_ Ur, Wedgwood’s Analyfil of A 
Loth in the manner of a cupel, * did the fame Magneha 
or chalk, would indeed vitrify in the clay veffel; out on flmt, 
no one of the known earths fhews any tendency to V.tnhcauon 
in that heat K In a cavity, fcooped in a lump of clnU . this 
fubftance, in the heat above mentioned, run _ into a ma 
roundhead, fmooth, whitilh, and opaque, not: ml the lea a - 
hering to the calcareous mafs. On a bed of powdered quick- 
lime ft formed i browffiffi (tom, which in great par, WM 
into the lime, and feemed to have united with it. On dr. 
Henry’s maguefia, uncalcined, it melted and funk m com- 
pletely, leaving only a flight brownhh ftam on the furface 
where it had lain. On beds of the barofehmte and baryt.c 
quicklime, it hkewife melted and funk in, leavmg a d.ico- 
Lred foot behind; but whether it really umted with the fub- 
ftrata or only penetrated into their interfaces, could not be 
determined with certainty, on account of the fmallnels of the 
quantity of the mineral 1 had to work upon. 
On a bed of powdered charcoal, in a crucible clofely lu e , 
this fubftance likewife melted ; and therefore it may be pre- 
* It may be proper juft to mention, that I find this to be a very commodious 
and fnre method of trying, in fmall, whether any given earthy body be fufi le 
with other earths. If the body is difpofed to vitrify with any proportion of clay 
or flint, for inftance, it will equally vitrify when a little of « » apphed or even 
dufted only, on the bottom of a fmall cup made of clay, or on a fmooth clofe bed 
^ finely powdered flint. The body, in this mode of applicanon, feems to unite 
with only juft fo much of the matter of the fubftratum as is reqmfite for them 
rooft p. r fea fufion together, and has nothing elfe m contaft with n, to t ha. no 
deception canarife; whereas, if mlx'J with the fame matter, there mtght be no 
, ppe Lnce of fufion, unlefs certain favourable proportions of the two fiiouU 
Chance to be hit upon ; and even then, if the quantity be fmall, it would no 
certain but that the fufion might have originated from the matter of the cruc.bK 
