Fo 
sthly, This falt fhould then be carried to a reverberatory 
furnace, in which the extraCtive matter is burned off and much of 
the water diffipated; hence it generally lofes from 10 to 15 per 
cent. of its weight. Particular care fhould be taken that it fhould 
not melt, as the extra@tive matter would not. be thoroughly con- 
fumed, and the alkali would form fuch a union with the earthy 
parts as could not eafily be diffolved. I added this caution, as 
Door Lewis and Mr. Dossiz have inadvertently direfted the 
contrary. This falt thus refined is called pearl afh, and muft be 
the fame as Dantzic pearl afh *. 
For the moft ceconomical conftruction of a laboratory and 
furnaces for the above operations I refer to the defcription given 
in a French tra@, called Jart de fabriquer le falin © Ja potaffe; 
and fhall only add, that if the falt were extracted by a fire 
fupported by vegetables whofe afhes might afterwards be employed, 
no inconfiderable advantage would be gained. Pearl afh is fre- 
quently tinged green or blue; this colour it acquires during 
fafion, not from any union of the falt with phlogifton, as was 
formerly fuppofed, but by reafon of the manganefe contained in 
the afhes oe almoft all vegetables, as Mr. Scheie has fhewn. 
When it is calcined without melting it is perfectly white as 
Dantzic pearl afh. Y 
SECTION 
* The French call the refined ath ot afo, and the unrefined /alin. 
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