 
Two drams of this clay, which had been treated with its 
weight of fixed alkaly, and deprived of its faline part, 
then calcined four different times, with a frelh portion 
sach time of oil of vitriol, produced ^ ff. and gr. xxiv. of 
good; 
