MERCURY 



227 



kiln. They bear a higher heat than the Hessian 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. 



The crucibles from Passau or Ipser are made from one part plastic clay from 

 Schildorf, and from two to three parts of an impure graphite, which, according to 

 Berthier's analysis, consists of 



Carbon ......... 34 



Silica 41 



Alumina 15 



Oxide of iron 8 



Magnesia, water . 2 



100 



Berthier has examined the crucibles of different districts ; his results are as follow : 



Mr. Anstey describes his patent process for making crucibles as follows : Take 

 two parts of fine-ground raw Stourbridge clay, and one part of the hardest gas-coke, 

 previously pulverised, and sifted through a sieve of one- eighth of an inch mesh (if the 

 coke is ground too fine, the pots are very apt to crack). Mix the ingredients together 

 with the proper quantity of water, and tread the mass 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 thickness 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 

 assist 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 cokes being previously 

 damped with cold ones in order to lessen the heat) ; more coke is then thrown in till 

 the pot is covered, and it is now brought gradually to a red heat. The pot is next 

 turned and fixed in a proper position in the surface, without being allowed to cool, 

 and is then charged with cold iron, so that the metal, when melted, shall have its sur- 

 face 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 successive meltings, provided it is not allowed to cool in the intervals ; 

 but if it is cool, 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. 



The Cornish crucible has been long known, and valued for all assaying purposes. 

 They are prepared in large quantities for the ordinary assays made in the county, and 

 are exported in considerable numbers. The base of these crucibles is the Poole and 

 Stourbridge clay, which is mixed with a certain proportion of sand obtained from 

 St. Agnes, and ground pots. 



Dr. Percy has favoured us with his analysis of the Cornish crucible : 



Silica 72-29 



Alumina 25'32 



Peroxide of iron 1'07 



Lime ...... 0'38 



Magnesia . trace 



Potash 1'14 



MBIT ACC ANTTE. An ore of titanium, found in the bed of a rivulet which flows 

 into the valley of Menaccan in Cornwall. 



MERCURY, or Quicksilver. This metal is distinguished by its fluidity at com- 

 mon temperatures ; its specific gravity =13'6; its silver-blue lustre; and its extreme 



02 



