1(3 
PROF. H. L. CALLENDAR ON THE VARIATION OF THE SPECIFIC 
O 
The current of air-free distilled water is supplied from a boiler C in which the 
level is kept constant by means of a float-feed B, from an auxiliary tank A, maintained 
at a temperature of about 80° C. From the boiler the current passes with a fall of 
about 15 feet to a reservoir r>i surrounded by a steam-jacket, in which it is again 
raised to the boiiing-point before entering the exchanger E. 
Tliere is an air-trap at the top of the reservoir D, and 
similarly at each of the highest points of the circulating 
system, to facilitate filling the apparatus completely with 
water before starting tlie flow. Just before entering the 
exchanger E, the current passes through thermometer- 
pocket Tj, the construction of which is shown on a larger 
scale in the section of the exchanger, fig. 5. In order to 
protect the thermometer-pocket itself from loss of heat, the 
current is made to circulate upwards through a jacket-tube 
surrounding the thermometer-pocket before circulating 
downwards past the thermometer. Any small loss of heat 
which may occur before reaching the thermometer is 
immaterial. The tliermonieter-pockets and other tubes 
throughout the exchanger are made of thick copper, with 
deep screw-threads carefully fitted to produce a spiral 
circulation of the current. After passing thermometer T^ 
the current flows downwards through the central tube to 
the Ijottom of the exchanger and thence upwards through 
a concentric tube, where it loses heat to the cold current. 
Its temperature on first leaving the exchanger is taken by 
a thermometer Ta in a pocket constructed similarly to Tj, 
but not shown in fig. 5, in order to avoid confusion. The 
thermometer-pockets are all connected to the exchanger by 
thin tubes about 2 cm. to 3 cm. long and O'5 cm. bore. 
These connections are exaggerated in the diagram, fig. 4, 
so as to permit the general course of the circulation to be 
more easily followed. After leaving T 2 at a temperature 
between 60° C. and 70° C., the current passes through 
a cooling-tube F surrounded by an easily regulated jacket 
of cooling water ; thence through a long tin spiral immersed 
in a large cooling tank G to steady the temperature, 
before reaching a similar spiral in the regulator tank K, where its temperature 
is reduced precisely to that required for the cold current. From the regulator 
tank the current passes directly through the thermometer-pocket T 3 before entering 
the exchanger again as a cold current. In order to prevent loss of heat from the 
exchanger to the regulator tank in which it is immersed, the current, at very 
Fig. 5. 
