Page:History of the Royal Society.djvu/299

 not coagulated, but swims upon the Peter, must be carefully poured off, and being mingled with new Liquors, must again pass the Ashes before it be boiled, else it will grow so greasy it will never generate any Salt.

you have made your Copper very clean, put in as much Water as you think will dissolve that quantity of Peter you purpose to Refine; when the Water is very hot cast in the Peter by little and little, stirring it about with a Ladle, that it may the sooner dissolve; then increase the Fire till your Liquor begin to boil: In the mean time feel with the Scummer, whether there be at the bottom any Salt undissolv'd, and take it out, for it is Common-Salt, and doth not so soon dissolve as the Peter; then as the Water boils scim off the Froth that swims at the top of it as fast as it riseth; when it hath boiled to the height that a drop of it will coagulate on a Plate (as hath been said above in the making of Salt-peter) then cast in by degrees either a Pint of the strongest Wine-vinegar, or else four Ounces of Allum beaten to powder (some choose burnt Allum) and you shall observe a black Scum to rife on the top of the Liquor, which when you have allowed some time to thicken, you may easily take off with the Scummer; repeat this so often till no more Scum arises. Some do use to throw in a Shovel full of Quick-Lime, and say it makes Peter Rh