20 
BULLETIN 1179, U. 
S. DEPARTMENT OF AGRICULTURE. 
will still be economically unsound to dispose of this power for the 
manufacture of a material as cheap as phosphate fertilizer must 
always be. 
COMPARATIVE COST OF THE THERMAL UNIT FURNISHED BY ELECTRIC POWER AND FUEL. 
In the volatilization process of producing phosphoric acid, how- 
ever, the chief function of the electric current is that of supplying 
the temperature necessary to effect the chemical reactions involved, 
and the electric furnace is merely a convenient type of apparatus to 
use in bringing about the decomposition of phosphate rock under 
reducing conditions. It logically follows, therefore, that if these 
same conditions can be fulfilled by employing fuel as a heating source 
in lieu of the electric arc, a great saving in the cost of the heat 
energy required should be effected. The following charts (figs. 7, 8, 9) 
and Table 10 give a fairly clear idea of how electric power and 
fuel compare in cost as sources of equivalent quantities of heat 
energy. 
Table 10. — Prices assumed for electric power and corresponding costs of standard fuels 
as sources of equivalent quantities of heat. 
Maximum prices at which standard fuels must 
be obtained to compete with electric power 
Electric 
at rates given in column 1. 
power > 
cost per 
kilowatt 
Natural 
year. 
Coal 2 per 
Fuel oil 3 
Coke* per 
gas 5 per 
long ton. 
per gallon. 
long ton. 
thousand 
cubic feet. 
$5 
$4.60 
$0. 022 
$4.60 
$0.18 
10 
9.20 
.044 
9.20 
.36 
15 
13.80 
.066 
13.80 
.54 
20 
18.40 
.088 
18.40 
.72 
25 
23.00 
.110 
23.00 
.90 
30 
27.60 
.132 
27.60 
1.08 
35 
32.20 
.154 
32.20 
1.26 
40 
36.80 
.176 
36.80 
1.44 
»3,415 B. t. u. per kilowatt hour. 
•14,000 B. t. u. per pound. 
•19,000 B. t. u. per pound. 
* 14,000 B. t. u. per pound. 
61,200 B. t. u. per cubic foot. 
In the curves given in Figure 7 the Tiost of a million British ther- 
mal units produced by certain standard fuels at various prices is 
compared with the cost of the heat equivalent produced by electric 
power at various rates per kilowatt hour. 
In Figure 8 curves are given for converting the cost of the thermal 
unit from mills per kilowatt hour into the terms of dollars per kilo- 
watt year or dollars per horsepower year, either of which is a more 
conventional method of expressing the cost of power which is con- 
sumed in large blocks. 
In Table 10 certain points along the curves given in Figure 7 are 
taken in order to show typical examples of the prices at which elec- 
tric power must be obtained to compete with fuel furnishing the 
same number of thermal units. 
In Figure 9 a comparison is made of the yield of product obtained 
by burning 1 pound of various fuels with that obtained by a power 
