An Introduction to Technical Electricity

An Introduction to Technical Electricity

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This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1922 edition. Excerpt: ... current to pass. ' In order to examine the arc, care must be taken to protect the eyes, by viewing it through smoked or ruby glass, because the intense light not only produces a painful impression but is very injurious to the eyes. Another useful method of observing the arc is to throw an image of it upon a white screen or piece of paper by means of a simple lens, as shown in Fig. 81. AB are the actual carbons and the current is supposed to enter at A FIG. 8l.--Inspection of the arc. Ix ARC BETWEEN CARBONS 89 and leave at B. A is then called the positive and B the negative carbon. The image produced by the lens L is seen at ab, and the illumination on the screen is not sufficiently great to be harmful to the eyes. This arrangement avoids the necessity for smoked glasses and has the further advantage of magnifying the arc. The first glance shows that both carbons are hot, but there is one spot on the positive carbon a at which the temperature is far higher than at the rest of either carbon. This spot is called the crater, because the carbon burns away much more rapidly here than elsewhere, so that the surface very soon becomes cup shaped, like the crater of a volcano. Owing to combustion of both carbons in air, the ends soon acquire a rounded, somewhat conical, form. Owing to the fact that the positive carbon is at a higher temperature than the negative, it burns away more rapidly. For this reason positive carbons are sometimes made to have about twice the area of cross section of the negative carbons. The carbons are usually made by mixing the carbon left on distilling coal tar, powdered graphite, and a syrup of sugar or gum, to form a paste. This is then forced through a circular die, to form it into circular rods, and these rods more

Product details

  • Paperback
  • 189 x 246 x 2mm | 95g
  • United States
  • English
  • black & white illustrations
  • 1236962168
  • 9781236962164