G.—ENGINEERING 151 
cheaper, the boiler plant requires a different and rather more expensive 
type of boiler, but not a larger output of steam, much of the subsidiary 
plant is the same as before the change, coal-handling plant being larger, 
water supply and handling are unchanged, boiler-house staff is little 
increased, and engine-room staff and plant are the only complete additions. 
The result is that capital costs for the additional plant are, overall, not 
more than half of those for the complete plant in a corresponding supply 
station, additional repairs, wages, and management also one-half, and 
coal not more than one-third of that in the best supply station. Hence 
even a small station of this kind can operate at a very low figure, little 
more than o-1 pence per unit, and the works in question will obtain 
their own mechanical power at this very favourable price. The only 
difficulty in the plan at present is in the utilisation of the surplus power. 
The works require a supply of steam depending on their processes, and 
if this is to pass through the turbines, the electrical output is fixed not 
by the consumers but by the process steam. An isolated plant cannot 
cope with two independent and variable loads, except by complex by-pass 
contrivances, steam accumulators, additional plant for evenings and 
Sundays and so forth, entailing so much extra cost and loss that the 
advantages: are dissipated. On a large scale the method is highly 
economical, and is well exhibited in the Billingham works of Imperial 
Chemical Industries. If, however, the factory electric station is con- 
nected to the grid, even a small one may put in all its spare output, no 
matter how irregular that may be, provided that consumers are not too 
far away, and that it can supply the energy at a price which will benefit 
all parties. 
How much power can be obtained from this source it would be 
laborious to ascertain. Each factory would require separate consideration, 
and the cost of altering existing boiler plants would be important. But 
the change can be introduced gradually, new factories or renewal of 
plant affording opportunities, until all suitable factories are absorbed 
into the scheme. By that time the increased demand will easily take up 
all the power without disturbing the other sources. 
Other possible sources of cheap electric energy are coke ovens and blast 
furnaces, both of which produce combustible gas. The coke-oven gas 
has a high calorific value, and will command a better price if distributed 
as town gas. The proposal to transmit town gas at high pressure to 
considerable distances, if it prove successful, will allow of the direct use 
of very large quantities of gas, if of high calorific value. It is not worth 
while to transmit the low-grade gas from blast furnaces, just as it does 
not pay to carry low-grade coal, and the gas may therefore drive electric 
plant, and all power in excess of works requirements can be put into the 
electric mains. This has been in operation at the North-Eastern Supply 
Company for many years, and while no great amount of power can be 
expected from this source, all cheap electricity at distributed points is 
helpful. The stations would operate like the small pit-head and the 
process steam stations, the output being controlled by the supply of 
gas and not by the consumer, so as to avoid the storage of gas. 
Two large consumers of coal are probable in the near future, the 
one being the proposed petrol factory, the other the low-temperature 
