HEAT OF EVAPORATION OF WATER. 277 
Any inflow of gas came down the tube f, and passed directly into the bottom of 
the flask at g. 
The stirrer S had two paddles, reaching from top to bottom of the flask; the 
blades and the central tube were of thin copper. Down this tube passed a steel. 
shaft, which hung at the lower extremity within a hole in a sheet of brass projecting 
from the side of the calorimeter. The bearings of the stirrer were entirely outside 
the calorimeter, and the lower end did not touch the base, or bear on the surrounding 
plate, whose only purpose was to check vibration. The paddles had a slight “ pitch,” 
so as to throw the liquid upwards, as well as cause it to rotate. The exterior 
bearings at the top of the glass tube S (fig. 3) were of the kind figured in Plate 2, 
Paper J., and were certainly sufficiently air-tight to prevent any diffusion, even when 
the stirrer was rotating rapidly, but, as the calorimeter was filled with a non-volatile 
liquid, the air-tightness of this joint was of little consequence, especially as the tem- 
perature of the calorimeter remained constant during the experiments and the air- 
space above the liquid was small. The rubbing surfaces were very true and always 
immersed in oil, thus the heat generated must in any case have been unimportant. 
The greater portion of any heat developed in the external bearings would pass to the 
brass tube, of which they formed a part, and, as the lower portion of this tube was 
washed by the tank water, its temperature would in any case rise but little. Any 
heat passing down the steel shaft (length 28 centims., diameter 0°35 centim.) would, 
of course, be included in the “stirring correction,” but I should imagine that it was 
in reality negligible, for about 4 inches of the glass tube down which it passed were 
also washed by the tank water. 
Further, slightly above the top of the calorimeter a section of ivory was inserted in 
the stirring shaft, in order to diminish conduction as much as possible. 
- The platinum-silver coil was wound on small ebonite tubes surrounding the narrow 
brass pillars of the rack, whose section is shown at R (fig. 2). The method by which 
the insulation of the rack was maintained, where the two brass pillars R, R, passed 
through the top of the calorimeter, is shown by the section (Plate 5, fig. 4). _ It must 
be remembered that these junctions had not only to be perfectly insulated, but that 
they had also to be absolutely air-tight, over a considerable range of temperature (10° to 
60° C.),* even to pressures of 1 atmosphere. 
The platinum-silver coil was about 100 centims. in length, and so wound that it 
was completely immersed when the depth of the liquid was 4 centims. ‘Two copper 
wires (B. W.G., 21) were soldered to each of the pillars R, and R, where they projected 
ubove the roof of the calorimeter at / and /’ (fig. 3), thus, in the steel lid, there were 
four junctions similar to those above described (see Plate 6, fig. 3). The blocks of 
ebonite forming the top slab of the junctions were, however, in this case, made 
nearly five inches in length; they projected as far as the lid cf the tank, and 
* The insulation of the whole circuit after all the apparatus was placed in position, was better than 1 
could measure, z.¢., LO’ ohms, 
