1922.] Jenkinson.—Development of the Locomotive. 301 
It was found that each pound of coal evaporated 9 lb. of water, and 
that the greater part of this water was turned into steam at 180 lb. gauge- 
pressure and at a temperature of 620° F. Assuming, however, that 10 per 
cent, of the steam is used in pumps, lubricators, safety-valves, &c., we find 
that of the 14,000 B.Th.U. in each pound of coal 11,550 are transmitted 
to the water in the boiler, giving an absolute efficiency of 83 per cent. 
The cycle-efficiency is, however, greater than this. The combustion of 1 lb. 
of coal requires 12 lb. of air, thus giving 13 lb. of gas, which passes away 
to the atmosphere at a temperature of at least 400° F., since the saturated- 
steam temperature is 379° F. This loss is unavoidable in the cycle of boiler 
generation under discussion, and should therefore be added to the useful 
work, making 12,650 units of heat accounted for, or a cycle-efficiency of 
90 per cent. When it is remembered that this 10 per cent, includes all 
the losses due to unburnt coal and incomplete combustion, to radiation, and 
to the heat in the exhaust gases above the 13 lb. absolutely necessary for 
combustion, it is clear that there is no ground for expecting any sensible 
increase in locomotive-boiler efficiency. 
The cylinder-efficiency is a more complex problem. There is no doubt 
about the heat brought to the cylinders by the incoming steam. This is 
analogous to the potential energy in a water-power problem. The height 
of the tail-race, or the heat-units in the exhaust steam, is, however, another 
matter. At first sight it would appear logical to assume that the steam 
could only be expanded to the state of dry steam at a pressure of 10 lb. 
above the atmosphere, since the engine is non-condensing and the exhaust 
steam is required to act as an inciter of boiler-draught. Table Y has been 
prepared on this assumption. 
Table V.— Efficiency of the Locomotive-cyltndeb. 
Satu- 
Super- 
Satu- 
Super- 
rated. 
heated. 
rated. 
heated. 
B.Th.U. in 1 lb. steam (180 lb. pressure) 
1,197 
1,330 
1,197 
1,330 
B Th.U. per 1 lb. exhaust steam, dry, at 10 lb. pressure 
B.Th.U. per 1 lb. exhaust steam, 0-082 moisture, at 
1,160 
1,160 
1,081 
1,083 
10 lb. pressure 
B.Th.U. available per 1 lb. steam 
37 
170 
116 
247 
B.Th.U. available per b.h.p.-hour 
1,110 
4,131 
3,495 
6,002 
B.Th.U. equivalent to b.h.p.-hour 
• • 
3,145 
• . 
Efficiency of cylinder 
283% 
76% 
90% 
52% 
It was found in the trials already quoted that 3 lb. of coal and 27 lb. 
of superheated steam were used per brake-horsepower-hour ; but approxi¬ 
mately 10 per cent, of this was used in air-pumps, lubricators, safety- 
valves, &c., leaving 24-3 lb. available for work. Now, each pound of steam 
delivered up, under the above assumption, 170 B.Th.U. to the cylinders, 
and therefore a brake-horsepower-hour is given for every 4,131 units of heat 
available for use in the cylinders. The theoretical equivalent, assuming 
that Joule’s equivalent applies to the reverse operation of turning heat into 
work, of a brake-horsepower-hour is 2,830 B.Th.U., and the cylinder- 
efficiency is therefore 70 per cent. But this includes all frictional losses 
between the piston and the driving-wheel rim, and as these are in the 
neighbourhood of 10 per cent., as determined by actual trial, the efficiency 
of the cylinder itself would seem to be 77 per cent. 
It is, however, when we apply a similar assumption to the saturated- 
steam engine tested in the same trials that it appears untenable. Since it 
used 25 per cent, more water than the superheated engine for the same 
