To judge when melted brass is at the proper temperature for pouring is a matter of experience. If the metal he too hot, porous castingswill result; if too cold, the mould will not be perfectly filled. A useful guide is to draw the pot immediately the metal gives off bluish white puffs of vapour, which is volatilising zinc; the latter is a part of the alloy. The heat of the metal will vary according as the castings are wanted large or small. The smaller the casting, the hotter is the metal.