Rowley- rag-ftofte and the Toad-ftone. 329 
mortar tempered fo hard that it will bear the grinding of ena- 
mel in it without difcolouration. 
4thly, Filtres are never employed, it being found impoflible 
to get the quantities accurate where they are ufed. The pow- 
dery parts are allowed to fubflde until the fupernatant liquor 
becomes clear. This fometimes requires days or weeks ; but 1 
am ignorant of a better method. By giving the veffels a cir- 
cular motion round their axes, I can greatly facilitate the fub- 
liding of the folid contents. If the feparating veffels are made 
like a common tart-difh, with a fpreading border, the liquors 
may be poured off very near, without difturbing the fediments. 
5thly, Phlogifticated alkaly means the vegetable fixed alkaly 
prepared by the deflagration of nitre and cryftals of tartar dif- 
folved in water, and boiled with Pruffian blue in fuch quantity 
that it will not any longer precipitate an earth from an acid. 
I remain, &c. 
W. WITHERING. 
R O W L E Y - R A G. 
THE ffone which is the fubjed of the following expe- 
riments forms a range of hills in the fouthern part of 
Staffordfhire. The lime-ftone rocks at Dudley bed up againft 
it, and the coal comes up to the furface againft the lime-ftone* 
The higheft part of the hills is near the village of Rowley. 
The fummit has a craggy, broken appearance, and the fields 
on each fide to a confiderable diftance are fcattered over with 
large fragments of the rock, many of which are funk in the 
ground. In a quarry near Dudley, where a pretty large open- 
Vol. LXXIL X x ing 
