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There happens an observation in the Calcina∣tion of Lead, as well as several other things, which very well deserves some reflection. 'Tis that although the Sulphurous or Volatile parts of Lead fly away in the Calcination, which loss
should indeed make it weigh the less, neverthe∣less after a long Calcining 'tis found, that instead of losing it increases in weight.
Some trying to explicate this Phaenomenon do say, that as long as the violence of the flame does open and divide the parts of the Calx of Lead, the acid of the Wood or other matter that burns, does insinuate into the pores of this Calx, where 'tis stopt or fixt by the Alkali; but this reason will not hold, when 'tis considered that this Aug∣mentation comes to pass as well when Lead is Cal∣cin'd with Coals as Wood, for Coals contain only a fixt Salt that rises not at all.
'Tis better therefore to refer this effect to the disposition of the pores of Lead in such a manner, that part of the fire insinuating into them does there remain imbodied, and can't get forth again, whence the weight comes to be encreased.
If you would revive this Calx of Lead by way of Fusion, its parts do squeez and express the igneous particles that were inclosed, and the Lead does thereby weigh less than it did when reduced into a Calx, for by this means the Sul∣phureous parts are separated and lost.