pound
7. Electric current 3,412 B.t.u. per kilowatt-hour

For the heat treatment specified only comparatively low temperatures
are required. No difficulty will be experienced in attaining the
desired maximum temperature of 1,800 deg.F. with any of the heating
medium above enumerated; but it should be noted that the producer
gas with a B.t.u. content of 170 per cubic foot and the electric
current would require _specially_ designed furnaces to obtain higher
temperatures than 1800 deg.F.

TABLE 28.--COMPARATTVE OPERATING COSTS

Assuming
Cost of oil- and gas-fired furnaces
installed as $100.00 per square foot of hearth
Cost of coal-fired furnace installed as 150.00 per square foot of hearth
Cost of electric furnace 100 kw.
capacity installed as 90.00 per kilowatt
Cost of electric furnace 150 kw.
capacity installed as 70.00 per kilowatt

Output 3,000 lb. charge, 8 hr. heat carburizing, 2 hr. heating
only. Annual service 7,200 hr. Fixed charges including interest,
depreciation, taxes, insurance and maintenance 15 per cent. Extra
operating labor for coal-fired furnace 60 cts. per hour, one man
four furnaces.

COST OF VARIOUS TYPES OF FURNACES
-------------------------------------------------------------------------------
| Class fuel | Fuel per | Unit fuel|Installation|Efficiency| Fixed |Cost per
| | charge | cost | cost | per cent |charges| charge
-|------------|------------|----------|------------|----------|-------|--------
| 1 | 2 | 3 | 4 | 5 | 6 | 7
-|------------|------------|----------|------------|----------|-------|--------
Carburizing
-|------------|------------|----------|------------|----------|-------|--------
1|Oil | 52.0 gal. |$0.15 gal.| $2,400.00 | 12.6 | $.40 | $8.20
2|Natural gas | 4.4 M | 0.50 M | 2,400.00 | 18.8 | 0.40 | 2.60
3|City gas | 8.3 M | 0.80 M | 2,400.00 | 17.0 | 0.40 | 7.04
4|Water gas | 18.7 M | 0.40 | 2,400.00 | 16.4 | 0.40 | 7.88
5|Producer gas| 37.3 M | 0.10 M | 2,400.00 | 14.5 | 0.40 | 4.13
6|Coal |814.0 lb. | 6.00 ton | 3,600.00 | 9.4 | 0.60 | 3.98
7|Electricity |500.0 kw-hr.| 0.015 kw.| 9,000.00 | 53.0 | 1.50 | 9.00
-|------------|------------|----------|------------|----------|-------|--------
Heating
-|----