148 SECTIONAL ADDRESSES 
the sea, but the greater part is burnt in the furnaces of the mine power 
station. The consumption is wasteful in the extreme, for burning is 
the cheapest way of getting rid of the otherwise useless material. About 
6 per cent. of the coal raised is used to produce steam for power to work 
the mines, whereas in a colliery where the coal is scrupulously saved 
and there is little waste, it is found that the fuel required is only 1-25 per 
cent. of the coal raised, and the quality of it is exceedingly low. Hence 
some 5 per cent. is immediately available for other purposes if it is used 
economically, to which can be added what is actually thrown away. 
Summing up all these actual and prospective sources of low-grade 
coal, it may be estimated that if an overall price of 5s. per ton at 
the cleaning floors were offered, in most districts a quantity equal to 
10 per cent. of the coal raised would be readily obtained, with a smaller 
proportion in the rest, and that this would yield some 18,000,000 tons 
per annum, with a calorific value averaging 10,000 B.Th.U. per lb. This 
is 50 per cent. more than is used to produce the present output of all the 
generating stations. 
Any arrangement by which a waste product from one industry is used 
in another requires some plan to prevent an excess or deficit in the 
product. In the present case an adequate supply of fuel is essential, as 
the sales of electricity cannot be controlled. ‘There is, however, an 
elastic amount of product, for the coal on the boundary line may be either 
used in the station or given a cleaning process, and a greater quantity 
will be available at a small increase in the price. The figure of five 
shillings will include much coal that now has almost no value, so it will 
also cover a fair proportion of coal of a higher value. 
The daily variation in the load curve requires no great storage, but 
the Saturday and Sunday demand must draw from a store, if the colliery 
raises coal on five days a week, as is usual. The seasonal variations 
will, to some extent, balance, for though the domestic load is less, the 
domestic coal demand is also less, and the waste coal corresponding to 
this will be reduced. But seasonal and trade fluctuations can be adjusted 
by altering the amount of boundary line coal. 
The general scheme should permit of using the waste coal from as 
many pits as possible, including even small isolated mines, for they 
assist in supplying the grid at points otherwise unprovided for, and 
reduce the distance of transmission. What the lower limit of economical 
pit station will be need not be elaborately discussed, for the isolated pits 
provide only a small part of the total coal, and their exclusion does not 
materially affect the available supply. As their small stations will have 
a larger cost of interest on plant, they will be advantageously allowed 
to run at full load, putting all their excess power into the grid. The 
wages costs will be little more than their present figure for boiler and 
steam engine attendants. In each case it will not be difficult to determine 
whether to include them as supplying stations, or to supply them from the 
grid and discard all coal that is quite unsaleable, or finally to leave them 
to use their waste coal as at present. The quantity and quality of the 
available coal, and the position of the pit, as regards other pits and as 
regards neighbouring consumers, will be the deciding factors. 
The greater part of the coal raised comes from pits which can be 
