402 MINERALS YEARBOOK

 tn this case, also, the average consumption for 1932 was actually higher
than for 1931, being 14.9 pounds as against 14.5 pounds.
 The conclusion seems warranted that while progress in economy of railroad-fuel
coal is by no means at an end the rate of change is slowing down.
~Electri~ public utilities.—In power generation at electric central.
stations economies continued in 1932 but at a slower rate than in any year
since the beginning of the record. The net reduction in the average consumption
per kilowatt-hour has been:
 Net reduction,
 pound
From 1917 to 1922 0. 97
From 1922 to 1927 . 66
From 1927 to 1932 . 34
 For 1932 the average was 1.50 pounds per kilowatt-hour against 1.55 pounds
in 1931 and represents a saving of 0.05 pound in a year, but a decade ago
the saving was running about 0.20 pound a year.
 The influence of the depression on the average efficiency has been mixed.
At a given station, lowering of the load factor tends, of course, to increase
unit consumption, but where the load is spread over many stations a smaller
load may render it unnecessary to utilize the less-efficient stand-by plants.
Whatever the cause, the curve of figure 21 shows a slowing down in the rate
of saving.
 Blast J'urnaces.—About one eighth of the national supply of bituminous
coal finds its way into iron blast furnaces in the form of coke. Here economies
in use have arisen, partly through increased yield of merchantable coke per
ton of coal carbonized in the coke oven and partly through decreased consumption
of coke per ton of pig iron made. The combined result of the two factors
is shown in figure 21.
 It will be seen at a glance that improvement in efficiency was comparatively
rapid during the early part of the period but that it has slowed down greatly
since 1927. By periods, the net reduction in pounds of coking coal required
per ton of pig iron was:
 Net reduction,
 pounds
From 1917 to 1921 287
From 1921 to 1926 188
From 1926 to 1930 70

 Byproduct colcing.—The introduction of the byproduct coke oven effected
large savings by recovery of the volatile matter in the coal which the beehive
oven wasted. In 1913 the surplus gas, breeze, tar, and light oil recovered
were equivalent to 2,600,000 tons of coal, and by 1929 this had increased
to 19,262,000 tons. Insofar as the byproduct coke produced displaced beehive
coke, the thermal byproducts involved displacement of raw coal. Fortunately
for the coal man, this item of saving is now approaching the saturation point,
with rapid elimination of the beehive oven. In 1929 the byproduct ovens produced
89 percent and in 1932 over 96 percent of the total output.
 With the decline in production of coke brought on by the depression, the
coal equivalent of the byproducts has declined also (fig. 21). A clear way
to show the progress is to note that the coal equivalent of the byproducts
now amounts to about 25 percent of the total coal charged into coke ovens.
As this is close to the theoretical limit, it