THE TECHNOLOGIST. [May 1, 1864. 



464 



A VISIT TO THE WORKS OF THE PATENT PLUMBAGO 

 CRUCIBLE COMPANY. 



BY J. C. BROUGH. 



Crucibles have been in use for melting and refining metals from that 

 distant point of time when man exchanged his stone hatchet and bone 

 chisel for implements of bronze. The earliest melting-pots were doubt- 

 Jess made of the plastic and infusible substance clay, and there is no 

 reason to suppose that they differed essentially from the earthen crucibles 

 now commonly used in our foundries. 



As an instrument of scientific research the crucible has held an 

 important position for at least a thousand years. It was constantly used 

 by the first alchemists, and may, indeed, be truly styled the cradle of 

 experimental chemistry.* 



At the present time crucibles of one form or another are extensively 

 employed by the refiner of gold and silver, the brass-founder, the melters 

 of copper, zinc, and malleable iron, the manufacturer of cast-steel, the 

 assayer, and the practical chemist. They are made in many different 

 shapes and sizes, and of many materials, according to the purposes for 

 which they are intended. For certain chemical experiments requiring 

 high temperature vessels of platinum, porcelain, and lime are adopted ; 

 but for ordinary metallurgical operations " clay crucibles " and " plum- 

 bago crucibles " are exclusively employed. We have now to confine our 

 remarks to these two important classes of crucibles. 



On examining a clay or plumbago crucible we find nothing to excite 

 our surprise. It t-eems to be merely a rough specimen of pottery that 

 might be easily imitated. Yet the successful makers of crucibles are 

 so few that they might almost be counted on the fingers of two hands. 

 When we take into consideration the qualities which are required in a 

 crucible to enable it to pass victoriously through the ordeal by fire, the 

 paucity of good makers becomes intelligible. The crucible should resist 

 a high temperature without fusing or softening in a sensible degree ; it 

 should not be liable to break or crumble when grasped with the tongs ; 

 and it ought to be but little affected by the chemical action of the ashes 

 of the fuel. Again, it might be required to withstand the corrosion and 

 permeation of such matters as melted oxide of lead. In some cases 

 crucibles should resist very sudden and great alternations of temperature 

 so that they may be plunged, while cold, into a furnace nearly white-hot 

 without cracking. In other cases, they are required to resist a high 

 temperature after having been gradually heated. Some crucibles are 

 specially remarkable for one quality, and others for another, so that 

 in selecting them the conditions to which they will be exposed must be 



* The word " crucible," from the Latin crux— cruris, recalls the alchemical 

 practice of making the vessel with the protective sign of the Cross. 



