BETWEEN THE FREEZING AND BOILING-POINTS. 
205 
a central solid platinum wire about '4 millims. in diameter, or six strands made up 
of 6-millim. platinum wire in parallel, or a flat wire twisted into a spiral down the 
fine tube. Of these the first proved to be the most satisfactory and gave the steadiest 
results when held central in a tube by a silk-covered rubber cord wound around it in 
spirals of about 1 centim. The stranded heating-wire, although excellent, was more 
difficult to handle, especially in putting the fittings of the calorimeter together. The 
flat wire did not require to have the rubber band wound around it, and it was of the 
full width of the tube. It was very difficult indeed to arrange the interior of the 
calorimeter when using this form of twisted heating-wire, as a small strain on the 
wire was almost sure to tear it apart. Moreover, in all experiments such as these, 
where water is heated by an electric current conveyed in a wire, the temperature of 
the wire is always above that of the water, so that as this form of wire touched the 
sides of the glass-tube the heat-loss was increased by the heating of the glass-tube at 
the points where it was in contact with the wire. Still, this arrangement gave 
excellent results for two calorimeters in which it was tried, and served as a satisfactory 
check on the results obtained by the other heating-wires. The solid heating-wire 
was finally adopted as offering the least mechanical difficulties. 
