PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 451 



ted for him at Greenpoint, N. Y., and also by diagrams of De- 

 ville's apparatus for cupelling with gas. Specimens of alumina, 

 and of clay "calcined, to show the change of color in proportion 

 to the iron present; and of bricks acted on by silicate of iron, 

 were also shown, as also both amorphous and crystallized quartz 

 penetrated by iron at the heat of a coke fire, without blast. 



Dr. Stevens. — I was informed at the steel works on Staten 

 Island, that the expense of crucibles, determines in a great de- 

 gree, the question whether the works can be carried on success- 

 fully or not. The clays used there for crucibles belong to the 

 Cretaceous age of the world, and are a decomposed felspar. They 

 do not differ chemically from the fireclays derived from the coal 

 formation of England. The Stourbridge clay, which is celebra- 

 ted for crucibles and firebrick, is found underlying a coal vein. 

 It would be of comparatively little value Avere it not ground up 

 very fine and passed under the inspection of the human eye, aided 

 by powerful magnifying glasses, so that every particle ©f the sul- 

 phuret of iron shall be taken from the clay. If we had some 

 chemical process which would take the sulphuret of iron out of 

 clays at a small expense, it would be one of the greatest aids 

 which could be furnished in the working of metals. 



Mr. Johnson stated, that in New Jersey, a magnet had been 

 used to aid in extracting the iron, and more recently the clay has 

 been passed through a bolt. By these means a large part of the 

 iron could be extracted. 



The Chairman stated that the crucibles manufactured by Mr. 

 Dixon, in Jersey City, are exported in considerable quantities, 

 and are used in England, France and Germany. None of the 

 materials employed by him are found in this country. They 

 consist principally of plumbago, which is brought from Ceylon, 

 and is the best in the world. The clay is brought from Holland. 



Mr. Dibben. — Those crucibles are the most durable in the 

 world. One of them will outlast ten of those that we imported 

 from England fifteen or twenty years ago. I have known them 

 to stand seventy-five meltings of brass. But these pots are not 

 of the proper material for making steel. They are apt to make 

 the steel foamy, or leave in it, after it is poured, small cavities 

 that cannot be welded together afterwards. That I found by 

 melting iron of the same kind in difierent kinds of crucibles. The 

 clay pots would not stand my fire. I used wrought iron and cast 

 iron mixed together. The metal had a small per centage of car- 



