The following are the resistances of Carré's carbons per meter (39.37
inches):
Diameter in Diameter in Resistance in Ohms.
Millimeters. Inches. @ 20° C. (98° F.)
1 .039 50.000
2 .078 12.5
3 .117 5.55
4 .156 3.125
5 .195 2.000
6 .234 1.390
8 .312 .781
10 .390 .5
12 .468 .348
15 .585 .222
18 .702 .154
20 .780 .125
At high temperatures the resistance is about one-third these amounts. A
layer of copper may increase the conductivity one hundred times and
prolong the duration 14 per cent. Thus a layer of copper 1/695
millimeter (1/17300 inch) thick increases the conductivity 4.5 times; a
coating 1/60 millimeter (1/1500 inch) thick increases the conductivity
one hundred and eleven times.
Carbon, Cored.
A carbon for arc lamps with a central core of softer carbon than the
exterior zone. It fixes the position of the arc, and is supposed to give
a steadier light.
Synonym--Concentric Carbon.
Carbon Holders.
In arc lamps, the fixed clamps for holding the ends of the carbons.
Carbonization.
The igniting in a closed vessel, protected from air, of an organic
substance so as to expel from it all the constituents except part of
the carbon; destructive distillation. (See Carbonized Cloth.)
Carbonized Cloth.
Cloth cut in discs and heated in vessels protected from the air, until
reduced to carbon. The heating is sometimes conducted in vacuo. They are
placed in a pile in a glass or other insulating tube, and offer a
resistance which can be varied by pressure. The greater the pressure the
less will be the resistance, and vice versa.
Carbon Dioxide.
A compound gas, CO2. It is composed of
Carbon, 12 parts by weight.
Oxygen. 32 "
Specific gravity, 1.524 (Dulong and Berzelins).
Molecular weight, 44.
It is a dielectric of about the resistance of air. Its specific
inductive capacity at atmospheric pressures is
1.000356 (Boltzmann).
1.0008 (Ayrton).
Synonyms--Carbonic Acid--Carbonic Acid Gas.