onductor employed.
The resistance of conductors is subject to change by changes in
temperature. While nearly all metals show an increase, carbon shows a
decrease in its resistance when heated.

The temperature coefficient of a conductor is a factor by which the
resistance of the conductor at a given temperature must be multiplied
in order to determine the change in resistance of that conductor
brought about by a rise in temperature of one degree.

TABLE V

Temperature Coefficients

+---------------------------+-----------------------------+
| PURE METALS | TEMPERATURE COEFFICIENTS |
+---------------------------+--------------+--------------+
| | CENTIGRADE | FAHRENHEIT |
+---------------------------+--------------+--------------+
| Silver (annealed) | 0.00400 | 0.00222 |
| Copper (annealed) | 0.00428 | 0.00242 |
| Gold (99.9%) | 0.00377 | 0.00210 |
| Aluminum (99%) | 0.00423 | 0.00235 |
| Zinc | 0.00406 | 0.00226 |
| Platinum (annealed) | 0.00247 | 0.00137 |
| Iron | 0.00625 | 0.00347 |
| Nickel | 0.0062 | 0.00345 |
| Tin | 0.00440 | 0.00245 |
| Lead | 0.00411 | 0.00228 |
| Antimony | 0.00389 | 0.00216 |
| Mercury | 0.00072 | 0.00044 |
| Bismuth | 0.00354 | 0.00197 |
+---------------------------+--------------+--------------+

_Positive and Negative Coefficients._ Those conductors, in which a
rise in temperature produces an increase in resistance, are said to
have positive temperature coefficients, while those in which a rise in
temperature produces a lowering of resistance are said to have
negative temperature coefficients.

The temperature coefficients of pure metals are always positive and
for some of the more familiar metals, have values, according to
Foster, as in Table V.

Iron, it will be noticed, has the highest temperature coefficient of
all. Carbon, on the other hand, has a large negative coefficient, as
proved by the fact that the filament of an ordinary incandescent lamp
has nearly twice the resistance when cold as when heated to full
candle-power.

Certain alloys have been produced which have very low temperature
coeffi