. An elementary book on electricity and magnetism and their applications. project intothe detonating cap and are connected by afine platinum wire. This wire becomes hotwhen the current flows ; and being embeddedin guncotton, which serves as priming ontop of the fulminating mixture, it ignites thisand sets fire to the charge. In this waysubmarine mines may be exploded beneaththe water and at any desired distance fromthe battery. 334. Electric furnaces. These furnacesare coming into extensive use commercially,not because the electricity plays any peculiar part in the process,but simply because t
. An elementary book on electricity and magnetism and their applications. project intothe detonating cap and are connected by afine platinum wire. This wire becomes hotwhen the current flows ; and being embeddedin guncotton, which serves as priming ontop of the fulminating mixture, it ignites thisand sets fire to the charge. In this waysubmarine mines may be exploded beneaththe water and at any desired distance fromthe battery. 334. Electric furnaces. These furnacesare coming into extensive use commercially,not because the electricity plays any peculiar part in the process,but simply because they furnish a convenient means of obtainingvery high temperatures which can be easily controlled. Forexample, in the ordinary chemical and metallurgical furnacestemperatures up to 2000° C. are obtainable, but in the electricfurnaces temperatures up to 3500° C. can be produced withoutspecial difficulty. In most places, however, when chemical ormetallurgical processes are now carried out, heat produced elec-trically is much more expensive than heat produced from Fig. 342. — Electricfuse used in ignit-ing the charge inblasting and ex-ploding mines. 488 ELECTRICITY AND MAGNETISM In general, it is convenient to divide electric furnaces intotwo classes: the resistance furnace, such as that used byAcheson in making carborundum, and the arc furnace, suchas that used by Heroult for making high-grade steel. It was in 1891, while trying to impregnate clay with carbon,that Acheson obtained a beautiful crystalline substance almostas hard as diamond. He thought this new substance wasderived from carbon and clay and so called it carborundum,but it has since been found to be a compound of carbon (C) and sand (Si02) and issilicon carbide (SiC).^ To-day carborundum— or silicon carbide istr gM doubtless the most im- ^tyH. - i - - J ±-Js§ portant abrasive on the c market. Fig. 343. — Section through carborundum The carborundum furnace. , furnace is shown incross section in figure
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectmagnetism, bookyear19
