1902 - 3 ;] Determining Latent Heat of Evaporation. 
451 
shows a section by a horizontal plane through the line a a in the 
elevation. 
The glass calorimeter resembles an inverted Wolff’s bottle, the 
lower end being provided with two tubulures, while the upper end 
is open. Through the tubulures there pass copper electrodes of 
\ inch diameter, joined to the glass tubulures with short sleeves of 
thick- walled india-rubber tubing. Between the upper ends of these 
electrodes are soldered four lengths in parallel of platinum wire 
*37 mm. in diameter, each 5'6 cms. long. The reasons for taking 
four fine wires in parallel were the following : — 
(1) They provide a larger area for the formation of small bubbles 
especially if they are bent into flat zigzags well separated from 
each other. (2) Bubbles form more easily on a small wire than on 
a large, and hence there is less superheating of the liquid in 
eontact with the wire. It is of great importance that the boiling 
take place with the formation of a large number of small bubbles 
distributed through the liquid, for the efficiency of jacketing by the 
saturated vapour itself depends on the assumption of equal 
temperatures for liquid and vapour. (3) The resistance of the coil 
can be increased if required by cutting one or more of the wires. 
The copper leads and soldering are well platinised. This was 
found necessary in consequence of some action between the copper 
and the indiarubber stoppers, which were formerly used, resulting 
after a few heatings in leakage along the electrodes. A light 
copper catch water, shown in elevation only, is fitted over the rubber 
tubes. Underneath the electrodes are placed copper mercury cups 
supported by rods of copper ^ inch in diameter. Alongside of 
these there are two copper uprights connected to terminals on the 
wooden base. These are intended to serve as potential leads for 
the measurement of potential differences between the electrodes. 
Except when this measurement is being made, they are not con- 
nected to anything inside the shield. 
Underneath the upper rim of the vessel, on the inside, there are 
three small glass hooks to which three short platinum wires are 
attached. These are soldered to a central platinum wire (of 
diameter inch) which is attached to the hook of the balance. 
The length of this wire and the heights of the hook and mercury cups 
have to be suitably arranged. In the first place, when a weighing 
