LoppEer.—On Compound Engines. 145 
rods being lengthened to enable both pistons of high and low pressure cylinders 
to be fixed on one rod, while the same pair of eccentrics were arranged to work 
the valves of the upper and lower cylinders of each combined engine. The 
steam from the upper cylinders exhausts into the valve chest of the lower. 
cylinders, exerting its remaining pressure in them. It then escapes into the 
surface condenser, whence it is conveyed back again to the neler in the 
shape of fresh water at a temperature of about 135° Fahr. 
Both of the old air-pumps are brought into use, one as a circulating 
pump to force the water through the tubes of the condenser, the other to 
operate in the usual way. By this cage” two separate compound engines are 
made, using the same condenser. 
The high-pressure cylinders are steam Boisko as also are the covers of 
the lower cylinders and the exhaust pipes leading from the upper cylinders to 
the lower ones. There is also an interheater placed in the lower steam chest 
between the slide valves to assist in keeping up the tension of the steam. 
The supply of steam for the jackets is taken from the superheater at a 
temperature probably of 350° Fahr. 
The surface condenser is cylindrical, and contains 735 brass tubes, four 
feet long and five-eighths of an inch outside diameter, giving a cooling surface 
of 465:5 square feet, the tubes being fixed into brass tube plates with screwed 
glands and indiarubber washers. 
The boiler is 7 ft. 3 in. in diameter by 9 ft. long, having two furnaces 2 ft. 
2 in. by 6 ft. There is a superheater with the uptake passing through it, and 
the total heating surface, including the superheater, is 502-56 square feet. 
These combined engines are of 38-8 horse-power, by Watt’s rule, and 45 
nominal horse-power by the Admiralty rule ; the ratio of cylinder areas is as 
6 to 1 nearly, all four cylinders cutting off at three-quarter stroke, so that the 
steam is expanded about eight times. 
On the trial trip the boiler pressure was 80 lbs. per square inch, and the 
diagrams taken by Mr. Stewart, Government Inspector of steamers, showed an 
initial pressure of 72 lbs. per inch ; mean pressure 61-75 Ibs., and the terminal 
pressure, 37:5 lbs. ; average number of revolutions per minute 80, indicating 
58 horse-power for the upper cylinders. 
The effective pressure in the lower cylinders was only 7-6 Ibs., indicating 
42 horse-power, making a total of 100 indicated horse-power for the combined 
engines, with a consumption of 376 lbs. per aoin or 3'76 lbs. per indicated 
horse-power per hour. 
The diagrams also showed that the steam in the lower cylinders is under 
atmospheric pressure, hence the smallness of the power in them as compared 
with the power given out in the upper cylinders. There ought to have been 
at least from 5 to 6 lbs. above the atmosphere in the lower cylinders. 
T 
