in practice that the
resistivity of commercial annealed copper is about 1-1/4% less than
that of hard-drawn copper. The standard now accepted for such copper,
on the recommendation of the 1899 Committee, is a wire of pure
annealed copper one metre long, weighing one gramme, whose resistance
at 0 deg. C. is 0.1421 international ohms, or at 60 deg. F., 0.150822
international ohms. The specific gravity of copper varies from about
8.89 to 8.95, and the standard value accepted for high conductivity
commercial copper is 8.912, corresponding to a weight of 555 lb per
cubic foot at 60 deg. F. Hence the volume-resistivity of pure annealed
copper at 0 deg. C. is 1.594 microhms per c.c., or 1594 C.G.S. units,
and that of pure hard-drawn copper at 0 deg. C. is 1.626 microhms per
c.c., or 1626 C.G.S. units. Since Matthiessen's researches, the most
careful scientific investigation on the conductivity of copper is that
of T. C. Fitzpatrick, carried out in 1890. (_Brit. Assoc. Report_,
1890, Appendix 3, p. 120.) Fitzpatrick confirmed Matthiessen's chief
result, and obtained values for the resistivity of hard-drawn copper
which, when corrected for temperature variation, are in entire
agreement with those of Matthiessen at the same temperature.

The volume resistivity of alloys is, generally speaking, much higher
than that of pure metals. Table V. shows the volume resistivity at 0
deg. C. of a number of well-known alloys, with their chemical
composition.

TABLE V.--_Volume-Resistivity of Alloys of known Composition at 0 deg.
C. in C.G.S. Units per Centimetre-cube. Mean Temperature Coefficients
taken at 15 deg. C._ (Fleming and Dewar.)

+-----------------------+-----------+-------------+-------------------+
| |Resistivity| Temperature |Composition in per |
| Alloys. | at 0 | Coefficient | cents. |
| | deg. C. |at 15 deg. C.| |
+-----------------------+-----------+-------------+-------------------+
|Platinum-silver | 31,582 | .000243 |Pt 33%, Ag 66% |
|Platinum-iridium | 30,896 | .000822 |Pt 80%, Ir 20% |
|Platinum-rhodium | 21,142 | .00143 |Pt 90%, Rd 10% |
|Gold-silver | 6,280 | .00124 |Au 90%, Ag 10% |
|Manganese-steel | 67,148 | .00127 |Mn 12%, Fe 78% |
|Nickel-