on Basalt, &c. 
293 
Reaumur's porcelain, does not arise from an evaporation of the 
alkali, as has been alleged, but from a regular arrangement of 
the molecules of the glass. It commences by the formation of 
fibres perpendicular to the surface of the glass, and penetrating 
into it. At nearly the same time, small radiated globules are 
formed in the interior of the glass, and the union of these with 
the fibres, by their mutual increase, forms the whole into a new 
substance; and, if the requisite temperature be longer main- 
tained, the fibres disappear, and the whole becomes fine-grained, 
and almost compact. This substance, from the improved state 
of its aggregation, is much stronger and more tenacious than 
before, and is not fusible at a heat sufficient to fuse the glass it 
was formed from ; but, if that aggregation be once destroyed, 
the glass resulting from its fusion is equally fusible with the 
original glass ; and a repetition of the process will again form 
Reaumur’s porcelain, which may be again fused, and so on 
repeatedly, for the quantity of alkali evaporated during the ope- 
ration is extremely small. The hardness and and brittleness of 
metals rapidly cooled, contrasted with the softness and tenacity 
resulting from their gradual refrigeration, are all analogous 
instances ; and all the processes in which annealing is employed, 
and more remarkably the tempering of steel, are proofs of the 
internal motions and arrangements of the particles of matter, 
at temperatures very much below the heat requisite for their 
fluidity. 
Whatever doubts may arise respecting the formation -of the 
crystals, there seems no reason to suppose that their gradual 
increase would cease, till all the molecules belonging to that 
species were exhausted, if the temperature favourable to their 
generation was continued. If the mass was entirely composed 
