Black lead

crucibles are made of two parts of graphite and one of fire clay; mixed with water into a paste, pre ed in moulds, and well dried; but not baked hard in the kiln. They bear a higher heat than the He ian crucibles, as well as sudden changes of temperature; have a smooth surface, and are therefore preferred by the melters of gold and silver. This compound forms excellent small or portable furnaces. Mr. Anstey describes his patent proce for making crucibles, as follows: Take two parts of fine ground raw Stour bridge clay, and one part of the hardest gas coak, previously pulverized, and sifted through a sieve of one-eighth of an inch mesh (if the coak is ground too fine, the pots are very apt to crack). Mix the ingredients together with the proper quantity of water, and tread the ma well. The pot is moulded by hand upon a wooden block, supported on a spindle which turns in a hole in the bench; there is a gauge to regulate the thickne of the melting pot, and a cap of linen or cotton placed wet upon the core before the clay is applied, to prevent the clay from sticking partially to the core, in the taking off; the cap adheres to the pot only while wet, and may be removed without trouble or hazard when dry. He employs a wooden bat to a ist in moulding the pot; when moulded it is carefully dried at a gentle heat. A pot dried as above, when wanted for use, is first warmed by the fire-side, and is then laid in the furnace with the mouth downwards (the red coaks being previously damped with cold ones in order to le en the heat); more coak is then thrown in till the pot is covered, and it is now brought up gradually to a red heat. The pot is next turned and fixed in a proper position in the furnace, without being allowed to cool, and is then charged with cold iron, so that the metal, when melted, shall have its surface a little below the mouth of the pot. The iron is melted in about an hour and a half, and no flux or addition of any kind is made use of. A pot will last for fourteen or even eighteen succe ive meltings, provided it is not allowed to cool in the intervals; but if it cool, it will probably crack. These pots it is said can bear a greater heat than others without softening, and will, consequently, deliver the metal in a more fluid state than the best Birmingham pots will. See a figure of the crucible mould under Steel .