May 1, 1864.] THE TECHNOLOGIST. 



THE PATENT PLUMBAGO CRUCIBLE COMPANY. 465 



kept in view. The crucibles which present the finest combination of 

 good qualities are those from which the Patent Plumbago Crucible Com- 

 pany takes its name. They support, even when of the largest size, the 

 greatest and most sudden alternations of temperature without cracking; 

 they can be used repeatedly, and their inner surface can be made so 

 smooth that there is no fear of the particles of metal hanging about their 

 sides. Their first cost is necessarily high, as plumbago is an expensive 

 raw material ; but the fact that they may be used for a great number of 

 meltings makes them, in reality, cheaper than the ordinary clay pots. As 

 fire-clay contracts considerably when exposed to a high temperature, it 

 cannot be used alone for large crucibles. The so-called " clay crucibles" 

 are made of a mixture of the plastic clay and some other substance, such 

 as highly-burnt fire-clay, silica, or coke, which counteracts in a measure 

 the evil due to contraction, and so lessens the tendency of the vessels to 

 crack. The large Stourbridge clay crucibles so extensively employed by 

 the brass-founders of Birmingham contain both burnt clay and coke. The 

 Cornish and Hessian crucibles are made of peculiar kinds of clay, in 

 admixture with sand. The great superiority of the plumbago crucibles 

 over these can be easily accounted for by the fact that graphite or plum- 

 bago is the most infusible of all substances known, and at the same time 

 a material that can be thoroughly incorporated with the clay without 

 impairing its plasticity. 



The works of the Patent Plumbago Crucible Company cover a large 

 space of ground at Battersea, and have a good river frontage. As we 

 proceed along the lane which leads from near Battersea Bridge, we 

 find that the ground gets blacker and blacker, and before we reach 

 the threshold of the office we notice the familiar black-lead polish beneath 

 our feet. Passing a regiment of clerks, we enter the private office of the 

 manager of the works, where we put on a very large coat and a very old 

 hat, which are kept for the use of clean visitors. There are many things 

 in this office which attract our attention. The walls are covered with 

 testimonials from British and foreign mints respecting the excellence of 

 the Company's manufactures, with here and there a prize medal. The 

 International Exhibition of 1862 is recalled, not merely by the Prize 

 Medals awarded to the Company for crucibles and black-leads, but also 

 by the splendid samples of plumbago, which formed such a striking 

 feature in Class I. In this collection every quality of plumbago is repre- 

 sented by specimens from all the most celebrated mines, particularly those 

 of Ceylon, Germany, Spain, Siberia, Canada, Finland, and Borrowdale. 

 We learn from the manager that some of the samples would not be 

 adapted for the manufactures of the Company. The Siberian plumbago, 

 for instance, contains too much iron, and although this could be entirely 

 removed by the Company's patented process for purifying plumbago, it 

 is found cheaper to work with the Ceylon plumbago, which contains but 

 little iron. 



Before we leave this snug office for the busy factory, we will jot down 



