Abstract
HIGH resistances to carry small currents, as in grid leaks and electrostatic work, can be very simply made by smoking a rod of silky quartz. A piece of this rod in its ordinary condition is wiped clean and fitted with end metal connexions of closely fitting metal tubes or of copper wire wound round and twisted tight; connecting wires are soldered on or left over from the winding; the dimensions of the quartz rod may be chosen as desired, for 1010 ohms 6 cm. length has been used, for 1014 ohms 10 cm.; the diameter has been 4 mm. The metal-quartz junction is then well covered with india-ink and dried by warming, the quartz surface being kept free from handling. The whole is now smoked over a small smoky gas flame given by burning, at the end of a glass tube, coal gas that has been led through petrol; a good dense deposit is made round the india-ink junctions, and over the rest of the quartz a fairly even deposit not too dense is formed. After the rod is allowed to cool, the resistance is measured and can then be very easily and quickly adjusted in value by evenly wiping off some of the deposit with clean dry cotton wool or by adding a little more soot. The resistance may then be sealed into a clean quartz tube or left bare or coated with paraffin wax, of good white quality, by simple dipping.
Published Version
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