Put a quarter of a pound of isinglass in a small stewpan, just cover it
with a little clear spring water, and add a piece of lump sugar the size
of a walnut, place it upon the fire, shaking the stewpan round
occasionally to prevent its sticking to the bottom; when upon the point
of simmering add the juice of half a lemon, let simmer about a quarter
of an hour, skim and pass it through a fine cloth; if the isinglass is
good it will be as clear as crystal, but if it should be a little
clouded (which it might be, and yet the isinglass tolerably good)
clarify it again thus: pour it into a larger stewpan adding half a gill
of water, place it upon the fire, and when on the point of boiling have
the white of an egg in a basin, whip well with half a gill of water,
pour it into the isinglass, which keep whisking over the fire until
boiling, when place it at the corner of the stove, and let reduce to its
former consistency, it will keep good some few days if kept in a cool
place; if required for crèmes or bavaroises it will not require
clarifying, but merely dissolving as at first directed.