^ 0 g Mr. Wedgwood’s Analyfis of a 
The white matter being walhed off, more fpirit of fait was 
added to the remainder, and the digeftion repeated, with a long 
tube inferted into the mouth of the glafs, fo as nearly to pre- 
vent evaporation. The acid, when cold and lettled fine, was 
poured off clear ; and on diluting it with water, the fame 
milky appearance w'as produced as at firft. 
The digeftion was repeated feveral times fucceffively, wit \ 
frelh quantities of the acid, till no milkinefs appeared on di- 
lution. The quantity of mineral employed was 24 grams ; 
and the refiduum, after the operations, walhed and dried, 
weighed fomewhat more than 19 grains; fo that about one- 
fifth of it had been diffolved. In feme parcels ot the mineral, 
taken up promifeuoufly, the proportion of foluble matter was 
much lefs, and in none greater. It is only the white part, an 
only a portion of this, that the acid appears to ad upon : the 
white fand, much of the white foft earth, and all the black 
particles, remain unaltered. 
To try whether this tedious procefs of folution could be ex- 
pedited by triture or calcination, fome of the mineral was 
rubbed in a mortar ; and in doing this, it appeared pretty re- 
markable, that though the black part bore but an inconfidera- 
ble proportion to the reft, yet the whitenefs of the other was 
loon covered and fupprefled by it, the whole becoming an 
uniformly black, Ihining, foft, unduous mafs, like black- 
lead rubbed in the fame manner ; with a few gritty particles 
perceptible on preffing hard with the peftle. A penny-weight 
of this mixt, fpread thin on the bottom of a porcelain veffel, 
was calcined about an hour, with a fire between 30 and 40 
degrees * ; it became of an uniform, dull, white, or grey colour, 
b excepting 
* Bv decrees of fire, or of heat above ignition, I mean thofe of my thermo. 
J ® meter 5 
