3IO	IRON  AND  STEEL  IN  BRITAIN
Durham coal fields probably contained the finest coking coals in
the world, but there was said to be little, if any, difference in the
metallurgical coke used in England, the U.S.A. and Germany.
The average quality of the coke used in Luxembourg and Belgium
was better than that in the United Kingdom, the regularity arising
from the large centralized coking plants. In this country the
regularity of physical conditions and analysis was not assured.
Improvements occurred, however, in the following directions:
 (1)	Coke screening and culling plants.
 (2)	Increased production in by-product ovens.
 (3)	Greater attention to coal blending.
 (4)	The handling of fines at the washery.
 (5)	The formation of Coke Research Committees.
The best features in Continental practice were being absorbed,
more especially the adoption of large-scale high-speed operations,
invoking the minimum of labour requirements. Attention was being
given to the recovery of the sensible heat in coke. In addition to
by-product recovery the disposal of surplus gas was being dealt
with. The National Fuel and Power Committee of the Board of
Trade investigated the Area Gas Supply System, and the scheme
was initiated in the Sheffield area.
number of coke ovens and average output
In 1930 the total number of coke ovens was greatest in the U.S.A.,
followed by Germany, Great Britain, France and Belgium. The pre-
ponderance of the U.S.A. was due to the vast number of beehive
ovens. The total number of ovens increased generally up to 1914.
Since 1918 they decreased in all countries due, of course, to beehives
passing out of service. The relatively small total number of ovens
in France and Belgium was, of course, due to the early development
of chamber ovens. They were practically all of by-product recovery
type.
The general average output per oven, which will be briefly
compared, increased slowly in all countries before 1913, but rapidly
afterwards. In the U.S.A. the number of beehives naturally caused
the average to be low. The average in Great Britain was higher
than in U.S.A. It was highest of all in Germany, but Belgium
followed closely in this resffect, having progressed rapidly since the
begmning of the century. The production per oven increased
rapidly in France towards the end of the period, and approached