Electrochemical and metallurgical industry . which are advanced to near the 455 center of the tube. These boats are so shaped as to touch thetube at only a few points, so that they do not conduct, them-selves, any appreciable amount of the current. As a jacketing material calcined magnesia was not foundsatisfactory, on account of very great shrinkage. Carborundumis considered to be a very excellent jacketing material. It is afairly good heat insulator and has the advantage of being a re-ducing agent, consequently protecting the carbon from burningaway. Messrs. Hutton and Patterson used carboru
Electrochemical and metallurgical industry . which are advanced to near the 455 center of the tube. These boats are so shaped as to touch thetube at only a few points, so that they do not conduct, them-selves, any appreciable amount of the current. As a jacketing material calcined magnesia was not foundsatisfactory, on account of very great shrinkage. Carborundumis considered to be a very excellent jacketing material. It is afairly good heat insulator and has the advantage of being a re-ducing agent, consequently protecting the carbon from burningaway. Messrs. Hutton and Patterson used carborundum in afine granular condition, the grains just passing-through a sieve,180 meshes to the linear inch. As soon as the graphite has at-tained a fairly high temperature these grains frit together,forming an adherent tube-shaped jacket around the graphitewhich serves to strengthen and protect it. Agglomerated Carbon-Tube most of their experimental work, Messrs. Hutton andPatterson use agglomerated carbon tubes, which can readily. FIG. 2.—AGGLOMERATED CARBON TUBE FURNACE. be obtained of almost any desired size from manufacturers ofarc carbon. The construction, as finally adopted, is spoken ofas very excellent in actual use. The ends of the carbon tube, which may with advantage besomewhat roughened by filing, are electro-coppered, and thensoft-soldered to thick copper tubes, just large enough to slipOver them. The copper tube is provided for a short distancewith a brazed-on water jacket, which effectively cools the jointand protects it, even when a very high current densuy is neces-sary; at the further end of the copper tube a copper clampconnected with flexible cables leads in the current. By soft-soldering the carbon to copper tubes with brazed water jackets,it is always possible to easily replace the carbon without anyfear of injuring the joints of the water jacket. The lengthover which the soldered joint has to be made obviously de-pends on the size of carbon tub
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