ON THE MECHANICAL EQUIVALENT OF HEAT. 
361 
^ The hot water discharged by the brake flowed from the bent rubber tube, pre¬ 
viously mentioned, into the lower end of the vertical 1-inch diameter copper pipe, A. 
This pipe carried a brass cross, B, at its upper end, while fitted to the top of the 
cross was the stuffing-box, C, in which was fixed a piece of f-inch diameter glass 
tubing^, D, forming the thermometer chamber. The upper end of this chamber was 
closed by a rubber stopper penetrated, as before, by a piece of |^-inch diameter brass 
pipe, connected by a piece of rubber tubing to the main discharge pipe above. 
The left arm of the cross carried an upward-turning elbow, and that again 
a f-inch diameter copper pipe, up which most of the water flowed. 
The thermometers, two of which were used, were hung to the lower end of 
the f-inch pipe in the rubber stopper, so that the bulbs were immersed in the whole 
stream of water flowing up the 1-inch copper pipe from the brake. One of these 
thermometers was only used as a finder to indicate the temperature of the water as 
it rose after first starting the engine, and no record of its readings was kept. 
The Condenser ,—(Part L, par. 18.) 
9. In order that there should not be a large loss of water before weighing, by 
evaporation from the tank into which it flowed from the brake, it was necessary 
to cool the stream to a temperature approaching that of the atmosphere. 
For this purpose a condenser was constructed after the ordinary chemical pattern. 
It consisted of a length of 21 feet of f-inch diameter pipe inserted in an equal length 
of If-inch diameter iron pipe. 
Stuffing-boxes were used to form the joints between the two pipes. The hot 
water from the brake flowed through the inner tube, while a supply of condensing 
water flowed in the opposite direction through the annular space between the two 
pipes. By means of this condenser the water entering the tank was always cooled 
at least to 100° Fahr,, and to lower temperatures in the earlier experiments when 
the water available in the mains was considerably colder. 
The Rising Pipe .—(Part I., par. 21.) 
10. The thermometer indicating the discharge temperature often gave readings 
more or less above 212° Fahr. 
To provide against any fall in temperature at the thermometer bulb, which might 
occur by reason of the formation of bubbles of steam in the water, it was found 
desirable to keep some pressure on the water at that part of its course. 
Accordingly, instead of discharging the water directly from the condenser into the 
tank, it was conducted up a vertical pipe, which was open at the top through a T 
to the atmosphere. The water then drained down another pipe provided with a 
nozzle at its lower end, opening into the two-way switch, to be described later. By 
VOL. CXC.—A. 3 A 
